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1

Functional and Structural Convergence of Temperate Grassland and Shrubland Ecosystems  

Microsoft Academic Search

We analyzed the similarity of structural and functional characteristics of temperate grassland and shrubland ecosystems of North and South America. We based our analyses on correlative models that describe the climatic controls of grassland and shrubland structure and functioning at regional scales. We evaluated models that describe the regional distribution of plant functional types (C 3 and C4 grasses and

Jose M. Paruelo; Esteban G. Jobbagy; Osvaldo E. Sala; William K. Lauenroth; Ingrid C. Burke

1998-01-01

2

Accounting for variability in soil microbial communities of temperate upland grassland ecosystems  

Microsoft Academic Search

This study aimed to determine the factors which regulate soil microbial community organisation and function in temperate upland grassland ecosystems. Soil microbial biomass (Cmic), activity (respiration and potential carbon utilisation) and community structure (phospholipid fatty acid (PLFA) analysis, culturing and community level physiological profiles (CLPP) (Biolog®)) were measured across a gradient of three upland grassland types; Festuca–Agrostis–Galium grassland (unimproved grassland,

S. J. Grayston; G. S. Griffith; J. L. Mawdsley; C. D. Campbell; R. D. Bardgett

2001-01-01

3

Net ecosystem productivity of temperate grasslands in northern China: An upscaling study  

USGS Publications Warehouse

Grassland is one of the widespread biome types globally, and plays an important role in the terrestrial carbon cycle. We examined net ecosystem production (NEP) for the temperate grasslands in northern China from 2000 to 2010. We combined flux observations, satellite data, and climate data to develop a piecewise regression model for NEP, and then used the model to map NEP for grasslands in northern China. Over the growing season, the northern China's grassland had a net carbon uptake of 158 ± 25 g C m?2 during 2000–2010 with the mean regional NEP estimate of 126 Tg C. Our results showed generally higher grassland NEP at high latitudes (northeast) than at low latitudes (central and west) because of different grassland types and environmental conditions. In the northeast, which is dominated by meadow steppes, the growing season NEP generally reached 200–300 g C m?2. In the southwest corner of the region, which is partially occupied by alpine meadow systems, the growing season NEP also reached 200–300 g C m?2. In the central part, which is dominated by typical steppe systems, the growing season NEP generally varied in the range of 100–200 g C m?2. The NEP of the northern China's grasslands was highly variable through years, ranging from 129 (2001) to 217 g C m?2 growing season?1 (2010). The large interannual variations of NEP could be attributed to the sensitivity of temperate grasslands to climate changes and extreme climatic events. The droughts in 2000, 2001, and 2006 reduced the carbon uptake over the growing season by 11%, 29%, and 16% relative to the long-term (2000–2010) mean. Over the study period (2000–2010), precipitation was significantly correlated with NEP for the growing season (R2 = 0.35, p-value < 0.1), indicating that water availability is an important stressor for the productivity of the temperate grasslands in semi-arid and arid regions in northern China. We conclude that northern temperate grasslands have the potential to sequester carbon, but the capacity of carbon sequestration depends on grassland types and environmental conditions. Extreme climate events like drought can significantly reduce the net carbon uptake of grasslands.

Zhang, Li; Guo, Huadong; Jia, Gensuo; Wylie, Bruce; Gilmanov, Tagir; Howard, Danny; Ji, Lei; Xiao, Jingfeng; Li, Jing; Yuan, Wenping; Zhao, Tianbao; Chen, Shiping; Zhou, Guangsheng; Kato, Tomomichi

2014-01-01

4

Nitrous oxide emissions from temperate grassland ecosystems in the Northern and Southern Hemispheres  

NASA Astrophysics Data System (ADS)

Nitrogen (N) fertilized or grazed grasslands in temperate regions of the Northern and Southern Hemisphere are important sources for atmospheric nitrous oxide (N2O). Following synthetic urine applications in a New Zealand grassland ecosystem, and ammonium (NH4+) and nitrate (NO3-) applications to a German grassland ecosystem, approximately 31, 16, and 5%, respectively, of the total emitted N2O (N2Otot) was produced by nitrification (N2Onit) with the rest being produced by denitrification (N2Oden). Analyses of the combined data set showed that 75% of all N2O emissions occurred above 60% water filled porosity (WFPS) and that more than 80% of all N2O emissions occurred at soil temperatures between 10° and 15°C. N2Oden emissions were associated with a WFPS value at around 80% at relatively low NO3- concentrations, while N2Onit emissions only occurred at high NH4+ levels shortly after N application at soil temperatures around 10°C. To increase the accuracy of predictions with simple mathematical models, such as the "hole-in-the-pipe-model," long-term validation data sets are needed where driving variables are related to measured N2Onit and N2Oden data.

Müller, Christoph; Sherlock, Robert R.

2004-03-01

5

Observing 13C labelling kinetics in CO2 respired by a temperate grassland ecosystem.  

PubMed

* The kinetic characteristics of the main sources of ecosystem respiration are quite unknown, partly because of methodological constraints. Here, we present a new open-top chamber (OTC) apparatus for continuous 13C/12C labelling and measurement of ecosystem CO2 fluxes, and report the tracer kinetics of nighttime respiration of a temperate grassland. * The apparatus includes four dynamic flow-through OTCs, a unit mixing CO2-free air with 13C-depleted CO2, and a CO2 analyser and an online isotope ratio mass spectrometer. * The concentration (367 +/- 6.5 micromol mol(-1)) and carbon isotopic composition, delta13C, (-46.9 +/- 0.4 per thousand) of CO2 in the OTCs were stable during photosynthesis as a result of high air through flux and minimal incursion through the buffered vent. Soil CO2 efflux was not affected by pressure effects during respiration measurements. The labelling kinetics of respiratory CO2 measured in the field agreed with that of excised soil + vegetation blocks measured in a laboratory-based system. The kinetics fitted a two-source system (r(2) = 0.97), with a rapidly labelled source (half-life 2.6 d) supplying 48% of respiration, and the other source (52%) releasing no tracer during 14 d of labelling. * Of the two sources supplying ecosystem respiration, one was closely connected to current photosynthesis (approximately autotrophic respiration) and the other was provided by decomposition of structural plant biomass (approximately heterotrophic respiration). PMID:19656304

Gamnitzer, Ulrike; Schäufele, Rudi; Schnyder, Hans

2009-07-27

6

Drought effects on above- and belowground production of a grazed temperate grassland ecosystem.  

PubMed

The effect of climatic variation on terrestrial aboveground productivity (ANPP) has been well studied. However, little is known about how variable climate, including drought, may influence belowground productivity (BNPP), which constitutes most of the annual primary production of grasslands. The objectives of this study were to (1) examine how a 3-year period of declining moisture, which began as climatically wet to average across Yellowstone National Park (YNP) and ended in drought, affected ANPP and BNPP in grasslands of YNP and (2) how herds of grazing ungulates, which were shown previously to stimulate grassland shoot and root growth in YNP, may have interacted with climatic conditions to influence grassland production. ANPP and 0-20 cm BNPP, representing the bulk of the root dynamics, were measured in grazed and ungrazed (fenced) grassland at nine sites ranging widely in elevation, soil conditions and plant production during the 3-year study. Results revealed that 0-20 cm BNPP was strongly influenced by drought (P = 0.0005) and declined from 1999 to 2001 among ungrazed and grazed grasslands by 39 and 49%, respectively. The greater reduction in 0-20 cm BNPP among grazed grasslands was due, in part, to a decline (P = 0.07) in the stimulatory effect of grazing, i.e., the ratio g BNPP stimulated: g shoot consumed. In contrast, ANPP was unaffected by drought in either type of grassland. Thus, the effect of this drought in YNP was a large reduction in BNPP, which was a function of (1) a direct negative influence of increased moisture stress on root growth and (2) a weak interaction between drought and herbivory that led to a decline in the positive feedback from grazers to BNPP. These findings highlight the need to better understand factors that control root growth and to study the effects of climatic variation on grasslands within an ecosystem framework to include potentially important climate-consumer interactions. PMID:17180369

Frank, Douglas A

2006-12-16

7

Ecosystem Modeling for an Integrated Wind-Erosion Scheme in Temperate Grasslands  

NASA Astrophysics Data System (ADS)

Severe dust events have increased in the arid and semiarid regions of Mongolia and China during the last decade. It poses a serious threat not only to the grassland livestock and human lives in the source regions but also in downwind regions. An early warning system needed to prevent this serious damage. However, it is difficult to predict dust events current wind-erosion-modeling for vegetated land, because detailed relationships among vegetation/soil moisture and dust emission are not well documented. Recent studies showed that dead leaves of grasses in spring, which were residues of vegetation from the preceding summer, suppressed dust outbreaks. In this study, we evaluated the DayCent4.5 ecosystem model for its ability to provide estimations of grass productivity in a grassland ecosystem at the Bayan Unjuul (BU) site in Mongolia. The model was parameterized with the field experiment data in 2010-2011 consisting of climatic, soil physical/chemical properties, vegetation and grazing data. The results from the model have been validated against a set of 10-year field data obtained at the grazed and un-grazed plots at the BU site. Generally, results showed a good correspondence between observed and estimated plant production, and soil C/N contents at the grazed and un-grazed area, and this model will be useful tool be used for dust early warning in Mongolia.

Nandintsetseg, B.; Shinoda, M.

2011-12-01

8

Bacterial Community Dynamics across a Floristic Gradient in a Temperate Upland Grassland Ecosystem  

Microsoft Academic Search

  Alterations in soil bacterial communities across a transect between a semi natural upland grassland and an agriculturally\\u000a improved enclosure were assessed using culture-based methods and a nucleic-acid-based method, terminal restriction fragment\\u000a length polymorphism (TRFLP). While plant diversity decreased across the transect towards the improved area, numbers of 16S\\u000a rDNA terminal restriction fragments increased, indicating an increase in numbers of bacterial

E. Brodie; S. Edwards; N. Clipson

2002-01-01

9

Interacting effects of temperature, soil moisture and plant biomass production on ecosystem respiration in a northern temperate grassland  

Microsoft Academic Search

Chamber measurements of total ecosystem respiration (TER) in a native Canadian grassland ecosystem were made during two study years with different precipitation. The growing season (April–September) precipitation during 2001 was less than one-half of the 30-year mean (1971–2000), while 2002 received almost double the normal growing season precipitation. As a consequence soil moisture remained higher in 2002 than 2001 during

Lawrence B. Flanagan; Bruce G. Johnson

2005-01-01

10

Using an ecosystem model linked to GCM-derived local weather scenarios to analyse effects of climate change and elevated CO2 on dry matter production and partitioning, and water use in temperate managed grasslands  

Microsoft Academic Search

Local effects of climate change (CC) and elevated CO2 (2 H CO2, 660 ?mol mol-1 )o n managed temperate grasslands were assessed by forcing a dynamic ecosystem model with weather scenarios. The aims of the study were to compare the relative importance of individual and combined effects of CC, 2 H CO2, and photosynthetic acclimation, and to assess the importance

MARCEL R IEDO; A NDREAS F ISCHLIN; JURG F UHRER

11

Relation of Chlorophyll Fluorescence Sensitive Reflectance Ratios to Carbon Flux Measurements of Montanne Grassland and Norway Spruce Forest Ecosystems in the Temperate Zone  

PubMed Central

We explored ability of reflectance vegetation indexes (VIs) related to chlorophyll fluorescence emission (R686/R630, R740/R800) and de-epoxidation state of xanthophyll cycle pigments (PRI, calculated as (R531 ? R570)/(R531 ? R570)) to track changes in the CO2 assimilation rate and Light Use Efficiency (LUE) in montane grassland and Norway spruce forest ecosystems, both at leaf and also canopy level. VIs were measured at two research plots using a ground-based high spatial/spectral resolution imaging spectroscopy technique. No significant relationship between VIs and leaf light-saturated CO2 assimilation (AMAX) was detected in instantaneous measurements of grassland under steady-state irradiance conditions. Once the temporal dimension and daily irradiance variation were included into the experimental setup, statistically significant changes in VIs related to tested physiological parameters were revealed. ?PRI and ?(R686/R630) of grassland plant leaves under dark-to-full sunlight transition in the scale of minutes were significantly related to AMAX (R2 = 0.51). In the daily course, the variation of VIs measured in one-hour intervals correlated well with the variation of Gross Primary Production (GPP), Net Ecosystem Exchange (NEE), and LUE estimated via the eddy-covariance flux tower. Statistical results were weaker in the case of the grassland ecosystem, with the strongest statistical relation of the index R686/R630 with NEE and GPP.

Ac, Alexander; Malenovsky, Zbynek; Urban, Otmar; Hanus, Jan; Zitova, Martina; Navratil, Martin; Vrablova, Martina; Olejnickova, Julie; Spunda, Vladimir; Marek, Michal

2012-01-01

12

The measurement of soil fungal:bacterial biomass ratios as an indicator of ecosystem self-regulation in temperate meadow grasslands  

Microsoft Academic Search

There is much interest in the development of agricultural land management strategies aimed at enhancing reliance on ecosystem\\u000a self-regulation rather than on artificial inputs such as fertilisers and pesticides. This study tested the usefulness of measures\\u000a of soil microbial biomass and fungal:bacterial biomass ratios as indicators of effective conversion from an intensive grassland\\u000a system, reliant mainly on fertilisers for crop

Richard D. Bardgett; Erica McAlister

1999-01-01

13

Microbial processes and the site of N 2O production in a temperate grassland soil  

Microsoft Academic Search

To understand nitrous oxide (N2O) emissions from terrestrial ecosystems it is necessary to understand the processes leading to N2O production. Here, for the first time, results are presented which identify in situ the processes of N2O production in a temperate grassland soil. A small portion of the nitrogen (N) applied in the summer to the grassland soil was rapidly transported

Christoph Müller; R. J Stevens; R. J Laughlin; H.-J Jäger

2004-01-01

14

Plant diversity effects on aboveground and belowground N pools in temperate grassland ecosystems: Development in the first 5 years after establishment  

NASA Astrophysics Data System (ADS)

Biodiversity is expected to improve ecosystem services, e.g., productivity or seepage water quality. The current view of plant diversity effects on element cycling is based on short-term grassland studies that discount possibly slow belowground feedbacks to aboveground diversity. Furthermore, these grasslands were established on formerly arable land associated with changes in soil properties, e.g., accumulation of organic matter. We hypothesize that the plant diversity-N cycle relationship changes with time since establishment. We assessed the relationship between plant diversity and (1) aboveground and soil N storage and (2) NO3-N and NH4-N availability in soil between 2003 and 2007 in the Jena Experiment, a grassland experiment established in 2002 in which the number of plant species varied from 1 to 60. The positive effect of plant diversity on aboveground N storage (mainly driven by biomass production) tended to increase through time. The initially negative correlation between plant diversity and soil NO3-N availability disappeared after 2003. In 2006 and 2007, a positive correlation between plant diversity and soil NH4-N availability appeared which coincided with a positive correlation between plant diversity and N mineralized from total N accumulated in soil. We conclude that the plant diversity-N cycle relationship in newly established grasslands changes with time because of accumulation of organic matter in soil associated with the establishment. While a positive relationship between plant diversity and soil N storage improves soil fertility and reduces fertilizing needs, increasingly closed N cycling with increasing plant diversity as illustrated by decreased NO3-N concentrations in diverse mixtures reduces the negative impact of agricultural N leaching on groundwater resources.

Oelmann, Yvonne; Buchmann, Nina; Gleixner, Gerd; Habekost, Maike; Roscher, Christiane; Rosenkranz, Stephan; Schulze, Ernst-Detlef; Steinbeiss, Sibylle; Temperton, Vicky M.; Weigelt, Alexandra; Weisser, Wolfgang W.; Wilcke, Wolfgang

2011-06-01

15

Temperate grasslands as a dust source: Knowledge, uncertainties, and challenges  

NASA Astrophysics Data System (ADS)

Temperate grasslands are sensitive to climate change and are significant, or potentially significant, dust sources. Temperate grassland aeolian processes are unique in that the vegetation growth-decay cycle and weathering process due to extreme temperature changes profoundly affect the occurrence and intensity of wind erosion and dust emission. Human activities, such as animal husbandry or cultivation, also may result in land degradation and enhanced wind erosion. So far, little systematic research on temperate grassland wind erosion has been done, but this issue deserves particular attention. In this review paper, we summarize the understanding of temperate grassland wind-erosion processes and identify the uncertainties and research needs. The needs include (1) a deeper understanding of the aerodynamic and physical controls of grassland vegetation on wind erosion and dust emission processes, (2) scaling known relationships upwards to model the regional scale, (3) quantifying critical parameters affecting dust emissions (i.e., surface and aerodynamic roughness) via remote-sensing techniques, and (4) integrated wind-erosion modeling that incorporates grassland aeolian database and vegetation modeling of both seasonal growth and decay plus the impacts of grazing and cultivation. We also outline the research being carried out by Japanese scientists in collaboration with colleagues at Mongolian, American, and German research institutes in developing a temperate grassland wind-erosion modeling system, which can be used as a pre-warning system of severe dust storms and as a tool for strategic management of temperate grasslands.

Shinoda, M.; Gillies, J. A.; Mikami, M.; Shao, Y.

2011-12-01

16

Experimental study on soil respiration of temperate grassland in China  

Microsoft Academic Search

Experimental study on soil respiration of typical temperate grassland in Inner Mongolia was conducted in the period of 1998\\u000a –2000. Closed chamber and GC\\/FID techniques were used for measurements of soil and plant respiration. Data analysis of three-year\\u000a measurements show that temperate grassland soil respiration varied in the range of 390–866 gC\\/m2 · a?1 and underwent evident seasonal and annual

Gengchen Wang; Rui Du; Qinxin Kong; Daren Lü

2004-01-01

17

Plant-soil Interactions in Temperate Grasslands  

Microsoft Academic Search

We present a conceptual model in which plant-soil interactions in grasslands are characterized by the extent to which water is limiting. Plant-soil interactions in dry grasslands, those dominated by water limitation (‘belowground-dominance’), are fundamentally different from plant-soil interactions in subhumid grasslands, where resource limitations vary in time and space among water, nitrogen, and light (‘indeterminate dominance’). In the belowground-dominance grasslands,

Ingrid C. Burke; William K. Lauenroth; Mary Ann Vinton; Paul B. Hook; Robin H. Kelly; Howard E. Epstein; Martin R. Aguiar; Marcos D. Robles; Manuel O. Aguilera; Kenneth L. Murphy; Richard A. Gill

1998-01-01

18

Grassland ecosystems in China: review of current knowledge and research advancement.  

PubMed

Grasslands are the dominant landscape in China, accounting for 40% of the national land area. Research concerning China's grassland ecosystems can be chronologically summarized into four periods: (i) pre-1950s, preliminary research and survey of grassland vegetation and plant species by Russians, Japanese and Western Europeans, (ii) 1950-1975, exploration and survey of vegetation, soils and topography as part of natural resource inventory programmes by regional and national institutions mainly led by the Chinese Academy of Sciences, (iii) 1976-1995, establishment of field stations for long-term ecological monitoring and studies of ecosystem processes, (iv) 1996-present, comprehensive studies of community dynamics and ecosystem function integrating multi-scale and multidisciplinary approaches and experimental manipulations. Major findings of scientific significance in China's grassland ecosystem research include: (i) improved knowledge on succession and biogeochemistry of the semi-arid and temperate grassland ecosystems, (ii) elucidation of life-history strategies and diapause characteristics of the native grasshopper species as one of the key grassland pests, and (iii) development of effective management strategies for controlling rodent pests in grassland ecosystems. Opportunities exist for using the natural grasslands in northern China as a model system to test ecosystem theories that so far have proven a challenge to ecologists worldwide. PMID:17317645

Kang, Le; Han, Xingguo; Zhang, Zhibin; Sun, Osbert Jianxin

2007-06-29

19

Elevated [CO2], temperature increase and N supply effects on the turnover of below-ground carbon in a temperate grassland ecosystem  

Microsoft Academic Search

The effects of elevated [CO2] (700 ?l l-1 CO2) and temperature increase (+3 °C) on carbon turnover in grassland soils were studied during 2.5 years at two N fertiliser\\u000a supplies (160 and 530 kg N ha-1 y-1) in an experiment with well-established ryegrass swards (Lolium perenne) supplied with the same amounts of irrigation water.\\u000a During the growing season, swards from

P. Loiseau; J. F. Soussana

1999-01-01

20

Characterizing fragmentation in temperate South America grasslands  

Microsoft Academic Search

In the last century, the grasslands of southern South America were rapidly converted to croplands, starting a fragmentation process that is still ongoing. Almost no information is available on the spatial patterns and environmental controls of these processes. Our objective was to characterize the degree of fragmentation and to analyze the environmental controls of landscape composition of the Río de

Germán Baldi; Juan Pablo Guerschman; José María Paruelo

2006-01-01

21

Nitrogen relationships in intensively managed temperate grasslands  

Microsoft Academic Search

Summary Most studies of N relationships in grassland have used cut swards. These have shown that for annual inputs of 200 to 400 kg N\\/ha from fertilizer or fixation, 55 to 80% of the N is recovered in harvested herbage. Generally, no more than 5 to 15% is lost through leaching and denitrification with most of the remaining N incorporated

P. Roger Ball; J. C. Ryden

1984-01-01

22

Short sampling intervals reveal very rapid root turnover in a temperate grassland.  

PubMed

Although root growth and mortality play critical regulatory roles in terrestrial ecosystems, little is known about the temporal scale of these dynamics. In temperate grasslands, root dynamics may be particularly rapid because of the high proportion of production allocated to very fine root biomass. In this study, we used minirhizotron tubes to estimate root growth and mortality in an upland grassland in Yellowstone National Park that was grazed by migratory herds of ungulates. Monthly rates of root growth and mortality were estimated from May to September 2005, by measuring the elongation (growth) and disappearance (mortality) of roots at 3-day intervals. Average daily growth (millimeters of root length) was approximately 5 times greater in May and June than in July, August, and September. Average daily mortality (millimeters of root length) did not differ among months. A comparison of the June-September rates of root growth and mortality derived from sampling at short (3-day) and long (1-month) time intervals indicated that the long sampling intervals underestimated both growth and mortality by approximately 60% relative to the short intervals. These results suggest that estimates of grassland root dynamics from minirhizotrons are influenced significantly by sampling interval length, and that rapid root turnover may play a more critical role in regulating energy and nutrient fluxes in temperate grasslands than has previously been recognized. PMID:18566834

Stewart, Anna M; Frank, Douglas A

2008-06-20

23

Temperate grasslands and global atmospheric change: a review  

Microsoft Academic Search

Summary Recent reviews confirm and extend previous observa- tions that elevated carbon dioxide (CO2) concentrations stimulate photosynthesis, leading to increased plant productivity. Elevated CO2 concentrations tend to reduce the sensitivity of grassland ecosystems to low levels of precipitation but induce progressive nitrogen (N) limitations on plant growth which can be alleviated by supplying a significant external input of N in

J. F. Soussana; A. Lüscher

2007-01-01

24

Soil Respiration and Organic Carbon Dynamics with Grassland Conversions to Woodlands in Temperate China  

PubMed Central

Soils are the largest terrestrial carbon store and soil respiration is the second-largest flux in ecosystem carbon cycling. Across China's temperate region, climatic changes and human activities have frequently caused the transformation of grasslands to woodlands. However, the effect of this transition on soil respiration and soil organic carbon (SOC) dynamics remains uncertain in this area. In this study, we measured in situ soil respiration and SOC storage over a two-year period (Jan. 2007–Dec. 2008) from five characteristic vegetation types in a forest-steppe ecotone of temperate China, including grassland (GR), shrubland (SH), as well as in evergreen coniferous (EC), deciduous coniferous (DC) and deciduous broadleaved forest (DB), to evaluate the changes of soil respiration and SOC storage with grassland conversions to diverse types of woodlands. Annual soil respiration increased by 3%, 6%, 14%, and 22% after the conversion from GR to EC, SH, DC, and DB, respectively. The variation in soil respiration among different vegetation types could be well explained by SOC and soil total nitrogen content. Despite higher soil respiration in woodlands, SOC storage and residence time increased in the upper 20 cm of soil. Our results suggest that the differences in soil environmental conditions, especially soil substrate availability, influenced the level of annual soil respiration produced by different vegetation types. Moreover, shifts from grassland to woody plant dominance resulted in increased SOC storage. Given the widespread increase in woody plant abundance caused by climate change and large-scale afforestation programs, the soils are expected to accumulate and store increased amounts of organic carbon in temperate areas of China.

Wang, Wei; Zeng, Wenjing; Chen, Weile; Zeng, Hui; Fang, Jingyun

2013-01-01

25

Mean age of carbon in fine roots from temperate forests and grasslands with different management  

NASA Astrophysics Data System (ADS)

Fine roots are the most dynamic portion of a plant's root system and a major source of soil organic matter. By altering plant species diversity and composition, soil conditions and nutrient availability, and consequently belowground allocations and dynamics of root carbon (C) inputs, land-use and management changes may influence organic C storage in terrestrial ecosystems. In three German regions we measured fine root radiocarbon (14C) content to estimate the mean time since C in root tissues was fixed from the atmosphere in 54 grassland and forest plots with different management and soil conditions. The mean age of C in fine roots in forest environments averaged 11.3±1.8 years (mean ± SE, n=27) and was significantly older and more variable compared to grassland environments (1.7±0.4 years, n=27). We further found that management affects the mean age of fine root C in temperate grasslands mediated by changes in plant species diversity and composition. Fine root mean C age is positively correlated to plant diversity (r=0.65) and to the number of perennial species (r=0.77). In temperate grasslands the mean age of fine root C is also influenced by the study region mainly due to differences in soil characteristics and climate, with averages of 0.7±0.1 years (n=9) on mostly organic sandy soils and of 1.8±0.3 years (n=9) and 2.6±0.3 (n=9) in more silty and clayey soils respectively. Our results indicate an internal redistribution of C in perennial species and suggest linkages between fine root C age and management in grasslands. These findings improve our ability to predict and model belowground C fluxes across broader spatial scales.

Solly, Emily; Schrumpf, Marion; Schöning, Ingo; Boch, Steffen; Trumbore, Susan

2013-04-01

26

Agronomic aspects of biodiversity targeted management of temperate grasslands in Europe - A review  

Microsoft Academic Search

Maintaining and enhancing the biodiversity of the agriculturally utilised area has a high priority in environmental policy worldwide. Temperate grasslands in Europe make an important contribution to the biodiversity of agricultural landscapes. The species and community diversity of grasslands is a result of a traditional extensive grassland management interacting with a broad range of site conditions. Until the early decades

J. Isselstein; B. Jeangros; V. Pavlu

2005-01-01

27

Above- and belowground biomass in relation to environmental factors in temperate grasslands, Inner Mongolia.  

PubMed

Above- and belowground biomasses of grasslands are important parameters for characterizing regional and global carbon cycles in grassland ecosystems. Compared with the relatively detailed information for aboveground biomass (AGB), belowground biomass (BGB) is poorly reported at the regional scales. The present study, based on a total of 113 sampling sites in temperate grassland of the Inner Mongolia, investigated regional distribution patterns of AGB, BGB, vertical distribution of roots, and their relationships with environmental factors. AGB and BGB increased from the southwest to the northeast of the study region. The largest biomass occurred in meadow steppe, with mean AGB and BGB of 196.7 and 1385.2 g/m2, respectively; while the lowest biomass occurred in desert steppe, with an AGB of 56.6 g/m2 and a BGB of 301.0 g/m2. In addition, about 47% of root biomass was distributed in the top 10 cm soil. Further statistical analysis indicated that precipitation was the primary determinant factor in shaping these distribution patterns. Vertical distribution of roots was significantly affected by precipitation, while the effects of soil texture and grassland types were weak. PMID:18246314

Ma, WenHong; Yang, YuanHe; He, JinSheng; Zeng, Hui; Fang, JingYun

2008-03-01

28

Scale-dependent relationships between plant diversity and above-ground biomass in temperate grasslands, south-eastern Mongolia  

Microsoft Academic Search

Relationships between plant diversity (H diversity index) and above-ground biomass (as a surrogate of productivity) were analysed using quadrat data and biomass measures from a precipitation gradient in length of ca. 1000km in temperate grasslands, south-eastern Mongolia. These analyses were performed both at different ecological scales including taxonomic or functional levels, such as species, community and ecosystem, and at different

J. Ni; G. H. Wang; Y. F. Bai; X. Z. Li

2007-01-01

29

Increasing land-use intensity decreases floral colour diversity of plant communities in temperate grasslands.  

PubMed

To preserve biodiversity and ecosystem functions in a globally changing world it is crucial to understand the effect of land use on ecosystem processes such as pollination. Floral colouration is known to be central in plant-pollinator interactions. To date, it is still unknown whether land use affects the colouration of flowering plant communities. To assess the effect of land use on the diversity and composition of flower colours in temperate grasslands, we collected data on the number of flowering plant species, blossom cover and flower reflectance spectra from 69 plant communities in two German regions, Schwäbische Alb (SA) and Hainich-Dün (HD). We analysed reflectance data of flower colours as they are perceived by honeybees and studied floral colour diversity based upon spectral loci of each flowering plant species in the Maxwell triangle. Before the first mowing, flower colour diversity decreased with increasing land-use intensity in SA, accompanied by a shift of mean flower colours of communities towards an increasing proportion of white blossom cover in both regions. By changing colour characteristics of grasslands, we suggest that increasing land-use intensity can affect the flower visitor fauna in terms of visitor behaviour and diversity. These changes may in turn influence plant reproduction in grassland plant communities. Our results indicate that land use is likely to affect communication processes between plants and flower visitors by altering flower colour traits. PMID:23568710

Binkenstein, Julia; Renoult, Julien P; Schaefer, H Martin

2013-04-09

30

Microbial responses to nitrogen addition in three contrasting grassland ecosystems  

Microsoft Academic Search

The effects of global N enrichment on soil processes in grassland ecosystems have received relatively little study. We assessed\\u000a microbial community response to experimental increases in N availability by measuring extracellular enzyme activity (EEA)\\u000a in soils from three grasslands with contrasting edaphic and climatic characteristics: a semiarid grassland at the Sevilleta\\u000a National Wildlife Refuge, New Mexico, USA (SEV), and mesic

Lydia H. Zeglin; Martina Stursova; Robert L. Sinsabaugh; Scott L. Collins

2007-01-01

31

Potential soil carbon sequestration in overgrazed grassland ecosystems  

Microsoft Academic Search

Excessive grazing pressure is detrimental to plant productivity and may lead to declines in soil organic matter. Soil organic matter is an important source of plant nutrients and can enhance soil aggregation, limit soil erosion, and can also increase cation exchange and water holding capacities, and is, therefore, a key regulator of grassland ecosystem processes. Changes in grassland management which

Richard T. Conant; Keith Paustian

2002-01-01

32

Studying mixed grassland ecosystems I: suitable hyperspectral vegetation indices  

Microsoft Academic Search

Hyperspectral remote sensing data with a greater number of bands and narrower bandwidths can be effectively exploited for the study of ecosystem patterns and processes. Hyperspectral remote sensing of semiarid mixed grassland faces the following two challenges, however: (i) providing a good understanding of the performance of different vegetation indices (VIs) in estimating biophysical properties of grassland with a small

Yuhong He; Xulin Guo; John Wilmshurst

2006-01-01

33

Mean age of carbon in fine roots from temperate forests and grasslands with different management  

NASA Astrophysics Data System (ADS)

Fine roots are the most dynamic portion of a plant's root system and a major source of soil organic matter. By altering plant species diversity and composition, soil conditions and nutrient availability, and consequently belowground allocation and dynamics of root carbon (C) inputs, land-use and management changes may influence organic C storage in terrestrial ecosystems. In three German regions we measured fine root radiocarbon (14C) content to estimate the mean time since C in root tissues was fixed from the atmosphere in 54 grassland and forest plots with different management and soil conditions. Although root biomass was on average greater in grasslands 5.1 ± 0.8 g (mean ± SE, n = 27) than in forests 3.1 ± 0.5 g (n = 27), the mean age of C in fine roots in forests averaged 11.3 ± 1.8 yr and was significantly older and more variable compared to grasslands 1.7 ± 0.4 yr. We further found that management affects the mean age of fine root C in temperate grasslands mediated by changes in plant species diversity and composition. Fine root mean C age is positively correlated to plant diversity (r = 0.65) and to the number of perennial species (r = 0.77). In temperate grasslands the mean age of fine root C is also influenced by the study region mainly driven by differences in soil characteristics and climate which reflect in plant composition variations, with averages of 0.7 ± 0.1 yr (n = 9) on mostly organic sandy soils in northern Germany and of 1.8 ± 0.3 yr (n = 9) and 2.6 ± 0.3 (n = 9) in more silty and clayey soils respectively in central and southern Germany. Our results indicate an internal redistribution of C in perennial species and suggest linkages between fine root C age and management in grasslands. These findings improve our ability to predict and model belowground C fluxes across broader spatial scales.

Solly, E.; Schöning, I.; Boch, S.; Müller, J.; Socher, S. A.; Trumbore, S. E.; Schrumpf, M.

2013-03-01

34

Off-season carbon dioxide exchange of a temperate mountain grassland in a warmer future climate  

NASA Astrophysics Data System (ADS)

It is well established that warming leads to an earlier onset and delayed termination of seasonal plant activity in the Northern hemisphere. Whether this goes along with an increase or decrease in the carbon dioxide (CO2) sink strength of terrestrial ecosystems, however, is much more controversial. We used a simple model that considers temperature and day length to simulate the off-season, i.e. between the end and the start of the carbon uptake period (CUP), CO2 exchange of a temperate mountain grassland in Austria. The model was calibrated with a 10-year record of eddy covariance CO2 flux measurements. Our major findings were: The end of the CUP of this managed grassland was determined not by environmental conditions but by the timing of the final harvest, because the temperature response of daytime net carbon uptake in autumn was too weak to compensate for nighttime carbon losses. A critical day length, reached by the end of March, exists below which net carbon gain was impossible on a daily basis. Using five climate scenarios and comparing the periods 1961-1990 and 2021-2050 we were able to show that earlier onsets of the CUP under future warmer conditions (+1.0 to +1.7°C) were by far offset by earlier snow melting dates and thus a lengthening of the period before the critical day length was reached. In total however, off-season losses hardly differed between the two investigated periods, which was due to compensating effects of larger CO2 losses in autumn and spring and smaller losses during winter. Taken together our study suggests the off-season CO2 exchange of temperate mountain grasslands to be resilient against climate change scenarios predicted for the middle of the 21st century.

Wohlfahrt, G.; Gobiet, A.; Hammerle, A.; Haslwanter, A.; Hörtnagl, L.; Irschick, Ch.; Themeßl, M.

2012-04-01

35

Mapping vegetation cover of grassland ecosystem for desertification monitoring in Hulun Buir of Inner Mongolia, China  

NASA Astrophysics Data System (ADS)

Grassland ecosystem degradation and desertification has been highly concerned in China for years because such degradation is perceived to directly relate with the occurrence of sandstorms invading into north China. In this study we intend to map the spatial-temporal variation of vegetation cover density from remote sensing data in Hulun Buir, a typical grassland ecosystem with the highest biomass productivity in Inner Mongolia of China. Since NDVI is a good indicator of vegetation, a practical approach had been developed in the study to map the spatial-temporal variation of the vegetation cover. The MODIS satellite data were used for the mapping. Results from our study indicated that the vegetation cover rate had been steadily decreasing in recent years, with relatively high spatial and temporal variation. Our study reveals that the rate on average has a trend of steadily decreasing in recent years. In 2000 the rate was above 80.6% on average, while it decreased to below 76.5% in 2006. Generally the west part of the region had much lower vegetation cover rate than the east part, probably due to the fact that the east part was dominated with forest ecosystem while the west part with fragile grassland. The counties of Xinbaerhuyou Banner and Manzhouli in the west part had the lowest vegetation cover rate among the 13 counties. As to the grassland types, lowland meadow had the highest vegetation cover rate while the temperate meadow and steppe had the lowest, indicating that ecosystem degradation was very serious in the temperate meadow and steppe, which were mainly distributed in the west part of the region. Though many factors might contribute to the decrease of vegetation cover, annual precipitation vibration had very good correspondence with the up-and-down change of vegetation cover in the region. In addition, overgrazing also played an important role in accelerating the degradation under the drought year. Therefore, we were able to conclude that the grassland ecosystem in Hulun Buir was under a very serious situation of degradation and desertification. Our study suggested that the change of vegetation cover rate could be an applicable indicator for grassland ecosystem monitoring required urgently to combat grassland degradation and desertification in arid and semiarid region.

Qin, Zhihao; Zhu, Yuxia; Li, Wenjuan; Xu, Bin

2008-10-01

36

A decision scheme to indicate dominant hydrological flow processes on temperate grassland  

Microsoft Academic Search

A decision scheme has been developed to indicate the likely dominant runoff forming on temperate grassland hill slopes. The decision scheme was developed from data collected from sprinkler experiments on 60 m2 plots at a number of grassland sites in Switzerland. The scheme requires input of hydrological properties of the surface and each major horizon of the soil. Worked examples

Simon Scherrer; Felix Naef

2003-01-01

37

Factors affecting the ozone sensitivity of temperate European grasslands: An overview  

Microsoft Academic Search

This overview of experimentally induced effects of ozone aims to identify physiological and ecological principles, which can be used to classify the sensitivity to ozone of temperate grassland communities in Europe. The analysis of data from experiments with single plants, binary mixtures and multi-species communities illustrates the difficulties to relate individual responses to communities, and thus to identify grassland communities

S. Bassin; M. Volk; J. Fuhrer

2007-01-01

38

Controls on winter ecosystem respiration in temperate and boreal ecosystems  

NASA Astrophysics Data System (ADS)

Winter CO2 fluxes represent an important component of the annual carbon budget in northern ecosystems. Understanding winter respiration processes and their responses to climate change is also central to our ability to assess terrestrial carbon cycle and climate feedbacks in the future. However, the factors influencing the spatial and temporal patterns of winter ecosystem respiration (Reco) of northern ecosystems are poorly understood. For this reason, we analyzed eddy covariance flux data from 57 ecosystem sites ranging from ~35° N to ~70° N. Deciduous forests were characterized by the highest winter Reco rates (0.90 ± 0.39 g C m-2 d-1), when winter is defined as the period during which daily air temperature remains below 0 °C. By contrast, arctic wetlands had the lowest winter Reco rates (0.02 ± 0.02 g C m-2 d-1). Mixed forests, evergreen needle-leaved forests, grasslands, croplands and boreal wetlands were characterized by intermediate winter Reco rates (g C m-2 d-1) of 0.70(±0.33), 0.60(±0.38), 0.62(±0.43), 0.49(±0.22) and 0.27(±0.08), respectively. Our cross site analysis showed that winter air (Tair) and soil (Tsoil) temperature played a dominating role in determining the spatial patterns of winter Reco in both forest and managed ecosystems (grasslands and croplands). Besides temperature, the seasonal amplitude of the leaf area index (LAI), inferred from satellite observation, or growing season gross primary productivity, which we use here as a proxy for the amount of recent carbon available for Reco in the subsequent winter, played a marginal role in winter CO2 emissions from forest ecosystems. We found that winter Reco sensitivity to temperature variation across space (QS) was higher than the one over time (interannual, QT). This can be expected because QS not only accounts for climate gradients across sites but also for (positively correlated) the spatial variability of substrate quantity. Thus, if the models estimate future warming impacts on Reco based on QS rather than QT, this could overestimate the impact of temperature changes.

Wang, T.; Ciais, P.; Piao, S. L.; Ottlé, C.; Brender, P.; Maignan, F.; Arain, A.; Cescatti, A.; Gianelle, D.; Gough, C.; Gu, L.; Lafleur, P.; Laurila, T.; Marcolla, B.; Margolis, H.; Montagnani, L.; Moors, E.; Saigusa, N.; Vesala, T.; Wohlfahrt, G.; Koven, C.; Black, A.; Dellwik, E.; Don, A.; Hollinger, D.; Knohl, A.; Monson, R.; Munger, J.; Suyker, A.; Varlagin, A.; Verma, S.

2011-07-01

39

Ecosystem respiration depends strongly on photosynthesis in a temperate heath  

Microsoft Academic Search

We measured net ecosystem CO2 flux (F\\u000a n) and ecosystem respiration (R\\u000a E), and estimated gross ecosystem photosynthesis (P\\u000a g) by difference, for two years in a temperate heath ecosystem using a chamber method. The exchange rates of carbon were high\\u000a and of similar magnitude as for productive forest ecosystems with a net ecosystem carbon gain during the second year

Klaus S. Larsen; Andreas Ibrom; Claus Beier; Sven Jonasson; Anders Michelsen

2007-01-01

40

Grasslands  

Microsoft Academic Search

\\u000a In this chapter, exchange dynamics of greenhouse gases over Hungarian grassland ecosystems are analyzed. Carbon dioxide (CO2) exchange was measured by eddy covariance technique at three sites (Bugac, Mátra, and Hegyhátsál). Methane (CH4) and nitrous oxide (N2O) fluxes were occasionally measured by static chamber method partly at the same grassland sites and at a wetland site. Dry\\u000a grasslands (Bugac and

Zoltán Nagy; Zoltán Barcza; László Horváth; János Balogh; Andrea Hagyó; Noémi Káposztás; Balázs Grosz; Attila Machon; Krisztina Pintér

41

Nitrogen retention efficiency and nitrogen losses of a managed and phytodiverse temperate grassland  

NASA Astrophysics Data System (ADS)

In consequence of the increasing global population, it is necessary to keep N losses at the minimum while maintaining soil fertility and high yields. The goal of our study was to assess how management practices and sward functional diversity affected N losses and N retention efficiency in a temperate grassland. We measured N retention efficiency as the ratio of N losses (N2O emission and NO3- and DON leaching) to soil available N (gross N mineralization rates). Our study was conducted in a grassland management experiment (GRASSMAN) located in Solling, Germany; the experimental design was three-factorial with two mowing frequencies (cut once and thrice per year), two fertilization treatments (180 - 30 - 100 kg NPK ha-1 yr-1 and no fertilization), and three sward compositions (dicot-enhanced swards with nearly equal proportions of dicots and monocots, control swards with ~ 70% monocots and ~ 30% dicots and monocot-enhanced swards with ~90% monocots and 10% dicots). N2O emission and NO3 leaching were significantly increased by fertilization and decreased by more frequent mowing. An interaction between these factors showed that frequent mowing can mitigate the negative effects of fertilization on N losses. N retention efficiency was largely influenced by fertilization and sward composition: N retention efficiencies were larger in unfertilized plots than fertilized plots, and decreased in the order of control > dicot-enhanced > monocot-enhanced swards. Microbial N immobilization turned out to be more important for N retention than plant N uptake. We concluded that over the past 5 decades the prevailing management practices have led to an equilibrium sward composition in this grassland ecosystem in which optimal proportions of monocots and dicots (i.e. unmanipulated control plots) developed to maximize N retention efficiency. Deviations from these proportions reduce N retention efficiency.

Keuter, A.

2012-04-01

42

Acetaldehyde exchange above a managed temperate mountain grassland  

NASA Astrophysics Data System (ADS)

An overview of acetaldehyde exchange above a managed temperate mountain grassland in Austria over four growing seasons is presented. The meadow acted as a net source of acetaldehyde in all four years, emitting between 7 and 28 mg C m-2 over the whole growing period. The cutting of the meadow resulted in huge acetaldehyde emission bursts on the day of harvesting or one day later. During undisturbed conditions, both uptake and emission fluxes were recorded. The bidirectional nature of acetaldehyde fluxes was also reflected by clear diurnal cycles during certain time periods, indicating strong deposition processes before the 1st cut and emission towards the end of the growing season. The analysis of acetaldehyde compensation points revealed a complex relationship between ambient acetaldehyde mixing ratios and respective fluxes, significantly influenced by multiple environmental parameters and variable throughout the year. As a major finding of this study, we identified both a positive and negative correlation between concentration and flux on a daily scale, where soil temperature and soil water content were the most significant factors in determining the direction of the slope. In turn, this bidirectional relationship on a daily scale resulted in compensation points between 0.40 ppbv and 0.54 ppbv, which could be well explained by collected ancillary data. We conclude that in order to model acetaldehyde fluxes at the site in Neustift on a daily scale over longer time periods, it is crucial to know the type of relationship, i.e. the direction of the slope, between mixing ratios and fluxes on a given day.

Hörtnagl, L.; Bamberger, I.; Graus, M.; Ruuskanen, T. M.; Schnitzhofer, R.; Walser, M.; Unterberger, A.; Hansel, A.; Wohlfahrt, G.

2013-10-01

43

Water relations in grassland and desert ecosystems exposed to elevated atmospheric CO2.  

PubMed

Atmospheric CO2 enrichment may stimulate plant growth directly through (1) enhanced photosynthesis or indirectly, through (2) reduced plant water consumption and hence slower soil moisture depletion, or the combination of both. Herein we describe gas exchange, plant biomass and species responses of five native or semi-native temperate and Mediterranean grasslands and three semi-arid systems to CO2 enrichment, with an emphasis on water relations. Increasing CO2 led to decreased leaf conductance for water vapor, improved plant water status, altered seasonal evapotranspiration dynamics, and in most cases, periodic increases in soil water content. The extent, timing and duration of these responses varied among ecosystems, species and years. Across the grasslands of the Kansas tallgrass prairie, Colorado shortgrass steppe and Swiss calcareous grassland, increases in aboveground biomass from CO2 enrichment were relatively greater in dry years. In contrast, CO2-induced aboveground biomass increases in the Texas C3/C4 grassland and the New Zealand pasture seemed little or only marginally influenced by yearly variation in soil water, while plant growth in the Mojave Desert was stimulated by CO2 in a relatively wet year. Mediterranean grasslands sometimes failed to respond to CO2-related increased late-season water, whereas semiarid Negev grassland assemblages profited. Vegetative and reproductive responses to CO2 were highly varied among species and ecosystems, and did not generally follow any predictable pattern in regard to functional groups. Results suggest that the indirect effects of CO2 on plant and soil water relations may contribute substantially to experimentally induced CO2-effects, and also reflect local humidity conditions. For landscape scale predictions, this analysis calls for a clear distinction between biomass responses due to direct CO2 effects on photosynthesis and those indirect CO2 effects via soil moisture as documented here. PMID:15156395

Morgan, J A; Pataki, D E; Körner, C; Clark, H; Del Grosso, S J; Grünzweig, J M; Knapp, A K; Mosier, A R; Newton, P C D; Niklaus, P A; Nippert, J B; Nowak, R S; Parton, W J; Polley, H W; Shaw, M R

2004-05-20

44

Carbon dioxide and water vapor exchange in a warm temperate grassland  

Microsoft Academic Search

Grasslands cover about 40% of the ice-free global terrestrial surface, but their contribution to local and regional water and carbon fluxes and sensitivity to climatic perturbations such as drought remains uncertain. Here, we assess the direction and magnitude of net ecosystem carbon exchange (NEE) and its components, ecosystem carbon assimilation ( A c) and ecosystem respiration ( R E), in

K. A. Novick; P. C. Stoy; G. G. Katul; D. S. Ellsworth; M. B. S. Siqueira; J. Juang; R. Oren

2004-01-01

45

Influence of organic and mineral N fertiliser on N 2O fluxes from a temperate grassland  

Microsoft Academic Search

The aim of this study was to quantify N2O release from temperate grassland receiving different forms of N, and to assess the importance of controlling variables in the environment. In 2002 and 2003 three organic manures (sewage sludge pellets, poultry manure and cattle slurry) and two mineral fertilisers (NH4NO3 and urea) were applied to grassland in SE Scotland. All plots

S. K. Jones; R. M. Rees; U. M. Skiba; B. C. Ball

2007-01-01

46

Effects of Predator Hunting Mode on Grassland Ecosystem Function  

Microsoft Academic Search

The way predators control their prey populations is determined by the interplay between predator hunting mode and prey antipredator behavior. It is uncertain, however, how the effects of such interplay control ecosystem function. A 3-year experiment in grassland mesocosms revealed that actively hunting spiders reduced plant species diversity and enhanced aboveground net primary production and nitrogen mineralization rate, whereas sit-and-wait

Oswald J. Schmitz

2008-01-01

47

Black carbon in grassland ecosystems of the world  

Microsoft Academic Search

Black carbon (BC) is the product of incomplete burning processes and a significant component of the passive soil organic carbon (SOC) pool. The role of BC in the global carbon cycle is still unclear. This study aimed to quantify and characterize BC in major grassland ecosystems of the world. Twenty-eight representative soil profiles (mainly Mollisols) were sampled in the Russian

Andrej Rodionov; Wulf Amelung; Norman Peinemann; Ludwig Haumaier; Xudong Zhang; Markus Kleber; Bruno Glaser; Inga Urusevskaya; Wolfgang Zech

2010-01-01

48

Grasslands ecosystems, endangered species, and sustainable ...  

Treesearch

Description: The semi-arid grasslands in the Mexico-United States border region are ... translations, and the papers have been printed in both languages. ... by U.S. Government employees on official time, and is therefore in the public domain.

49

Assessing catchment-scale erosion and yields of suspended solids from improved temperate grassland.  

PubMed

This paper quantifies the yields of suspended solids (SS) from a headwater catchment managed as improved temperate grassland, providing the first direct, catchment-scale evidence of the rates of erosion from this land-use in the UK and assessing the threat posed to aquatic ecosystems. High-resolution monitoring of catchment hydrology and the concentrations of SS and volatile organic matter (VOM) were carried out in the first-order channel of the Den Brook headwater catchment in Devon (UK) during the 2006-2007 hydrological season. The widely used 'rating curve' (discharge-concentration) approach was employed to estimate yields of SS, but as demonstrated by previous researchers, this study showed that discharge is a poor predictor of SS concentrations and therefore any yields estimated from this technique are likely to be highly uncertain. Nevertheless, for the purpose of providing estimates of yields that are comparable to previous studies on other land uses/sources, this technique was adopted albeit in an uncertainty-based framework. The findings suggest that contrary to the common perception, grasslands can be erosive landscapes with SS yields from this catchment estimated to be between 0.54 and 1.21 t ha(-1) y(-1). In terms of on-site erosion problems, this rate of erosion does not significantly exceed the commonly used 'tolerable' threshold in the UK ( approximately 1 t ha(-1) y(-1)). In terms of off-site erosion problems, it is argued here that the conventional expression of SS yield as a bulk annual figure has little relevance to the water quality and ecological status of surface waters and therefore an alternative technique (the concentration-frequency curve) is developed within this paper for the specific purpose of assessing the ecological threat posed by the delivery of SS into surface waters. This technique illustrates that concentrations of SS recorded at the catchment outlet frequently exceed the water quality guidelines, such as those of the EU Freshwater Fisheries Directive (78/659/EC), and pose a serious threat to aquatic organisms. It is suggested that failure to recognise improved temperate grasslands as a potential source of particulate material could result in the non-compliance of surface waters to water quality guidelines, deterioration of ecological status and failure of water quality remediation measures. PMID:20445863

Bilotta, G S; Krueger, T; Brazier, R E; Butler, P; Freer, J; Hawkins, J M B; Haygarth, P M; Macleod, C J A; Quinton, J N

2010-01-15

50

Irrigation and enhanced soil carbon input effects on below-ground carbon cycling in semiarid temperate grasslands.  

PubMed

Global climate change is generally expected to increase net primary production, resulting in increased soil carbon (C) inputs. To gain an understanding of how such increased soil C inputs would affect C cycling in the vast grasslands of northern China, we conducted a field experiment in which the responses of plant and microbial biomass and respiration were studied. Our experiment included the below-ground addition of particulate organic matter (POM) at rates equivalent to 0, 60, 120 and 240 g C m(-2), under either natural precipitation or under enhanced precipitation during the summer period (as predicted for that region in recent simulations using general circulation models). We observed that addition of POM had a large effect on soil microbial biomass and activity and that a major part of the added C was rapidly lost from the system. This suggests that microbial activity in the vast temperate grassland ecosystems of northern China is energy-limited. Moreover, POM addition (and the associated nutrient release) affected plant growth much more than the additional water input. Although we performed no direct fertilization experiments, the response of plant productivity to POM addition (and associated release of nutrients) leads us to believe that plant productivity in the semiarid grassland ecosystems of northern China is primarily limited by nutrients and not by water. PMID:17504466

Xiao, Chunwang; Janssens, Ivan A; Liu, Ping; Zhou, Zhiyong; Sun, Osbert J

2007-01-01

51

Water-mediated responses of ecosystem carbon fluxes to climatic change in a temperate steppe.  

PubMed

Global warming and a changing precipitation regime could have a profound impact on ecosystem carbon fluxes, especially in arid and semiarid grasslands where water is limited. A field experiment manipulating temperature and precipitation has been conducted in a temperate steppe in northern China since 2005. A paired, nested experimental design was used, with increased precipitation as the primary factor and warming simulated by infrared radiators as the secondary factor. The results for the first 2 yr showed that gross ecosystem productivity (GEP) was higher than ecosystem respiration, leading to net C sink (measured by net ecosystem CO(2) exchange, NEE) over the growing season in the study site. The interannual variation of NEE resulted from the difference in mean annual precipitation. Experimental warming reduced GEP and NEE, whereas increased precipitation stimulated ecosystem C and water fluxes in both years. Increased precipitation also alleviated the negative effect of experimental warming on NEE. The results demonstrate that water availability plays a dominant role in regulating ecosystem C and water fluxes and their responses to climatic change in the temperate steppe of northern China. PMID:17944829

Niu, Shuli; Wu, Mingyu; Han, Yi; Xia, Jianyang; Li, Linghao; Wan, Shiqiang

2007-10-17

52

Ecosystem Consequences of Exotic Earthworm Invasion of North Temperate Forests  

Microsoft Academic Search

The invasion of north temperate forests by exotic species of earthworms is an important issue that has been overlooked in the study and management of these forests. We initiated research to address the hypothesis that earthworm invasion will have large consequences for nutrient retention and uptake in these ecosystems. In this special feature of Ecosystems, we present five papers describing

Patrick J. Bohlen; Peter M. Groffman; Timothy J. Fahey; Melany C. Fisk; Esteban Suarez; Derek M. Pelletier; Robert T. Fahey

2004-01-01

53

Predicting risk of habitat conversion in native temperate grasslands.  

PubMed

Native grasslands that support diverse populations of birds are being converted to cropland at an increasing rate in the Prairie Pothole Region of North America. Although limited funding is currently available to mitigate losses, accurate predictions of probability of conversion would increase the efficiency of conservation measures. We studied conversion of native grassland to cropland in the Missouri Coteau region of North and South Dakota (U.S.A.) during 1989-2003. We estimated the probability of conversion of native grassland to cropland with satellite imagery and logistic regression models that predicted risk of conversion and by comparing the overlap between areas of high biological value and areas most vulnerable to conversion. Annualized probability of conversion was 0.004, and 36,540 ha of native grassland were converted to cropland during the period of our study. Our predictive models fit the data and correctly predicted 70% of observed conversions of grassland. Probability of conversion varied spatially and was correlated with landscape features like amount of surrounding grassland, slope, and soil productivity. Tracts of high biological value were not always at high risk of conversion. We concluded the most biologically valuable areas that are most vulnerable to conversion should be prioritized for conservation. This approach can be applied broadly to other systems and offers great utility for implementing conservation in areas with spatially variable biological value and probability of conversion. PMID:18717691

Stephens, Scott E; Walker, Johann A; Blunck, Darin R; Jayaraman, Aneetha; Naugle, David E; Ringelman, James K; Smith, Aaron J

2008-08-19

54

Soil water retention after natural and simulated rainfall on a temperate grassland  

Microsoft Academic Search

Recent climate change scenarios resulting from elevated trace gasses may alter environmental temperature and moisture. The ecological consequences, however, are uncertain requiring an understanding of how soil-plant systems will respond to different conditions. This study examines the temporal characteristics of soil water retention in a temperate grassland following natural and simulated summer showers. We have used weighting lysimeters located in

J. M. Welker; S. McClelland; T. Weaver

1991-01-01

55

INTERACTIONS BETWEEN FIRE AND INVASIVE PLANTS IN TEMPERATE GRASSLANDS OF NORTH AMERICA  

Microsoft Academic Search

A substantial number of invasive grasses, forbs and woody plants have invaded temperate grasslands in North America. Among the invading species are winter annuals, biennials, cool-season perennials, warm-season perennials, vines, shrubs, and trees. Many of these species have been deliberately introduced and widely planted; some are still used for range improvement, pastures, lawns, and as ornamentals, though many are listed

James B. Grace; Melinda D. Smith; Susan L. Grace; Scott L. Collins; Thomas J. Stohlgren

2002-01-01

56

Snake species distributions and temperate grasslands: A case study from the American tallgrass prairie  

Microsoft Academic Search

Many snake species are declining globally, yet data unavailability in temperate grasslands hinders snake conservation in one of the world’s most endangered biomes. To encourage and inform the conservation of snakes in these regions, I examined snake species diversity and abundance during 2 years of a mark-recapture study at 22 sites located in six American tallgrass prairie preserves in northern

Nicolette L. Cagle

2008-01-01

57

Seasonal variation of arbuscular mycorrhizal fungi in temperate grasslands along a wide hydrologic gradient  

Microsoft Academic Search

We studied seasonal variation in population attributes of arbuscular mycorrhizal (AM) fungi over 2 years in four sites of temperate grasslands of the Argentinean Flooding Pampas. The sites represent a wide range of soil conditions, hydrologic gradients, and floristic composition. Lotus glaber, a perennial herbaceous legume naturalised in the Flooding Pampas, was dominant at the four plant community sites. Its

Viviana Escudero; Rodolfo Mendoza

2005-01-01

58

The carbon budget of newly established temperate grassland depends on management intensity  

Microsoft Academic Search

The carbon exchange of managed temperate grassland, previously converted from arable rotation, was quantified for two levels of management intensities over a period of 3 years. The original field on the Swiss Central Plateau had been separated into two plots of equal size, one plot was subjected to intensive management with nitrogen inputs of 200kgha?1year?1 and frequent cutting, and the

C. Ammann; C. R. Flechard; J. Leifeld; A. Neftel; J. Fuhrer

2007-01-01

59

Effects of recurring summer droughts on ecosystem photosynthesis and respiration in a mountain grassland  

NASA Astrophysics Data System (ADS)

Climatic changes in mountain regions play a key role in current and future grassland ecosystem processes. It is currently expected that droughts and heatwaves will become more frequent in a changing climate. All around the world mountain regions have been labelled as sensitive zones, where declining water availability and increasing temperature are expected to increase the vulnerability of these ecosystems. However, the effects of such extreme events on ecosystem carbon (C) fluxes and their coupling in temperate and so far non-water limited Alpine grasslands are not yet well understood. We studied effects of recurring summer drought on the C dynamics of a mountain meadow at 1820 m and an abandoned grassland at 2000 m in the Austrian Central Alps. The aim of the study was (1) to analyse the multiannual effect of drought on net ecosystem CO2 exchange (NEE) and its major component processes, i.e. gross primary productivity (GPP) and ecosystem respiration (Reco), and (2) to trace drought effects on the use of recent C in soil respiration. We tested the hypothesis that drought reduces NEE, GPP and Reco and the ratio of GPP / Reco and causes a reduction in the use of recent photoassimilates in belowground respiration. At each study site, exclusion of rainfall was achieved by establishing rain-out shelters for a period of two months (June, July), while control plots remained exposed to natural precipitation. To trace the fate of recent C from assimilation to respiration 13CO2 pulse-labelling was carried out at the meadow site, and the carbon isotope composition of soil respired CO2 was continuously monitored with an open dynamic-chamber system coupled with a quantum cascade laser. Our results showed that at both sites NEE, GPP and Reco showed a consistent reduction with reduction in soil water level. Drought reduced ecosystem respiration to a lesser extent than photosynthesis. We observed memory effects on all flux processes after 3 years of recurring drought on the mountain meadow, which was likely due to shifts in the abundance of dominant species. Within the first 30 days after labelling, the contribution of recent C to the main component process of ecosystem respiration (soil respiration) was slightly reduced in the drought plots. We conclude that 1) a summer drought may potentially alter the carbon balance of mountain grasslands towards decreasing photosynthesis and assimilation area, whereas 2) repeated drought may lead to adaptation of the ecosystem which reduces the drought response of C fluxes, and 3) summer drought may reduce the contribution of recent C to belowground respiration.

Schmitt, Michael; Ingrisch, Johannes; Sturm, Patrick; Ladreiter-Knauss, Thomas; Hasibeder, Roland; Bramboeck, Peter; Berger, Vanessa; Bahn, Michael

2013-04-01

60

Ecosystem carbon and nitrogen accumulation after grazing exclusion in semiarid grassland.  

PubMed

The grazing exclusion in degraded grassland has been extensively used to prevent the loss of grassland resources and to improve grassland services. The effects of grazing exclusion on C and N balance, however, have not been well addressed but are essential for assessing grassland C sinks, the sustainable use of grassland resources and the support of grassland services. To understand the response of ecosystem C and N to grazing exclusion in semiarid grassland, we determined the C and N in litter, aboveground biomass, roots and soils from ungrazed grassland fenced at different times in northwest China. Our results showed that the aboveground biomass, root biomass and plant litter were 70-92%, 56-151% and 59-141% higher, respectively, in grazer excluded grassland than in grazed grassland. Grazing exclusion significantly increased C and N stored in plant biomass and litter and increased the concentrations and stocks of C and N in soils. Grazing exclusion thus significantly increased the C and N stored in grassland ecosystems. The increase in C and N stored in soil contributed to more than 95% and 97% of the increases in ecosystem C and N storage. The highest C and N stocks in ecosystems were observed in 17-year grazer excluded grassland. The results from this study indicate that grazing exclusion has the potential to increase C and N storage in degraded semiarid grassland and that the recovery of ecosystem C and N was mainly due to the accumulation of C and N in soils. PMID:23383191

Qiu, Liping; Wei, Xiaorong; Zhang, Xingchang; Cheng, Jimin

2013-01-30

61

Ecosystem Carbon and Nitrogen Accumulation after Grazing Exclusion in Semiarid Grassland  

PubMed Central

The grazing exclusion in degraded grassland has been extensively used to prevent the loss of grassland resources and to improve grassland services. The effects of grazing exclusion on C and N balance, however, have not been well addressed but are essential for assessing grassland C sinks, the sustainable use of grassland resources and the support of grassland services. To understand the response of ecosystem C and N to grazing exclusion in semiarid grassland, we determined the C and N in litter, aboveground biomass, roots and soils from ungrazed grassland fenced at different times in northwest China. Our results showed that the aboveground biomass, root biomass and plant litter were 70–92%, 56–151% and 59–141% higher, respectively, in grazer excluded grassland than in grazed grassland. Grazing exclusion significantly increased C and N stored in plant biomass and litter and increased the concentrations and stocks of C and N in soils. Grazing exclusion thus significantly increased the C and N stored in grassland ecosystems. The increase in C and N stored in soil contributed to more than 95% and 97% of the increases in ecosystem C and N storage. The highest C and N stocks in ecosystems were observed in 17-year grazer excluded grassland. The results from this study indicate that grazing exclusion has the potential to increase C and N storage in degraded semiarid grassland and that the recovery of ecosystem C and N was mainly due to the accumulation of C and N in soils.

Qiu, Liping; Wei, Xiaorong; Zhang, Xingchang; Cheng, Jimin

2013-01-01

62

Factors affecting the ozone sensitivity of temperate European grasslands: an overview.  

PubMed

This overview of experimentally induced effects of ozone aims to identify physiological and ecological principles, which can be used to classify the sensitivity to ozone of temperate grassland communities in Europe. The analysis of data from experiments with single plants, binary mixtures and multi-species communities illustrates the difficulties to relate individual responses to communities, and thus to identify grassland communities most at risk. Although there is increasing evidence that communities can be separated into broad classes of ozone sensitivity, the database from experiments under realistic conditions with representative systems is too small to draw firm conclusions. But it appears that risk assessments, based on results from individuals or immature mixtures exposed in chambers, are only applicable to intensively managed, productive grasslands, and that the risk of ozone damage for most of perennial grasslands with lower productivity tends to be less than previously expected. PMID:16904248

Bassin, S; Volk, M; Fuhrer, J

2006-08-10

63

Trophic diversity in two grassland ecosystems.  

PubMed

The roles of consumers (top-down forces) versus resources (bottom-up forces) as determinants of alpha diversity in a community are not well studied. Numerous community ecology models and empirical studies have provided a framework for understanding how density at various trophic levels responds to variation in the relative strength of top-down and bottom-up forces. The resulting trophic theory can be applied to understanding variation in insect diversity at different trophic levels. The objective of this research was to elucidate the strengths of direct and indirect interactions between plants and entire arthropod communities to determine the effects of trophic interactions on arthropod diversity. Grassland plant and insect diversity was measured in July 2001 to document patterns of diversity at multiple trophic levels. The study site includes riparian grasslands in North-Central Colorado on the Carpenter Ranch, owned and managed by The Nature Conservancy. This pastureland consists of sites with different management regimes: unmanaged pasture intermixed along riparian forest, and cattle grazed pasture with flood irrigation. Plant abundance and richness were higher on the grazed-irrigated pasture versus the unmanaged field. Path analysis revealed strong effects of herbivore diversity on diversity of other trophic levels. For the managed fields, top-down forces were important, with increases in enemy diversity depressing herbivore diversity, which in turn depressed plant abundance. For the unmanaged fields, bottom-up forces dominated, with increases in plant diversity causing increased herbivore diversity, which in turn increased enemy diversity. These results support hypotheses from other empirical studies, demonstrating that changes in diversity of a single trophic level can cascade to effect diversity at other, nonadjacent trophic levels. PMID:19537996

Pearson, Clark V; Dyer, Lee A

2006-01-01

64

Plant Functional Group Composition Modifies the Effects of Precipitation Change on Grassland Ecosystem Function  

PubMed Central

Temperate grassland ecosystems face a future of precipitation change, which can alter community composition and ecosystem functions through reduced soil moisture and waterlogging. There is evidence that functionally diverse plant communities contain a wider range of water use and resource capture strategies, resulting in greater resistance of ecosystem function to precipitation change. To investigate this interaction between composition and precipitation change we performed a field experiment for three years in successional grassland in southern England. This consisted of two treatments. The first, precipitation change, simulated end of century predictions, and consisted of a summer drought phase alongside winter rainfall addition. The second, functional group identity, divided the plant community into three groups based on their functional traits- broadly described as perennials, caespitose grasses and annuals- and removed these groups in a factorial design. Ecosystem functions related to C, N and water cycling were measured regularly. Effects of functional groupidentity were apparent, with the dominant trend being that process rates were higher under control conditions where a range of perennial species were present. E.g. litter decomposition rates were significantly higher in plots containing several perennial species, the group with the highest average leaf N content. Process rates were also very strongly affected by the precipitation change treatmentwhen perennial plant species were dominant, but not where the community contained a high abundance of annual species and caespitose grasses. This contrasting response could be attributable to differing rooting patterns (shallower structures under annual plants, and deeper roots under perennials) and faster nutrient uptake in annuals compared to perennials. Our results indicate that precipitation change will have a smaller effect on key process rates in grasslandscontaining a range of perennial and annual species, and that maintaining the presence of key functional groups should be a crucial consideration in future grassland management.

Fry, Ellen L.; Manning, Pete; Allen, David G. P.; Hurst, Alex; Everwand, Georg; Rimmler, Martin; Power, Sally A.

2013-01-01

65

Plant functional group composition modifies the effects of precipitation change on grassland ecosystem function.  

PubMed

Temperate grassland ecosystems face a future of precipitation change, which can alter community composition and ecosystem functions through reduced soil moisture and waterlogging. There is evidence that functionally diverse plant communities contain a wider range of water use and resource capture strategies, resulting in greater resistance of ecosystem function to precipitation change. To investigate this interaction between composition and precipitation change we performed a field experiment for three years in successional grassland in southern England. This consisted of two treatments. The first, precipitation change, simulated end of century predictions, and consisted of a summer drought phase alongside winter rainfall addition. The second, functional group identity, divided the plant community into three groups based on their functional traits- broadly described as perennials, caespitose grasses and annuals- and removed these groups in a factorial design. Ecosystem functions related to C, N and water cycling were measured regularly. Effects of functional groupidentity were apparent, with the dominant trend being that process rates were higher under control conditions where a range of perennial species were present. E.g. litter decomposition rates were significantly higher in plots containing several perennial species, the group with the highest average leaf N content. Process rates were also very strongly affected by the precipitation change treatmentwhen perennial plant species were dominant, but not where the community contained a high abundance of annual species and caespitose grasses. This contrasting response could be attributable to differing rooting patterns (shallower structures under annual plants, and deeper roots under perennials) and faster nutrient uptake in annuals compared to perennials. Our results indicate that precipitation change will have a smaller effect on key process rates in grasslandscontaining a range of perennial and annual species, and that maintaining the presence of key functional groups should be a crucial consideration in future grassland management. PMID:23437300

Fry, Ellen L; Manning, Pete; Allen, David G P; Hurst, Alex; Everwand, Georg; Rimmler, Martin; Power, Sally A

2013-02-20

66

Effects of grassland conversion to croplands on soil organic carbon in the temperate Inner Mongolia.  

PubMed

This study investigated the effects of grassland conversion to croplands on soil organic carbon (SOC) in a typical grassland-dominated basin of the Inner Mongolia using direct field samplings. The results indicated that SOC contents decreased usually with increasing soil depth, with significant differences between the upper horizons (0-30cm) and the underlying horizons (30-100cm). Also, SOC densities decreased with an increase in the depth of soils. Average SOC densities in the upper horizons were 2.6-3.7 and 6.0-8.3kgCm(-2) for desert grassland-cropland sites (sites 1 and 2) and meadow-cropland sites (sites 3 and 4), respectively, with significant differences between grasslands and croplands (P<0.05). However, the SOC densities in the underlying horizons did not significantly differ between the land uses. The SOC densities up to 100cm depth were much higher in the meadow-cropland sites than in the desert grassland-cropland sites, reaching approximately 16 and 6kgCm(-2), respectively. The SOC: total nitrogen (TN) ratios were approximately 10, with no significant difference among the soil horizons of grasslands and croplands. The conversion of grasslands to croplands induced a slight loss of SOC, with a range of from -4% to 22% for the 0-100cm soil depth over about a 35-year period, in the temperate Inner Mongolia. PMID:17254695

Wang, Zhi-Ping; Han, Xing-Guo; Li, Ling-Hao

2007-01-24

67

Effects of predator functional diversity on grassland ecosystem function.  

PubMed

Predator species individually are known to have important effects on plant communities and ecosystem functions such as production, decomposition, and elemental cycling, the nature of which is determined by a key functional trait, predator hunting mode. However, it remains entirely uncertain how predators with different hunting modes combine to influence ecosystem function. I report on an experiment conducted in a New England grassland ecosystem that quantified the net effects of a sit-and-wait and an actively hunting spider species on the plant composition and functioning of a New England grassland ecosystem. I manipulated predator functional diversity by varying the dominance ratio of the two predator species among five treatments using a replacement series design. Experimentation revealed that predator functional diversity effects propagated down the live plant-based chain to affect the levels of plant diversity, and plant litter quality, elemental cycling, and production. Moreover, many of these effects could be approximately by the weighted average of the individual predator species effects, suggesting that this kind of predator diversity effect on ecosystems is not highly nonlinear. PMID:19769111

Schmitz, Oswald J

2009-09-01

68

Soil fungal community structure in a temperate upland grassland soil  

Microsoft Academic Search

Alterations in soil microfungal community structure across a transect between a semi-natural upland grassland and an agriculturally improved enclosure were assessed using an indirect measurement of active fungal biomass (ergosterol), together with a nucleic acid approach, terminal restriction fragment length polymorphism (TRFLP), which was compared to a commonly used but less sensitive community fingerprinting technique, denaturing gradient gel electrophoresis (DGGE).

Eoin Brodie; Suzanne Edwards; Nicholas Clipson

2003-01-01

69

Short-term effects of dairy slurry amendment on carbon sequestration and enzyme activities in a temperate grassland  

Microsoft Academic Search

Land application of animal wastes from intensive grassland farming has resulted in growing environmental problems relating to greenhouse gas emissions, ammonia volatilisation, and nitrate and phosphorus leaching into surface and groundwater. We examined the short-term effects of dairy slurry amendment on carbon sequestration and enzyme activities in a temperate grassland (Southwest England). Slurry was collected from cows fed either on

R. Bol; E. Kandeler; W. Amelung; B. Glaser; M. C. Marx; N. Preedy; K. Lorenz

2003-01-01

70

Effects of predator hunting mode on grassland ecosystem function.  

PubMed

The way predators control their prey populations is determined by the interplay between predator hunting mode and prey antipredator behavior. It is uncertain, however, how the effects of such interplay control ecosystem function. A 3-year experiment in grassland mesocosms revealed that actively hunting spiders reduced plant species diversity and enhanced aboveground net primary production and nitrogen mineralization rate, whereas sit-and-wait ambush spiders had opposite effects. These effects arise from the different responses to the two different predators by their grasshopper prey-the dominant herbivore species that controls plant species composition and accordingly ecosystem functioning. Predator hunting mode is thus a key functional trait that can help to explain variation in the nature of top-down control of ecosystems. PMID:18276890

Schmitz, Oswald J

2008-02-15

71

Soil respiration flux in northern coastal temperate rainforest ecosystems  

Microsoft Academic Search

Forest carbon budgets are of increasing concern because of their linkages with changing climate. The potential source strength of northern forested ecosystems is of great interest due to the large carbon stock of these systems, especially the extensive peatlands. Where very few long-term measurements of soil carbon cycles have been made, such as the North Pacific coastal temperate margin, peatlands

D. V. D'Amore; S. M. Nay; R. Edwards; D. W. Valentine; E. W. Hood

2009-01-01

72

Soil respiration flux in northern coastal temperate rainforest ecosystems  

Microsoft Academic Search

Forest carbon budgets are of increasing concern because of their linkages with changing climate. The potential source strength of northern forested ecosystems is of great interest due to the large carbon stock of these systems, especially the extensive peatlands. Where very few long-term measurements of soil carbon cycles have been made, such as the North Pacific coastal temperate margin, peatlands

David D'Amore; S. Mark Nay; Richard Edwards; David Valentine; Eran Hood

2010-01-01

73

Tracing dung-derived carbon in temperate grassland using 13C natural abundance measurements  

Microsoft Academic Search

To understand the role of dung-derived carbon in the carbon cycle of grazed temperate grasslands, we need a procedure to trace dung-derived C. The natural 13C tracer technique of applying C4 dung to a C3 grass pasture allowed us to succesfully quantify the fate of cattle dung in the soil environment. Dung was collected from beef steers fed on either

R. Bol; W. Amelung; C. Friedrich; N. Ostle

2000-01-01

74

Grazing increases the temperature sensitivity of soil organic matter decomposition in a temperate grassland  

NASA Astrophysics Data System (ADS)

We tested the effects of ungulate grazing and nutrient availability on the temperature sensitivity of soil respiration (CO2) and methane (CH4) emissions in semi-natural temperate grassland. To do this, soil taken from long term grazed and ungrazed grassland was incubated at four temperatures (4, 10, 15 and 20?°C) with two levels of nutrient (NP) addition. The results showed that the variation in soil CO2 and CH4 emissions was explained by temperature and grazing, with grazing increasing the temperature sensitivity of CO2 and CH4 production by between 15 and 20?°C. This response was constrained by nutrient availability for CO2, but not CH4. These findings suggest that grazing could potentially have important impacts on the temperature sensitivity of greenhouse gas emissions in nutrient limited grasslands.

Paz-Ferreiro, Jorge; Medina-Roldán, Eduardo; Ostle, Nick J.; McNamara, Niall P.; Bardgett, Richard D.

2012-03-01

75

An analysis of soil respiration across northern hemisphere temperate ecosystems  

Microsoft Academic Search

Over two-thirds of terrestrial carbon is stored belowground and a significant amount of atmospheric CO2 is respired by roots and microbes in soils. For this analysis, soil respiration (Rs) data were assembled from 31 AmeriFlux and CarboEurope sites representing deciduous broadleaf, evergreen needleleaf, grasslands, mixed deciduous\\/evergreen and woodland\\/savanna ecosystem types. Lowest to highest rates of soil respiration averaged over the

K. A. Hibbard; B. E. Law; M. Reichstein; J. Sulzman

2005-01-01

76

Extensive management promotes plant and microbial nitrogen retention in temperate grassland.  

PubMed

Leaching losses of nitrogen (N) from soil and atmospheric N deposition have led to widespread changes in plant community and microbial community composition, but our knowledge of the factors that determine ecosystem N retention is limited. A common feature of extensively managed, species-rich grasslands is that they have fungal-dominated microbial communities, which might reduce soil N losses and increase ecosystem N retention, which is pivotal for pollution mitigation and sustainable food production. However, the mechanisms that underpin improved N retention in extensively managed, species-rich grasslands are unclear. We combined a landscape-scale field study and glasshouse experiment to test how grassland management affects plant and soil N retention. Specifically, we hypothesised that extensively managed, species-rich grasslands of high conservation value would have lower N loss and greater N retention than intensively managed, species-poor grasslands, and that this would be due to a greater immobilisation of N by a more fungal-dominated microbial community. In the field study, we found that extensively managed, species-rich grasslands had lower N leaching losses. Soil inorganic N availability decreased with increasing abundance of fungi relative to bacteria, although the best predictor of soil N leaching was the C/N ratio of aboveground plant biomass. In the associated glasshouse experiment we found that retention of added (15)N was greater in extensively than in intensively managed grasslands, which was attributed to a combination of greater root uptake and microbial immobilisation of (15)N in the former, and that microbial immobilisation increased with increasing biomass and abundance of fungi. These findings show that grassland management affects mechanisms of N retention in soil through changes in root and microbial uptake of N. Moreover, they support the notion that microbial communities might be the key to improved N retention through tightening linkages between plants and microbes and reducing N availability. PMID:23227252

de Vries, Franciska T; Bloem, Jaap; Quirk, Helen; Stevens, Carly J; Bol, Roland; Bardgett, Richard D

2012-12-05

77

Ecosystem change along a woody invasion chronosequence in a California grassland  

Microsoft Academic Search

Woody species have increased in abundance in many grassland ecosystems during the last century. To investigate the consequences of Baccharis pilularis encroachment into coastal California grasslands, we established a chronosequence of sites naturally invaded by Baccharis zero to 25 years ago. Increasing above- and below-ground biomass increase along the chronosequence drove increases in ecosystem N sequestration of ?700% and in

E. S. Zavaleta; L. S. Kettley

2006-01-01

78

Experimental evidence that soil fauna enhance nutrient mineralization and plant nutrient uptake in montane grassland ecosystems  

Microsoft Academic Search

This microcosm study is concerned with understanding those factors which regulate ecosystem processes of nutrient cycling and plant productivity in a montane grassland ecosystem. We examined the effects of different groups of soil fauna, namely bacterial-feeding nematodes and Collembola, on nutrient mineralization (N and P) in an acid, organic soil taken from a montane grassland in the Peak District National

Richard D Bardgett; Kin F Chan

1999-01-01

79

Carbon dioxide budget in a temperature grassland ecosystem  

NASA Astrophysics Data System (ADS)

Eddy correlation measurements of CO2 flux made during May-October 1987 and June-August 1989 were employed, in conjunction with simulated data, to examine the net exchange of CO2 in a temperature grassland ecosystem. Simulated estimates of CO2 uptake were used when flux measurements were not available. These estimates were based on daily intercepted photosynthetically active radiation, air temperature, and extractable soil water. Soil CO2 flux and dark respiration of the aerial part of plants were estimated using the relationships developed by Norman et al. (1992) and Polley et al. (1992) at the study site. The results indicate that the CO2 exchange between this ecosystem and the atmosphere is highly variable. The net ecosystem CO2 exchange reached its peak value (12-18 g/sq m d) during the period when the leaf area index was maximum. Drought, a frequent occurrence in this region, can change this ecosystem from a sink to a source for atmospheric CO2. Comparison with data on dry matter indicated that the aboveground biomass accounted for about 45-70 percent of the net carbon uptake, suggesting the importance of the below ground biomass in estimating net primary productivity in this ecosystem.

Kim, Joon; Verma, Shashi B.; Clement, Robert J.

1992-04-01

80

Effects of vegetation control on ecosystem water use efficiency within and among four grassland ecosystems in China  

Microsoft Academic Search

Through 2-3-year (2003-2005) continuous eddy covariance measurements of carbon dioxide and water vapor fluxes, we examined the seasonal, inter-annual, and inter- ecosystem variations in the ecosystem-level water use efficiency (WUE, defined as the ratio of gross primary production, GPP, to evapotranspiration, ET) at four Chinese grassland ecosystems in the Qinghai-Tibet Plateau and North China. Representing the most prevalent grassland types

ZHONGMIN H U; UI Y U; Y INGNIAN L Iz; PEILI S HI; Z HENG

81

Grasslands  

Microsoft Academic Search

\\u000a In this chapter, we examine the effects of site-specific environmental conditions and management activities on water, carbon\\u000a dioxide (CO2), methane (CH4), and nitrous oxide (N2O) fluxes of Hungarian grasslands using two process-based ecosystem models. Biome-BGC is used to simulate the CO2 budget, while DNDC is applied to simulate the CH4 and N2O budgets. Biome-BGC was originally developed to simulate the

Dóra Hidy; Attila Machon; László Haszpra; Zoltán Nagy; Krisztina Pintér; Galina Churkina; Balázs Grosz; László Horváth; Zoltán Barcza

82

Controls on soil organic carbon and nitrogen in Inner Mongolia, China: A cross-continental comparison of temperate grasslands  

NASA Astrophysics Data System (ADS)

Most global ecosystem models assume that controls over soil organic matter are alike in climatically similar regions. In this study, we tested the generality of controls over soil organic carbon (SOC) and soil organic nitrogen (SON) in temperate grasslands. We measured organic matter pools in Inner Mongolia, China, along the Northeast China Transect, and analyzed the relationship of SOC and SON to climate, soil texture, and land use variables. We then compared our data to values simulated by a regression model developed in the U.S. Great Plains and also to Century model simulations. We found that, as in the U.S. Great Plains, climate and soil texture variables could explain a large proportion of variation in observed SOC and SON, but a regression model developed in the Great Plains overestimated SOC and underestimated SON in Inner Mongolia. Using Century, we found that simulated SOC and SON values were sensitive to both inclusion of altered land use and changes in N deposition and that the model that best fit our data included higher-intensity grazing and N deposition values higher than that in the Great Plains. This model also produced aboveground net primary production (ANPP) values comparable with values observed in the literature for Inner Mongolian grasslands, but these values were higher than ANPP predicted by previously published regression models. These results suggest that different controls over SOC and SON cycling in Inner Mongolia may affect our ability to predict SOC and SON pool sizes using relationships in other regional models.

Evans, Sarah E.; Burke, Ingrid C.; Lauenroth, William K.

2011-09-01

83

Carbon dioxide and water vapor exchange in a warm temperate grassland.  

PubMed

Grasslands cover about 40% of the ice-free global terrestrial surface, but their contribution to local and regional water and carbon fluxes and sensitivity to climatic perturbations such as drought remains uncertain. Here, we assess the direction and magnitude of net ecosystem carbon exchange (NEE) and its components, ecosystem carbon assimilation ( A(c)) and ecosystem respiration ( R(E)), in a southeastern United States grassland ecosystem subject to periodic drought and harvest using a combination of eddy-covariance measurements and model calculations. We modeled A(c) and evapotranspiration (ET) using a big-leaf canopy scheme in conjunction with ecophysiological and radiative transfer principles, and applied the model to assess the sensitivity of NEE and ET to soil moisture dynamics and rapid excursions in leaf area index (LAI) following grass harvesting. Model results closely match eddy-covariance flux estimations on daily, and longer, time steps. Both model calculations and eddy-covariance estimates suggest that the grassland became a net source of carbon to the atmosphere immediately following the harvest, but a rapid recovery in LAI maintained a marginal carbon sink during summer. However, when integrated over the year, this grassland ecosystem was a net C source (97 g C m(-2) a(-1)) due to a minor imbalance between large A(c) (-1,202 g C m(-2) a(-1)) and R(E) (1,299 g C m(-2) a(-1)) fluxes. Mild drought conditions during the measurement period resulted in many instances of low soil moisture (theta<0.2 m(3)m(-3)), which influenced A(c) and thereby NEE by decreasing stomatal conductance. For this experiment, low theta had minor impact on R(E). Thus, stomatal limitations to A(c) were the primary reason that this grassland was a net C source. In the absence of soil moisture limitations, model calculations suggest a net C sink of -65 g C m(-2) a(-1) assuming the LAI dynamics and physiological properties are unaltered. These results, and the results of other studies, suggest that perturbations to the hydrologic cycle are key determinants of C cycling in grassland ecosystems. PMID:14628214

Novick, K A; Stoy, P C; Katul, G G; Ellsworth, D S; Siqueira, M B S; Juang, J; Oren, R

2003-11-20

84

The Role of Photodegradation in Surface Litter Decomposition Across a Grassland Ecosystem Precipitation Gradient  

Microsoft Academic Search

Differences in litter decomposition patterns among mesic, semiarid, and arid grassland ecosystems cannot be accurately explained\\u000a by variation in temperature, moisture, and litter chemistry alone. We hypothesized that ultraviolet (UV) radiation enhances\\u000a decomposition in grassland ecosystems via photodegradation, more so in arid compared to mesic ecosystems, and in litter that\\u000a is more recalcitrant to microbial decomposition (with high compared to

L. A. Brandt; J. Y. King; S. E. Hobbie; D. G. Milchunas; R. L. Sinsabaugh

2010-01-01

85

Forests tend to cool the land surface in the temperate zone: An analysis of the mechanisms controlling radiometric surface temperature change in managed temperate ecosystems  

NASA Astrophysics Data System (ADS)

Vegetation is an important control on the surface energy balance and thereby surface temperature. Boreal forests and arctic shrubs are thought to warm the land surface by absorbing more radiation than the vegetation they replace. The surface temperatures of tropical forests tend to be cooler than deforested landscapes due to enhanced evapotranspiration. The effects of reforestation on surface temperature change in the temperate zone is less-certain, but recent modeling efforts suggest forests have a global warming effect. We quantified the mechanisms driving radiometric surface changes following landcover changes using paired ecosystem case studies from the Ameriflux database with energy balance models of varying complexity. Results confirm previous findings that deciduous and coniferous forests in the southeastern U.S. are ca. 1 °C cooler than an adjacent field on an annual basis because aerodynamic/ecophysiological cooling of 2-3 °C outweighs an albedo-related warming of <1 °C. A 50-70% reduction in the aerodynamic resistance to sensible and latent heat exchange in the forests dominated the cooling effect. A grassland ecosystem that succeeded a stand-replacing ponderosa pine fire was ca. 1 °C warmer than unburned stands because a 1.5 °C aerodynamic warming offset a slight surface cooling due to greater albedo and soil heat flux. An ecosystem dominated by mesquite shrub encroachment was nearly 2 °C warmer than a native grassland ecosystem as aerodynamic and albedo-related warming outweighed a small cooling effect due to changes in soil heat flux. The forested ecosystems in these case studies are documented to have higher carbon uptake than the non-forested systems. Results suggest that temperate forests tend to cool the land surface and suggest that previous model-based findings that forests warm the Earth’s surface globally should be reconsidered.Changes to radiometric surface temperature (K) following changes in vegetation using paired ecosystem case studies C4 grassland and shrub ecosystem surface temperatures were adjusted for differences in air temperature across sites.

Stoy, P. C.; Katul, G. G.; Juang, J.; Siqueira, M. B.; Novick, K. A.; Essery, R.; Dore, S.; Kolb, T. E.; Montes-Helu, M. C.; Scott, R. L.

2010-12-01

86

Separating drought effects from roof artefacts on ecosystem processes in a grassland drought experiment  

NASA Astrophysics Data System (ADS)

Given the predictions of increasing risk of long drought periods under various climate change scenarios, there have been numerous experimental field studies simulating drought using transparent roofs in different ecosystems and regions. Such roofs may, however, have unknown side effects, here called artefacts, on the response variables potentially confounding experimental results and misleading conclusions. Knowing the ecosystem response to such roof artefacts is therefore indispensible to correctly predict the effects of drought on the composition and functioning of ecosystems. We therefore aimed at filling this gap by studying the relevance of roof artefacts in a temperate grassland ecosystem. We compared pure drought effects to roof artefacts by measuring the response of three ecosystem properties (aboveground biomass, litter decomposition and plant metabolite profiles). We realized three treatments: a drought treatment simulated by means of transparent roofs, an unroofed control treatment receiving natural rainfall and a roofed control, with rain water applied according to ambient conditions. The roof constructions in our experiment caused a slight change in air (+0.14 °C during night) and soil (-0.45°C on warm days, +0.25 °C on cold nights) temperatures while photosynthetically active radiation was decreased (-16%) on bright days. Aboveground plant community biomass was reduced in the drought treatment (-41%), but there was no significant difference between the roofed and unroofed control, thus there was no measurable response of aboveground biomass to roof artefacts, but a considerable response to drought. Compared to the unroofed control, litter decomposition was decreased both in the drought treatment (-26%) and in the roofed control treatment (-18%), suggesting a response of litter decomposition to roof artefacts in addition to drought. Similarly, aboveground metabolite profiles in the model plant species Medicago x varia were significantly different from the unroofed control both in the drought and in the roofed control treatments. Our results stress the need for roofed control treatments when using transparent roofs for studying drought effects because of significant roof artefacts.

Vogel, Anja; Fester, Thomas; Eisenhauer, Nico; Scherer-Lorenzen, Michael; Schmid, Bernhard; Weisser, Wolfgang W.; Weigelt, Alexandra

2013-04-01

87

Identifying priority areas for ecosystem service management in South African grasslands.  

PubMed

Grasslands provide many ecosystem services required to support human well-being and are home to a diverse fauna and flora. Degradation of grasslands due to agriculture and other forms of land use threaten biodiversity and ecosystem services. Various efforts are underway around the world to stem these declines. The Grassland Programme in South Africa is one such initiative and is aimed at safeguarding both biodiversity and ecosystem services. As part of this developing programme, we identified spatial priority areas for ecosystem services, tested the effect of different target levels of ecosystem services used to identify priority areas, and evaluated whether biodiversity priority areas can be aligned with those for ecosystem services. We mapped five ecosystem services (below ground carbon storage, surface water supply, water flow regulation, soil accumulation and soil retention) and identified priority areas for individual ecosystem services and for all five services at the scale of quaternary catchments. Planning for individual ecosystem services showed that, depending on the ecosystem service of interest, between 4% and 13% of the grassland biome was required to conserve at least 40% of the soil and water services. Thirty-four percent of the biome was needed to conserve 40% of the carbon service in the grassland. Priority areas identified for five ecosystem services under three target levels (20%, 40%, 60% of the total amount) showed that between 17% and 56% of the grassland biome was needed to conserve these ecosystem services. There was moderate to high overlap between priority areas selected for ecosystem services and already-identified terrestrial and freshwater biodiversity priority areas. This level of overlap coupled with low irreplaceability values obtained when planning for individual ecosystem services makes it possible to combine biodiversity and ecosystem services in one plan using systematic conservation planning. PMID:21334134

Egoh, Benis N; Reyers, Belinda; Rouget, Mathieu; Richardson, David M

2011-02-18

88

Effects of liming on soil properties and plant performance of temperate mountainous grasslands.  

PubMed

The application of lime or liming materials to acid-soil grasslands might help mitigate soil acidity, a major constraint to forage productivity in many temperate mountainous grasslands. Nowadays, in these mountainous grasslands, it is essential to promote agricultural practices to increase forage yield and nutritive value while preserving biodiversity and agroecosystem functioning. Two different field experiments were conducted in the Gorbeia Natural Park, northern Spain: (i) one in a calcareous mountainous grassland (Arraba) and (ii) the other in a siliceous mountainous grassland (Kurtzegan) to study the effects of a single application of two liming products, i.e. 2429 kg lime (164.3% CaCO(3)) ha(-1) and 4734 kg calcareous sand (84.3% CaCO(3)) ha(-1), applied one month before the beginning of the sheep grazing season (May-October), on soil chemical (pH, organic C, total N, C/N ratio, %Al saturation, Olsen P, exchangeable K(+) and Ca(2+)) and biological parameters (dehydrogenase, beta-glucosidase, urease, acid phosphatase and arylsulphatase activity) as well as on botanical diversity (graminoids, forbs, shrubs) and forage yield and nutritive value (crude protein, modified acid detergent fibre, digestibility). Untreated control plots were also included in the experiment. Soil sampling was carried out at the end of the sheep grazing season (6 months after liming treatment), while botanical composition was determined one year after treatments application. Although no increase in soil pH was observed in Arraba, liming significantly increased dehydrogenase activity (an indicator of soil microbial activity) by 30.4 and 86.7% at Arraba and Kurtzegan site, respectively. Liming treatments significantly improved forage yield and nutritive value in Arraba but not in Kurtzegan. Furthermore, no differences in soil biological quality, evaluated using the "treated-soil quality index" as proposed in this work, were observed between treated and untreated soils, and between the two different lime treatments (lime, calcareous sand). It was concluded that, in acid-soil temperate mountainous grasslands, moderate liming treatments have no negative short-term effects either on soil quality or botanical composition, while resulting in improvements in forage yield and nutritive value under some conditions. PMID:20538406

Mijangos, Iker; Albizu, Isabel; Epelde, Lur; Amezaga, Ibone; Mendarte, Sorkunde; Garbisu, Carlos

2010-06-09

89

Effects of Water and Nitrogen Addition on Species Turnover in Temperate Grasslands in Northern China  

PubMed Central

Global nitrogen (N) deposition and climate change have been identified as two of the most important causes of current plant diversity loss. However, temporal patterns of species turnover underlying diversity changes in response to changing precipitation regimes and atmospheric N deposition have received inadequate attention. We carried out a manipulation experiment in a steppe and an old-field in North China from 2005 to 2009, to test the hypothesis that water addition enhances plant species richness through increase in the rate of species gain and decrease in the rate of species loss, while N addition has opposite effects on species changes. Our results showed that water addition increased the rate of species gain in both the steppe and the old field but decreased the rates of species loss and turnover in the old field. In contrast, N addition increased the rates of species loss and turnover in the steppe but decreased the rate of species gain in the old field. The rate of species change was greater in the old field than in the steppe. Water interacted with N to affect species richness and species turnover, indicating that the impacts of N on semi-arid grasslands were largely mediated by water availability. The temporal stability of communities was negatively correlated with rates of species loss and turnover, suggesting that water addition might enhance, but N addition would reduce the compositional stability of grasslands. Experimental results support our initial hypothesis and demonstrate that water and N availabilities differed in the effects on rate of species change in the temperate grasslands, and these effects also depend on grassland types and/or land-use history. Species gain and loss together contribute to the dynamic change of species richness in semi-arid grasslands under future climate change.

Xu, Zhuwen; Wan, Shiqiang; Ren, Haiyan; Han, Xingguo; Li, Mai-He; Cheng, Weixin; Jiang, Yong

2012-01-01

90

Effects of water and nitrogen addition on species turnover in temperate grasslands in northern China.  

PubMed

Global nitrogen (N) deposition and climate change have been identified as two of the most important causes of current plant diversity loss. However, temporal patterns of species turnover underlying diversity changes in response to changing precipitation regimes and atmospheric N deposition have received inadequate attention. We carried out a manipulation experiment in a steppe and an old-field in North China from 2005 to 2009, to test the hypothesis that water addition enhances plant species richness through increase in the rate of species gain and decrease in the rate of species loss, while N addition has opposite effects on species changes. Our results showed that water addition increased the rate of species gain in both the steppe and the old field but decreased the rates of species loss and turnover in the old field. In contrast, N addition increased the rates of species loss and turnover in the steppe but decreased the rate of species gain in the old field. The rate of species change was greater in the old field than in the steppe. Water interacted with N to affect species richness and species turnover, indicating that the impacts of N on semi-arid grasslands were largely mediated by water availability. The temporal stability of communities was negatively correlated with rates of species loss and turnover, suggesting that water addition might enhance, but N addition would reduce the compositional stability of grasslands. Experimental results support our initial hypothesis and demonstrate that water and N availabilities differed in the effects on rate of species change in the temperate grasslands, and these effects also depend on grassland types and/or land-use history. Species gain and loss together contribute to the dynamic change of species richness in semi-arid grasslands under future climate change. PMID:22768119

Xu, Zhuwen; Wan, Shiqiang; Ren, Haiyan; Han, Xingguo; Li, Mai-He; Cheng, Weixin; Jiang, Yong

2012-06-29

91

Regional patterns and controls of ecosystem salinization with grassland afforestation along a rainfall gradient  

NASA Astrophysics Data System (ADS)

Vegetation change affects water fluxes and influences the direction and intensity of salt exchange between ecosystems and groundwater. In some conditions it can also lead to an intense accumulation of salts in soils and aquifers, as has been documented for the conversion of native grassland to tree plantations in the plains of Argentina, Hungary and Russia. In this paper we present a hierarchical framework to predict salt accumulation following vegetation change that is based on climatic, hydrogeological and biological factors. We evaluated this spatially explicit framework in temperate South America using a network of 32 pairs of adjacent plantation and grassland stands studied with detailed field measurements and remotely sensed imagery from MODIS. Our sites cover a broad precipitation gradient (770 to 1500 mm a-1) and are underlain by shallow water tables (<2.5 m of depth). At the regional scale, geoelectric surveying revealed that the salinization of plantation soils depended strongly on climate, occurring only where the annual water balance (mean precipitation-Penman-Monteith potential evapotranspiration) was <100 mm a-1 (p < 0.0001, n = 24). At the local scale, we observed that groundwater salinities observed under ˜50-year old plantations of different species were associated with their tolerance to salinity (p < 0.001, n = 10). Salinization occurred rapidly where rainfall was insufficient to meet the water requirements of tree plantations and where groundwater use compensated for this deficit, driving salt accumulating in the ecosystem. A general understanding of the vegetation-groundwater relationship will help predict and manage the negative and positive consequences of groundwater use from stand to regional levels of analysis.

Nosetto, M. D.; JobbáGy, E. G.; Tóth, T.; Jackson, R. B.

2008-06-01

92

Biotic, abiotic and management controls on methanol fluxes above a temperate mountain grassland  

NASA Astrophysics Data System (ADS)

It was previously hypothesised that (i) stomatal conductance and plant growth play a key role in the emission of methanol (Hüve et al. 2007, Niinemets et al. 2004), (ii) methanol fluxes increase with air temperature (Niinemets and Reichstein 2003), and (iii) during cutting (leaf wounding) events and during drying high amounts of methanol are emitted into the atmosphere (Davison et al. 2008). Methanol fluxes were measured above a managed, temperate mountain grassland in Stubai Valley (Tyrol, Austria) during two growing seasons (2008 and 2009). Half-hourly flux values were calculated by means of the disjunct eddy covariance method using 3-dimensional wind-data of a sonic anemometer and mixing ratios of methanol measured with a proton-transfer-reaction-mass-spectrometer (PTR-MS). The surface conductance to water vapour was derived from measured evapotranspiration by inverting the Penman-Monteith combination equation (Wohlfahrt et al., 2009) for dry canopy conditions and used as a proxy for canopyscale stomatal conductance. Methanol fluxes exhibited a clear diurnal cycle with closetozero fluxes during nighttime and emissions, up to 10 nmol m-2 s-1, which followed the diurnal course of radiation and air temperature during daytime. Higher emissions of up to 30 nmol m-2 s-1were observed during cut events and spreading of organic manure. Methanol fluxes showed positive correlations with air temperature, stomatal conductance, and photosynthetically active radiation (PAR), confirming previous studies (e.g. Niinemets and Reichstein 2003). All three previously mentioned factors combined together were able to explain 40% of the observed flux variability. The influence of rapid changes in stomatal conductance on methanol fluxes, pointed out in earlier studies at the leaf-level (e.g. Niinemets and Reichstein 2003), could not be confirmed on ecosystem scale, possibly due to within-canopy gradients in stomatal conductance and the fact that fluxes were determined as half-hourly averages. As methanol is produced in expanding cell walls, the change in the measured green area index (?GAI) was used as a proxy for plant growth. However ?GAI was poorly correlated with methanol fluxes, possible explanations will be discussed. References: Davison, B., Brunner, A., Amman, C., Spirig, C., Jocher, M., Neftel, A. Cut-induced VOC emissions from agricultural grasslands. Plant Biol. 10, 76-85, 2008. Harley, P., Greenberg, J., Niinemets, Ü., and Guenther, A..: Environmental controls over methanol emission from leaves. Biogeosciences, 4, 1083-1099, 2007. Hüve, K., Christ, M., Kleist, E., Uerlings, R., Niinemets, Ü., Walter, A. and Wildt, J.: Simultaneous growth and emission measurements demonstrate an interactive control of methanol release by leaf expansion and stomata. doi:10.1093/jxb/erm038, Journal of Experimental Botany, 2007. Niinemets, Ü. and Reichstein, M.: Controls on the emission of plant volatiles through stomata: A sensitivity analysis. J. Geophys. Res., 108, 4211, doi:10.1029/2002JD002626, 2003. Niinemets, Ü., Loreto, F. and Reichstein, M.: Physiological and physicochemical controls on foliar volatile organic compound emissions. Trends in Plant Science,9, 2004. Wohlfahrt G., Haslwanter A., Hörtnagl L., Jasoni R.L., Fenstermaker L.F., Arnone J.A. III, Hammerle A. (2009) On the consequences of the energy imbalance for calculating surface conductance to water vapour. Agricultural and Forest Meteorology 149, 15561559.

Hörtnagl, Lukas; Bamberger, Ines; Graus, Martin; Ruuskanen, Taina; Schnitzhofer, Ralf; Müller, Markus; Hansel, Armin; Wohlfahrt, Georg

2010-05-01

93

Components of surface energy balance in a temperate grassland ecosystem  

Microsoft Academic Search

Eddy correlation measurements were made of fluxes of moisture, heat and momentum at a tallgrass prairie site near Manhattan, Kansas, U.S.A. during the First ISLSCPISLSCP: International Satellite Land Surface Climatology Project (for details, see Sellers et al., 1988). Field Experiment (FIFE) in 1987. The study site is dominated by three C4 grass species: big bluestem (Andropogon gerardii), indiangrass (Sorghastrum nutans),

Joon Kim; Shashi B. Verma

1990-01-01

94

Carbon dioxide exchange in a temperate grassland ecosystem  

Microsoft Academic Search

Carbon dioxide exchange was measured, using the eddy correlation technique, over a tallgrass prairie in northeastern Kansas, U.S.A., during a six-month period in 1987. The diurnal patterns of daytime and nocturnal CO2 fluxes are presented on eight selected days. These days were distributed throughout most of the growing season and covered a wide range of meteorological and soil water conditions.

Joon Kim; Shashi B. Verma

1990-01-01

95

Resistance and resilience of soil respiration to recurring summer drought in temperate mountain grassland  

NASA Astrophysics Data System (ADS)

Mountain grasslands are highly sensitive to climatic changes and soil respiration (Rs) is their largest source for CO2 emissions. As a contribution to the EU-project Carbo-Extreme and a national (FWF) project we studied how experimental summer drought and subsequent rewetting affects soil respiration over five subsequent years. The study site was a temperate mountain meadow at 1820m in the Austrian Central Alps. Drought was simulated with rain-out-shelters keeping off precipitation over a period of ca. 2 months of each year, which reduced the soil water content in the main rooting horizon to less than 20%vol (i.e. 20-30% relative extractable water). Rs measurements were performed with automated chambers and were complemented by episodic manual measurements on shallow and deep collars. Rs and its temperature sensitivity decreased at a soil moisture threshold of 20 - 30%vol, with the threshold increasing to higher values from the first to the last year of drought. Soil CO2 efflux was strongly stimulated after rainfall following drought, where Rs exceeded the flux rates of the control plots. Post-rewetting Rs remained enhanced for weeks in the first three years of the experiment. In the fourth and fifth year rewetting caused only a short pulse of soil CO2 emissions, after which Rs decreased below values in control plots for weeks. We conclude that recurring summer drought may alter the resistance and resilience of soil respiration in temperate grassland, with implications for its annual carbon balance.

Ladreiter-Knauss, Thomas; Walter, Eric; Gruber, Verena; Schmitt, Michael; Ingrisch, Johannes; Hasibeder, Roland; Bahn, Michael

2013-04-01

96

The impact of human-environment interactions on the stability of forest-grassland mosaic ecosystems.  

PubMed

Forest-grassland mosaic ecosystems can exhibit alternative stables states, whereby under the same environmental conditions, the ecosystem could equally well reside either in one state or another, depending on the initial conditions. We develop a mathematical model that couples a simplified forest-grassland mosaic model to a dynamic model of opinions about conservation priorities in a population, based on perceptions of ecosystem rarity. Weak human influence increases the region of parameter space where alternative stable states are possible. However, strong human influence precludes bistability, such that forest and grassland either co-exist at a single, stable equilibrium, or their relative abundance oscillates. Moreover, a perturbation can shift the system from a stable state to an oscillatory state. We conclude that human-environment interactions can qualitatively alter the composition of forest-grassland mosaic ecosystems. The human role in such systems should be viewed as dynamic, responsive element rather than as a fixed, unchanging entity. PMID:24048359

Innes, Clinton; Anand, Madhur; Bauch, Chris T

2013-09-19

97

The impact of human-environment interactions on the stability of forest-grassland mosaic ecosystems  

PubMed Central

Forest-grassland mosaic ecosystems can exhibit alternative stables states, whereby under the same environmental conditions, the ecosystem could equally well reside either in one state or another, depending on the initial conditions. We develop a mathematical model that couples a simplified forest-grassland mosaic model to a dynamic model of opinions about conservation priorities in a population, based on perceptions of ecosystem rarity. Weak human influence increases the region of parameter space where alternative stable states are possible. However, strong human influence precludes bistability, such that forest and grassland either co-exist at a single, stable equilibrium, or their relative abundance oscillates. Moreover, a perturbation can shift the system from a stable state to an oscillatory state. We conclude that human-environment interactions can qualitatively alter the composition of forest-grassland mosaic ecosystems. The human role in such systems should be viewed as dynamic, responsive element rather than as a fixed, unchanging entity.

Innes, Clinton; Anand, Madhur; Bauch, Chris T.

2013-01-01

98

Prairie dog decline reduces the supply of ecosystem services and leads to desertification of semiarid grasslands.  

PubMed

Anthropogenic impacts on North American grasslands, a highly endangered ecosystem, have led to declines of prairie dogs, a keystone species, over 98% of their historical range. While impacts of this loss on maintenance of grassland biodiversity have been widely documented, much less is known about the consequences on the supply of ecosystem services. Here we assessed the effect of prairie dogs in the supply of five ecosystem services by comparing grasslands currently occupied by prairie dogs, grasslands devoid of prairie dogs, and areas that used to be occupied by prairie dogs that are currently dominated by mesquite scrub. Groundwater recharge, regulation of soil erosion, regulation of soil productive potential, soil carbon storage and forage availability were consistently quantitatively or qualitatively higher in prairie dog grasslands relative to grasslands or mesquite scrub. Our findings indicate a severe loss of ecosystem services associated to the absence of prairie dogs. These findings suggest that contrary to a much publicize perception, especially in the US, prairie dogs are fundamental in maintaining grasslands and their decline have strong negative impacts in human well - being through the loss of ecosystem services. PMID:24130691

Martínez-Estévez, Lourdes; Balvanera, Patricia; Pacheco, Jesús; Ceballos, Gerardo

2013-10-09

99

Prairie Dog Decline Reduces the Supply of Ecosystem Services and Leads to Desertification of Semiarid Grasslands  

PubMed Central

Anthropogenic impacts on North American grasslands, a highly endangered ecosystem, have led to declines of prairie dogs, a keystone species, over 98% of their historical range. While impacts of this loss on maintenance of grassland biodiversity have been widely documented, much less is known about the consequences on the supply of ecosystem services. Here we assessed the effect of prairie dogs in the supply of five ecosystem services by comparing grasslands currently occupied by prairie dogs, grasslands devoid of prairie dogs, and areas that used to be occupied by prairie dogs that are currently dominated by mesquite scrub. Groundwater recharge, regulation of soil erosion, regulation of soil productive potential, soil carbon storage and forage availability were consistently quantitatively or qualitatively higher in prairie dog grasslands relative to grasslands or mesquite scrub. Our findings indicate a severe loss of ecosystem services associated to the absence of prairie dogs. These findings suggest that contrary to a much publicize perception, especially in the US, prairie dogs are fundamental in maintaining grasslands and their decline have strong negative impacts in human well – being through the loss of ecosystem services.

Martinez-Estevez, Lourdes; Balvanera, Patricia; Pacheco, Jesus; Ceballos, Gerardo

2013-01-01

100

Effect of degradation intensity on grassland ecosystem services in the alpine region of Qinghai-Tibetan Plateau, China.  

PubMed

The deterioration of alpine grassland has great impact on ecosystem services in the alpine region of Qinghai-Tibetan Plateau. However, the effect of grassland degradation on ecosystem services and the consequence of grassland deterioration on economic loss still remains a mystery. So, in this study, we assessed four types of ecosystem services following the Millennium Ecosystem Assessment classification, along a degradation gradient. Five sites of alpine grassland at different levels of degradation were investigated in Guoluo Prefecture of Qinghai Province, China. The species composition, aboveground biomass, soil total organic carbon (TOC), and soil total nitrogen (TN) were tested to evaluate major ecological services of the alpine grassland. We estimated the value of primary production, carbon storage, nitrogen recycling, and plant diversity. The results show the ecosystem services of alpine grassland varied along the degradation gradient. The ecosystem services of degraded grassland (moderate, heavy and severe) were all significantly lower than non-degraded grassland. Interestingly, the lightly degraded grassland provided more economic benefit from carbon maintenance and nutrient sequestration compared to non-degraded. Due to the destruction of the alpine grassland, the economic loss associated with decrease of biomass in 2008 was $198/ha. Until 2008, the economic loss caused by carbon emissions and nitrogen loss on severely degraded grassland was up to $8 033/ha and $13 315/ha, respectively. Urgent actions are required to maintain or promote the ecosystem services of alpine grassland in the Qinghai-Tibetan Plateau. PMID:23469278

Wen, Lu; Dong, Shikui; Li, Yuanyuan; Li, Xiaoyan; Shi, Jianjun; Wang, Yanlong; Liu, Demei; Ma, Yushou

2013-03-04

101

Agricultural impacts on ecosystem functioning in temperate areas of North and South America  

NASA Astrophysics Data System (ADS)

Land use has a large impact on ecosystem functioning, though evidences of these impacts at the regional scale are scarce. The objective of this paper was to analyze the impacts of agricultural land use on ecosystem functioning (radiation interception and carbon uptake) in temperate areas of North and South America. From land cover maps generated using high-resolution satellite images we selected sites dominated by row crops (RC), small grain crops (SG), pastures (PA), and rangelands (RA) in the Central Plains of USA and the Pampas of Argentina. These two regions share climatic characteristics and the agricultural conditions (crop types) are also very similar. Both areas were originally dominated by temperate grasslands. In these sites we extracted the temporal series of the normalized difference vegetation index (NDVI) from the NOAA satellites for the period 1989 1998 and calculated the mean seasonal NDVI curve for each site. Additionally, we calculated the mean annual NDVI, the maximum NDVI, the date of the year when the max NDVI was recorded and the interannual variability of these three attributes. We compared the mean values of each NDVI-derived attribute between land cover types and between continents. The NDVI seasonal patterns for each land cover type were roughly similar between the Central Plains and the Pampas during the growing season. The largest differences were observed during the winter and spring, when the NDVI of all land cover types in the Central Plains remained at lower values than in the Pampas. This was probably caused by the high annual thermal amplitude in the Central Plains that results in a much more restricted growing season. As a result of these differences in the shape of the NDVI curve, the mean annual NDVI in the Central Plains was lower than in the Pampas for all land cover types but the maximum NDVI did not differ importantly. In both regions, row crops delayed the date of the NDVI peak, small grain crops advanced it and pastures did not change it importantly, compared with rangelands. The interannual variability of the NDVI attributes was higher for small grains than for row crops in both regions. However, small grains crops were consistently more variable between years in the Central Plains than in the Pampas. The opposite occurred with pastures and rangelands, which were more variable in the Pampas than in the Central Plains. This paper confirms and generalizes previous findings that showed important imprints of land use on ecosystem functioning in temperate ecosystems. Our results support the idea that the changes in land cover that have occurred in the Central Plains and the Pampas leaded to similar changes in the way that ecosystems absorb solar radiation and in the patterns of carbon uptake.

Guerschman, Juan Pablo; Paruelo, José María

2005-07-01

102

Untangling the roles of fire, grazing and rainfall on small mammal communities in grassland ecosystems  

Microsoft Academic Search

In grassland systems across the globe, ecologists have been attempting to understand the complex role of fire, grazing and\\u000a rainfall in creating habitat heterogeneity and the consequences of anthropogenic control of these factors on ecosystem integrity\\u000a and functioning. Using a South African grassland ecosystem as a model, we investigated the impact of fire and grazing pressure\\u000a on small mammal communities

R. W. Yarnell; D. M. Scott; C. T. Chimimba; D. J. Metcalfe

2007-01-01

103

Nitrogen enrichment enhances the dominance of grasses over forbs in a temperate steppe ecosystem  

NASA Astrophysics Data System (ADS)

Chinese grasslands are extensive natural ecosystems that comprise 40 % of the total land area of the country and are sensitive to N deposition. A field experiment with six N rates (0, 30, 60, 120, 240, and 480 kg N ha-1 yr-1) was conducted at Duolun, Inner Mongolia, during 2005 and 2010 to identify some effects of N addition on a temperate steppe ecosystem. The dominant plant species in the plots were divided into two categories, grasses and forbs, on the basis of species life forms. Enhanced N deposition, even as little as 30 kg N ha-1 yr-1 above ambient N deposition (16 kg N ha-1 yr-1), led to a decline in species richness. The cover of grasses increased with N addition rate but their species richness showed a weak change across N treatments. Both species richness and cover of forbs declined strongly with increasing N deposition as shown by linear regression analysis (p < 0.05). Increasing N deposition elevated aboveground production of grasses but lowered aboveground biomass of forbs. Plant N concentration, plant ?15N and soil mineral N increased with N addition, showing positive relationships between plant ?15N and N concentration, soil mineral N and/or applied N rate. The cessation of N application in the 480 kg N ha-1 yr-1 treatment in 2009 and 2010 led to a slight recovery of the forb species richness relative to total cover and aboveground biomass, coinciding with reduced plant N concentration and soil mineral N. The results show N deposition-induced changes in soil N transformations and plant N assimilation that are closely related to changes in species composition and biomass accumulation in this temperate steppe ecosystem.

Song, L.; Bao, X.; Liu, X.; Zhang, Y.; Christie, P.; Fangmeier, A.; Zhang, F.

2011-08-01

104

Ecosystem Change in California Grasslands: Impacts of Species Invasion  

NASA Astrophysics Data System (ADS)

Grassland ecosystems of California have undergone dramatic changes, resulting in the almost complete replacement of native perennial grasses by non-native annuals across millions of hectares of grassland habitat. Our research investigates the effects of this community shift on carbon, water and energy cycles at two sites in northern coastal California. Our goal was to understand how changes to California’s grasslands have affected climate through 1. shifting the balance of carbon storage between terrestrial stocks and the atmosphere, and 2. altering the water and energy regimes that heat or cool the earth's surface. To compare the processes that govern material exchange before and after annual grass invasion, we made use of sites where native vegetation is found adjacent to locations that have undergone non-native invasion. In plots of each vegetation type, we monitored whole plant productivity, root and litter decay rates and soil respiration, as well as soil climatic controls on these processes. At one site, we also measured surface albedo and the components of the surface energy balance in each grass community, using the surface renewal method. Although seemingly subtle, the shift in California grassland communities from native perennial to non-native annual grass dominance has had profound consequences for ecosystem biogeochemical, radiative and hydrological cycles. Soil carbon storage was found to be significantly greater in native perennial grass communities. Across both study sites, we found that non-native grass invasion has resulted in the transfer of from 3 to 6 tons of carbon per hectare from the soil to the atmosphere, dependent on site and species. A soil density fractionation and a radiocarbon analysis also revealed the carbon to be more recalcitrant in native grass dominated locations. The primary plant traits that help explain why soil carbon losses follow annual grass invasion are: 1. differences between annual and perennial grasses in above/ belowground allocation, 2. differences in growth plasticity in response to inter-annual precipitation variability, and 3. the effect of differences in rooting depth and aboveground morphology on soil moisture content and soil respiration. Over the years 2004-2006, we found energy partitioning into latent and sensible heat flux to be similar among annual and perennial grass communities during periods of sufficient soil moisture availability. When water becomes scarce in the late spring, however, and annual grasses die, the ratio of latent to sensible heat loss is reduced in annual grass communities relative to perennials. The deep roots of perennial grasses prolong the period over which transpiration occurs. We also found that albedo differs year-round between perennial and annual grasses, tracking differences in grass phenology. Albedo differences are at a maximum during the summer and autumn months. At this time, the lower albedo in non-native annual communities can raise near surface temperatures up to 6 oC midday relative to native perennials.

Koteen, L. E.; Harte, J.; Baldocchi, D. D.

2009-12-01

105

Black carbon in grassland ecosystems of the world  

NASA Astrophysics Data System (ADS)

Black carbon (BC) is the product of incomplete burning processes and a significant component of the passive soil organic carbon (SOC) pool. The role of BC in the global carbon cycle is still unclear. This study aimed to quantify and characterize BC in major grassland ecosystems of the world. Twenty-eight representative soil profiles (mainly Mollisols) were sampled in the Russian Steppe, the U.S. Great Plains, the Argentinian Pampa, the Manchurian Plains in China, and the Chernozem region in central Germany. Black carbon contents were estimated using benzene polycarboxylic acids (BPCA) as a molecular marker, and indications about the origin of the BC were derived from bulk and compound-specific ?13C analyses and radiocarbon dating of bulk soil organic matter (SOM). Our findings suggest that between 5% and 30% of SOC stocks consist of BC. Maximum BC contributions to SOC frequently were found at deeper parts of the A horizon with 14C ages younger than 7000 years BP; that is, incorporation of C as charred particles accompanied ecosystem development since the mid-Holocene. Most of this BC formed from local vegetation, as indicated by a 13C isotope signature similar to that of bulk SOM. At some sites, also nonlocal sources contributed to soil BC, e.g., fossil fuel BC inputs at the German sites. Black carbon stocks were highest in Chernozems and lowest in Kastanozems. The Russian Steppe and Chinese Manchurian sites stored about 3-4 times more BC (around 3 kg m-2) than did the other sites because of thicker A horizons that were rich in BC. On a global scale, we estimate that steppe ecosystems contain between 4 and 17 Pg BC.

Rodionov, Andrej; Amelung, Wulf; Peinemann, Norman; Haumaier, Ludwig; Zhang, Xudong; Kleber, Markus; Glaser, Bruno; Urusevskaya, Inga; Zech, Wolfgang

2010-09-01

106

Fast turnover of low molecular weight components of the dissolved organic carbon pool of temperate grassland field soils  

Microsoft Academic Search

Large amounts of low molecular weight (LMW;<250Da) carbon (C) are lost from roots into the rhizosphere as a consequence of root turnover and exudation. Their rates of turnover after release into the soil remain poorly understood. We extracted soil solution from a temperate grassland Eutric Cambisol, isotopically labeled the glucose and amino acid components, and then re-injected the solution back

Elizabeth Boddy; Paul W. Hill; John Farrar; David L. Jones

2007-01-01

107

No consistent effects of plant diversity on root biomass, soil biota and soil abiotic conditions in temperate grassland communities  

Microsoft Academic Search

We examined the effects of decreasing plant diversity and functional group identity on root biomass, soil bulk density, soil nitrate and ammonium concentrations, microbial basal respiration, density of predaceous and non-predaceous nematodes, earthworm biomass and density and Shannon–Wiener indices of earthworm diversity in a temperate grassland. Plant species and functional group diversity did not have significant effects on any of

A Gastine; M Scherer-Lorenzen; P. W Leadley

2003-01-01

108

Water relations in grassland and desert ecosystems exposed to elevated atmospheric CO 2  

Microsoft Academic Search

Atmospheric CO 2 enrichment may stimulate plant growth directly through (1) enhanced photosynthesis or indirectly, through (2) reduced plant water consumption and hence slower soil moisture depletion, or the combination of both. Herein we describe gas exchange, plant biomass and species responses of five native or semi-native temperate and Mediterranean grasslands and three semi-arid systems to CO 2 enrichment, with

J. A. Morgan; D. E. Pataki; C. Körner; H. Clark; S. J. Del Grosso; J. M. Grünzweig; A. K. Knapp; A. R. Mosier; P. C. D. Newton; P. A. Niklaus; J. B. Nippert; R. S. Nowak; W. J. Parton; H. W. Polley; M. R. Shaw

2004-01-01

109

Molecular Investigation of the Short-term Sequestration of Natural Abundance 13C -labelled Cow Dung in the Surface Horizons of a Temperate Grassland Soil  

NASA Astrophysics Data System (ADS)

An adequate understanding of the carbon (C) sequestration potential of grasslands requires that the quantity and residence times of C inputs be measured. Herbivore dung is largely comprised of plant cell wall material, a significant source of stable C in intensively grazed temperate grassland ecosystems that contributes to the soil carbon budget. Our work uses compound-specific isotope analysis to identify the pattern of input of dung-derived compounds from natural abundance 13C/-labelled cow dung into the surface horizons of a temperate grassland soil over one year. C4 dung (? 13C \\-12.6 ‰ ) from maize fed cows was applied to a temperate grassland surface (? 13C \\-29.95 ‰ ) at IGER-North Wyke (Devon, UK), and dung remains and soil cores beneath the treatments collected at ? = 7, 14, 28, 56, 112, 224 and 372 days. Bulk dung carbon present in the 0\\-1 cm and 1\\-5 cm surface horizons of a grassland soil over one year was estimated using ? 13C between C4 dung and C3 dung, after Bol {\\et al.} (2000). The major biochemical components of dung were quantified using proximate forage fibre analyses, after Goering and Van Soest (1970) and identified using `wet' chemical and GC-MS methods. Plant cell wall polysaccharides and lignin were found to account for up to 67 {%} of dung dry matter. Hydrolysed polysaccharides were prepared as alditol acetates for analyses (after Docherty {\\et al.}, 2001), and a novel application of an off-line pyrolysis method applied to measure lignin-derived phenolic compounds (after Poole & van Bergen, 2002). This paper focuses on major events in the incorporation of dung carbon, estimated using natural abundance 13C&-slash;labelling technique. This revealed a major bulk input of dung carbon after a period of significant rainfall with a consequent decline in bulk soil ? 13C values until the end of the experiment (Dungait {\\et al.}, submitted). Findings will be presented revealing contribution of plant cell wall polysaccharides and lignin to these bulk ? 13C values, and their potential for sequestration considered. References: Bol, R., Amelung, W., Friedrich, C. Ostle, N. (2000). Tracing dung-derived carbon in temperate grassland using 13C natural abundance measurements. Soil Biology and Biochemistry, 32, 1337-1343. Goering and Van Soest (1970). Forage fibre analysis (apparatus, reagents, procedures and some applications). In: USDA-ARS Agricultural Handbook, 379. U. S. Government Printing Office, Washington D.C. Docherty, G., Jones, V. and Evershed, R.P. (2001). Practical and theoretical considerations in the gas chromatography/combustion/isotope ratio mass spectrometry ? 13C analysis of small polyfunctional compounds. Rapid Communications in Mass Spectrometry, 15, 730-738. Poole, I. & van Bergen, P. F. (2002). Carbon isotope ratio analysis of organic moieties from fossil mummified wood: establishing optimum conditions for off-line pyrolysis extraction using gas chromatography/mass spectrometry. Rapid Communications in Mass Spectrometry, 16, 1976-1981. Dungait, J. A. J., Bol, R. and Evershed, R.P. (submitted). The Fate of Dung Carbon in Temperate Grassland Soil: 1. Preliminary Findings Based on Bulk Stable Carbon Isotope Determinations. Isotopes in Health and Environmental Studies

Dungait, J.; Bol, R.; Evershed, R. P.

2004-12-01

110

Assessing value of grassland ecosystem services in Gansu Province, northwest of China  

Microsoft Academic Search

There are three characteristics for ecosystem services, zonal characteristics, complexity and conventional civilization, which affect ecological valuation directly. Considering regional environment and anthropogenic influence, grassland's ecosystem services in Gansu Province are concluded 11 types, including gas regulation, climate regulation, disturbance regulation, wind erosion control and sand fixture, water resource provision, soil erosion control, waste treatment, gene resistance, food production, raw

Chen Zhenghua; Wang Jian; Ma Qingyuan; Yang Zhen

2007-01-01

111

Independent Evolution of Leaf and Root Traits within and among Temperate Grassland Plant Communities  

PubMed Central

In this study, we used data from temperate grassland plant communities in Alberta, Canada to test two longstanding hypotheses in ecology: 1) that there has been correlated evolution of the leaves and roots of plants due to selection for an integrated whole-plant resource uptake strategy, and 2) that trait diversity in ecological communities is generated by adaptations to the conditions in different habitats. We tested the first hypothesis using phylogenetic comparative methods to test for evidence of correlated evolution of suites of leaf and root functional traits in these grasslands. There were consistent evolutionary correlations among traits related to plant resource uptake strategies within leaf tissues, and within root tissues. In contrast, there were inconsistent correlations between the traits of leaves and the traits of roots, suggesting different evolutionary pressures on the above and belowground components of plant morphology. To test the second hypothesis, we evaluated the relative importance of two components of trait diversity: within-community variation (species trait values relative to co-occurring species; ? traits) and among-community variation (the average trait value in communities where species occur; ? traits). Trait diversity was mostly explained by variation among co-occurring species, not among-communities. Additionally, there was a phylogenetic signal in the within-community trait values of species relative to co-occurring taxa, but not in their habitat associations or among-community trait variation. These results suggest that sorting of pre-existing trait variation into local communities can explain the leaf and root trait diversity in these grasslands.

Kembel, Steven W.; Cahill, James F.

2011-01-01

112

Interannual and seasonal variability of CH4 and N2O exchange over a temperate mountain grassland  

NASA Astrophysics Data System (ADS)

Methane (CH4) and nitrous oxide (N2O) are major greenhouse gases and therefore play an important role in the atmosphere due to their warming potential. The various processes and mechanisms associated with the release and uptake of both compounds need further investigation to reliably assess CH4 and N2O budgets in different ecosystems. The exchange of CO2, CH4 and N2O was measured over 2 years at a temperate mountain grassland managed as a hay meadow near the village Neustift in the Stubai Valley, Austria. The three wind components, the speed of sound and the CO2mole densities were acquired at a time resolution of 20 Hz and used to calculate true eddy covariance CO2fluxes. CH4and N2O concentration values were recorded at 2 Hz, resulting in a disjunct time series when compared to the 20 Hz wind data. Fluxes of both compounds were then calculated using the virtual disjunct eddy covariance method (vDEC). The net ecosystem exchange of CO2 is monitored since 2001, while the measurement of CH4 and N2O fluxes started in April 2010. During the vegetation period, typical concentration values for CH4 and N2O were around 2.0 and 0.3 ppm, respectively, with both compounds exhibiting distinct diurnal cycles. Preliminary flux calculations showed minor, close-to-zero fluxes for both CH4 and N2O associated with large uncertainties owing to a number of corrections that need to be applied during post-processing. In this presentation we present final fluxes over two vegetation periods and investigate drivers on observed CH4and N2O emission patterns. The role of management events like harvesting of the vegetation and the spreading of manure will be investigated in detail and set in relation to previously published studies.

Hörtnagl, L.; Wohlfahrt, G.

2012-04-01

113

Ecosystem services to and from North American arid grasslands  

Technology Transfer Automated Retrieval System (TEKTRAN)

Arid grasslands throughout North America are characterized by low and variable precipitation, nutrient-poor soils, and high spatial and temporal variability in plant production. These grasslands have provided a variety of goods and services, with the provisioning of food and fiber dominating through...

114

Simulated annual carbon fluxes of grassland ecosystems in extremely arid conditions  

Microsoft Academic Search

In order to understand how changes in climate and land cover affect carbon cycles and structure and function of regional grassland\\u000a ecosystems, we developed a grassland landscape productivity model, proposed an approach that combined both process-based modeling\\u000a and spatial analysis with field measurements, and provided an example of semiarid region in Inner Mongolia, China, in extremely\\u000a arid conditions. The modeled

Na Zhang; Ying-Shi Zhao; Gui-Rui Yu

2009-01-01

115

Winter photosynthetic activity of twenty temperate semi-desert sand grassland species.  

PubMed

The winter photosynthetic activity (quantified by net CO(2) assimilation rates and chlorophyll (Chl) a fluorescence parameters) of 20 plant species (including two lichens and two mosses) of a Hungarian temperate semi-desert sand grassland was determined on one occasion per year in 1984, 1989 and 1994. Throughout winter, the overwintering green shoots, leaves or thalli were regularly exposed to below zero temperatures at night and daytime temperatures of 0-5 degrees C. In situ tissue temperature varied between -2.1 and +6.9 degrees C and the photosynthetic photon flux density (PPFD) between 137 and 351 micromol m(-2)s(-1). Under these conditions 18 of the grassland species exhibited photosynthetic CO(2) uptake (range: vascular plants ca. 0.2-3.8 micromol m(-2)s(-1), cryptogams 0.3-2.79 micromol kg(-1)s(-1)) and values of 0.9-5.1 of the Chl fluorescence decrease ratio R(Fd). In 1984, Festuca vaginata and Sedum sexangulare had net CO(2) assimilation at leaf temperatures of -0.85 to -1.2 degrees C. In 1989, all species except Cladonia furcata showed net CO(2) assimilation at tissue temperatures of 0 to +3.3 degrees C, with the highest rates observed in Poa bulbosa and F. vaginata. The latter showed a net CO(2) assimilation saturation at a PPFD of 600 micromol m(-2)s(-1) and a temperature optimum between +5 and +18 degrees C. At the 1994 measurements, the photosynthetic rates were higher at higher tissue water contents. The two mosses and lichens had a net photosynthesis (range: 1.1-2.79 micromol CO(2)kg(-1)s(-1)) at 2 degrees C tissue temperature and at 4-5 degrees C air temperature. Ca. 80% of the vascular grassland plant species maintained a positive C-balance during the coldest periods of winter, with photosynthetic rates of 1.5-3.8 micromol CO(2)m(-2)s(-1). In an extremely warm beginning March of the relatively warm winter of 2006/2007, the dicotyledonous plants had much higher CO(2) assimilation rates on a Chl (range 6-14.9 micromol g(-1)Chl s(-1)) and on a dry weight basis (9-48 micromol kg(-1)dw s(-1)) than in the cold winter of 1994. However, the assimilation rates of the three investigated cryptogams (Tortula and two Cladonia) and the two grasses Festuca and Poa were not affected by this increase. The results indicate that the photosynthetic activity of temperate semi-desert sand grassland species can help somewhat in slowing the general CO(2) rise in winter and function as a potential carbon sink of the investigated semi-desert Hungarian grassland species. PMID:18346813

Tuba, Zoltán; Csintalan, Zsolt; Szente, Kálmán; Nagy, Zoltán; Fekete, Gábor; Larcher, Walter; Lichtenthaler, Hartmut K

2008-03-17

116

How do sheep affect plant communities and arthropod populations in temperate grasslands?  

PubMed

Grasslands being used in sheep farming systems are managed under a variety of agricultural production, recreational and conservational objectives. Although sheep grazing is rarely considered the best method for delivering conservation objectives in seminatural temperate grasslands, the literature does not provide unequivocal evidence on the impact of sheep grazing on pasture biodiversity. Our aim was therefore to review evidence of the impacts of stocking rate, grazing period and soil fertility on plant communities and arthropod populations in both mesotrophic grasslands typical of agriculturally improved areas and in native plant communities. We therefore conducted a literature search of articles published up to the end of the year 2010 using 'sheep' and 'grazing' as keywords, together with variables describing grassland management, plant community structure or arthropod taxa. The filtering process led to the selection of 48 articles, with 42 included in the stocking rate dataset, 9 in the grazing period dataset and 10 in the soil fertility dataset. The meta-analysis did not reveal any significant trends for plant species richness or plant community evenness along a wide stocking rate gradient. However, we found frequent shifts in functional groups or plant species abundance that could be explained by the functional properties of the plants in the community. The meta-analysis confirmed that increasing soil fertility decreased plant species richness. Despite the very limited dataset, plant species richness was significantly greater in autumn-grazed pastures than in ungrazed areas, which suggests that choosing an appropriate grazing period would be a promising option for preserving biodiversity in sheep farming systems. Qualitative review indicated that low grazing intensity had positive effects on Orthoptera, Hemiptera (especially phytophagous Auchenorrhyncha) and, despite a diverse range of feeding strategies, for the species richness of Coleoptera. Lepidoptera, which were favoured by more abundant flowering plants, also benefited from low grazing intensities. Spider abundance and species richness were higher in ungrazed than in grazed pastures. In contrast, there are insufficient published studies to draw any firm conclusions on the benefits of late grazing or stopping fertilization on insect diversity, and no grounds for including any of this information in decision support tools at this stage. PMID:23031474

Scohier, A; Dumont, B

2012-07-01

117

Nonlinearly combined impacts of initial perturbation from human activities and parameter perturbation from climate change on the grassland ecosystem  

NASA Astrophysics Data System (ADS)

Human activities and climate change are important factors that affect grassland ecosystems. A new optimization approach, the approach of conditional nonlinear optimal perturbation (CNOP) related to initial and parameter perturbations, is employed to explore the nonlinearly combined impacts of human activities and climate change on a grassland ecosystem using a theoretical grassland model. In our study, it is assumed that the initial perturbations and parameter perturbations are regarded as human activities and climate change, respectively. Numerical results indicate that the climate changes causing the maximum effect in the grassland ecosystem are different under disparate intensities of human activities. This implies the pattern of climate change is very critical to the maintenance or degradation of grassland ecosystem in light of high intensity of human activities and that the grassland ecosystem should be rationally managed when the moisture index decreases. The grassland ecosystem influenced by the nonlinear combination of human activities and climate change undergoes abrupt change, while the grassland ecosystem affected by other types of human activities and climate change fails to show the abrupt change under a certain range of perturbations with the theoretical model. The further numerical analyses also indicate that the growth of living biomass and the evaporation from soil surface shaded by the wilted biomass may be crucial factors contributing to the abrupt change of the grassland equilibrium state within the theoretical model.

Sun, G.; Mu, M.

2011-11-01

118

Nitrogen enrichment enhances the dominance of grasses over forbs in a temperate steppe ecosystem  

NASA Astrophysics Data System (ADS)

Chinese grasslands are extensive natural ecosystems that comprise 40 % of the total land area of the country and are sensitive to N deposition. A field experiment with six N rates (0, 30, 60, 120, 240, and 480 kg N ha-1 yr-1) was conducted at Duolun, Inner Mongolia, during 2005 and 2010 to identify some effects of N addition on a temperature steppe ecosystem. The dominant plant species in the plots were divided into two categories, grasses and forbs, on the basis of species life forms. Enhanced N deposition, even as little as 30 kg N ha-1 yr-1 above ambient N deposition (16 kg N ha-1 yr-1), led to a decline in species richness. The cover of grasses increased with N addition rate but their species richness showed a weak change across N treatments. Both species richness and cover of forbs declined strongly with increasing N deposition as shown by linear regression analysis (p<0.05). Increasing N deposition elevated aboveground production of grasses but lowered aboveground biomass of forbs. Plant N concentration, plant ?15N and soil mineral N increased with N addition, showing positive relationships between plant ?15N and N concentration, soil mineral N and/or applied N rate. The cessation of N application in the 480 kg N ha-1 yr-1 treatment in 2009 and 2010 led to a slight recovery of the forb species richness relative to total cover and aboveground biomass, coinciding with reduced plant N concentration and soil mineral N. The results show that N deposition induced changes in soil N transformations and plant N assimilation that are key to changes in species composition and biomass accumulation in this temperate steppe ecosystem.

Song, L.; Bao, X. M.; Liu, X. J.; Zhang, Y.; Christie, P.; Fangmeier, A.; Zhang, F. S.

2011-05-01

119

Effects of nitrogen fertilization on soil respiration in temperate grassland in Inner Mongolia, China  

Microsoft Academic Search

Nitrogen addition to soil can play a vital role in influencing the losses of soil carbon by respiration in N-deficient terrestrial\\u000a ecosystems. The aim of this study was to clarify the effects of different levels of nitrogen fertilization (HN, 200 kg N ha?1 year?1; MN, 100 kg N ha?1 year?1; LN, 50 kg N ha?1 year?1) on soil respiration compared with non-fertilization (CK, 0 kg N ha?1 year?1), from July 2007 to September 2008, in temperate

Qin Peng; Yunshe Dong; Yuchun Qi; Shengsheng Xiao; Yating He; Tao Ma

2011-01-01

120

Dependence of ecosystem respiration on soil temperature, moisture and plant biomass in a semi-arid grassland  

Microsoft Academic Search

The Mongolian steppe zone is one of the main components of central-Asian grasslands. Ecosystem respiration rates between the atmosphere and the steppe ecosystem were measured in a Mongolian semi- arid grassland in July 2004, May 2005, July 2005, September 2005, and June 2006 by using a closed- chamber technique. The study area is dominated by Poaceous grasses and was enclosed

T. Nakano; M. Shinoda

2008-01-01

121

Rapid response of a grassland ecosystem to an experimental manipulation of a keystone rodent and domestic livestock  

Technology Transfer Automated Retrieval System (TEKTRAN)

Megaherbivores and small burrowing mammals commonly co-exist and play important functional roles in grassland ecosystems worldwide. The interactive effects of these two functional groups of herbivores in shaping the structure and function of grassland ecosystems are poorly understood. In North Ameri...

122

Measurement of net ecosystem production and ecosystem respiration in a Zoysia japonica grassland, central Japan, by the chamber method  

Microsoft Academic Search

Measuring light, temperature, soil moisture, and growth provides a better understanding of net ecosystem production (NEP),\\u000a ecosystem respiration (R\\u000a eco), and their response functions. Here, we studied the variations in NEP and R\\u000a eco in a grassland dominated by a perennial warm-season C4 grass, Zoysia japonica. We used the chamber method to measure NEP and R\\u000a eco from August to

Deepa Dhital; Hiroyuki Muraoka; Yuichiro Yashiro; Yoko Shizu; Hiroshi Koizumi

2010-01-01

123

Ungulate and topographic control of arbuscular mycorrhizal fungal spore community composition in a temperate grassland.  

PubMed

Large herbivores and topo-edaphic gradients are well-documented, major determinants of grassland plant production and species composition. In contrast, there is limited information about how these factors together may influence the composition of the arbuscular mycorrhizal fungus (AMF) communities associated with plants. AMF are a common component of grassland ecosystems where they can influence plant productivity, diversity, and soil stability. In this study, AMF community composition was analyzed in paired plots located inside and outside 40-44-year-old ungulate exclosures at six grassland sites in Yellowstone National Park (YNP), USA, that varied in soil moisture and the availability of soil nitrogen (N) and phosphorus (P). AMF spore abundance, species richness, and the relative abundance of AMF species were determined from soil samples collected (1) randomly (n = 5 samples) within each of the 12 plots and (2) from beneath the dominant grass (n = 5 samples per plot) at each site. Randomly collected soil samples explored the effects of ungulates and topographic position on AMF composition at the plant community level, subsuming potential effects of ungulates on plant species composition. Dominant plant samples examined how grazers, in particular, influenced AMF communities, while controlling for host-plant identity. Grazing decreased AMF spore abundance across the landscape (examined by random sampling) but increased the AMF species richness associated with dominant plants. Grazing influenced the AMF species composition at the plant community level and at the host-plant level by shifting the relative abundances of individual AMF species. Individual AMF species responded differently to grazing and N and P availability. Our results demonstrate how soil moisture and N and P availability across the landscape interact with grazing to influence AMF species composition. PMID:20426339

Murray, Tanya R; Frank, Douglas A; Gehring, Catherine A

2010-03-01

124

NDVI-based increase in growth of temperate grasslands and its responses to climate changes in China  

Microsoft Academic Search

This study analyzes the temporal change of Normalized Difference Vegetation Index (NDVI) for temperate grasslands in China and its correlation with climatic variables over the period of 1982–1999. Average NDVI of the study area increased at rates of 0.5%yr?1 for the growing season (April–October), 0.61%yr?1 for spring (April and May), 0.49%yr?1 for summer (June–August), and 0.6%yr?1 for autumn (September and

Shilong Piao; Anwar Mohammat; Jingyun Fang; Qiang Cai; Jianmeng Feng

2006-01-01

125

Legumes in temperate Australia: A survey of naturalisation and impact in natural ecosystems  

Microsoft Academic Search

Some of the most damaging weeds of natural ecosystems in temperate Australia and similar Mediterranean environments are legumes. A study was undertaken to determine the level of naturalisation and impact of exotic legumes in temperate Australia. This was the first step in attempting to develop a method of evaluating the weed risk of future legume species introductions. A study of

Jason Emms; John G. Virtue; Christopher Preston; William D. Bellotti

2005-01-01

126

The response of ecosystem CO 2 exchange to small precipitation pulses over a temperate steppe  

Microsoft Academic Search

In water-limited grassland ecosystems, discrete and occasional precipitation events trigger brief but important episodes of\\u000a biological activity. Differential responses of above- and below-ground biota to precipitation pulses may constrain biogeochemical\\u000a transformations at the ecosystem scale. We examined the short-term dynamics of the whole ecosystem response to small precipitation\\u000a events during 2003 and 2004 in a steppe on the Inner Mongolia

Yanbin Hao; Yanfen Wang; Xurong Mei; Xiaoyong Cui

2010-01-01

127

Environmental effects of oil and gas lease sites in a grassland ecosystem.  

PubMed

The northern Great Plains of Saskatchewan is one of the most significantly modified landscapes in Canada. While the majority of anthropogenic disturbances to Saskatchewan's grasslands are the result of agricultural practices, development of petroleum and natural gas (PNG) resources is of increasing concern for grassland conservation. Although PNG developments require formal assessment and regulatory approval, follow-up and monitoring of the effects of PNG development on grasslands is not common practice. Consequently, the effects of PNG activity on grasslands and the spatial and temporal extent of such impacts are largely unknown. This paper examines the spatial and temporal extent of PNG development infrastructure from 1955 to 2006 in a grassland ecosystem in southwest Saskatchewan. The effects of PNG development on grassland ecology were assessed from measurements of ground cover characteristics, soil properties, and plant community composition at 31 sites in the study area. PNG lease sites were found to have low cover of herbaceous plants, club moss (Lycopodiaceae), litter, and shallow organic (Ah) horizons. Lease sites were also characterized by low diversity of desirable grassland plants and low range health values compared to off-lease reference sites. These impacts were amplified at active and highly productive lease sites. Impacts of PNG development persisted for more than 50 years following well site construction, and extended outward 20 m-25 m beyond the direct physical footprint of PNG well infrastructure. These results have significant implications with regard to the current state of monitoring and follow-up of PNG development, and the cumulative effective of PNG activity on grassland ecosystems over space and time. PMID:20880628

Nasen, Lawrence C; Noble, Bram F; Johnstone, Jill F

2010-09-28

128

Mediterranean grassland soil fungi: Patterns of biodiversity, functional redundancy and soil carbon storage  

Microsoft Academic Search

Soil organic matter is a relevant carbon reservoir and CO2 sink in temperate grassland ecosystems and increased carbon uptake may mitigate climate change. Relatively little is known about the relationship between ecosystem function and soil fungal biodiversity in grasslands. However, this relationship is important because the saprotrophic microorganisms within the decomposer chain may, given their important role in the decomposition

A. M. Persiani; O. Maggi; J. Montalvo; M. A. Casado; F. D. Pineda

2008-01-01

129

Warming and increased precipitation have differential effects on soil extracellular enzyme activities in a temperate grassland.  

PubMed

Few studies have conducted the responses of soil extracellular enzyme activities (EEA) to climate change, especially over the long term. In this study, we investigated the six-year responses of soil EEA to warming and increased precipitation in a temperate grassland of northern China at two depths of 0-10 and 10-20 cm. These extracellular enzymes included carbon-acquisition enzymes (?-glucosidase, BG), nitrogen-acquisition enzymes (N-acetylglucosaminidase, NAG; Leucine aminopeptidase, LAP) and phosphorus-acquisition enzymes (acid and alkaline phosphatases). The results showed that warming significantly increased acid phosphatase at the 0-10 cm depth and NAG at the 10-20 cm depth, but dramatically decreased BG and acid phosphatase in the subsurface. In contrast, increased precipitation significantly increased NAG, LAP and alkaline phosphatase in the surface and NAG, LAP and acid phosphatase in the subsurface. There was a significant warming and increased precipitation interaction on BG in the subsurface. Redundancy analysis indicated that the patterns of EEA were mainly driven by soil pH and NH(4)(+)-N and NO(3)(-)-N in the surface, while by NH(4)(+)-N and microbial biomass in the subsurface. Our results suggested that soil EEA responded differentially to warming and increased precipitation at two depths in this region, which may have implications for carbon and nutrient cycling under climate change. PMID:23298760

Zhou, Xiaoqi; Chen, Chengrong; Wang, Yanfen; Xu, Zhihong; Han, Hongyan; Li, Linghao; Wan, Shiqiang

2013-01-07

130

Recovery of soil microbial community structure after fire in a sagebrush-grassland ecosystem  

Technology Transfer Automated Retrieval System (TEKTRAN)

Recovery of the soil microbial community after fire in a sagebrush-grassland ecosystem was examined using a chronosequence of four sites ranging in time since fire from 3-39 years. The successional stage communities examined included Recent Burn (3 years since fire, ysf), Establishment (7 ysf), Expa...

131

Effects of ground water and harvest intensity on alkaline grassland ecosystem dynamics – a simulation study  

Microsoft Academic Search

A model for the alkaline grassland ecosystems, MAGE, was applied to plant communities dominated by three species. Field observations on two communities dominated respectively by Puccinellia tenuiflora and Suaeda corniculata were used to parameterize the model for multiple species interaction. The model behaves reasonably in following the seasonal variations of water content, soluble sodium cation and calcium cation in surface

Qiong Gao; Mei Yu; Chunping Li; Rui Yun

1998-01-01

132

Transfer parameter values in temperate forest ecosystems: a review.  

PubMed

Compared to agricultural lands, forests are complex ecosystems as they can involve diverse plant species associations, several vegetative strata (overstorey, shrubs, herbaceous and other annual plant layer) and multi-layered soil profiles (forest floor, hemi-organic and mineral layers). A high degree of variability is thus generally observed in radionuclide transfers and redistribution patterns in contaminated forests. In the long term, the soil compartment represents the major reservoir of radionuclides which can give rise to long-term plant and hence food contamination. For practical reasons, the contamination of various specific forest products has commonly been quantified using the aggregated transfer factor (T(ag) in m(2)kg(-1)) which integrates various environmental parameters including soil and plant type, root distribution as well as nature and vertical distribution of the deposits. Long lasting availability of some radionuclides was shown to be the source of much higher transfer in forest ecosystems than in agricultural lands. This study aimed at reviewing the most relevant quantitative information on radionuclide transfers to forest biota including trees, understorey vegetation, mushrooms, berries and game animals. For both radiocaesium and radiostrontium in trees, the order of magnitude of mean T(ag) values was 10(-3)m(2)kg(-1) (dry weight). Tree foliage was usually 2-12 times more contaminated than trunk wood. Maximum contamination of tree components with radiocaesium was associated with (semi-)hydromorphic areas with thick humus layers. The transfer of radionuclides to mushrooms and berries is high, in comparison with foodstuffs grown in agricultural systems. Concerning caesium uptake by mushrooms, the transfer is characterized by a very large variability of T(ag), from 10(-3) to 10(1)m(2)kg(-1) (dry weight). For berries, typical values are around 0.01-0.1 m(2)kg(-1) (dry weight). Transfer of radioactive caesium to game animals and reindeer and the rate of activity reduction, quantified as an ecological half-life, reflect the soil and pasture conditions at individual locations. Forests in temperate and boreal regions differ with respect to soil type and vegetation, and a faster decline of muscle activity concentrations in deer occurs in the temperate zone. However, in wild boar the caesium activity concentration shows no decline because of its special feeding habits. In the late phase, i.e. at least a few months since the external radionuclide contamination on feed plants has been removed, a T(ag) value of 0.01 m(2)kg(-1) (fresh weight) is common for (137)Cs in the muscles of adult moose and terrestrial birds living in boreal forests, and 0.03 m(2)kg(-1) (fresh weight) for arctic hare. Radiocaesium concentrations in reindeer muscle in winter may exceed the summer content by a factor of more than two, the mean T(ag) values for winter ranging from 0.02 to 0.8 m(2)kg(-1) (fresh weight), and in summer from 0.04 to 0.4m(2)kg(-1). The highest values are found in the year of initial contamination, followed by a gradual reduction. In waterfowl a relatively fast decline in uptake of (137)Cs has been found, with T(ag) values changing from 0.01 to 0.002 m(2)kg(-1) (fresh weight) in the three years after the contaminating event, the rate being determined by the dynamics of (137)Cs in aquatic ecosystems. PMID:19100665

Calmon, Philippe; Thiry, Yves; Zibold, Gregor; Rantavaara, Aino; Fesenko, Sergei

2008-12-18

133

Carbon dioxide fluxes in a spatially and temporally heterogeneous temperate grassland.  

PubMed

Landscape position, grazing, and seasonal variation in precipitation and temperature create spatial and temporal variability in soil processes, and plant biomass and composition in grasslands. However, it is unclear how this variation in plant and soil properties affects carbon dioxide (CO2) fluxes. The aim of this study is to explore the effect of grazing, topographic position, and seasonal variation in soil moisture and temperature on plant assimilation, shoot and soil respiration, and net ecosystem CO2 exchange (NEE). Carbon dioxide fluxes, vegetation, and environmental variables were measured once a month inside and outside long-term ungulate exclosures in hilltop (dry) to slope bottom (mesic) grassland throughout the 2004 growing season in Yellowstone National Park. There was no difference in vegetation properties and CO2 fluxes between the grazed and the ungrazed sites. The spatial and temporal variability in CO2 fluxes were related to differences in aboveground biomass and total shoot nitrogen content, which were both related to variability in soil moisture. All sites were CO2 sinks (NEE>0) for all our measurements taken throughout the growing season; but CO2 fluxes were four- to fivefold higher at sites supporting the most aboveground biomass located at slope bottoms, compared to the sites with low biomass located at hilltops or slopes. The dry sites assimilated more CO2 per gram aboveground biomass and stored proportionally more of the gross-assimilated CO2 in the soil, compared to wet sites. These results indicate large spatio-temporal variability of CO2 fluxes and suggest factors that control the variability in Yellowstone National Park. PMID:16205950

Risch, Anita C; Frank, Douglas A

2005-10-05

134

Simulating root responses to grazing of a Mongolian grassland ecosystem  

Microsoft Academic Search

A new Sim-CYCLE grazing model has been obtained by combining a grazing model (Seligman et al. 1992, Ecol. Model. 60: 45–61)\\u000a with the Sim-CYCLE model (Ito and Oikawa 2002, Ecol. Model. 151: 143–176). The new model has been validated against a set\\u000a of field data obtained at Kherlen Bayaan-Ulaan (KBU) grassland. On the basis of the model, the root responses to

Yuxiang Chen; Pilzae Lee; Gilzae Lee; Shigeru Mariko; Takehisa Oikawa

2006-01-01

135

Agricultural impacts on ecosystem functioning in temperate areas of North and South America  

Microsoft Academic Search

Land use has a large impact on ecosystem functioning, though evidences of these impacts at the regional scale are scarce. The objective of this paper was to analyze the impacts of agricultural land use on ecosystem functioning (radiation interception and carbon uptake) in temperate areas of North and South America. From land cover maps generated using high-resolution satellite images we

Juan Pablo Guerschman; José María Paruelo

2005-01-01

136

Vegetation composition, dynamics, and management of a bracken-grassland and northern-dry forest ecosystem.  

PubMed

We investigated differences in vegetation composition and dynamics for two globally rare ecosystems, bracken-grasslands and northern-dry forests of northern Wisconsin. These ecosystems commonly have been viewed as degraded pine barrens. Bracken-grasslands contained a high dominance of exotic species, low native richness, and no obvious prairie species, suggesting logging-era anthropogenic origins. Differences in cover for common plants among ecosystems were examined using Mann-Whitney U tests of equivalence. Cover of all 8 graminoid species, 4 of 5 Ericaceae and Myricaceae species, and 10 of 17 species of forbs were significantly different between ecosystems. Vegetation changes over a 4-year period were examined through detrended correspondence analysis (DCA) and analysis of variance (ANOVA) repeated measures. DCA analyses of community composition failed to detect significant temporal trends within individual management units, although differences were apparent between ecosystems, regardless of sample year. In addition, no apparent patterns could be detected between years when comparing dominant individual species to management history (prescribed fire). This is contrary to what would be expected for a degraded pine barrens and questions the efficacy of using repeated prescribed fire as a management tool in bracken-grasslands. Methods for conservation and restoration of xeric ecosystems of northern Wisconsin have historically relied heavily on single species (e.g., sharp-tailed grouse) wildlife models, without full consideration of other factors. We suggest that stakeholders involved in these restoration projects examine historic processes and reference conditions prior to formulating management goals. Greater attention to the differentiation and individual management needs of pine barrens, northern-dry forests, and bracken-grasslands is needed. PMID:14565700

Nielsen, Scott E; Haney, Alan

2003-06-01

137

A review of the most economically important poisonous plants to the livestock industry on temperate grasslands of China.  

PubMed

The majority of the literature on poisonous plant species in China is published in Chinese and not available to the majority of interested researchers and grassland managers in other countries. Therefore, a review of the Chinese literature was conducted to summarize the occurrence of poisonous plant species on temperate grasslands in China. We reviewed the literature to obtain general information on poisonous species but focus on locoweeds (Astragalus and Oxytropis spp.), drunken horse grass [Achnatherum inebrians (Hance) Keng ex Tzvelev] and langdu (Stellera chamaejasme L.) for information on their toxins, distribution and ecology, control methods and alternate uses. Of the almost 1300 poisonous species found on grasslands in China, these species are responsible for an estimated 80% of all livestock losses. This includes loss of performance as well as mortality. The locoweeds are a complex made up of Oxytropis and Astragalus species. The toxic principle in this complex, as well as in drunken horse grass, is the result of an endophyte fungus whereas in langdu it is produced by the plant. All these species are native to the grasslands, which suggest they have been a problem ever since herding began. Over that period of at least several millennia, herders would have learned and adapted to the presence of poisonous species. Strategies were developed and therapies employed to allow the animals to cope before and after poisoning. Nevertheless, grazing management could still be refined that would allow the use of the toxic legumes, while preventing poisonous symptoms, as has been tested elsewhere. PMID:23015535

Zhao, Mengli; Gao, Xinlei; Wang, Jing; He, Xiaolei; Han, Bing

2012-09-27

138

Interactions between above- and belowground biota: importance for small-scale vegetation mosaics in a grassland ecosystem  

Microsoft Academic Search

Grasslands are often characterised by small-scale mosaics in plant community composition that contribute to their diversity. Although above- and belowground biota can both cause such mosaics, few studies have addressed their interacting effects. We studied multi-trophic interactions between aboveground vertebrate grazers. subterranean ants, plant-pathogenic soil biota (especially nematodes) and the vegetation in a temperate grassland. We found that when rabbits

N. M. Blomqvist; H. Olff; M. B. Blaauw; T. Bongers; W. H. Van der Putten

2000-01-01

139

Land use affects the net ecosystem CO(2) exchange and its components in mountain grasslands.  

PubMed

Changes in land use and management have been strongly affecting mountain grassland, however, their effects on the net ecosystem exchange of CO(2) (NEE) and its components have not yet been well documented. We analysed chamber-based estimates of NEE, gross primary productivity (GPP), ecosystem respiration (R) and light use efficiency (LUE) of six mountain grasslands differing in land use and management, and thus site fertility, for the growing seasons of 2002 to 2008. The main findings of the study are that: (1) land use and management affected seasonal NEE, GPP and R, which all decreased from managed to unmanaged grasslands; (2) these changes were explained by differences in leaf area index (LAI), biomass and leaf-area-independent changes that were likely related to photosynthetic physiology; (3) diurnal variations of NEE were primarily controlled by photosynthetically active photon flux density and soil and air temperature; seasonal variations were associated with changes in LAI; (4) parameters of light response curves were generally closely related to each other, and the ratio of R at a reference temperature/ maximum GPP was nearly constant across the sites; (5) similarly to our study, maximum GPP and R for other grasslands on the globe decreased with decreasing land use intensity, while their ratio remained remarkably constant. We conclude that decreasing intensity of management and, in particular, abandonment of mountain grassland lead to a decrease in NEE and its component processes. While GPP and R are generally closely coupled during most of the growing season, GPP is more immediately and strongly affected by land management (mowing, grazing) and season. This suggests that management and growing season length, as well as their possible future changes, may play an important role for the annual C balance of mountain grassland. PMID:23293657

Schmitt, M; Bahn, M; Wohlfahrt, G; Tappeiner, U; Cernusca, A

2010-08-01

140

Land use affects the net ecosystem CO2 exchange and its components in mountain grasslands  

PubMed Central

Changes in land use and management have been strongly affecting mountain grassland, however, their effects on the net ecosystem exchange of CO2 (NEE) and its components have not yet been well documented. We analysed chamber-based estimates of NEE, gross primary productivity (GPP), ecosystem respiration (R) and light use efficiency (LUE) of six mountain grasslands differing in land use and management, and thus site fertility, for the growing seasons of 2002 to 2008. The main findings of the study are that: (1) land use and management affected seasonal NEE, GPP and R, which all decreased from managed to unmanaged grasslands; (2) these changes were explained by differences in leaf area index (LAI), biomass and leaf-area-independent changes that were likely related to photosynthetic physiology; (3) diurnal variations of NEE were primarily controlled by photosynthetically active photon flux density and soil and air temperature; seasonal variations were associated with changes in LAI; (4) parameters of light response curves were generally closely related to each other, and the ratio of R at a reference temperature/ maximum GPP was nearly constant across the sites; (5) similarly to our study, maximum GPP and R for other grasslands on the globe decreased with decreasing land use intensity, while their ratio remained remarkably constant. We conclude that decreasing intensity of management and, in particular, abandonment of mountain grassland lead to a decrease in NEE and its component processes. While GPP and R are generally closely coupled during most of the growing season, GPP is more immediately and strongly affected by land management (mowing, grazing) and season. This suggests that management and growing season length, as well as their possible future changes, may play an important role for the annual C balance of mountain grassland.

Schmitt, M.; Bahn, M.; Wohlfahrt, G.; Tappeiner, U.; Cernusca, A.

2011-01-01

141

The biogeochemistry of a north-temperate grassland with native ungulates: Nitrogen dynamics in Yellowstone National Park  

Microsoft Academic Search

Nutrient dynamics of large grassland ecosystems possessing abundant migratory grazers are poorly understood. We examined N cycling on the northern winter range of Yellowstone National Park, home for large herds of free-roaming elk (Cervus elaphus) and bison (Bison bison). Plant and soil N, net N mineralization, and the deposition of ungulate fecal-N were measured at five sites, a ridgetop, mid-slope

Douglas A. Frank; Richard S. Inouye; Nancy Huntly; G. WAYNE MINSHALL; Jay E. Anderson

1994-01-01

142

Effects of management of ecosystem carbon pools and fluxes in grassland ecosystems  

NASA Astrophysics Data System (ADS)

Grasslands represent a large land-use footprint and have considerable potential to sequester carbon (C) in soil. Climate policies and C markets may provide incentives for land managers to pursue strategies that optimize soil C storage, yet we lack robust understanding of C sequestration in grasslands. Previous research has shown that management approaches such as organic amendments or vertical subsoiling can lead to larger soil C pools. These management approaches can both directly and indirectly affect soil C pools. We used well-replicated field experiments to explore the effects of these management strategies on ecosystem C pools and fluxes in two bioclimatic regions of California (Sierra Foothills Research and Extension Center (SFREC) and Nicasio Ranch). Our treatments included an untreated control, compost amendments, plowed (vertical subsoil), and compost + plow. The experiment was conducted over two years allowing us to compare dry (360 mm) and average (632 mm) rainfall conditions. Carbon dioxide (CO2) fluxes were measured weekly using a LI-8100 infrared gas analyzer. Methane (CH4) and nitrous oxide (N2O) fluxes were measured monthly using static flux chambers. Aboveground and belowground biomass were measured at the end of the growing season as an index of net primary productivity (NPP) in the annual plant dominated system. Soil moisture and temperature were measured continuously and averaged on hourly and daily timescales. Soil organic C and N concentrations were measured prior to the application of management treatments and at the ends of each growing season. Soils were collected to a 10 cm depth in year one and at four depth increments (0-10, 10-30, 30-50, and 50-100 cm) in year two. Soil C and N concentrations were converted to content using bulk density values for each plot. During both growing seasons, soil respiration rates were higher in the composted plots and lower in the plowed plots relative to controls at both sites. The effects on C loss via soil respiration were stronger in the first year, with compost soils experiencing a 21 ± 1 % greater cumulative loss at SFREC and 16 ± 3 % more at Nicasio. The second year showed a similar trend, but with a lower magnitude loss. Aboveground NPP responded positively to compost additions and negatively to plowing at both sites. At SFREC, we measured 58 % more ANPP in composted relative to control plots in year one (369 vs 230 g C/m2) and 56 % more in year two (327 vs 209 g C/m2). Aboveground NPP on plowed plots was 129 g C/m2 in year one, and 185 g C/m2 in year two. Plowed soils also showed a significant decline in soil C and N concentrations (C= 2.67 ± 0.13%, N = 0.20 ± 0.01%). Compost additions increased soil C and N concentrations (C= 3.92 ± 0.29%, N = 0.32 ± 0.02%) relative to control soils (C= 3.52 ± 0.20%, N = 0.27 ± 0.07%). Throughout the experiment, we did not detect significant treatment differences in CH4 or N2O fluxes, nor did we detect significant differences at any individual sampling point. These results suggest that compost addition can lead to an increase in ecosystem C storage, with a small offset from elevated soil respiration.

Ryals, R.; Silver, W. L.

2010-12-01

143

Fluxes of CO 2 , N 2 O and CH 4 from a typical temperate grassland in Inner Mongolia and its daily variation  

Microsoft Academic Search

Using a dark enclosed chamber technique, the fluxes of CO2, N2O and CH4 from nature and disturbed grassland were measured on the spot in Inner Mongolian Temperate Grassland along the annual rainfall\\u000a gradient section ranging from 450 to 200 mm. The results showed that the measured mean fluxes of CO2, N2O and CH4 were (1 180.4 ± 308.7), (0.010 ±

Yunshe Dong; Shen Zhang; Yuchun Qi; Zuozhong Chen; Yuanbo Geng

2000-01-01

144

Similarities and Differenes in Carbon and Energy Fluxes Between Grassland and Agricultural Ecosystems  

NASA Astrophysics Data System (ADS)

Grasslands and managed agricultural ecosystems comprise a significant fraction of the terrestrial biosphere. Compared to forested ecosystems, the growing season of grasslands and agricultural systems (periods of carbon sinks) are generally short and are closely linked to the water cycle due to shallow rooting zones. Measurements of carbon and energy fluxes, along with spectral signatures which provide information on the leaf area index, are used to explore the similarities and differences in seasonality of these fluxes and the critical environmental factors that affect the overall net exchange of carbon and energy. Comparisons will not only focus on the growing season when both carbon fixation and transpiration are at their peak values, but the analysis will include the spring and fall periods when the ground is covered with dead plant material that acts as an insulating mulch layer, and the impact this layer has on the fluxes.

Meyers, T. P.

2004-12-01

145

Soil heavy metal concentrations, microbial biomass and enzyme activities in a contaminated grassland ecosystem  

Microsoft Academic Search

Soil enzyme activities and microbial biomass were measured in a grassland ecosystem with a wide range of heavy metal concentrations ranging from 7.2 to 48.1 mmol kg?1 (As, Cd, Cr, Cu, Ni, Pb and Zn) in portions of the U.S. Army's Aberdeen Proving Ground, Maryland, U.S.A. Total and fluorescein diacetate active (FDA) fungal biomass, FDA-active bacterial biomass, substrate-induced respiration (SIR),

Roman G. Kuperman; Margaret M. Carreiro

1997-01-01

146

Response of the grassland ecosystem to climate change in a theoretical model  

Microsoft Academic Search

The response of a grassland ecosystem to climate change was investigated within a theoretical model. An optimization approach, i.e., a conditional nonlinear optimal perturbation related to parameter (CNOP-P) approach, was employed in this study. The CNOP-P, which is a perturbation of a moisture index in the theoretical model, represents a nonlinear climate perturbation. A linear climate perturbation was also used

Guodong Sun; Mu Mu

2010-01-01

147

Can we understand and predict the regulation of biological N 2 fixation in grassland ecosystems?  

Microsoft Academic Search

We discuss results from controlled environment studies including mesocosms, grazing experiments and long term field experiments\\u000a which show how biological N2 fixation in legume based systems is tightly coupled to the N demand at scales ranging from the individual plant to the grassland\\u000a ecosystem. We further test the consequences of this hypothesis of a feedback regulation of biological N2 fixation

Jean-François Soussana; Tiphaine Tallec

2010-01-01

148

Trajectories of grassland ecosystem change in response to experimental manipulations of precipitation  

NASA Astrophysics Data System (ADS)

Understanding and predicting the dynamics of ecological systems has always been central to Ecology. Today, ecologists recognize that in addition to natural and human-caused disturbances, a fundamentally different type of ecosystem change is being driven by the combined and cumulative effects of anthropogenic activities affecting earth's climate and biogeochemical cycles. This type of change is historically unprecedented in magnitude, and as a consequence, such alterations are leading to trajectories of change in ecological responses that differ radically from those observed in the past. Through both short- and long-term experiments, we have been trying to better understand the mechanisms and consequences of ecological change in grassland ecosystems likely to result from changes in precipitation regimes. We have manipulated a key resource for most grasslands (water) and modulators of water availability (temperature) in field experiments that vary from 1-17 years in duration, and used even longer-term monitoring data from the Konza Prairie LTER program to assess how grassland communities and ecosystems will respond to changes in water availability. Trajectories of change in aboveground net primary production (ANPP) in sites subjected to 17 years of soil water augmentation were strongly non-linear with a marked increase in the stimulation of ANPP after year 8 (from 25% to 65%). Lags in alterations in grassland community composition are posited to be responsible for the form of this trajectory of change. In contrast, responses in ANPP to chronic increases in soil moisture variability appear to have decreased over a 10-yr period of manipulation, although the net effects of more variable precipitation inputs were to reduce ANPP, alter the genetic structure of the dominant grass species, increase soil nitrogen availability and reduce soil respiration. The loss of sensitivity to increased resource variability was not reflected in adjacent plots where precipitation was manipulated for only a single year. And when similar short-term experimental manipulations of precipitation variability were conducted in more arid grasslands, responses in ANPP were opposite those in mesic grassland. This suggests that grassland responses to alterations in precipitation inputs may vary dramatically depending on the long-term hydrologic regime.

Knapp, Alan; Smith, Melinda; Collins, Scott; Blair, John; Briggs, John

2010-05-01

149

Productivity and sustainability influenced by biodiversity in grassland ecosystems  

Microsoft Academic Search

THE functioning and sustainability of ecosystems may depend on their biological diversity1-8. Elton's9 hypothesis that more diverse ecosystems are more stable has received much attention1,3,6,7,10-14, but Darwin's proposal6,15 that more diverse plant communities are more productive, and the related conjectures4,5,16,17 that they have lower nutrient losses and more sustainable soils, are less well studied4-6,8,17,18. Here we use a well-replicated field

David Tilman; David Wedin; Johannes Knops

1996-01-01

150

Amino acids as a nitrogen source in temperate upland grasslands: the use of dual labelled ((13)C, (15)N) glycine to test for direct uptake by dominant grasses.  

PubMed

It is becoming increasingly apparent that soil amino acids are a principal source of nitrogen (N) for certain plants, and especially those of N-limited environments. This study of temperate upland grasslands used glycine-2-(13)C-(15)N and ((15)NH4)(2)SO(4) labelling techniques to test the hypothesis that plant species which dominate 'unimproved' semi-natural grasslands (Festuca-Agrostis-Galium) are able to utilise amino acid N for growth, whereas those plants which dominate 'improved' grasslands (Lolium-Cynosurus), that receive regular applications of inorganic fertiliser, use inorganic N forms as their main N source. Data from field experiments confirmed that 'free' amino acids were more abundant in 'unimproved' than 'improved' grassland and that glycine was the dominant amino acid type (up to 42% of total). Secondly, the injection of representative amounts of glycine-2-(13)C-(15)N (4.76 and 42.86 mM) into intact soil cores from the two grassland types provided evidence of direct uptake of glycine by plants, with both (15)N and (13)C being detected in plant material of both grasslands. Finally, a microcosm experiment demonstrated no preferential uptake of amino acid N by the grasses which dominate the grassland types, namely Holcus lanatus, Festuca rubra, Agrostis capillaris from the 'unimproved' grassland, and Lolium perenne from the 'improved' grassland. Again, both (13)C and (15)N were detected in all grass species suggesting uptake of intact glycine by these plants. PMID:10920354

Streeter, T C; Bol, R; Bardgett, R D

2000-01-01

151

Watershed and ecosystem responses to invasive grass establishment and dominance across a desert grassland watershed  

NASA Astrophysics Data System (ADS)

Compared to aridland systems that have undergone rapid change in dominant vegetation growth form, the consequences to watershed and ecosystem processes following a shift in dominance between similar growth forms have not been well-studied. Following a five year drought period, strong summer monsoon rains in 2006 across the USDA-ARS Walnut Gulch Experimental Watershed near Tombstone, AZ, were accompanied by widespread native perennial grass mortality, a transient increase in annual forbs, followed by establishment and sustained dominance by the invasive South African bunchgrass, Lehmann lovegrass (Eragrostis lehmanniana) across a semiarid grassland watershed (Kendall grassland, WS#112). This loss of ecological diversity occurred across a watershed already instrumented for quantifying long-term climate, watershed, hill-slope, and ecosystem-level gas exchange. Salient findings from these data sets were: 1) annual watershed sediment discharge rapidly returned to pre-invasion levels following a large spike in 2006 that accounted for 65% of the total sediment yield summed over 35 years, 2) plot-level experimental runoff studies showed hill-slope sediment yields consistently doubled, as did growing season soil evaporation contributions to ET, and 3) the grassland was a carbon sink during dry conditions under lovegrass dominance. These findings show that while some aspects of watershed and ecosystem function rapidly re-established (i.e. sediment yield and net primary productivity), processes acting at lower spatial and temporal scales have been negatively impacted by lovegrass dominance. We believe these lower-order processes underlie the strong ecological effects associated with Lehmann lovegrass invasion, and may also accelerate landform processes and change the basic ecohydrological characteristics of semi-arid grassland watersheds.

Hamerlynck, E.; Scott, R.; Polyakov, V.; Sugg, Z.; Moran, M. S.; Stone, J.; Nearing, M.

2012-04-01

152

Microbial community composition and rhizodeposit-carbon assimilation in differently managed temperate grassland soils  

Microsoft Academic Search

Rhizodeposit-carbon provides a major energy source for microbial growth in the rhizosphere of grassland soils. However, little is known about the microbial communities that mediate the rhizosphere carbon dynamics, especially how their activity is influenced by changes in soil management. We combined a 13CO2 pulse-labeling experiment with phospholipid fatty acid (PLFA) analysis in differently managed Belgian grasslands to identify the

Karolien Denef; Dries Roobroeck; Mihiri C. W. Manimel Wadu; Peter Lootens; Pascal Boeckx

2009-01-01

153

A comparison of sound propagation and song frequency in temperate marsh and grassland habitats  

Microsoft Academic Search

Attenuation of pure tones was measured in marsh and grassland habitat. At surface level, in grassland, the ground effect strongly attenuated frequencies below 2.0 kHz (Fig. 2). The ground effect was reduced by increasing source-receiver elevation. In marsh habitat the ground effect did not occur, and low frequencies were optimal for sound propagation (Fig. 3). As predicted from sound propagation

Susan E. Cosens; J. Bruce Falls

1984-01-01

154

[Effect of grazing on sandy grassland ecosystem in Inner Mongolia].  

PubMed

This experiment was carried out for 5 years in Horqin sandy land, lnner Mongolia, which had 4 treatments: Non-grazing (NG), light grazing (LG), moderate grazing (MG) and over grazing (OG). The results showed that different grazing intensities resulted in different development trend of the pasture ecosystem, of which, the injury of OG on pasture ecosystem was very great. The plant diversity, vegetation coverage, plant height and primary productivity under continuous overgrazing for 5 year were 87.9%, 82.1%, 94.0% and 57.0%, respectively, lower than those in NG. The biomass on the OG pasture was only 2.1% of NG, and the contents of soil clay, C and N as well as the quantities of soil microbes and small animals in OG were respectively 6.0%, 31.9%, 25.0%, 95.0% and 75.9% lower than those in NG, but the soil hardness was raised by 274.0%. Especially, the secondary productivity of the pasture became negative from the third year, and the productive foundation of the pasture ecosystem was completely destroyed. Non-grazing was beneficial to pasture, and enclosure caused an increase in vegetation coverage, plant height and primary productivity. The vegetation coverage, plant height and soil status in LG and MG were not as good as those in NG, but were stable and didn't show worsening trend. Based on the above results, it's considered that on the sandy pasture in the semi-arid area of Inner Mongolia, the rational grass utilization ratio is 45%-50%, and the suitable loading capacity is 3-4 sheep unit.hm-2. PMID:15227991

Zhao, Halin; Zhang, Tonghui; Zhao, Xueyong; Zhou, Ruilian

2004-03-01

155

The effects of global climate change on the species composition and ecosystem function in the central grasslands  

Microsoft Academic Search

Alterations to the Earth`s environment are projected to be of an amplitude not experienced in the recent biological history. How ecosystems will respond to these changes is a matter of great uncertainty. Using the ecosystem model CENTURY, we evaluated the responses of five grass species, common to the Central Grasslands Region to changing climates. The altered climates used in this

M. B. Falkner; D. S. Ojima; W. J. Parton

1995-01-01

156

Groundwater–soil water–vegetation dynamics in a temperate forest ecosystem along a slope  

Microsoft Academic Search

Groundwater can have a profound effect on water availability to vegetation in temperate climate regions. Here we attempt to model groundwater, soil water, and vegetation dynamics in groundwater controlled ecosystems and to assess how these depend on climate and topography. We focus on the possible location of a boundary between two vegetation types on a slope. One vegetation type is

R. J. Brolsma; M. F. P. Bierkens

2007-01-01

157

Groundwater-soil water-vegetation dynamics in a temperate forest ecosystem along a slope  

Microsoft Academic Search

Groundwater can have a profound effect on water availability to vegetation in temperate climate regions. Here we attempt to model groundwater, soil water, and vegetation dynamics in groundwater controlled ecosystems and to assess how these depend on climate and topography. We focus on the possible location of a boundary between two vegetation types on a slope. One vegetation type is

R. J. Brolsma; M. F. P. Bierkens

2007-01-01

158

Ecosystem Respiration in an Undisturbed, Old-Growth, Temperate Rain Forest  

Microsoft Academic Search

Old-growth forests are usually close to carbon neutral, and climate change may push them towards becoming net carbon sources. Ecosystem carbon exchange and its component fluxes, were measured in a temperate rainforest in South Westland, New Zealand. The forest, which receives over 3 m of rain a year, is dominated by 400 year-old podocarp trees, and is on a low

J. E. Hunt; A. S. Walcroft; T. M. McSeveny; G. N. Rogers; D. Whitehead

2008-01-01

159

Net ecosystem CO 2 exchange in a temperate cattail marsh in relation to biophysical properties  

Microsoft Academic Search

Net ecosystem exchange (NEE) of carbon dioxide (CO2) was measured at a temperate cattail marsh using the eddy covariance technique in order to examine the relationships between NEE, weather, and vegetation properties. Analyses of CO2 fluxes for a complete year (May 9, 2005 to May 30, 2006) showed that the marsh wetland was a net CO2 sink for each month

Marie-Claude Bonneville; Ian B. Strachan; Elyn R. Humphreys; Nigel T. Roulet

2008-01-01

160

SHRUBS EFFECTS ON CARBON DIOXIDE AND WATER VAPOR FLUXES OVER GRASSLANDS  

Technology Transfer Automated Retrieval System (TEKTRAN)

Temperate grasslands are a species rich ecosystem that may be important in mitigating the increase in atmospheric carbon dioxide. The effect of shrub invasion on carbon dioxide fluxes in Northern Great Plains grasslands is not known. The objectives of this research were to determine carbon dioxide...

161

Ecosystem performance assessment for grasslands in the Greater Platte River Basin: implications for cellulosic biofuel development  

NASA Astrophysics Data System (ADS)

This study identifies lands suitable for cellulosic biofuel (e.g., switchgrass) development across the Northern Great Plains, with an initial emphasis on the Greater Platte River Basin (GPRB), using satellite observations, climate data, and ecosystem models. Our approach is based on previous successful ecosystem performance (EP) studies in the Yukon River Basin and the Upper Colorado River Basin. We hypothesize that areas with fairly consistent high grassland productivity (i.e., high site potential) in fair to good range condition (persistent ecosystem overperformance or normal performance with few ecological disturbances) are potentially suitable for cellulosic biofuel (switchgrass) development. Ecosystem site potential was calculated using a 9-year (2000-2008) average of annually integrated growing season Normalized Difference Vegetation Index (GSN), geophysical and biophysical data, climate data, and a rule-based piecewise regression tree model. The GSN derived from eMODIS (expedited Moderate Resolution Imaging Spectroradiometer) observations was used as a proxy for the actual ecosystem performance. The weather-based expected EP (EEP) was computed using site potential, yearly seasonal climate variables, and piecewise regression tree models. The ecosystem performance anomaly (EPA) for a specific year was estimated based on the difference between the actual EP and the EEP during that year. The final EPA maps were categorized as normal performance, underperformance, and overperformance at the 90% confidence levels. Pixels that either overperformed or normally performed for three of four years from 2005 to 2008 and that have moderate or high site potential within the GPRB are identified as probable areas for future cellulosic biofuel development. Results from this study will help land managers and decision makers make optimal land use decisions for cellulosic biofuel development and sustainability within the grassland regions of the GPRB.

Gu, Y.; Boyte, S. P.; Wylie, B. K.; Tieszen, L. L.

2010-12-01

162

Responses of soil respiration to elevated CO[sub 2] in two California grassland ecosystems  

SciTech Connect

Estimates of soil respiration (SR) in current and elevated CO[sub 2] are critical for predicting future global carbon budgets. We measured SR in two California grassland ecosystems (sandstone and serpentine) growing at ambient and ambient+350 ppm CO[sub 2]. SR was higher in elevated CO[sub 2] for both ecosystems in the field, but differences were not significant. At peak plant growth, SR was approximately 6 [mu]mol m[sup [minus]2]s[sup [minus]1] in elevated CO[sub 2] and 5 [mu]mol m[sup [minus]2] s[sup [minus]1] in ambient CO[sub 2] for both ecosystems. We also examined soil respiration in monocultures of 7 grassland species grown in microecosystems (10-cm diameter by 1-m deep tubes). SR was approximately 2 [mu]mol m[sup [minus]2]s[sup [minus]1] for Plantago, Bromus, Hemizona, and Calycadenia and 7 [minus] 8 [mu]mol m[sup [minus]2]s[sup [minus]2] for Lolium, Avena, and Vulpia. Elevated CO[sub 2] significantly increased soil respiration by 20-30% in Bromus, Hemizonia and Lolium monocultures. SR was significantly correlated with total plant biomass as averaged across all species.

Luo, Y.; Jackson, R.B.; Field, C.B.; Mooney, H.A. (Stanford Univ., CA (United States))

1994-06-01

163

A field method to store samples from temperate mountain grassland soils for analysis of phospholipid fatty acids  

PubMed Central

The storage of soil samples for PLFA analysis can lead to shifts in the microbial community composition. We show here that conserving samples in RNAlater, which is already widely used to store samples for DNA and RNA analysis, proved to be as sufficient as freezing at ?20 °C and preferable over storage at 4 °C for temperate mountain grassland soil. The total amount of extracted PLFAs was not changed by any storage treatment. Storage at 4 °C led to an alteration of seven out of thirty individual biomarkers, while freezing and storage in RNAlater caused changes in the amount of fungal biomarkers but had no effect on any other microbial group. We therefore suggest that RNAlater could be used to preserve soil samples for PLFA analysis when immediate extraction or freezing of samples is not possible, for example during sampling campaigns in remote areas or during transport and shipping.

Schnecker, Jorg; Wild, Birgit; Fuchslueger, Lucia; Richter, Andreas

2012-01-01

164

A field method to store samples from temperate mountain grassland soils for analysis of phospholipid fatty acids.  

PubMed

The storage of soil samples for PLFA analysis can lead to shifts in the microbial community composition. We show here that conserving samples in RNAlater, which is already widely used to store samples for DNA and RNA analysis, proved to be as sufficient as freezing at -20 °C and preferable over storage at 4 °C for temperate mountain grassland soil. The total amount of extracted PLFAs was not changed by any storage treatment. Storage at 4 °C led to an alteration of seven out of thirty individual biomarkers, while freezing and storage in RNAlater caused changes in the amount of fungal biomarkers but had no effect on any other microbial group. We therefore suggest that RNAlater could be used to preserve soil samples for PLFA analysis when immediate extraction or freezing of samples is not possible, for example during sampling campaigns in remote areas or during transport and shipping. PMID:22865936

Schnecker, Jörg; Wild, Birgit; Fuchslueger, Lucia; Richter, Andreas

2012-08-01

165

Temperature and soil moisture interactively affected soil net N mineralization in temperate grassland in Northern China  

Microsoft Academic Search

Intact soil cores from three adjacent sites (Site A: grazed, Site B: fenced for 4 years, and Site C: fenced for 24 years) were incubated in the laboratory to examine effects of temperature, soil moisture, and their interactions on net nitrification and N mineralization rates in the Inner Mongolia grassland of Northern China. Incubation temperature significantly influenced net nitrification and

Changhui Wang; Shiqiang Wan; Xuerong Xing; Lei Zhang; Xingguo Han

2006-01-01

166

Seasonal changes in soil microbial communities along a fertility gradient of temperate grasslands  

Microsoft Academic Search

This study aimed to: (1) determine whether soil microbial communities along a gradient from intensive (fertilized) to low-input (unfertilized) grassland management, shift in their composition as shown by an increase in the abundance of fungi relative to bacteria and (2) whether these shifts in soil microbial communities vary depending on season. At all sample dates soil microbial biomass-C and -N,

Richard D. Bardgett; Roger D. Lovell; Phil J. Hobbs; Steve C. Jarvis

1999-01-01

167

Low amounts of root herbivory positively influence the rhizosphere microbial community in a temperate grassland soil  

Microsoft Academic Search

It has been suggested that an important factor relating the dynamics of microbial communities and nutrient flux in grassland soils is a change in nondetrital inputs, such as root exudates, associated with below-ground herbivory. Our objective was to quantify the effects of different amounts of root infestation, and hence herbivory, by clover cyst nematodes (Heterodera trifolii) on the biomass and

Crystal S Denton; Richard D Bardgett; Roger Cook; Philip J Hobbs

1998-01-01

168

Spatial and temporal scaling of beta diversity in grazed temperate grasslands  

Technology Transfer Automated Retrieval System (TEKTRAN)

Grazed grasslands contribute greatly to the economy and environment of the northeastern United States, though their ecology has not been extensively studied. Plant community composition was sampled in five to seven fields in each of five grazing farms: two in New York, two in Pennsylvania, and one i...

169

The Effects of Warming-Shifted Plant Phenology on Ecosystem Carbon Exchange Are Regulated by Precipitation in a Semi-Arid Grassland  

PubMed Central

Background The longer growing season under climate warming has served as a crucial mechanism for the enhancement of terrestrial carbon (C) sink over the past decades. A better understanding of this mechanism is critical for projection of changes in C cycling of terrestrial ecosystems. Methodology/Principal Findings A 4-year field experiment with day and night warming was conducted to examine the responses of plant phenology and their influences on plant coverage and ecosystem C cycling in a temperate steppe in northern China. Greater phenological responses were observed under night than day warming. Both day and night warming prolonged the growing season by advancing phenology of early-blooming species but without changing that of late-blooming species. However, no warming response of vegetation coverage was found for any of the eight species. The variances in species-level coverage and ecosystem C fluxes under different treatments were positively dependent upon the accumulated precipitation within phenological duration but not the length of phenological duration. Conclusions/Significance These plants' phenology is more sensitive to night than day warming, and the warming effects on ecosystem C exchange via shifting plant phenology could be mediated by precipitation patterns in semi-arid grasslands.

Xia, Jianyang; Wan, Shiqiang

2012-01-01

170

Simulating the impacts of land use in Northwest Europe on Net Ecosystem Exchange (NEE): The role of arable ecosystems, grasslands and forest plantations in climate change mitigation.  

PubMed

In this study, we compared measured and simulated Net Ecosystem Exchange (NEE) values from three wide spread ecosystems in the southeast of Ireland (forest, arable and grassland), and investigated the suitability of the DNDC (the DeNitrification-DeComposition) model to estimate present and future NEE. Although, the field-DNDC version overestimated NEE at temperatures >5°C, forest-DNDC under-estimated NEE at temperatures >5°C. The results suggest that the field/forest DNDC models can successfully estimate changes in seasonal and annual NEE from these ecosystems. Differences in NEE were found to be primarily land cover specific. The annual NEE was similar for the grassland and arable sites, but due to the contribution of exported carbon, the soil carbon increased at the grassland site and decreased at the arable site. The NEE of the forest site was an order of magnitude larger than that of the grassland or arable ecosystems, with large amounts of carbon stored in woody biomass and the soil. The average annual NEE, GPP and Reco values over the measurement period were -904, 2379 and 1475gCm(-2) (forest plantations), -189, 906 and 715gCm(-2) (arable systems) and -212, 1653 and 1444gCm(-2) (grasslands), respectively. The average RMSE values were 3.8gCm(-2) (forest plantations), 0.12gCm(-2) (arable systems) and 0.21gCm(-2) (grasslands). When these models were run with climate change scenarios to 2060, predictions show that all three ecosystems will continue to operate as carbon sinks. Further, climate change may decrease the carbon sink strength in the forest plantations by up to 50%. This study supports the use of the DNDC model as a valid tool to predict the consequences of climate change on NEE from different ecosystems. PMID:23384575

Abdalla, Mohamed; Saunders, Matthew; Hastings, Astley; Williams, Mike; Smith, Pete; Osborne, Bruce; Lanigan, Gary; Jones, Mike B

2013-02-04

171

Testing the Link between Functional Diversity and Ecosystem Functioning in a Minnesota Grassland Experiment  

PubMed Central

The functional diversity of a community can influence ecosystem functioning and reflects assembly processes. The large number of disparate metrics used to quantify functional diversity reflects the range of attributes underlying this concept, generally summarized as functional richness, functional evenness, and functional divergence. However, in practice, we know very little about which attributes drive which ecosystem functions, due to a lack of field-based tests. Here we test the association between eight leading functional diversity metrics (Rao’s Q, FD, FDis, FEve, FDiv, convex hull volume, and species and functional group richness) that emphasize different attributes of functional diversity, plus 11 extensions of these existing metrics that incorporate heterogeneous species abundances and trait variation. We assess the relationships among these metrics and compare their performances for predicting three key ecosystem functions (above- and belowground biomass and light capture) within a long-term grassland biodiversity experiment. Many metrics were highly correlated, although unique information was captured in FEve, FDiv, and dendrogram-based measures (FD) that were adjusted by abundance. FD adjusted by abundance outperformed all other metrics in predicting both above- and belowground biomass, although several others also performed well (e.g. Rao’s Q, FDis, FDiv). More generally, trait-based richness metrics and hybrid metrics incorporating multiple diversity attributes outperformed evenness metrics and single-attribute metrics, results that were not changed when combinations of metrics were explored. For light capture, species richness alone was the best predictor, suggesting that traits for canopy architecture would be necessary to improve predictions. Our study provides a comprehensive test linking different attributes of functional diversity with ecosystem function for a grassland system.

Butterfield, Bradley J.; Reich, Peter B.

2012-01-01

172

Decomposition of cellulose, soil organic matter and plant litter in a temperate grassland soil  

Microsoft Academic Search

The formation of mor humus in an experimental grassland plot, which has been acidified by long-term fertiliser treatment,\\u000a has been studied by comparing the rates of cellulose, soil organic matter and plant litter decay with those in an adjacent\\u000a plot with near-neutral pH and mull humus. The decomposition of cellulose filter paper in litter bags of 5 mm, 1-mm and

D. W. Hopkins; D. M. Ibrahim; A. G. O'donnell; R. S. Shiel

1990-01-01

173

Temperate Grassland Responses to Climate Change: an Analysis using the Hurley Pasture Model  

Microsoft Academic Search

The Hurley Pasture Model is process-based and couples the carbon, nitrogen and water cycles in the soil-grass-animal system. It was used to examine the responses of grasslands in southern, lowland and northern, upland climates in Britain. Short-term response to step-wise increases in CO2concentration (350 to 700 ?mol mol?1) and temperature (5 °C) were contrasted with long-term equilibrium (the term ‘equilibrium’

J. H. M. THORNLEY; M. G. R. CANNELL

1997-01-01

174

Dormancy patterns, germination ecology, and seed-bank types of twenty temperate fen grassland species  

Microsoft Academic Search

The germination ecology, including primary and secondary dormancy, mortality of seeds, and seed-bank type, of 20 fen grassland\\u000a species from Northern Germany was investigated using a combination of burial and germination experiments. To analyze primary\\u000a dormancy and effects of after-ripening (dry storage for 28 days) on freshly matured seeds, germination was measured at two\\u000a fluctuating temperature regimes (15\\/25°C and 5\\/15°C)

Kai Jensen

2004-01-01

175

Carbon dioxide fluxes in a spatially and temporally heterogeneous temperate grassland  

Microsoft Academic Search

Landscape position, grazing, and seasonal variation in precipitation and temperature create spatial and temporal variability\\u000a in soil processes, and plant biomass and composition in grasslands. However, it is unclear how this variation in plant and\\u000a soil properties affects carbon dioxide (CO2) fluxes. The aim of this study is to explore the effect of grazing, topographic position, and seasonal variation in

Anita C. Risch; Douglas A. Frank

2006-01-01

176

Seasonal and interannual variation in evapotranspiration, energy balance and surface conductance in a northern temperate grassland  

Microsoft Academic Search

The eddy covariance technique was used to measure evapotranspiration and sensible heat flux continuously for 2.5 years (three growing seasons) in a northern grassland near Lethbridge, Alta., Canada. The 1999 growing season had precipitation (226.9mm) near the 30-year average value (1971–2000; 206.4±77.5; mean±S.D.). In contrast, the 1998 growing season precipitation (295.3mm) was significantly above average and almost four times greater

Linda A Wever; Lawrence B Flanagan; Peter J Carlson

2002-01-01

177

Inter-annual Variability in Net Ecosystem Exchange of Carbon Dioxide and Methane Emissions in a Temperate Freshwater Marsh  

Microsoft Academic Search

There exists very little information on greenhouse gas (GHG) exchange in marsh wetlands, especially in temperate climates. Measurements of carbon dioxide (CO2) and methane (CH4) fluxes were made from May 2005 to June 2008 in a temperate freshwater cattail marsh in Eastern Ontario, Canada. The net ecosystem exchange (NEE) of CO2 was measured continuously using the eddy covariance technique, and

M. Bonneville; I. Strachan

2009-01-01

178

Potential climate change impacts on temperate forest ecosystem processes  

USGS Publications Warehouse

Large changes in atmospheric CO2, temperature and precipitation are predicted by 2100, yet the long-term consequences for carbon, water, and nitrogen cycling in forests are poorly understood. We applied the PnET-CN ecosystem model to compare the long-term effects of changing climate and atmospheric CO2 on productivity, evapotranspiration, runoff, and net nitrogen mineralization in current Great Lakes forest types. We used two statistically downscaled climate projections, PCM B1 (warmer and wetter) and GFDL A1FI (hotter and drier), to represent two potential future climate and atmospheric CO2 scenarios. To separate the effects of climate and CO2, we ran PnET-CN including and excluding the CO2 routine. Our results suggest that, with rising CO2 and without changes in forest type, average regional productivity could increase from 67% to 142%, changes in evapotranspiration could range from –3% to +6%, runoff could increase from 2% to 22%, and net N mineralization could increase 10% to 12%. Ecosystem responses varied geographically and by forest type. Increased productivity was almost entirely driven by CO2 fertilization effects, rather than by temperature or precipitation (model runs holding CO2 constant showed stable or declining productivity). The relative importance of edaphic and climatic spatial drivers of productivity varied over time, suggesting that productivity in Great Lakes forests may switch from being temperature to water limited by the end of the century.

Peters, Emily B.; Wythers, Kirk R.; Zhang, Shuxia; Bradford, John B.; Reich, Peter B.

2013-01-01

179

How plant functional traits cascade to microbial function and ecosystem services in mountain grasslands  

NASA Astrophysics Data System (ADS)

1. There is growing evidence that plant functional diversity and microbial communities of soil are tightly coupled, and that this coupling influences a range of ecosystem functions. Moreover, it has been hypothesized that changes in the nature of interactions between plant functional diversity and microbial communities along environmental gradients contributes to variation in the delivery of ecosystem services. Although there is empirical support for such relationships using broad plant and microbial functional classifications, or from studies of plant monocultures, such relationships and their consequences for ecosystem services have not been quantified under complex field conditions with diverse plant communities. 2. We aimed to provide an explicit quantification of how plant and microbial functional properties interplay to determine key ecosystem functions underlying ecosystem services provided by grasslands. At three mountain grassland sites in the French Alps, Austrian Tyrol and northern England, we quantified, along gradients of management intensity, (i) plant functional diversity, (ii) soil microbial community composition and parameters associated with nitrogen cycling, and (iii) key ecosystem processes related to the carbon and nitrogen cycles including aboveground biomass production, standing litter, litter decomposition, soil organic matter and nitrate and ammonium leaching . Considering that plants strongly determine microbial communities, we used a hierarchical approach that considered first direct effects of plant traits and then effects of soil microorganisms on processes, to determine the relative effects of plant and microbial functional parameters on key ecosystem properties. 3. We identified a gradient of relative effects of plant and microbial traits from properties controlled mostly by aboveground processes, such as plant biomass production and standing litter, to properties controlled mostly by microbial processes, such as soil leaching of inorganic N (NO3 or NH4). Soil organic matter illustrated an intermediate situations with joint control by plant and microbial traits. 4. Across all sites, we found that increasing management intensity, and concomitant changes in soil fertility, was associated with more exploitative plant strategies (high Specific Leaf Area and Leaf Nitrogen Concentration) and taller vegetation. These vegetation functional properties provided the benefit of greater production, but at the cost of poor carbon and nutrient retention, notably because they were associated with microbial communities dominated by bacteria and with rapid rates of nitrification. Conversely, decreasing management intensity resulted in dominance by plants with conservative strategies (high Leaf Dry Matter Content and C/N ratio), usually low production, but benefits for carbon sequestration and soil nutrient retention by favouring microbial communities dominated by fungi co-occuring with bacteria with slow activities.

Lavorel, S.; Grigulis, K.; Krainer, U.; Legay, N.; Turner, C.; Dumont, M.; Kastl, E.; Arnoldi, C.; Bardgett, R.; Poly, F.; Pommier, T.; Schloter, M.; Tappeiner, U.; Bahn, M.; Clément, J.-C.

2012-04-01

180

Wood ash applications to temperate forest ecosystems—potential benefits and drawbacks  

Microsoft Academic Search

The objectives of the present work were (a) to quantify the effects of wood ash on forest ecosystems through a meta-analysis\\u000a approach associated with a detailed review of the literature (mainly composed of work carried out in Nordic countries) and\\u000a (b) to extrapolate the effects on forest growth to other contexts (i.e. warm temperate countries) by identifying the cases\\u000a for

L. Augusto; M. R. Bakker; C. Meredieu

2008-01-01

181

Characterizing forest fragments in boreal, temperate, and tropical ecosystems.  

PubMed

An increased ability to analyze landscapes in a spatial manner through the use of remote sensing leads to improved capabilities for quantifying human-induced forest fragmentation. Developments of spatially explicit methods in landscape analyses are emerging. In this paper, the image delineation software program eCognition and the spatial pattern analysis program FRAGSTATS were used to quantify patterns of forest fragments on six landscapes across three different climatic regions characterized by different moisture regimes and different influences of human pressure. Our results support the idea that landscapes with higher road and population density are more fragmented; however, there are other, equally influential factors contributing to fragmentation, such as moisture regime, historic land use, and fire dynamics. Our method provided an objective means to characterize landscapes and assess patterns of forest fragments across different forested ecosystems by addressing the limitations of pixel-based classification and incorporating image objects. PMID:19205180

Meddens, Arjan J H; Hudak, Andrew T; Evans, Jeffrey S; Gould, William A; González, Grizelle

2008-12-01

182

Ecosystem response to experimentally increased precipitation variability in a Chihuahuan Desert grassland  

NASA Astrophysics Data System (ADS)

Global climate change is predicted to increase precipitation variability, with more extreme rainfall events punctuated by longer dry intervals. Changes in rainfall distribution are especially important in semi-arid environments where precipitation driven spatial and temporal patterns of soil water content are a key control on ecosystem function. The “bucket model” predicts an increase in soil respiration and primary production in arid ecosystems as extreme precipitation events alleviate drought stress through deep soil water recharge. To determine the effects of altered precipitation regimes on a Chihuahuan Desert grassland, we experimentally altered precipitation frequency and intensity in a monsoon rainfall manipulation experiment at the Sevilleta LTER site in central New Mexico, USA. Treatments included ambient rainfall plus one 20mm rain event each month during the summer monsoon and ambient plus four 5mm rain events each month. Soil processes were measured by in situ CO2, temperature and moisture sensors at 30 minute intervals. Leaf-level photosynthesis, stomatal conductance and pre-dawn water potential of Bouteloua eriopoda were measured in association with experimental rainfall events. Aboveground net primary productivity (ANPP) was measured bi-annually. Our results support the bucket model which predicts that a small number of large events (more extreme events) will increase soil moisture in aridland ecosystems leading to increased soil respiration and primary productivity. When compared to ambient plots, large rainfall events significantly increased mean %soil water content and this corresponded with a significant increase in soil CO2 efflux and ANPP (207.10 g m-2 vs 97.60 g m-2). Moreover, rainfall treatments significantly decreased pre-dawn leaf water potential and increased leaf-level photosynthetic rates by 32%. Overall our results show that desert grasslands dominated by B. eriopoda are highly sensitive to changes in precipitation regime. Our results indicate that more extreme precipitation regimes may increase ANPP, yet because these systems have high potential decomposition rates the overall impact of climate change on C dynamics remains uncertain.

Collins, S. L.; Thomey, M.; Vargas, R.; Brown, R.; Johnson, J.; Natvig, D.; Friggens, M.

2009-12-01

183

Ecosystem-level evidence for top-down and bottom-up control of production in a grassland stream system  

Microsoft Academic Search

Ecosystem-wide effects of introduced brown trout (Salmo trutta L.) and native river galaxias (Galaxiaseldoni McDowall) were studied by analysing ecosystem production budgets for two adjacent tributaries of a grassland stream-system\\u000a in the South Island of New Zealand. One tributary was inhabited by brown trout, the other by river galaxias. No other fish\\u000a species were present in either stream. The budget

Alexander D. Huryn

1998-01-01

184

Plant functional types and climate along a precipitation gradient in temperate grasslands, north-east China and south-east Mongolia  

Microsoft Academic Search

Using data from three field surveys along a precipitation gradient of temperate grasslands in north-east China (the Northeast China Transect, NECT) and south-east Mongolia, the spatial distribution of six plant functional types (PFTs): C3 species, C4 species, grasses, shrubs, forbs and succulents and their relationships with climate were analysed. The spatial distribution of different PFTs varies in different regions and

Jian Ni

2003-01-01

185

Study on the strategies of sustainable development with the grassland ecosystem environment and yak industry in Ganzi prefecture  

Microsoft Academic Search

Summary This paper introduces the basic circumstance of Ganzi prefecture, the position and present condition of grassland ecosystem environment. It also discusses the process of transforming light energy (sun energy) into plant energy (grass) from photosynthesis of green plant and then transforming plant energy into animal energy (yak products). Finally, it puts forward the countermeasures of sustained development with yak.

Li Ping; Ye Zhongming; Yu Qing

186

The expansion of grassland ecosystems in Africa in relation to mammalian evolution and the origin of the genus Homo  

Microsoft Academic Search

The relationship between climatic change and human evolution can be framed in terms of three major hypotheses. A modern version of the long-held savanna hypothesis posits that the expansion of grassland ecosystems in Africa was driven by global climatic change and led to the divergence of hominins from the apes and to the origin of the Homo clade. A related

Anna K. Behrensmeyer

2004-01-01

187

Winter warming pulses affect the development of planted temperate grassland and dwarf-shrub heath communities  

Microsoft Academic Search

Background: Winter conditions are changing considerably due to climate change. Resulting alterations in the frequency of soil freeze–thaw cycles (FTCs) are ecologically important.Aim: We quantified the impact of winter soil-warming pulses on the community structure of temperate plant communities.Methods: The cover of vascular plant species in two vegetation types, each at three diversity levels, was recorded 1 year before to

Juergen Kreyling; Gerald Jurasinski; Kerstin Grant; Vroni Retzer; Anke Jentsch; Carl Beierkuhnlein

2011-01-01

188

Assessment of structure and function in metal polluted grasslands using Terrestrial Model Ecosystems.  

PubMed

Ecosystem effects of metal pollution in field situations are hard to predict, since metals occur often in mixtures and links between structural (organisms) and functional endpoints (ecosystem processes) are not always that clear. In grasslands, both structure and functioning was suspected to be affected by a mixture of copper, lead, and zinc. Therefore, the structural and functional variables were studied simultaneously using Terrestrial Model Ecosystems (TMEs). Comparing averages of low- and high-polluted soil, based on total metal concentrations, did not show differences in structural and functional variables. However, nematode community structure (Maturity Index) negatively correlated with metal concentrations. Next to that, multivariate statistics showed that enchytraeid, earthworm and, to lesser extent, nematode diversity decreased with increasing metal concentrations and a lower pH in the soil. Bacterial CFU and nematode biomass were positively related with decomposer activity and nitrate concentrations. Nitrate concentrations were negatively related to ammonium concentrations. Earthworm biomass, CO(2) production and plant yield were not related to metal concentrations. The most metal-sensitive endpoint was enchytraeid biomass. In all analyses, soil pH was a significant factor, indicating direct effects on organisms, or indicating indirect effects by influencing metal availability. In general, structural diversity seemed more positively related to functional endpoints than structural biomass. TMEs proved valuable tools to assess the structure and function in metal polluted field situations. The outcome feeds modeling effort and direct future research. PMID:18539329

Kools, Stefan A E; Boivin, Marie-Elène Y; Van Der Wurff, André W G; Berg, Matty P; Van Gestel, Cornelis A M; Van Straalen, Nico M

2008-06-09

189

Plant community composition promotes multiple ecosystem functions in grassland at low and high soil fertility  

NASA Astrophysics Data System (ADS)

It is well known that plant species richness can enhance primary productivity through complementarity in resource use by component plant species. Fewer studies have explored the role of plant species diversity and composition for the delivery of other ecosystem services than primary production and its dependency on resource availability. In this study we investigated how carbon (C) and nitrogen (N) stocks in vegetation, soil and soil microbes, the loss of C and N from soil through leaching and ecosystem exchange rates of CO2 are affected by the composition and richness of grassland plant communities and soil fertility. We used two soils of contrasting fertility in which we planted plant communities using a pool of six plant species from one of three functional groups (legumes, forbs and C3 grasses). The levels of plant species richness were one, two, three or six species and were composed of one, two or three functional groups. Soil fertility stimulated pools of C and N in shoots and roots, and the soil microbial biomass, but also increased significantly with increased plant functional group and plant species richness. Moreover, plant diversity suppressed N and water loss via soil leaching. We also found changes in the C and N content in soil, but these were not related to the richness of plant species or functional groups. The changes in soil were rather specifically due to the abundance of the legumes. The leaching of water and N was related negative to plant species richness but also specifically to the abundance of the forb species. Our findings show that the relation between plant community composition and storage of C and N in vegetation is not directly reflected in the changes in C and N storage in soil. These soil based storage functions, and the leaching of N from soil, appeared to be most strongly related to different key plant species. Together these results indicate that the maintenance of plant diversity is important to sustain the multiple functions grasslands provide.

de Deyn, Gerlinde; Ostle, Nick; Bardgett, Richard

2010-05-01

190

Water- and Plant-Mediated Responses of Ecosystem Carbon Fluxes to Warming and Nitrogen Addition on the Songnen Grassland in Northeast China  

PubMed Central

Background Understanding how grasslands are affected by a long-term increase in temperature is crucial to predict the future impact of global climate change on terrestrial ecosystems. Additionally, it is not clear how the effects of global warming on grassland productivity are going to be altered by increased N deposition and N addition. Methodology/Principal Findings In-situ canopy CO2 exchange rates were measured in a meadow steppe subjected to 4-year warming and nitrogen addition treatments. Warming treatment reduced net ecosystem CO2 exchange (NEE) and increased ecosystem respiration (ER); but had no significant impacts on gross ecosystem productivity (GEP). N addition increased NEE, ER and GEP. However, there were no significant interactions between N addition and warming. The variation of NEE during the four experimental years was correlated with soil water content, particularly during early spring, suggesting that water availability is a primary driver of carbon fluxes in the studied semi-arid grassland. Conclusion/Significance Ecosystem carbon fluxes in grassland ecosystems are sensitive to warming and N addition. In the studied water-limited grassland, both warming and N addition influence ecosystem carbon fluxes by affecting water availability, which is the primary driver in many arid and semiarid ecosystems. It remains unknown to what extent the long-term N addition would affect the turn-over of soil organic matter and the C sink size of this grassland.

Jiang, Li; Guo, Rui; Zhu, Tingcheng; Niu, Xuedun; Guo, Jixun; Sun, Wei

2012-01-01

191

Nitrogen Limitation and Trophic vs. Abiotic Influences on Insect Herbivores in a Temperate Grassland  

Microsoft Academic Search

Plant resources, predators, and abiotic conditions represent three major fac- tors that potentially influence insect herbivore abundance in terrestrial ecosystems. In ni- trogen (N)-limited environments the potential for bottom-up (plant resource) control is strong because plant quality may limit herbivore abundance. However, extremes in abiotic conditions, such as temperature and moisture, can mask such effects. I tested these hy- potheses

Mark E. Ritchie

2000-01-01

192

Transfer of a cyanobacterial neurotoxin within a temperate aquatic ecosystem suggests pathways for human exposure  

PubMed Central

?-methylamino-L-alanine (BMAA), a neurotoxic nonprotein amino acid produced by most cyanobacteria, has been proposed to be the causative agent of devastating neurodegenerative diseases on the island of Guam in the Pacific Ocean. Because cyanobacteria are widespread globally, we hypothesized that BMAA might occur and bioaccumulate in other ecosystems. Here we demonstrate, based on a recently developed extraction and HPLC-MS/MS method and long-term monitoring of BMAA in cyanobacterial populations of a temperate aquatic ecosystem (Baltic Sea, 2007–2008), that BMAA is biosynthesized by cyanobacterial genera dominating the massive surface blooms of this water body. BMAA also was found at higher concentrations in organisms of higher trophic levels that directly or indirectly feed on cyanobacteria, such as zooplankton and various vertebrates (fish) and invertebrates (mussels, oysters). Pelagic and benthic fish species used for human consumption were included. The highest BMAA levels were detected in the muscle and brain of bottom-dwelling fishes. The discovery of regular biosynthesis of the neurotoxin BMAA in a large temperate aquatic ecosystem combined with its possible transfer and bioaccumulation within major food webs, some ending in human consumption, is alarming and requires attention.

Jonasson, Sara; Eriksson, Johan; Berntzon, Lotta; Spacil, Zdenek; Ilag, Leopold L.; Ronnevi, Lars-Olof; Rasmussen, Ulla; Bergman, Birgitta

2010-01-01

193

Transfer of a cyanobacterial neurotoxin within a temperate aquatic ecosystem suggests pathways for human exposure.  

PubMed

beta-methylamino-L-alanine (BMAA), a neurotoxic nonprotein amino acid produced by most cyanobacteria, has been proposed to be the causative agent of devastating neurodegenerative diseases on the island of Guam in the Pacific Ocean. Because cyanobacteria are widespread globally, we hypothesized that BMAA might occur and bioaccumulate in other ecosystems. Here we demonstrate, based on a recently developed extraction and HPLC-MS/MS method and long-term monitoring of BMAA in cyanobacterial populations of a temperate aquatic ecosystem (Baltic Sea, 2007-2008), that BMAA is biosynthesized by cyanobacterial genera dominating the massive surface blooms of this water body. BMAA also was found at higher concentrations in organisms of higher trophic levels that directly or indirectly feed on cyanobacteria, such as zooplankton and various vertebrates (fish) and invertebrates (mussels, oysters). Pelagic and benthic fish species used for human consumption were included. The highest BMAA levels were detected in the muscle and brain of bottom-dwelling fishes. The discovery of regular biosynthesis of the neurotoxin BMAA in a large temperate aquatic ecosystem combined with its possible transfer and bioaccumulation within major food webs, some ending in human consumption, is alarming and requires attention. PMID:20439734

Jonasson, Sara; Eriksson, Johan; Berntzon, Lotta; Spácil, Zdenek; Ilag, Leopold L; Ronnevi, Lars-Olof; Rasmussen, Ulla; Bergman, Birgitta

2010-05-03

194

Partitioning Ecosystem Respiration Using Stable Carbon Isotopes in a Mixed C3 Annual Grassland  

NASA Astrophysics Data System (ADS)

The stable carbon isotope ratio (? 13C) of respired CO2 has been used to partition soil respiration into root and microbial components by exploiting the different ? 13C signals from C3 plants growing in a previously C4 dominated system (Rouchette, Angers and Flanagan 1999). We extend this approach and present data that attempts to partition ecosystem respiration using ? 13C analyses of all of the ecosystem compartments in a mixed C3 annual grassland that has not experienced recent C4 inputs. From December 2000 to February 2001 we measured ? 13C-CO2 respired from leaves, roots and sieved soil collected from a winter-active grassland near Ione, California. Two-source mixing models were used to calculate the contribution of each source to total system respiration by comparing their isotope signals to those from whole ecosystem respiration and soil surface efflux. Isotope ratios were measured on 10mL air samples in septum-capped vials using a Finnigan MAT Delta PlusXL IRMS/Gas Bench II interfaced to an autosampler (after Tu et al. 2001). The vials were filled with sample air in the field using a double-holed needle connected in a closed loop to a LI-6200 IRGA and a bottle containing the isolated samples (leaf, root, sieved soil, etc.). Leaves were clipped at ground level and roots and soil were separated by sieving soil cores. Sample ? 13CO2 signatures were determined by plotting the change in ? 13C against the inverse of CO2 concentration. On average, CO2 respired from sieved soil (-27.4o/oo+/-1.4) was slightly more depleted than that from leaves (-27.2o/oo+/-0.5), but much more depleted than the whole ecosystem (-24.9o/oo+/-0.6), the soil surface efflux (-23.8o/oo+/-0.9), and plant roots (-20.5o/oo+/-0.8). Based on these isotope values, leaf respiration comprised 33% of ecosystem respiration with 36% from roots and 31% from soil microbial respiration. Thus, over two-thirds of ecosystem respiration was autotrophic (plant-based) in origin with roughly one-third being heterotrophic. Belowground respiration, comprised of both autotrophic (root) and heterotrophic (microbial) components, accounted for nearly two-thirds of total ecosystem respiration. Root and microbial respiration each contributed to nearly half of total belowground respiration (53% and 47%, respectively). Similarly, plant respiration was divided nearly equally between that from roots (52%) and leaves (48%). Partitioning using natural abundance stable carbon isotope ratios was made possible because of the relatively large differences in ? 13C values among the various sources in this entirely C3 system. To our knowledge, such large isotopic differences in respired CO2 among different plant tissues and belowground components have not been documented before. Further research is needed to determine how such differences may arise and to establish if similar differences exist in other ecosystems or at different times of the growing season. Our results also imply that interpretation of above-canopy Keeling plot intercepts may be complicated by both multiple (and isotopically distinct) sources and by isotopic fractionation that occurs either during the respiration process itself or during the transfer of carbon compounds prior to respiration.

Tu, K. P.

2001-12-01

195

Assessing shifts in microbial community structure across a range of grasslands of differing management intensity using CLPP, PLFA and community DNA techniques  

Microsoft Academic Search

This study aimed to characterise soil microbial community structure and function in temperate upland grassland ecosystems. We compared the use of community level physiological profiles (CLPP), phospholipid fatty acid (PLFA) profiles and community DNA (%G+C base distribution) approaches to quantify soil microbial community structure and potential activity across a gradient of three upland grassland types at 10 geographically distinct sites

S. J Grayston; C. D Campbell; R. D Bardgett; J. L Mawdsley; C. D Clegg; K Ritz; B. S Griffiths; J. S Rodwell; S. J Edwards; W. J Davies; D. J Elston; P Millard

2004-01-01

196

Wind and water erosion and transport in semi-arid shrubland, grassland and forest ecosystems: quantifying dominance of horizontal wind-driven transport  

Microsoft Academic Search

Soil erosion is an important process in dryland ecosystems, yet measurements and comparisons of wind and water erosion within and among such ecosystems are lacking. Here we compare wind erosion and transport field measurements with water erosion and transport from rainfall-simulation for three different semi-arid ecosystems: a shrubland near Carlsbad, New Mexico; a grassland near Denver, Colorado; and a forest

David D. Breshears; Jeffrey J. Whicker; Mathew P. Johansen; John E. Pinder

2003-01-01

197

Response of temperate grasslands at different altitudes to simulated summer drought differed but scaled with annual precipitation  

NASA Astrophysics Data System (ADS)

Water is an important resource for plant life. Since climate scenarios for Switzerland predict an average reduction of 20% in summer precipitation until 2070, understanding ecosystem responses to water shortage, e.g. in terms of plant productivity, is of major concern. Thus, we tested the effects of simulated summer drought on three managed grasslands along an altitudinal gradient in Switzerland from 2005 to 2007, representing typical management intensities at the respective altitude. We assessed the effects of experimental drought on above- and below-ground productivity, stand structure (LAI and vegetation height) and resource use (carbon and water). Responses of community above-ground productivity to reduced precipitation input differed among the three sites but scaled positively with total annual precipitation at the sites (R2=0.85). Annual community above-ground biomass productivity was significantly reduced by summer drought at the alpine site receiving the least amount of annual precipitation, while no significant decrease (rather an increase) was observed at the pre-alpine site receiving highest precipitation amounts in all three years. At the lowland site (intermediate precipitation sums), biomass productivity significantly decreased in response to drought only in the third year, after showing increased abundance of a drought tolerant weed species in the second year. No significant change in below-ground biomass productivity was observed at any of the sites in response to simulated summer drought. However, vegetation carbon isotope ratios increased under drought conditions, indicating an increase in water use efficiency. We conclude that there is no general drought response of Swiss grasslands, but that sites with lower annual precipitation seem to be more vulnerable to summer drought than sites with higher annual precipitation, and thus site-specific adaptation of management strategies will be needed, especially in regions with low annual precipitation.

Gilgen, A. K.; Buchmann, N.

2009-11-01

198

Response of temperate grasslands at different altitudes to simulated summer drought differed but scaled with annual precipitation  

NASA Astrophysics Data System (ADS)

Water is an important resource for plant live. Since climate scenarios for Switzerland predict an average reduction of 20% in summer precipitation until 2070, understanding ecosystem responses to water shortage, e.g. in terms of plant productivity, is of major concern. Thus, we tested the effects of simulated summer drought on three managed grasslands along an altitudinal gradient in Switzerland from 2005 to 2007, representing typical management intensities at the respective altitude. We assessed the effects of drought on above- and below-ground productivity, stand structure (LAI and vegetation height) and resource use (carbon and water). Drought responses of community above-ground productivity differed among the three sites but scaled positively with total annual precipitation at the sites (R2=0.85). Annual community above-ground biomass productivity was significantly reduced by summer drought at the alpine site receiving the least amount of annual precipitation, while no significant decrease (rather an increase) was observed at the pre-alpine site receiving highest precipitation amounts in all three years. At the lowland site (intermediate precipitation sums), biomass productivity significantly decreased in response to drought only in the third year, after showing increased abundance of a drought tolerant weed species in the second year. No significant change in below-ground biomass productivity was observed at any of the sites in response to simulated summer drought. However, community carbon isotope ratios increased under drought conditions, indicating an increase in water use efficiency. We conclude that there is no general drought response of Swiss grasslands, but that sites with lower annual precipitation seem to be more vulnerable to summer drought than sites with higher annual precipitation, and thus site-specific adaptation measures will be needed especially in regions with low annual precipitation.

Gilgen, A. K.; Buchmann, N.

2009-05-01

199

Biology, chance, or history? The predictable reassembly of temperate grassland communities.  

PubMed

Many studies have examined invasion resistance in plant communities, but few have explored the mechanisms of invasion and how subsequent community reassembly affects community functioning. Using natural dispersal and deliberate seed addition into grassland communities with different compositional and richness histories, we show that invaders establish in a nonrandom manner due to negative effects of resident functional groups on invading species from the same functional group. Invaders hence complement communities with originally low richness levels. Consequently, communities converge toward similar levels of species richness, high functional richness, and evenness, but not always maximum productivity. Invasion processes are faster but qualitatively similar when the effect of chance, in the form of dispersal stochasticity, is reduced by seed addition. Thus, dispersal limitation may influence community assembly, but it does not override functionally predictable assembly mechanisms. Some of the most productive communities prior to invasion are unstable in the face of invasion, leading to decreased productivity following invasion. We suggest that invasion into such communities occurs possibly because a pathogen-free niche is available rather than a resource niche. Thus, pathogens in addition to resource niches may be important biological drivers of community assembly. PMID:20392006

Petermann, Jana S; Fergus, Alexander J F; Roscher, Christiane; Turnbull, Lindsay A; Weigelt, Alexandra; Schmid, Bernhard

2010-02-01

200

Plant and soil microbial responses to defoliation in temperate semi-natural grassland  

Microsoft Academic Search

There is much interest in understanding the nature of feedback mechanisms between plants and soil organisms in grazed ecosystems.\\u000a In this study, we examine the effects of different intensities of defoliation on the growth of three dominant grass species,\\u000a and observe how these plant responses relate to the biomass and activity of the microbial community in the root zone. Our

Ramon Guitian; Richard D. Bardgett

2000-01-01

201

Plant species richness drives the density and diversity of Collembola in temperate grassland  

NASA Astrophysics Data System (ADS)

Declining biodiversity is one of the most important aspects of anthropogenic global change phenomena, but the implications of plant species loss for soil decomposers are little understood. We used the experimental grassland community of the Jena Experiment to assess the response of density and diversity of Collembola to varying plant species richness, plant functional group richness and plant functional group identity. We sampled the experimental plots in spring and autumn four years after establishment of the experimental plant communities. Collembola density and diversity significantly increased with plant species and plant functional group richness highlighting the importance of the singular hypothesis for soil invertebrates. Generally, grasses and legumes beneficially affected Collembola density and diversity, whereas effects of small herbs usually were detrimental. These impacts were largely consistent in spring and autumn. By contrast, in the presence of small herbs the density of hemiedaphic Collembola and the diversity of Isotomidae increased in spring whereas they decreased in autumn. Beneficial impacts of plant diversity as well as those of grasses and legumes were likely due to increased root and microbial biomass, and elevated quantity and quality of plant residues serving as food resources for Collembola. By contrast, beneficial impacts of small herbs in spring probably reflect differences in microclimatic conditions, and detrimental effects in autumn likely were due to low quantity and quality of resources. The results point to an intimate relationship between plants and the diversity of belowground biota, even at small spatial scales, contrasting the findings of previous studies. The pronounced response of soil animals in the present study was presumably due to the fact that plant communities had established over several years. As decomposer invertebrates significantly impact plant performance, changes in soil biota density and diversity are likely to have major feedbacks on plant community productivity and composition.

Sabais, Alexander C. W.; Scheu, Stefan; Eisenhauer, Nico

2011-05-01

202

Effects of grazing on leaf traits and ecosystem functioning in Inner Mongolia grasslands: scaling from species to community  

NASA Astrophysics Data System (ADS)

More attention has focused on using some easily measured plant functional traits to predict grazing influence on plant growth and ecosystem functioning. However, there has been much controversy on leaf traits response to grazing, thus more research should be conducted at the species level. Here we investigated the leaf area, leaf mass and specific leaf area (SLA) of 263 species in eight grassland communities along a soil moisture gradient in the Xilin River Basin, a semiarid grassland of northern China, to explore the grazing effects on ecosystem functioning. Results demonstrated that grazing decreased the leaf area and leaf mass in more than 56% of species in the Xilin River Basin, however, responses of SLA to grazing varied widely between species. Grazing increased SLA in 38.4% of species, decreased SLA in 31.3% of species and had no effect on 30.3% of species. Annuals and biennials generally developed high SLA as grazing tolerance traits, while perennial graminoids developed low SLA as grazing avoidance traits. Considering the water ecotypes, the SLA-increased and SLA-unchanged species were dominated by hygrophytes and mesophytes, while the SLA-decreased species were dominated by xerophytes. At the community level, grazing decreased the mean leaf area index (LAI) of six communities by 16.9%, leaf biomass by 35.2% and standing aboveground biomass (SAB) by 35.0% in the Xilin River Basin, indicating that overgrazing greatly decreased the ecosystem functioning in the semi-arid grassland of northern China. Soil properties, especially fielding holding capacity and soil organic carbon and total nitrogen could mediate the negative grazing impacts. The results suggest SLA is a better leaf trait to reveal plant adaptability to grazing. Our findings have practical implications for range management and productivity maintenance in the semiarid grassland, and it is feasible to take some measures such as ameliorating soil water and nutrient availabilities to prevent grassland degradation.

Zheng, S. X.; Ren, H. Y.; Lan, Z. C.; Li, W. H.; Bai, Y. F.

2009-10-01

203

Vegetation-soil water interaction within a dynamical ecosystem model of grassland in semi-arid areas  

NASA Astrophysics Data System (ADS)

A dynamical ecosystem model with three variables, living biomass, wilted biomass and available soil wetness, is developed to examine the vegetation-soil water interaction in semi-arid areas. The governing equations are based on the mass conservation law. The physical and biophysical processes are formulated with the parameters estimated from observational data. Both numerical results and qualitative analysis of the model as well as observational data indicate that the maintenance of a grassland requires a minimum precipitation (or equivalently, a minimum moisture index), and the grassland and desert ecosystem can coexist when precipitation is within a range above this threshold. Sensitivity studies show that these numerical results are robust with respect to model parameters and the transformation functions. It is also found that the wilted vegetation plays a very important role in shaping the transition between grassland and desert. By using the theories of an attractor basin and multiple equilibrium states, the conditions for grassland maintenance and the strategy of grazing are also analysed.

Zeng, Xiaodong; Zeng, Xubin; Shen, Samuel S. P.; Dickinson, Robert E.; Zeng, Qing-Cun

2005-07-01

204

Ecosystem-scale fluxes in seminatural Pyrenean grasslands: role of annual dynamics of plant functional types  

NASA Astrophysics Data System (ADS)

The net ecosystem exchange (NEE) and the annual C balance of a site are in general modulated by light, temperature and availability of water and other resources to the plants. In grasslands, NEE is expected to depend strongly on the vegetation with a relationship that can be summarized by the above-ground biomass, its amount and dynamics. Any factor controlling the amount of green biomass is expected to have a strong impact on the short-term NEE, such as amount of solar radiation, water availability and grazing pressure. These controls are modulated differently depending on the plant functional type enduring them. Furthermore, as different guilds follow different functional strategies for optimization of the resources, they also present different patterns of change in their capacities such as photosynthetic fixation, belowground C allocation, and C loss via respiration. We examined these relationships at several semi-natural pastures to determine how the seasonal distribution of plant functional types is detected in the short-term ecosystem exchange and what role it plays. We have looked into these patterns to determine the general variation of key processes and whether different temporal patterns arise between different guilds. The study sites are in the Pyrenees, on the mountain pastures of La Bertolina, Alinyà, and Castellar at 1300, 1700, 1900 m a.s.l. respectively. We performed ecosystem-scale flux measurements by means of micrometeorologial stations combined with a thorough description of the vegetation including below- and above-ground biomass and leaf area as well as monitoring of natural abundance of C isotopes, discriminated by plant functional types. We present here the results of the study.

Altimir, Nuria; Ibañez, Mercedes; Elbers, Jan; Rota, Cristina; Arias, Claudia; Carrara, Arnaud; Nogues, Salvador; Sebastia, Maria-Teresa

2013-04-01

205

Responses of a dominant temperate grassland plant (Leymus chinensis) to elevated carbon dioxide and nitrogen addition in China.  

PubMed

The impact of elevated atmospheric CO(2) concentration on plant communities is varied and strongly dependent on the dominant species response, as well as nutrient conditions. Responses of a dominant species (Leymus chinensis) to elevated CO(2) and N application were examined with open-top chambers in a typical temperate grassland in northern China for 3 yr. The significant effect of elevated CO(2) on L. chinensis growth was mainly reflected in the higher photosynthetic rates, increased leaf number, larger shoot and root biomass, and higher root/shoot (R/S) ratio. Enhancement of root biomass induced by elevated CO(2) was larger (40%) than that of shoot biomass (9%). In contrast, N application had a significant impact on most growth indices examined in this study, which was reflected in the enhanced aboveground growth and depressed belowground growth. Nitrogen application significantly reduced the R/S ratio by an average of 40%. Nitrogen addition significantly enhanced the proportion of senescent biomass and decreased the proportion of green leaf biomass under elevated CO(2). There were no CO(2) x N interactions on most of the measured variables, except on photosynthetic rate and the proportion of aboveground biomass. Plant growth variables showed high interannual variation. These results indicate that belowground growth of L. chinensis is more sensitive to elevated CO(2) than is the aboveground. Aboveground growth of L. chinensis is much more sensitive to N application than to CO(2) enrichment. Therefore, the effect of elevated CO(2) on L. chinensis steppe is more likely to be underestimated if only aboveground parts are considered. PMID:20048313

Zhang, Lin; Yang, Yunxia; Zhan, Xiaoyun; Zhang, Canjuan; Zhou, Shuangxi; Wu, Dongxiu

2009-12-30

206

Cyclic voles and shrews and non-cyclic mice in a marginal grassland within European temperate forest.  

PubMed

Cyclic population dynamics of small mammals are not restricted to the boreal and arctic zones of Eurasia and North America, but long-term data series from lower latitudes are still less common. We demonstrated here the presence of periodic oscillations in small mammal populations in eastern Poland using 22-year (1986-2007) trapping data from marginal meadow and river valley grasslands located in the extensive temperate woodland of Bia?owie?a Primeval Forest. The two most common species inhabiting meadows and river valleys, root vole Microtus oeconomus and common shrew Sorex araneus, exhibited synchronous periodic changes, characterised by a 3-year time lag as indicated by an autocorrelation function. Moreover, the cycles of these two species were synchronous within both habitats. Population dynamics of the striped field mouse Apodemus agrarius was not cyclic. However, this species regularly reached maximum density 1 year before the synchronized peak of root voles and common shrews, which may suggest the existence of interspecific competition. Dynamics of all three species was dominated by direct density-dependent process, whereas delayed density dependent feedback was significant only in the root vole and common shrew. Climatic factors acting in winter and spring (affecting mainly survival and initial reproduction rates) were more important than those acting in summer and autumn and affected significantly only the common shrew. High temperatures in winter and spring had positive effects on autumn-to-autumn changes in abundance of this species, whereas deep snow in combination with high rainfall in spring negatively affected population increase rates in common shrew. PMID:22707756

Zub, K; J?drzejewska, B; J?drzejewski, W; Barto?, K A

2012-02-14

207

The use of Ge/Si ratios to quantify Si transformations in grassland ecosystems  

NASA Astrophysics Data System (ADS)

Germanium (Ge) has been shown to behave as a heavy isotope of silicon (Si), enabling the use of Ge/Si ratios as a weathering tracer in terrestrial environments. The two major mechanisms of Ge/Si fractionation in soils result from mineral weathering reactions and biogenic silica formation by plants. The role of plants in Ge fractionation has been deduced from relatively few field studies, and geochemical Ge fractionation data in temperate systems are lacking. The objectives of this research were to quantify biologic Ge fractionation, and to utilize differences in Ge/Si values among the major biogeochemical pools across a grassland bioclimosequence to examine stream water silica provenance. Quantification of biological Ge fractionation was carried out under controlled experimental conditions. Plant phytoliths grown in hydroponic solutions fractionated against Ge (comparing Ge/Sisolution with Ge/Siphytolith) by an average of 82%. Differences in Ge/Si values between roots, stems, and leaves indicate fractionation likely occurs at the root/solution interface. Phytoliths from plants grown in two different soil mediums fractionated against Ge, averaging 44% to 63%, with no clear trends among the species. From the field study, the greater fractionation factor (Kw, where Kw = (Ge/Siclay)/(Ge/Sibedrock)) of the tallgrass (Kw =2.8) vs. shortgrass sites (Kw =1.4) results from the increased weathering intensity across the bioclimosequence. Plant phytoliths exhibit relatively low Ge/Si values (0.15-0.44; x =0.29; n=15), compared to those of the corresponding surface soil water Ge/Si (0.22-0.94; x =0.66; n=6). Stream water Ge/Si values along the grassland climosequence (0.07-1.29, x = 0.34; n = 20) are typical of natural water Ge/Si values. Higher groundwater Ge values (0.42-3.4; x = 1.3; n=16) may represent an increased residence time or contact with minerals of higher Ge/Si ratios. The lack of Ge/Si separation among the major terrestrial pools confounds stream Si provenance. The data suggest that stream water Si is not derived entirely from ground water and that biogenic sources are plausible.

Blecker, S. W.; Derry, L. A.; Chadwick, O. A.; Kelly, E. F.

2005-12-01

208

How do more extreme rainfall regimes affect ecosystem fluxes in seasonally water-limited Northern Hemisphere temperate shrublands and forests?  

NASA Astrophysics Data System (ADS)

As a result of climate change, rainfall regimes became more extreme over the course of the 20th century, characterised by fewer and larger rainfall events. Such changes are expected to continue throughout the current century. The effect of changes in the temporal distribution of rainfall on ecosystem carbon fluxes is poorly understood, with most available information coming from experimental studies of grassland ecosystems. Here, continuous measurements of ecosystem carbon fluxes and precipitation from the worldwide FLUXNET network of eddy-covariance sites are exploited to investigate the effects of differences in rainfall distribution on the carbon balance of seasonally water-limited shrubland and forest sites. Once the strong dependence of ecosystem fluxes on total annual rainfall amount is accounted for, results show that sites with more extreme rainfall distributions have significantly lower gross productivity, slightly lower ecosystem respiration and consequently a smaller net ecosystem productivity.

Ross, I.; Misson, L.; Rambal, S.; Arneth, A.; Scott, R. L.; Carrara, A.; Cescatti, A.; Genesio, L.

2011-09-01

209

Analysis of Grassland Ecosystem Physiology at Multiple Scales Using Eddy Covariance, Stable Isotope and Remote Sensing Techniques  

NASA Astrophysics Data System (ADS)

Grassland ecosystems typically exhibit very large annual fluctuations in above-ground biomass production and net ecosystem productivity (NEP). Eddy covariance flux measurements, plant stable isotope analyses, and canopy spectral reflectance techniques have been applied to study environmental constraints on grassland ecosystem productivity and the acclimation responses of the ecosystem at a site near Lethbridge, Alberta, Canada. We have observed substantial interannual variation in grassland productivity during 1999-2005. In addition, there was a strong correlation between peak above-ground biomass production and NEP calculated from eddy covariance measurements. Interannual variation in NEP was strongly controlled by the total amount of precipitation received during the growing season (April-August). We also observed significant positive correlations between a multivariate ENSO index and total growing season precipitation, and between the ENSO index and annual NEP values. This suggested that a significant fraction of the annual variability in grassland productivity was associated with ENSO during 1999-2005. Grassland productivity varies asymmetrically in response to changes in precipitation with increases in productivity during wet years being much more pronounced than reductions during dry years. Strong increases in plant water-use efficiency, based on carbon and oxygen stable isotope analyses, contribute to the resilience of productivity during times of drought. Within a growing season increased stomatal limitation of photosynthesis, associated with improved water-use efficiency, resulted in apparent shifts in leaf xanthophyll cycle pigments and changes to the Photochemical Reflectance Index (PRI) calculated from hyper-spectral reflectance measurements conducted at the canopy-scale. These shifts in PRI were apparent before seasonal drought caused significant reductions in leaf area index (LAI) and changes to canopy-scale "greenness" based on NDVI values. With further progression of the seasonal drought, LAI and canopy-scale NDVI also declined in strong correlation. In addition, we have observed strong correlation between NDVI calculated from canopy-scale reflectance measurements and NDVI determined by MODIS. Continued reflectance measurements will help to understand and document the response of the grassland to seasonal and annual environmental change.

Flanagan, L. B.; Geske, N.; Emrick, C.; Johnson, B. G.

2006-12-01

210

Productivity of World Ecosystems. Proceedings of a Symposium presented August 31-September 1, 1972, at the General Assembly (5th) of the Special Committee for the International Biological Program in Seattle, Washington.  

National Technical Information Service (NTIS)

The report presents papers by scientists, each dealing with some aspect of productivity of oceans, fresh water, grassland, desert, temperate forests, or tundra. These papers consider the ranges of productivity in each ecosystem, factors providing the main...

1975-01-01

211

Impacts of diurnal temperature range on ecosystem carbon balance: an experimental test in grassland mesocosms  

NASA Astrophysics Data System (ADS)

Although extensive research has determined ecosystem responses to equal increases in day and night temperatures, current temperature increases have generally been asymmetrical, with increases in minimum temperature (Tmin) exceeding increases in maximum temperature (Tmax), or vice versa, depending on location. We conducted an ecosystem warming experiment in a perennial grassland to determine the effects of asymmetrically elevated diel temperature profiles using precision climate-controlled sunlit environmental chambers. Asymmetrically warmed chambers (+5/+2°C, Tmin/Tmax) were compared with symmetrically warmed (+3.5°C continuously) and control chambers (ambient). We tested three alternative hypotheses comparing the carbon balance under symmetric (SYM) and asymmetric (ASYM) warming: H1) SYM < ASYM, due either to a shorter growing season in the SYM treatment from lower Tmin, or to higher respiratory costs from higher Tmax; H2) SYM > ASYM, because warmer nights in the ASYM treatment increase respiration more then photosynthesis, reducing plant growth; H3) SYM = ASYM, due to a combination of effects. Results from the third growing season support H3, that carbon balance is the same under the two elevated diel temperature profiles. During the early part of the growing season, asymmetric warming resulted in higher nighttime respiratory losses than symmetric warming, but these greater loses were compensated by increased early morning photosynthesis. As a result, carbon balance was not different in the two warming treatments at daily time steps. Furthermore, declines in soil moisture over the growing season may have important modulating impacts on the temperature sensitivity of carbon fluxes. As soils dried, carbon fluxes became less sensitive to diel temperature fluctuations, and more similar in the symmetric and asymmetric treatments.

Phillips, C. L.; Gregg, J. W.; Wilson, J. K.; Pangle, L. A.; Bailey, D.

2009-12-01

212

Will anticipated future climatic conditions affect belowground C utilization? - Insights into the role of microbial functional groups in a temperate heath/grassland.  

NASA Astrophysics Data System (ADS)

The global terrestrial soil organic matter stock is the biggest terrestrial carbon pool (1500 Pg C) of which about 4 % is turned over annually. Thus, terrestrial ecosystems have the potential to accelerate or diminish atmospheric climate change effects via belowground carbon processes. We investigated the effect of elevated CO2 (510 ppm), prolonged spring/summer droughts and increased temperature (1 ?C) on belowground carbon allocation and on the recovery of carbon by the soil microbial community. An in-situ 13C-carbon pulse-labeling experiment was carried out in a temperate heath/grassland (Denmark) in May 2011. Recently assimilated 13C-carbon was traced into roots, soil and microbial biomass 1, 2 and 8 days after pulse-labeling. The importance of the microbial community in C utilization was investigated using 13C enrichment patterns in microbial functional groups on the basis of phospholipid fatty acids (PLFAs) in roots. Gram-negative and gram-positive bacteria were distinguished from the decomposer groups of actinomycetes (belonging to the group of gram-positive bacteria) and saprophytic fungi. Mycorrhizal fungi specific PLFAs were not detected probably due to limited sample size in combination with restricted sensitivity of the used GC-c-IRMS setup. Climate treatments did not affect 13C allocation into roots, soil and microbial biomass carbon and also the total microbial biomass size stayed unchanged as frequently observed. However, climate treatments changed the composition of the microbial community: elevated CO2 significantly reduced the abundance of gram-negative bacteria (17:0cy) but did not affect the abundance of decomposers. Drought favored the bacterial community whereas increased temperatures showed reduced abundance of gram-negative bacteria (19:0cy) and changed the actinomycetes community (10Me16:0, 10Me18:0). However, not only the microbial community composition was affected by the applied climatic conditions, but also the activity of microbial functional groups in their utilization of recently assimilated carbon. Particularly the negative effect of the future treatment combination (CO2×T×D) on actinomycetes activity was surprising. By means of activity patterns of gram-negative bacteria, we observed the fastest carbon turnover rate under elevated CO2, and the slowest under extended drought conditions. A changed soil microbial community in combination with altered activities of different microbial functional groups leads to the conclusion that carbon allocation belowground was different under ambient and future climatic conditions and indicated reduced utilization of soil organic matter in the future due to a change of actinomycetes abundance and activity.

Reinsch, Sabine; Michelsen, Anders; Sárossy, Zsuzsa; Egsgaard, Helge; Kappel Schmidt, Inger; Jakobsen, Iver; Ambus, Per

2013-04-01

213

Investigating Ecosystem Functional Development Along a Temperate Rainforest Chronosequence Using Stable Isotope Techniques  

NASA Astrophysics Data System (ADS)

Soil chronosequences are valuable systems for investigating ecosystem development by natural substitution of space for time. The Franz Josef chronosequence in New Zealand comprises temperate mixed conifer/hardwood rainforests formed on glacial surfaces of varying age. It is particularly useful as it includes both early build-up and decline phases over a relatively short time period (ca. 120 k years). Along the sequence, soil phosphorus decreases 8-fold, from 778 to 8 mg kg-1 soluble P. In contrast, nitrogen availability increases to peak at about 500 years, due to early successional N2-fixing shrubs, after which it slowly declines. Ecosystem development along the sequence is characterised by marked changes in both plant species richness and tree height, with progression up to 5 k years and retrogression at older sites (ie > 14 k years). The carbon isotope ratio (? 13CL) of sunlit canopy leaves from three dominant species sampled from within each of six sites, representing the full length of the sequence, decreased from -26.2 to -31.0 per mil with increasing ecosystem age. Independent measurements of photosynthetic capacity confirmed that the decrease was due to declining maximum photosynthetic rate: N2-fixers > early successional angiosperms > late successional angiosperms > late successional conifers. Stable oxygen and nitrogen isotope ratios of canopy leaves are interpreted in terms of stomatal regulation of water loss and changing nitrogen source, respectively. Carbon isotope analysis of CO2 sampled at night at different heights within the canopy allowed estimation of ecosystem discrimination (? 13CR) using Keeling plots. Similarly to ? 13CL, ? 13CR decreased with increasing soil age, suggesting that in high rainfall environments ? 13CR is a good integrator of ecosystem photosynthetic capacity.

Barbour, M. M.; Hunt, J. E.; Richardson, S. J.; Peltzer, D. A.; Whitehead, D.

2003-12-01

214

Comparison of the structure and composition of bacterial communities from temperate and tropical freshwater ecosystems.  

PubMed

We used a partial 16S rRNA sequencing approach to compare the structure and composition of the bacterial communities in three large, deep subalpine lakes in France with those of communities in six shallow tropical reservoirs in Burkina Faso. Despite the very different characteristics of these ecosystems, we found that their bacterial communities share the same composition in regard to the relative proportions of the different phyla, suggesting that freshwater environmental conditions lead to convergence in this composition. In the same way, we found no significant difference in the richness and diversity of the bacterial communities in France and Burkina Faso. We defined core and satellite operational taxonomic units (OTUs) (sequences sharing at least 98% identity) on the basis of their abundance and their geographical distribution. The core OTUs were found either ubiquitously or only in temperate or tropical and subtropical areas, and they contained more than 70% of all the sequences retrieved in this study. In contrast, satellite OTUs were characterized by having a more restricted geographical distribution and by lower abundance. Finally, the bacterial community composition of these freshwater ecosystems in France and Burkina Faso was markedly different, showing that the history of these ecosystems and regional environmental parameters have a greater impact on the relative abundances of the different OTUs in each bacterial community than the local environmental conditions. PMID:19508336

Humbert, Jean-F; Dorigo, Ursula; Cecchi, Philippe; Le Berre, Brigitte; Debroas, Didier; Bouvy, Marc

2009-06-07

215

Juniper Shade Enables Terricolous Lichens and Mosses to Maintain High Photochemical Efficiency in a Semiarid Temperate Sand Grassland  

Microsoft Academic Search

On a semiarid sand grassland (Festucetum vaginatae) colonised by juniper (Juniperus communis L.) shrubs terricolous lichens and mosses segregate strongly between microhabitats: certain species grow in the open grassland, others almost exclusively in the shade of junipers. The contrasting irradiances of these microhabitats influence much the metabolism of these organisms, and thus affect their small-scale distribution. This was confirmed by

T. Kalapos; K. Mázsa

2001-01-01

216

Effects of land use and fine-scale environmental heterogeneity on net ecosystem production over a temperate coniferous forest landscape  

Microsoft Academic Search

In temperate coniferous forests, spatial variation in net ecosystem production (NEP) is often associated with variation in stand age and heterogeneity in environmental factors such as soil depth. However, coarse spatial resolution analyses used to evaluate the terrestrial contribution to global NEP do not generally incorporate these effects. In this study, a fine-scale (25 m grid) analysis of NEP over

David P. Turner; Michael Guzy; Michael A. Lefsky; Steve van Tuyl; Osbert Sun; Chris Daly; Beverly E. Law

2003-01-01

217

Measured and simulated nitrous oxide emissions from ryegrass- and ryegrass/white clover-based grasslands in a moist temperate climate.  

PubMed

There is uncertainty about the potential reduction of soil nitrous oxide (N(2)O) emission when fertilizer nitrogen (FN) is partially or completely replaced by biological N fixation (BNF) in temperate grassland. The objectives of this study were to 1) investigate the changes in N(2)O emissions when BNF is used to replace FN in permanent grassland, and 2) evaluate the applicability of the process-based model DNDC to simulate N(2)O emissions from Irish grasslands. Three grazing treatments were: (i) ryegrass (Lolium perenne) grasslands receiving 226 kg FN ha(-1) yr(-1) (GG+FN), (ii) ryegrass/white clover (Trifolium repens) grasslands receiving 58 kg FN ha(-1) yr(-1) (GWC+FN) applied in spring, and (iii) ryegrass/white clover grasslands receiving no FN (GWC-FN). Two background treatments, un-grazed swards with ryegrass only (G-B) or ryegrass/white clover (WC-B), did not receive slurry or FN and the herbage was harvested by mowing. There was no significant difference in annual N(2)O emissions between G-B (2.38±0.12 kg N ha(-1) yr(-1) (mean±SE)) and WC-B (2.45±0.85 kg N ha(-1) yr(-1)), indicating that N(2)O emission due to BNF itself and clover residual decomposition from permanent ryegrass/clover grassland was negligible. N(2)O emissions were 7.82±1.67, 6.35±1.14 and 6.54±1.70 kg N ha(-1) yr(-1), respectively, from GG+FN, GWC+FN and GWC-FN. N(2)O fluxes simulated by DNDC agreed well with the measured values with significant correlation between simulated and measured daily fluxes for the three grazing treatments, but the simulation did not agree very well for the background treatments. DNDC overestimated annual emission by 61% for GG+FN, and underestimated by 45% for GWC-FN, but simulated very well for GWC+FN. Both the measured and simulated results supported that there was a clear reduction of N(2)O emissions when FN was replaced by BNF. PMID:22028829

Li, Dejun; Lanigan, Gary; Humphreys, James

2011-10-10

218

FUNCTIONAL AND STRUCTURAL CONVERGENCE OF TEMPERATE GRASSLAND AND SHRUBLAND ECOSYSTEMS. (R824993)  

EPA Science Inventory

The perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Concl...

219

ECOSYSTEM CARBON EXCHANGE AND EVAPOTRANSPIRATION IN A SHRUB AND GRASSLAND PLANT COMMUNITY 1646  

Technology Transfer Automated Retrieval System (TEKTRAN)

ABSTRACT Understanding carbon exchange and evapotranspiration in semiarid shrub and grassland areas is important in determining the functionality and interaction of the plant communities. The hypothesis is that a C4 grassland can uptake more carbon per unit of water loss than C3 shrub plant commu...

220

Microbial Enzymatic Response to Reduced Precipitation and Added Nitrogen in a Southern California Grassland Ecosystem  

NASA Astrophysics Data System (ADS)

Microbial enzymes play a fundamental role in ecosystem processes and nutrient mineralization. Although there have been many studies concluding that global climate change affects plant communities, the effects on microbial communities in leaf litter have been much less studied. We measured extracellular enzyme activities in litter decomposing in plots with either reduced precipitation or increased nitrogen in a grassland ecosystem in Loma Ridge National Landmark in Southern California. We used a reciprocal transplant design to examine the effects of plot treatment, litter origin, and microbial community origin on litter decomposition and extracellular enzyme activity. Our hypothesis was that increased nitrogen would increase activity because nitrogen often limits microbial growth, while decreased precipitation would decrease activity due to lower litter moisture levels. Samples were collected in March 2011 and analyzed for the activities of cellobiohydrolase (CBH), ?-glucosidase (BG), ?-glucosidase (AG), N-acetyl-?-D-glucosaminidase (NAG), ?-xylosidase (BX), acid phosphatase (AP), and leucine aminopeptidase (LAP). None of the factors in the nitrogen manipulation had a significant effect on any of the enzymes, although BG, CBH, and NAG increased marginally significantly in plots with nitrogen addition (p = 0.103, p = 0.082, and p = 0.114, respectively). For the precipitation manipulation, AG, BG, BX, CBH, and NAG significantly increased in plots with reduced precipitation (p = 0.015, p <0.001, p<0.001, and p<0.001, respectively) while LAP significantly decreased (p = 0.002). LAP catalyzes the hydrolysis of polypeptides, so reduced LAP activity could result in lower rates of enzyme turnover in the reduced precipitation treatment. We also observed that AP significantly increased (p = 0.014) in litter originating from reduced precipitation plots, while AG, BX, and LAP significantly decreased (p = 0.011, p = 0.031, and 0.005, respectively). There were no significant correlations found between fungal or bacterial mass and enzymatic activity with either of the treatment types. Our results suggest that increased enzymatic activity due to drought could mitigate negative effects of moisture limitation on decomposition. However, this mitigating effect may be offset by declines in enzyme activity due to changes in plant community composition and associated litter chemistry in response to drought.

Alster, C. J.; German, D.; Allison, S. D.

2011-12-01

221

Dependence of ecosystem respiration on soil temperature, moisture and plant biomass in a semi-arid grassland  

NASA Astrophysics Data System (ADS)

The Mongolian steppe zone is one of the main components of central-Asian grasslands. Ecosystem respiration rates between the atmosphere and the steppe ecosystem were measured in a Mongolian semi- arid grassland in July 2004, May 2005, July 2005, September 2005, and June 2006 by using a closed- chamber technique. The study area is dominated by Poaceous grasses and was enclosed by a fence (300 m x 300 m) in June 2004 to prevent livestock from grazing. Along with the respiration measurements, soil temperature, precipitation, and soil volumetric water content were continuously measured. Aboveground plant biomass (AGB) was also determined by clipping vegetation for each observation period. From the measured data of ecosystem respiration and environmental variables, their quantitative relationships were examined. Individual rates of respiration showed the highest rank correlation coefficient with AGB. The correlation between respiration rate and soil moisture was higher at 3 cm depth than at 10 cm depth, which suggested that soil moisture near the soil surface was better proxy than that at deeper layer for accounting for variations in respiration rate. The respiration rate was exponentially related to the soil temperature and the relationship modified by soil moisture. The amount of respiration rate and its temperature sensitivity (Q10) declined with decreasing soil moisture. Standardized rates of respiration at 20°C were expressed well as a bivariate function of AGB and soil moisture at 3 cm depth. Approximately 88% of the fluctuation in standardized respiration rate was explained by the interaction of these two factors.

Nakano, T.; Shinoda, M.

2008-12-01

222

Rapid top-down regulation of plant C:N:P stoichiometry by grasshoppers in an Inner Mongolia grassland ecosystem.  

PubMed

Understanding how food web interactions alter the processing of limiting nutrient elements is an important goal of ecosystem ecology. An experiment manipulating densities of the grasshopper Oedaleus asiaticus was performed to assess top-down effects of grasshoppers on C:N:P stoichiometry of plants and soil in a grassland ecosystem in Inner Mongolia (China). With increased grasshopper feeding, plant biomass declined fourfold, litter abundance increased 30%, and the plant community became dominated by non-host plant taxa. Plant stoichiometric response depended on whether or not the plant was a grasshopper host food species: C:N and C:P ratios increased with increasing grasshopper density (GD) for host plants but decreased in non-host plants. These data suggest either a direct transfer of grasshopper-recycled nutrients from host to non-host plants or a release of non-host plants from nutrient competition with heavily grazed host plants. Litterfall C:N and C:P decreased across moderate levels of grasshopper density but no effects on C:N:P stoichiometry in the surface soil were observed, possibly due to the short experimental period. Our observations of divergent C:N:P stoichiometric response among plant species highlight the important role of grasshopper herbivory in regulating plant community structure and nutrient cycling in grassland ecosystems. PMID:21267596

Zhang, Guangming; Han, Xingguo; Elser, James J

2011-01-26

223

Ecosystem carbon exchange over a warm-temperate mixed plantation in the lithoid hilly area of the North China  

NASA Astrophysics Data System (ADS)

In recent decades, forest area in China increased rapidly by afforestation and reforestation, especially in its temperate parts. However, lack of information on carbon exchange in temperate plantations in China reduced the accuracy of estimation on regional carbon budget. In this study, CO2 flux was measured using the eddy covariance method over a broadleaf dominant mixed plantation in the lithoid hilly area of the North China. The results showed that annual maximum photosynthetic capacity (Amax) varied from 0.81 to 1.22 mg CO2 m-2 s-1 and annual initial light use efficiency (?) from 0.014 to 0.026. Net CO2 uptake was depressed when vapor pressure deficit (VPD) was more than 2.5 kPa. Annual temperature sensitivity coefficient (Q10) for ecosystem respiration, ranged from 1.84 to 2.35, was negatively correlated with base ecosystem respiration (R0) (P < 0.05). Annual R0 decreased but Q10 increased evidently when winter drought occurred. From 2006 to 2010, annual net ecosystem carbon exchange (NEE), Gross primary productivity (GPP) and ecosystem respiration (Rec) were -355 ± 34, 1196 ± 21 and 841 ± 43 g C m-2 yr-1, respectively. The warm-temperate mixed plantation in the lithoid hilly area of the North China was a strong carbon sink of the atmosphere, which was usually weaken when spring drought happened.

Tong, Xiaojuan; Meng, Ping; Zhang, Jinsong; Li, Jun; Zheng, Ning; Huang, Hui

2012-03-01

224

Evidence for non-diffusive transport as an important mechanism determining the soil CO2 efflux in a temperate grassland  

NASA Astrophysics Data System (ADS)

Research on soil respiration has largely focused on the emission of CO2 from soils and far less on the production and subsequent transport of CO2 from soil to atmosphere. The limited knowledge of CO2 transport through the soil, restricts our understanding of the various abiotic and biotic processes underlying emissions of CO2 from terrestrial ecosystems. Soil CO2 efflux is most often measured using soil chambers, but since the early 2000s, solid-state CO2 sensors that measure soil CO2 concentrations at different depths, are becoming more popular. From these continuous high-frequency measurements of the CO2 gradient, the flux can easily be calculated in a very cost-efficient way with minimal disturbance of the natural conditions. This so-called flux-gradient method is based on Fick's law, assuming diffusion to be the only transport mechanism. To test to what extend diffusion is indeed the governing transport process, we compared the CO2 efflux from chamber measurements with the CO2 efflux calculated from soil CO2 concentration profiles for a grassland site in the Austrian Alps. The four commonly used models for diffusivity that we tested, all underestimated the soil chamber effluxes and their amplitudes. What is more, we observed that transport rates correlated well with irradiation (PAR) and -below a certain soil moisture content- with wind speed. Indeed, correlation coefficients of the fits of observed transport rate versus PAR were consistently positive, and those of observed transport rate versus wind speed were positive on days that were not extremely wet (soil water content below 33%). Also, we found that the coupling of transport rate and PAR became stronger as wind speed increased. Our results suggest that non-diffusive bulk air transport mechanisms, such as advective mass transport and pressure pumping, could considerably contribute to soil CO2 transport at this site. We therefore emphasize the importance of investigating alternative transport processes before using solid-state CO2 concentration measurements to estimate soil CO2 emissions at any given site.

Roland, Marilyn; Vicca, Sara; Bahn, Michael; Schmitt, Michael; Janssens, Ivan

2013-04-01

225

Soil microbial community composition and land use history in cultivated and grassland ecosystems of coastal California  

Microsoft Academic Search

Phospholipid ester-linked fatty acid (PLFA) profiles were used to evaluate soil microbial community composition for 9 land use types in two coastal valleys in California. These included irrigated and non-irrigated agricultural sites, non-native annual grasslands and relict, never-tilled or old field perennial grasslands. All 42 sites were on loams or sandy loams of similar soil taxa derived from granitic and

Kerri L. Steenwerth; Louise E. Jackson; Francisco J. Calderón; Mark R. Stromberg; Kate M. Scow

2003-01-01

226

Soil microbial community composition and land use history in cultivated and grassland ecosystems of coastal California  

Microsoft Academic Search

Phospholipid ester-linked fatty acid (PLFA) profiles were used to evaluate soil microbial community composition for 9 land use types in two coastal valleys in California. These included irrigated and non-irrigated agricultural sites, non-native annual grasslands and relict, never-tilled or old field perennial grasslands. All 42 sites were on loams or sandy loams of similar soil taxa derived from granitic and

Kerri L. Steenwerth; Louise E. Jackson; Francisco J. Calderón; Mark R. Stromberg; Kate M. Scow

2002-01-01

227

Invasive C4 Perennial Grass Alters Net Ecosystem Exchange in Mixed C3/C4 Savanna Grassland  

NASA Astrophysics Data System (ADS)

The invasion of ecosystems by non-native plants that differ from native plants in physiological characteristics and phenology has the potential to alter ecosystem function. In Texas and other regions of the southern central plains of the United States, the introduced C4 perennial grass, Bothriochloa ischaemum, invades C3/C4 mixed grasslands and savannas, resulting in decreased plant community diversity (Gabbard 2003; Harmoney et al 2004). The objective of this study was to quantify how the conversion of these mixed grass communities to C4 dominated, B. ischaemum monocultures impacts carbon cycling and sequestration. Seasonal measurements of Net Ecosystem Exchange (NEE) of CO2, leaf level gas exchange and soil respiration were compared between savanna grassland plots composed of either naturally occurring B. ischaemum monocultures or native mixed grasses (n=16). NEE was measured using a closed system chamber that attached to permanently installed stainless steel bases. Temperature, soil moisture, aerial percent species cover and leaf area index were also monitored in plots to explain variability in measured responses. Results showed that NEE differed seasonally between invaded and native plots due to 1) greater leaf surface area per unit ground area in invaded plots, 2) differences in phenological patterns of plant activity and 3) differences in responses to water limitation between invaded and native plots. Cold season and summer drought NEE were driven primarily by belowground respiration in both plot types, however spring uptake activity commenced two months later in invaded plots. This later start in invaded plots was compensated for by greater uptake throughout the growing season and in particular during the drier summer months. Differences in NEE between plot types were not due to differences in soil respiration nor were they due to greater leaf level photosynthetic capabilities of B. ischaemum relative to the dominant native grasses. NEE, soil respiration and biomass accumulation were limited by temperature and soil moisture in both native and invaded plots; however, invaded areas were less sensitive to both higher temperatures and lower soil moisture. Preliminary modeling results suggest that from January-August 2006, invaded grasslands stored approximately one third more carbon than native grasslands, making them 20% less of a carbon source than native plots during this year of record high temperatures and drought. Gabbard, BL. 2003. The Population Dynamics and Distribution of the Exotic Grass,Bothriochloa ischaemum, PhD Dissertation, University of Texas, Austin, TX Harmoney et al. 2004. Herbicide Effects on Established Yellow Old World Bluestem (Bothriochloa ischaemum). Weed Technology 18:545 550

Basham, T. S.; Litvak, M.

2006-12-01

228

? 13C of ecosystem-respired CO2 along a gradient of C3 woody-plant encroachment into C4 grassland  

NASA Astrophysics Data System (ADS)

Woody plant encroachment into grassland has the potential to affect net primary production, in part by changing the sensitivities of photosynthesis and respiration to precipitation. Encroachment of mesquite (Prosopis) into floodplain sacaton (Sporobolus) grassland along the San Pedro River in southeastern Arizona has altered the magnitude and seasonal pattern of net ecosystem carbon exchange and ecosystem respiration. We hypothesized that because mesquite accesses ground water in these floodplain environments, its advancement and dominance in former grassland reduces the sensitivities of photosynthesis and autotrophic respiration to inputs of growing season precipitation. The observed elevated rates of ecosystem respiration following rainfall inputs are likely to result from microbial decomposition of labile organic matter derived from the highly productive mesquite trees. We used the Keeling plot method to monitor carbon-13 composition of nocturnal ecosystem-respired CO2 (? 13CR) during the growing seasons of 2005 and 2006 at three sites spanning a gradient of mesquite invasion: C4 sacaton grassland, mixed mesquite/grass shrubland and C3 mesquite woodland. ? 13CR in the C4 grassland increased from -18.8‰ during the dry premonsoon period to -16.7‰ after the onset of summer rains, whereas ? 13CR in the mixed shrub/grass and woodland ecosystems declined from -20.9‰ to - 24‰ and from -20.8‰ to -24.7‰, respectively, following the onset of summer rains. The ? 13CR of respired CO2 was collected separately from soil, roots, leaves and surface litter to evaluate the contribution of each of these components to ecosystem respiration. Partitioning of ecosystem respiration using these isotope end-members and responses to short-term (days) changes in shallow (0-5cm) soil moisture content suggest that in former grassland now occupied by mesquite woodland, rainfall inputs primarily stimulate microbial decomposition and have little effect on autotrophic respiration. Autotrophic respiration in grassland was stimulated by rainfall inputs to a much greater degree than in woodland. As expected, ecosystem respiration responses to rainfall at the mixed shrubland site was complicated by the heterogeneous plant cover and microsite variation. Partitioning ecosystem respiration into component fluxes is necessary to model and forecast the sensitivity of net primary production to climate and land-use changes.

Sun, W.; Scott, R. L.; Resco, V.; Cable, J. M.; Huxman, T. E.; Williams, D. G.

2006-12-01

229

A transmission model for the ecology of an avian blood parasite in a temperate ecosystem.  

PubMed

Most of our knowledge about avian haemosporidian parasites comes from the Hawaiian archipelago, where recently introduced Plasmodiumrelictum has contributed to the extinction of many endemic avian species. While the ecology of invasive malaria is reasonably understood, the ecology of endemic haemosporidian infection in mainland systems is poorly understood, even though it is the rule rather than the exception. We develop a mathematical model to explore and identify the ecological factors that most influence transmission of the common avian parasite, Leucocytozoonfringillinarum (Apicomplexa). The model was parameterized from White-crowned Sparrow (Zonotrichialeucophrys) and S. silvestre / craigi black fly populations breeding in an alpine ecosystem. We identify and examine the importance of altricial nestlings, the seasonal relapse of infected birds for parasite persistence across breeding seasons, and potential impacts of seasonal changes in black fly emergence on parasite prevalence in a high elevation temperate system. We also use the model to identify and estimate the parameters most influencing transmission dynamics. Our analysis found that relapse of adult birds and young of the year birds were crucial for parasite persistence across multiple seasons. However, distinguishing between nude nestlings and feathered young of the year was unnecessary. Finally, due to model sensitivity to many black fly parameters, parasite prevalence and sparrow recruitment may be most affected by seasonal changes in environmental temperature driving shifts in black fly emergence and gonotrophic cycles. PMID:24073288

Murdock, Courtney C; Foufopoulos, Johannes; Simon, Carl P

2013-09-20

230

A Transmission Model for the Ecology of an Avian Blood Parasite in a Temperate Ecosystem  

PubMed Central

Most of our knowledge about avian haemosporidian parasites comes from the Hawaiian archipelago, where recently introduced Plasmodiumrelictum has contributed to the extinction of many endemic avian species. While the ecology of invasive malaria is reasonably understood, the ecology of endemic haemosporidian infection in mainland systems is poorly understood, even though it is the rule rather than the exception. We develop a mathematical model to explore and identify the ecological factors that most influence transmission of the common avian parasite, Leucocytozoonfringillinarum (Apicomplexa). The model was parameterized from White-crowned Sparrow (Zonotrichialeucophrys) and S. silvestre / craigi black fly populations breeding in an alpine ecosystem. We identify and examine the importance of altricial nestlings, the seasonal relapse of infected birds for parasite persistence across breeding seasons, and potential impacts of seasonal changes in black fly emergence on parasite prevalence in a high elevation temperate system. We also use the model to identify and estimate the parameters most influencing transmission dynamics. Our analysis found that relapse of adult birds and young of the year birds were crucial for parasite persistence across multiple seasons. However, distinguishing between nude nestlings and feathered young of the year was unnecessary. Finally, due to model sensitivity to many black fly parameters, parasite prevalence and sparrow recruitment may be most affected by seasonal changes in environmental temperature driving shifts in black fly emergence and gonotrophic cycles.

Murdock, Courtney C.; Foufopoulos, Johannes; Simon, Carl P.

2013-01-01

231

Stakeholder perceptions of grassland ecosystem services in relation to knowledge on soil fertility and biodiversity  

Microsoft Academic Search

The concept of ecosystem services is increasingly being used by scientists and policy makers. However, most studies in this\\u000a area have focussed on factors that regulate ecosystem functions (i.e. the potential to deliver ecosystem services) or the\\u000a supply of ecosystem services. In contrast, demand for ecosystem services (i.e. the needs of beneficiaries) or understanding\\u000a of the concept and the relative

Pénélope Lamarque; Ulrike Tappeiner; Catherine Turner; Melanie Steinbacher; Richard D. Bardgett; Ute Szukics; Markus Schermer; Sandra Lavorel

232

The abundance, richness and functional role of soil meso- and macrofauna in temperate grassland—A case study  

Microsoft Academic Search

This paper reviews the abundance and species richness, and factors that cause these parameters to vary, of mesofauna and macrofauna in an upland grassland soil studied intensively under the NERC Soil Biodiversity Programme. The concept that competitive exclusion does not act within soil communities is reviewed in light of these findings, which are placed in the context of the wider

Lisa Cole; Mark A. Bradford; Peter J. A. Shaw; Richard D. Bardgett

2006-01-01

233

Gross primary production variability associated with meteorology, physiology, leaf area, and water supply in contrasting woodland and grassland semiarid riparian ecosystems  

NASA Astrophysics Data System (ADS)

Understanding ecosystem-atmosphere carbon exchanges in dryland environments has been more challenging than in mesic environments, likely due to more pronounced nonlinear responses of ecosystem processes to environmental variation. To better understand diurnal to interannual variation in gross primary productivity (GPP) variability, we coupled continuous eddy-covariance derived whole ecosystem gas exchange measurements with an ecophysiologic model based on fundamental principles of diffusion, mass balance, reaction kinetics, and biochemical regulation of photosynthesis. We evaluated the coupled data-model system to describe and understand the dynamics of 3 years of growing season GPP from a riparian grassland and woodland in southern Arizona. The data-model fusion procedure skillfully reproduced the majority of daily variation GPP throughout three growing seasons. While meteorology was similar between sites, the woodland site had consistently higher GPP rates and lower variability at daily and interannual timescales relative to the grassland site. We examined the causes of this variation using a new state factor model analysis that partitioned GPP variation into four factors: meteorology, physiology, leaf area, and water supply. The largest proportion of GPP variation was associated with physiological differences. The woodland showed a greater sensitivity than the grassland to water supply, while the grassland showed a greater sensitivity to leaf area. These differences are consistent with hypotheses of woody species using resistance mechanisms, stomatal regulation, and grassland species using resilience mechanisms, leaf area regulation, in avoiding water stress and have implications for future GPP sensitivity to climate variability following wood-grass transitions.

Jenerette, G. D.; Scott, R. L.; Barron-Gafford, G. A.; Huxman, T. E.

2009-12-01

234

Statistic-mathematical interpretation of some assessment parameters of the grassland ecosystem according to soil characteristics  

NASA Astrophysics Data System (ADS)

Significant parameters of permanent grasslands are represented by the pastoral value and Shannon and Simpson biodiversity indices. The dynamics of these parameters has been studied in several plant associations in Banat Plain, Romania. From the point of view of their typology, these permanent grasslands belong to the steppe area, series Festuca pseudovina, type Festuca pseudovina-Achilea millefolium, subtype Lolium perenne. The methods used for the purpose of this research included plant cover analysis (double meter method, calculation of Shannon and Simpson indices), and statistical methods of regression and correlation. The results show that, in the permanent grasslands in the plain region, when the pastoral value is average to low, the level of interspecific biodiversity is on the increase.

Samfira, Ionel; Boldea, Marius; Popescu, Cosmin

2012-09-01

235

[Effects of desertification on C and N storages in grassland ecosystem on Horqin sandy land].  

PubMed

Sandy grassland is widespread in northern China, where desertification is very common because of overgrazing and estrepement. However, little is known about the effects of desertification on grassland C and N storages in this region. A field survey was conducted on Horqin sandy grassland, and desertification gradients were established to evaluate the effects of desertification on C and N storages in soil, plant, and litter. The results showed that desertification had deep effects on the contents and storages of grassland C and N. The C and N contents and storages in the grassland decreased significantly with increasing desertification degree. Comparing with those in un-desertified grassland, the C and N contents in lightly, moderately, heavily, and severely desertified grasslands decreased by 56.06% and 48.72%, 78.43% and 74.36%, 88.95% and 84.62%, and 91.64% and 84.62% in 0-100 cm soil layer, and by 8.61% and 6.43%, 0.05% and 25.71%, 2.58% and 27.14%, and 8. 61% and 27. 86% in plant components, respectively. Relevantly, the C and N storages decreased by 50.95% and 43.38%, 75.19% and 71.04%, 86.76% and 81.48%, and 91.17% and 83.17% in plant underground components in 0-100 cm soil layer, and by 25.08% and 27.62%, 30.90% and 46.55%, 73.84% and 80.62%, and 90.89% and 87.31% in plant aboveground components, respectively. In 2000, the total area of desertified grassland in Horqin sandy land was 30152. 7 km2, and the C and N loss via desertification reached up to 107.53 and 9.97 Mt, respectively. Correlation analysis indicated that the decrease of soil C and N contents was mainly come from the decreased soil fine particles caused by wind erosion in the process of desertification, and the degradation of soil texture- and nutrient status led finally to the rapid decrease of C and N storages in plant biomass and litter. PMID:18260440

Zhao, Ha-lin; Li, Yu-qiang; Zhou, Rui-lian

2007-11-01

236

Comparison of Carbon Sequestration Rates and Energy Balance of Turf in the Denver Urban Ecosystem and an Adjacent Native Grassland  

NASA Astrophysics Data System (ADS)

Urban ecosystems are currently characterized by rapid growth, are expected to continually expand and, thus, represent an important driver of land use change. A significant component of urban ecosystems is lawns, potentially the single largest irrigated "crop" in the U.S. Beginning in March of 2011 (ahead of the growing season), eddy covariance measurements of net carbon exchange and evapotranspiration along with energy balance fluxes were conducted for a well-watered, fertilized lawn (rye-bluegrass-mix) in metropolitan Denver and for a nearby tallgrass prairie (big bluestem, switchgrass, cheatgrass, blue grama). Due to the semi-arid climate conditions of the Denver region, differences in management (i.e., irrigation and fertilization) are expected to have a discernible impact on ecosystem productivity and thus on carbon sequestration rates, evapotranspiration, and the sensible and latent heat partitioning of the energy balance. By mid-July, preliminary data indicated that cumulative evapotranspiration was approximately 270 mm and 170 mm for urban and native grasslands, respectively, although cumulative carbon sequestration at that time was similar for both (approximately 40 mg/m2). However, the pattern of carbon exchange differed between the grasslands. Both sites showed daily net uptake of carbon starting in late May, but the urban lawn displayed greater diurnal variability as well as greater uptake rates in general, especially following fertilization in mid-June. In contrast, the trend of carbon uptake at the prairie site was occasionally reversed following strong convective precipitation events, resulting in a temporary net release of carbon. The continuing acquisition of data and investigation of these relations will help us assess the potential impact of urban growth on regional carbon sequestration.

Thienelt, T. S.; Anderson, D. E.; Powell, K. M.

2011-12-01

237

Nitric oxide emission from arid grassland and shrubland ecosystems in southern New Mexico  

Microsoft Academic Search

Soil nitrogen losses are characteristic of the transition from semi-arid grassland to arid shrubland in the southwestern United States. Nitrogen gas emission from soil microbial activity contributes to the long-term reduction of soil fertility associated with desertification. We investigated nitric Oxide (NO) emission from arid soils in the Jornada Experimental Range, near Las Cruces, New Mexico. During the dry season,

A. E. Hartley; W. H. Schlesinger

1993-01-01

238

Complex Interactions Among Resources Drive Grassland Ecosystem Responses in two Transplanting Experiments  

NASA Astrophysics Data System (ADS)

Changes in patterns of above- and belowground biomass, biodiversity, plant species and guild composition, and biogeochemical cycles were assessed in two transplanting experiments in mesic mountain grasslands in the Pyrenees. In both experiments, turf sods were transplanted from upland to lowland locations. The first experiment aimed to evaluate general responses to warming and drought, and the second to disentangle the effects of possible underlying mechanisms through resource manipulation by means of a nitrogen x phosphorus fertilisation experiment. Mesic grasslands showed strong shifts in plant diversity and composition after a short period of warming and drought, as a consequence of acute vulnerability of some dominant grasses, rare species losses, and aggregate and trigger effects of originally uncommon forb species. Environmental factors interacted in complex ways, producing changes in biomass distribution and guild proportions. Grasses dominated in the upland and at high resource levels while forbs dominated in the lowland and when water and nutrients decreased. The increased aboveground biomass in grassland sods transplanted to the lowland suggests that biomass production was more temperature-limited than water-limited. The enhancement effect found in the upland sods following phosphorus fertilization supports the hypothesis of a strong limitation arising from reduced nutrient availability, confirming the central role played by phosphorus in these grasslands. Nitrogen addition did not stimulate total biomass but affected guild composition. The counterintuitive effect of increased biomass with decreased water in the lowland was related to shifts in dominance from grasses to forbs, probably enabled by decreased nutrient availability under drought conditions.

Sebastia, M. T.

2007-12-01

239

Understanding coupled climatic and ecosystem responses to global climate change in the Central Grasslands  

Microsoft Academic Search

A long-term National Park Service research program to assess the potential effect of global climate change on the Central Grasslands Biogeographic Area is underway. The program consists of two integrated projects: Projecting climate and vegetation change at regional to landscape scales; and Predicting the effect of global change on vegetation in park landscapes at the plot to landscape scales. Together,

M. B. Falkner; J. Detling; D. Ojima; R. A. Pielke; T. J. Stohlgren; T. G. F. Kittel; J. Lenihan; R. Neilson; W. Reiners

1993-01-01

240

Impacts of altered rainfall timing and warming in a mesic grassland ecosystem  

Technology Transfer Automated Retrieval System (TEKTRAN)

Grasslands are highly responsive to inter- and intra-annual variability in precipitation and temperature, which interact to affect soil water dynamics and the plant and soil processes mediated by soil water availability. In the U.S. Central Plains mean temperatures are expected to increase and rain...

241

Carbon dynamics in a temperate grassland soil after 9 years exposure to elevated CO 2 (Swiss FACE)  

Microsoft Academic Search

Elevated pCO2 increases the net primary production, C\\/N ratio, and C input to the soil and hence provides opportunities to sequester CO2–C in soils to mitigate anthropogenic CO2. The Swiss 9 y grassland FACE (free air carbon-dioxide enrichment) experiment enabled us to explore the potential of elevated pCO2 (60Pa), plant species (Lolium perenne L. and Trifolium repens L.) and nitrogen

Zubin Xie; Georg Cadisch; Grant Edwards; Elizabeth M. Baggs; Herbert Blum

2005-01-01

242

The effects of global climate change on the species composition and ecosystem function in the central grasslands  

SciTech Connect

Alterations to the Earth`s environment are projected to be of an amplitude not experienced in the recent biological history. How ecosystems will respond to these changes is a matter of great uncertainty. Using the ecosystem model CENTURY, we evaluated the responses of five grass species, common to the Central Grasslands Region to changing climates. The altered climates used in this simulation, based on CCC GCM outputs, were 2.5 - 4{degrees}C increase in mean annual temperature and a 1% increase in mean annual precipitation with significant variation in seasonal distribution. The species included Agrostis scabra (C{sub 3} grass), Agropyron repens (C{sub 3} grass), Poa pratensis (C{sub 3} grass), Schizachyrium scoparium (C{sub 4} grass), and Andropogon gerardii (C{sub 4} grass). Soil carbon decreased for all five species under the modified climate scenario. Annual production varied among species. Agropyron repens showed a slight increase, A. scabra showed a slight decrease, while the two C{sub 4} species, S. scoparium and A. gerardii, and the C{sub 3} invasive grass Poa pratensis showed larger increases in annual production. The increased annual production of P. pratensis under the modified climate scenario may indicate the potential for this species to further expand its range. What impact a range expansion of P. pratensis will have on ecosystem function and overall species composition is unclear.

Falkner, M.B.; Ojima, D.S.; Parton, W.J. [Colorado State Univ., Fort Collins, CO (United States)

1995-06-01

243

Linking the Response of Annual Grasslands to Warming and Altered Rainfall Across Scales of Gene Expression, Species, and Ecosystem  

NASA Astrophysics Data System (ADS)

Climate change can influence terrestrial ecosystems at multiple biological levels: gene expression, species, and ecosystem. We are studying California grassland mesocosms with seven annual species (five grasses, two forbs) that were started in 2005. In the 2006-2007 growing season, they were exposed to three rainfall treatments (297, 552, and 867 mm y-1) and soil and air temperature (ambient and elevated +4oC) in replicated greenhouses. This presentation will combine plant and ecosystem level results with transcript level analyses associated with key enzymes, such as rubisco and glutamine synthetase (GS). Because rainfall is the dominant climate variable for most processes in this Mediterranean ecosystem, the effect of warming was strongly mediated by rainfall. In fact, we saw significant interactions between temperature and rainfall treatments at all three biological levels. For example, at the ecosystem level, warming led to a decrease in aboveground and total NPP under low rainfall, and an increase under high rainfall. For the dominant species, Avena barbata, warming had no effect under high rainfall, but suppressed Avena NPP in low rainfall. At the same time, warmer, wetter conditions accelerated Avena flowering by almost 15 days. This shift in phenology was presaged by observations at the transcript level. Specifically, in the high temperature, high rainfall treatment, the levels of mRNAs for RbcS and GS2 (encoding the small subunit of rubisco and the chloroplastic isoform of GS, respectively) declined while GS1 (encoding the cytosolic isoform of GS) was upregulated several weeks before heading. The transcript level response (along with soil and plant nitrogen data) indicated the leaf had switched from a carbon and nitrogen sink to a source - consistent with more mature plant function and earlier flowering. Soil CO2 respiration also showed strong rain-by-temperature interactions that were due mainly to changes in root response (respiration and/or exudates) rather than in microbial respiration. Overall, the pervasive rain-by-temperature interactions mean that it may be very difficult to predict the effect of warming alone, without accounting for changes in precipitation (in our Mediterranean system). While predictions of warming of 3-6°C in the next 100 years are fairly certain, changes in precipitation are much more uncertain, with some forecasts drier and others wetter for a given location. We suggest that uncertainty about future precipitation and the interacting influences of temperature and moisture on ecosystems are currently key limitations in predicting ecosystem response to climate change, particularly in Mediterranean ecosystems such as the one studied here.

Torn, M. S.; Bernard, S. M.; Castanha, C.; Fischer, M. L.; Hopkins, F. M.; Placella, S. A.; St. Clair, S. B.; Salve, R.; Sudderth, E.; Herman, D.; Ackerly, D.; Firestone, M. K.

2007-12-01

244

Recovery of plant species composition and ecosystem function after cessation of grazing in a Mediterranean grassland  

Microsoft Academic Search

Short- and long-term changes in species composition, plant biomass production, and litter decomposition after cessation of\\u000a grazing were examined in a Mediterranean grassland with high dominance of annual species and strong seasonality in biomass\\u000a production. Short-term changes were assessed during three consecutive years in plots previously exposed to different grazing\\u000a pressures and compared to plots in long-term (30–40 years) exclosures. Short-term

Carly Golodets; Jaime Kigel; Marcelo Sternberg

2010-01-01

245

High Resolution Quantitative Mapping of Surface Soil Moisture in Grassland Ecosystems using Dual Polarized L-band SAR Data  

NASA Astrophysics Data System (ADS)

The moisture content of the upper few centimeters of the land surface is a key parameter with respect to fluxes of water and energy at the land-atmosphere interface and also plays a crucial role in determining the partitioning of rainfall into infiltration and surface runoff. Numerous studies have shown that SAR satellites have the potential to provide spatially distributed estimates of near-surface soil water contents. Grassland ecosystems are one of the important land cover classes of the Earth's land surface, however, only few SAR related studies on grassland can be found in the literature. In general, a major impediment to accurate quantitative retrievals of soil moisture is the presence of a vegetation cover characterized by gradual variations between different satellite passes. With classical single-channel SAR systems it is not possible to separate the different scattering contributions of soil and vegetation components to the radar cross section. Hence, an accurate estimation of soil moisture under vegetation required the use of additional a priori knowledge on vegetation type and vegetation state. The dual polarized coherent-on-receive mode (FBD343) of PALSAR aboard the Advanced Land Observing Satellite (ALOS "Daichi") provides an additional cross polarized channel (HV) allowing the exploitation of the distributed target (2x2) complex covariance matrix ([C2]) raw binary data off-diagonal elements. The eigenvectors constructed from the [C2] matrix can be used to calculate the dual-pol target parameters entropy (H), anisotropy (A), and alpha angle (?) by applying the H/A/? decomposition. In this study we consider development of a dedicated semi-empirical soil moisture retrieval model for grassland ecosystems based on correlation analysis between multitemporal partial polarimetric PALSAR observables and extensive in situ measurements. A total of 13 FBD acquisitions taken over the study area were used. The proposed inversion algorithm is capable of taking into account the varying surface states and allows estimating surface soil moisture with an accuracy of 4.1 Vol.-% (RMSE). Moreover, our results indicate that at L-band the attenuation effects caused by the amount of above ground vegetation and its geometric properties are neglectable if the amount of fresh weight plant biomass is lower than 2 kg/sqm. Instead it was found that the thatch layer constitutes the major source of disturbance in terms of radar interactions with the ground surface. The thatch thereby acts as an absorbing layer which becomes more and more absorbing as its water content increases.

Koyama, C. N.; Schneider, K.

2011-12-01

246

Aeolian process effects on vegetation communities in an arid grassland ecosystem  

PubMed Central

Many arid grassland communities are changing from grass dominance to shrub dominance, but the mechanisms involved in this conversion process are not completely understood. Aeolian processes likely contribute to this conversion from grassland to shrubland. The purpose of this research is to provide information regarding how vegetation changes occur in an arid grassland as a result of aeolian sediment transport. The experimental design included three treatment blocks, each with a 25 × 50 m area where all grasses, semi-shrubs, and perennial forbs were hand removed, a 25 × 50 m control area with no manipulation of vegetation cover, and two 10 × 25 m plots immediately downwind of the grass-removal and control areas in the prevailing wind direction, 19° north of east, for measuring vegetation cover. Aeolian sediment flux, soil nutrients, and soil seed bank were monitored on each treatment area and downwind plot. Grass and shrub cover were measured on each grass-removal, control, and downwind plot along continuous line transects as well as on 5 × 10 m subplots within each downwind area over four years following grass removal. On grass-removal areas, sediment flux increased significantly, soil nutrients and seed bank were depleted, and Prosopis glandulosa shrub cover increased compared to controls. Additionally, differential changes for grass and shrub cover were observed for plots downwind of vegetation-removal and control areas. Grass cover on plots downwind of vegetation-removal areas decreased over time (2004–2007) despite above average rainfall throughout the period of observation, while grass cover increased downwind of control areas; P. glandulosa cover increased on plots downwind of vegetation-removal areas, while decreasing on plots downwind of control areas. The relationships between vegetation changes and aeolian sediment flux were significant and were best described by a logarithmic function, with decreases in grass cover and increases in shrub cover occurring with small increases in aeolian sediment flux.

Alvarez, Lorelei J; Epstein, Howard E; Li, Junran; Okin, Gregory S

2012-01-01

247

Analysis of atmospheric inputs of nitrate to a temperate forest ecosystem from ?17O isotope ratio measurements  

NASA Astrophysics Data System (ADS)

Determining the fate of atmospheric N deposited in forest ecosystems is essential to understanding the ecological impact of increased anthropogenic N deposition. We hypothesize that a significant fraction of soil nitrate (dry deposited HNO3 and wet deposited NO3-) in northern Michigan is derived from atmospheric deposition. To test this idea, soil, rainfall, and cloud water were sampled in a temperate forest in northern Lower Michigan. The fraction of the soil solution NO3- pool directly from atmospheric deposition was quantified using the natural isotopic tracer, ?17O. Our results show that on average 9% of the soil solution NO3- is unprocessed (no microbial turnover) N derived directly from the atmosphere. This points to the potential importance of anthropogenic N deposition and contributes to the long-standing need to improve our understanding of the impacts of atmospheric nitrogen processing and deposition on forest ecosystems and forest productivity.

Costa, A. W.; Michalski, G.; Schauer, A. J.; Alexander, B.; Steig, E. J.; Shepson, P. B.

2011-08-01

248

Nitric oxide emission from arid grassland and shrubland ecosystems in southern New Mexico  

SciTech Connect

Soil nitrogen losses are characteristic of the transition from semi-arid grassland to arid shrubland in the southwestern United States. Nitrogen gas emission from soil microbial activity contributes to the long-term reduction of soil fertility associated with desertification. We investigated nitric Oxide (NO) emission from arid soils in the Jornada Experimental Range, near Las Cruces, New Mexico. During the dry season, mean NO fluxes from coarse-textured soils in a Boutelcua grassland and a Larrea shrubland were similar (0.12 and 0.15 ng NO-N cm[sup [minus]2] hr[sup [minus]1], respectively), and higher than flexes from fine-textured soils in a Flourensia shrubland (0.02 ng NO-N cm[sup [minus]2] hr[sup [minus]1]). In a wetting experiment, mean NO fluxes were higher under shrub canopies of Larrea and Flourensia, reflecting the accumulation of soil organic matter under shrubs in islands of fertility. In the Larrea shrubland, mean NO fluxes were ten times higher under shrubs than between shrubs (12.9 vs. 1.29 ng NO-N cm[sup [minus]2] hr[sup [minus]1]).

Hartley, A.E.; Schlesinger, W.H. (Duke Univ., Durham, NC (United States))

1993-06-01

249

Ecosystem-scale measurements of nitrous oxide fluxes for an intensely grazed, fertilized grassland  

NASA Astrophysics Data System (ADS)

An eddy covariance (EC) system with a tunable diode laser trace gas analyzer was used in a field setting in Ireland to measure N2O emissions on a continuous basis over an eight-month period, spanning a range of seasonal conditions. Intensely-grazed grassland fields within the footprint area of the EC sensors were subject to chemical fertilizer and slurry applications in order to boost grassland yield, and the amounts of these applications were documented by the farmers on a monthly basis. Three major emission events, covering a timeframe of 16 days (6.6% of the measurement period) contributed to over half (51.1%) of the observed cumulative flux. Two of these events occurred during the summer, while the third occurred during the winter, with vastly different soil moisture and soil temperature conditions associated with these times of the year. The type of N applications (fertilizer vs. slurry), soil moisture and temperature status had implications for controlling the short-term rates of N2O emissions. Cumulative N2O emissions, however, were driven by fertilizer and slurry N applications, as the emission factor of approximately 3.0% displayed consistency throughout the eight-month period.

Scanlon, Todd M.; Kiely, Ger

2003-08-01

250

Relationships among soil properties, plant nutrition and arbuscular mycorrhizal fungi-plant symbioses in a temperate grassland along hydrologic, saline and sodic gradients.  

PubMed

Temporal variations in the relationships among plant nutrient concentrations, soil properties and arbuscular-mycorrhizal (AM) fungal dynamics were studied along a topographic and saline gradient in a temperate grassland soil. Soil and plant (Lotus tenuis, Paspalum vaginatum, Stenotaphrum secundatum) samples were collected on four seasonally based occasions. The morphology of AM root colonization had a similar pattern in the plants studied. Maximum arbuscular colonization occurred at the beginning of the growing season in late winter and was minimal in late summer, but maximal vesicular colonization occurred in summer and was minimal in winter, suggesting a preferential production of these morphological phases by the fungus with respect to season. The greatest arbuscular colonization was associated with the highest N and P concentrations in plant tissue, suggesting a correspondence with increases in the rate of nutrient transfer between the symbiotic partners. Water content, salinity and sodicity in soil were positively associated with AM root colonization and arbuscule colonization in L. tenuis, but negatively so in the grasses. There were distinct seasonally related effects with respect to both spore density and AM colonization, which were independent of particular combinations of plant species and soil sites. PMID:18205811

García, Ileana V; Mendoza, Rodolfo E

2008-01-17

251

Seasonal changes in surface soil moisture and vegetation observed by ERS-1 SAR over temperate grassland and semi-arid savannah  

NASA Astrophysics Data System (ADS)

Soil moisture exerts an important control on the transfer of energy and water at the land surface and its availability determines, to a large extent, the development of vegetation. Satellite remote sensing using synthetic aperture radar has the potential to monitor spatial and temporal changes in surface soil moisture provided the effects of, primarily, vegetation and surface roughness are understood. The results obtained from ground validation measurements undertaken during an annual vegetation cycle in contrasting temperate and semi-arid climates enabled the sensitivity of the SAR to be tested over a wide range of soil moisture and vegetation conditions. In the UK, flat, grassland sites were used to simplify the modeling of vegetation over three contrasting soil types. Both manually read and data-logged instruments were used to monitor moisture conditions both at the surface and within the soil moisture profile for modeling their interrelationships over time. Vegetation parameters were determined through destructive sampling. In Niger the soils were of almost pure sand under both the natural vegetation of fallow savannah and the main crop of millet. As a result of the high permeability of the sand, the timing of SAR data acquisition relative to the last rainfall event was believed to be an important factor affecting radar backscatter. For both areas, seasonal variations in radar backscatter were present and evidence to demonstrate the contribution of the vegetation and soil components is given.

Blyth, Ken

1995-01-01

252

Changes in grassland ecosystem function due to extreme rainfall events: implications for responses to climate change  

Technology Transfer Automated Retrieval System (TEKTRAN)

Climate change driven by increasing atmospheric CO2 concentrations is causing measurable changes in precipitation patterns. Most climate change scenarios forecast continuing increases in extreme precipitation patterns for North American terrestrial ecosystems, manifest as larger precipitation event...

253

Effects of Future Climate Shifts on CO2 Exchange of a Grassland Ecosystem  

Microsoft Academic Search

Increases in atmospheric CO2 concentration not only affects climate variables such as precipitation, water vapor concentration, and air temperature, but also affects intrinsic ecosystem physiological properties such as the maximum carboxylation capacity and stomatal conductance. De-convolving these two effects remains uncertain in biosphere-atmosphere water and carbon cycling. Using a simplified analytical net ecosystem CO2 exchange (NEE) model, tested with recently

C. Hsieh

2004-01-01

254

Patterns of above- and belowground biomass allocation in China's grasslands: evidence from individual-level observations.  

PubMed

Above- and belowground biomass allocation not only influences growth of individual plants, but also influences vegetation structures and functions, and consequently impacts soil carbon input as well as terrestrial ecosystem carbon cycling. However, due to sampling difficulties, a considerable amount of uncertainty remains about the root: shoot ratio (R/S), a key parameter for models of terrestrial ecosystem carbon cycling. We investigated biomass allocation patterns across a broad spatial scale. We collected data on individual plant biomass and systematically sampled along a transect across the temperate grasslands in Inner Mongolia as well as in the alpine grasslands on the Tibetan Plateau. Our results indicated that the median of R/S for herbaceous species was 0.78 in China's grasslands as a whole. R/S was significantly higher in temperate grasslands than in alpine grasslands (0.84 vs. 0.65). The slope of the allometric relationship between above- and belowground biomass was steeper for temperate grasslands than for alpine. Our results did not support the hypothesis that aboveground biomass scales isometrically with belowground biomass. The R/S in China's grasslands was not significantly correlated with mean annual temperature (MAT) or mean annual precipitation (MAP). Moreover, comparisons of our results with previous findings indicated a large difference between R/S data from individual plants and communities. This might be mainly caused by the underestimation of R/S at the individual level as a result of an inevitable loss of fine roots and the overestimation of R/S in community-level surveys due to grazing and difficulties in identifying dead roots. Our findings suggest that root biomass in grasslands tended to have been overestimated in previous reports of R/S. PMID:20697874

Wang, Liang; Niu, Kechang; Yang, Yuanhe; Zhou, Peng

2010-08-10

255

Dew water isotopic ratios and their relationships to ecosystem water pools and fluxes in a cropland and a grassland in China  

Microsoft Academic Search

Dew formation has the potential to modulate the spatial and temporal variations of isotopic contents of atmospheric water\\u000a vapor, oxygen and carbon dioxide. The goal of this paper is to improve our understanding of the isotopic interactions between\\u000a dew water and ecosystem water pools and fluxes through two field experiments in a wheat\\/maize cropland and in a short steppe\\u000a grassland

Xue-Fa WenXuhui; Xuhui Lee; Xiao-Min Sun; Jian-Lin Wang; Zhong-Min Hu; Sheng-Gong Li; Gui-Rui Yu

256

Complex facilitation and competition in a temperate grassland: loss of plant diversity and elevated CO2 have divergent and opposite effects on oak establishment.  

PubMed

Encroachment of woody vegetation into grasslands is a widespread phenomenon that alters plant community composition and ecosystem function. Woody encroachment is often the result of fire suppression, but it may also be related to changes in resource availability associated with global environmental change. We tested the relative strength of three important global change factors (CO(2) enrichment, nitrogen deposition, and loss of herbaceous plant diversity) on the first 3 years of bur oak (Quercus macrocarpa) seedling performance in a field experiment in central Minnesota, USA. We found that loss of plant diversity decreased initial oak survival but increased overall oak growth. Conversely, elevated CO(2) increased initial oak seedling survival and reduced overall growth, especially at low levels of diversity. Nitrogen deposition surprisingly had no net effect on survival or growth. The magnitude of these effects indicates that long-term woody encroachment trends may be most strongly associated with those few individuals that survive, but grow much larger in lower diversity patches. Further, while the CO(2) results and the species richness results appear to describe opposing trends, this is due only to the fact that the natural drivers are moving in opposite directions (decreasing species richness and increasing CO(2)). Interestingly, the mechanisms that underlie both patterns are very similar, increased CO(2) and increased species richness both increase herbaceous biomass which (1) increases belowground competition for resources and (2) increases facilitation of early plant survival under a more diverse plant canopy; in other words, both competition and facilitation help determine community composition in these grasslands. PMID:22865092

Wright, Alexandra; Schnitzer, Stefan A; Dickie, Ian A; Gunderson, Alex R; Pinter, Gabriella A; Mangan, Scott A; Reich, Peter B

2012-08-05

257

Timing of climate variability and grassland productivity  

PubMed Central

Future climates are forecast to include greater precipitation variability and more frequent heat waves, but the degree to which the timing of climate variability impacts ecosystems is uncertain. In a temperate, humid grassland, we examined the seasonal impacts of climate variability on 27 y of grass productivity. Drought and high-intensity precipitation reduced grass productivity only during a 110-d period, whereas high temperatures reduced productivity only during 25 d in July. The effects of drought and heat waves declined over the season and had no detectable impact on grass productivity in August. If these patterns are general across ecosystems, predictions of ecosystem response to climate change will have to account not only for the magnitude of climate variability but also for its timing.

Craine, Joseph M.; Nippert, Jesse B.; Elmore, Andrew J.; Skibbe, Adam M.; Hutchinson, Stacy L.; Brunsell, Nathaniel A.

2012-01-01

258

Timing of climate variability and grassland productivity.  

PubMed

Future climates are forecast to include greater precipitation variability and more frequent heat waves, but the degree to which the timing of climate variability impacts ecosystems is uncertain. In a temperate, humid grassland, we examined the seasonal impacts of climate variability on 27 y of grass productivity. Drought and high-intensity precipitation reduced grass productivity only during a 110-d period, whereas high temperatures reduced productivity only during 25 d in July. The effects of drought and heat waves declined over the season and had no detectable impact on grass productivity in August. If these patterns are general across ecosystems, predictions of ecosystem response to climate change will have to account not only for the magnitude of climate variability but also for its timing. PMID:22331914

Craine, Joseph M; Nippert, Jesse B; Elmore, Andrew J; Skibbe, Adam M; Hutchinson, Stacy L; Brunsell, Nathaniel A

2012-02-13

259

Geographical and interannual variability in biomass partitioning in grassland ecosystems: a synthesis of field data  

Microsoft Academic Search

Summary • Biomass partitioning is an important variable in terrestrial ecosystem carbon modeling. However, geographical and interannual variability in f BNPP , defined as the fraction of belowground net primary productivity (BNPP) to total NPP, and its relationship with climatic variables, have not been explored. • Here we addressed these issues by synthesizing 94 site-year field biomass data at 12

Dafeng Hui; Robert B. Jackson

2006-01-01

260

Seasonal patterns of ammonium and nitrate uptake in nine temperate forest ecosystems  

Microsoft Academic Search

Summary Seasonal patterns of net N mineralization and nitrification in the 0–10 cm mineral soil of 9 temperate forest sites were analyzed using approximately monthlyin situ soil incubations. Measured nitrification rates in incubated soils were found to be good estimates of nitrification in surrounding forest soils. Monthly net N mineralization rates and pools of ammonium-N in soil fluctuated during the

Knute J. Nadelhoffer; John D. Aber; Jerry M. Melillo

1984-01-01

261

The Coastal Temperate Rainforests of Canada: The need for Ecosystem-Based Management  

Microsoft Academic Search

The Central and North Coast and Haida Gwaii\\/Queen Charlotte Islands regions of British Columbia (B.C.) contain the world's largest remaining areas of intact coastal temperate rainforest. The region has been the focus of intense conflict among environmentalists, forestry companies, First Nations and other interests over the management of these high conservation value old growth forests. Recently completed land use planning

F. M. Moola; D. Martin; B. Wareham; J. Calof; C. Burda; P. Grames

2004-01-01

262

Litter decomposition and soil respiration in response to increased rainfall variability, winter warming and altered cutting frequency in a temperate grassland  

NASA Astrophysics Data System (ADS)

Climate change is likely to alter decomposition rates through direct effects on soil biotic activity and indirect effects on litter quality with possible impacts on the global carbon budget and nutrient cycling. Currently, there is an urgent need to study combined effects of various climatic drivers and of agricultural practise on decomposition. In an in-situ litter bag experiment, we studied effects of rainfall variability (including drought plus heavy rain pulses and regular irrigation) interacting with winter warming and increased winter precipitation and with changes in cutting frequency, on decomposition in a temperate grassland. Litter bags contained mixed and species-specific litter out of all different climate and land-use manipulations and were placed within the plots of litter origin. Moreover, we aimed to disentangle causes for altered decomposition by following two further approaches: To study effects of changed leaf chemicals due to the manipulations we placed litter out of the experiment that has been pre-exposed to the manipulations before on an untreated standard plot outside the experiment. To assess effects of changed soil faunal activity, we investigated decomposition of standard material under differing rainfall variability. We further compare the observed decomposition results with soil respiration data. Decomposition was reduced when litter bags were exposed to drought for six weeks within an 11 months period. Neither additional winter rain nor winter warming had an effect on decomposition, probably because winter warming reduced snow cover and increased variability of surface temperatures. Climate manipulations did not change litter quality. Further, decomposition on the untreated standard plot was not affected by the climate manipulations that the litter previously was exposed to. Thus, reduced decomposition under extreme rainfall variability and drought may be mainly caused by a decrease in soil biotic activity, as indicated by reduced decomposition of standard material during drought. More frequent cutting strongly stimulated decomposition, however, this stimulating effect was absent under extreme rainfall variability including drought. The stimulation of decomposition under more frequent cutting was attributed to changes in litter quality, namely a decrease in C/N ratio. Accordingly, litter from more frequently cut communities decomposed faster on the untreated control plot outside the experiment. Projected increases in drought frequency and increased rainfall variability under climate change may inhibit decomposition and alter nutrient and carbon cycling along with soil quality. Especially decomposition in frequently cut grassland appears vulnerable towards drought.

Kreyling, Juergen; Walter, Julia; Grant, Kerstin; Beierkuhnlein, Carl; Jentsch, Anke

2013-04-01

263

Denitrification and N2O:N2 production in temperate grasslands: Processes, measurements, modelling and mitigating negative impacts.  

PubMed

In this review we explore the biotic transformations of nitrogenous compounds that occur during denitrification, and the factors that influence denitrifier populations and enzyme activities, and hence, affect the production of nitrous oxide (N2O) and dinitrogen (N2) in soils. Characteristics of the genes related to denitrification are also presented. Denitrification is discussed with particular emphasis on nitrogen (N) inputs and dynamics within grasslands, and their impacts on the key soil variables and processes regulating denitrification and related gaseous N2O and N2 emissions. Factors affecting denitrification include soil N, carbon (C), pH, temperature, oxygen supply and water content. We understand that the N2O:N2 production ratio responds to the changes in these factors. Increased soil N supply, decreased soil pH, C availability and water content generally increase N2O:N2 ratio. The review also covers approaches to identify and quantify denitrification, including acetylene inhibition, (15)N tracer and direct N2 quantification techniques. We also outline the importance of emerging molecular techniques to assess gene diversity and reveal enzymes that consume N2O during denitrification and the factors affecting their activities and consider a process-based approach that can be used to quantify the N2O:N2 product ratio and N2O emissions with known levels of uncertainty in soils. Finally, we explore strategies to reduce the N2O:N2 product ratio during denitrification to mitigate N2O emissions. Future research needs to focus on evaluating the N2O-reducing ability of the denitrifiers to accelerate the conversion of N2O to N2 and the reduction of N2O:N2 ratio during denitrification. PMID:23260378

Saggar, Surinder; Jha, N; Deslippe, J; Bolan, N S; Luo, J; Giltrap, D L; Kim, D-G; Zaman, M; Tillman, R W

2012-12-20

264

Seasonal variation in leaf properties and ecosystem carbon budget in a cool-temperate deciduous broad-leaved forest: simulation analysis at Takayama site, Japan  

Microsoft Academic Search

Seasonal changes in gross primary production (GPP) and net ecosystem production (NEP) in temperate deciduous forests are mostly driven by environmental conditions and the phenology of leaf demography. This study addresses another factor, temporal changes in leaf properties, i.e., leaf aging from emergence to senescence. A process-based model was used to link the ecosystem-scale carbon budget with leaf-level properties on

Akihiko Ito; Hiroyuki Muraoka; Hiroshi Koizumi; Nobuko Saigusa; Shohei Murayama; Susumu Yamamoto

2006-01-01

265

Relationship between annual canopy photosynthesis and ecosystem respiration in humid-temperate pastures  

Technology Transfer Automated Retrieval System (TEKTRAN)

Increasing nitrogen fertilization of a mature cool-season pasture increased annual photosynthetic C uptake (GPP) and forage yield but also increased ecosystem respiration (Re), such that net ecosystem exchange (NEE) and soil C sequestration were not affected by the increased fertility. A nine-year s...

266

Community Level Offset of Rain Use- and Transpiration Efficiency for a Heavily Grazed Ecosystem in Inner Mongolia Grassland  

PubMed Central

Water use efficiency (WUE) is a key indicator to assess ecosystem adaptation to water stress. Rain use efficiency (RUE) is usually used as a proxy for WUE due to lack of transpiration data. Furthermore, RUE based on aboveground primary productivity (RUEANPP) is used to evaluate whole plant water use because root production data is often missing as well. However, it is controversial as to whether RUE is a reliable parameter to elucidate transpiration efficiency (TE), and whether RUEANPP is a suitable proxy for RUE of the whole plant basis. The experiment was conducted at three differently managed sites in the Inner Mongolia steppe: a site fenced since 1979 (UG79), a winter grazing site (WG) and a heavily grazed site (HG). Site HG had consistent lowest RUEANPP and RUE based on total net primary productivity (RUENPP). RUEANPP is a relatively good proxy at sites UG79 and WG, but less reliable for site HG. Similarly, RUEANPP is good predictor of transpiration efficiency based on aboveground net primary productivity (TEANPP) at sites UG79 and WG but not for site HG. However, if total net primary productivity is considered, RUENPP is good predictor of transpiration efficiency based on total net primary productivity (TENPP) for all sites. Although our measurements indicate decreased plant transpiration and consequentially decreasing RUE under heavy grazing, productivity was relatively compensated for with a higher TE. This offset between RUE and TE was even enhanced under water limited conditions and more evident when belowground net primary productivity (BNNP) was included. These findings suggest that BNPP should be considered when studies fucus on WUE of more intensively used grasslands. The consideration of the whole plant perspective and “real” WUE would partially revise our picture of system performance and therefore might affect the discussion on the C-sequestration and resilience potential of ecosystems.

Gao, Ying Z.; Giese, Marcus; Gao, Qiang; Brueck, Holger; Sheng, Lian X.; Yang, Hai J.

2013-01-01

267

Community level offset of rain use- and transpiration efficiency for a heavily grazed ecosystem in inner mongolia grassland.  

PubMed

Water use efficiency (WUE) is a key indicator to assess ecosystem adaptation to water stress. Rain use efficiency (RUE) is usually used as a proxy for WUE due to lack of transpiration data. Furthermore, RUE based on aboveground primary productivity (RUEANPP) is used to evaluate whole plant water use because root production data is often missing as well. However, it is controversial as to whether RUE is a reliable parameter to elucidate transpiration efficiency (TE), and whether RUEANPP is a suitable proxy for RUE of the whole plant basis. The experiment was conducted at three differently managed sites in the Inner Mongolia steppe: a site fenced since 1979 (UG79), a winter grazing site (WG) and a heavily grazed site (HG). Site HG had consistent lowest RUEANPP and RUE based on total net primary productivity (RUENPP). RUEANPP is a relatively good proxy at sites UG79 and WG, but less reliable for site HG. Similarly, RUEANPP is good predictor of transpiration efficiency based on aboveground net primary productivity (TEANPP) at sites UG79 and WG but not for site HG. However, if total net primary productivity is considered, RUENPP is good predictor of transpiration efficiency based on total net primary productivity (TENPP) for all sites. Although our measurements indicate decreased plant transpiration and consequentially decreasing RUE under heavy grazing, productivity was relatively compensated for with a higher TE. This offset between RUE and TE was even enhanced under water limited conditions and more evident when belowground net primary productivity (BNNP) was included. These findings suggest that BNPP should be considered when studies fucus on WUE of more intensively used grasslands. The consideration of the whole plant perspective and "real" WUE would partially revise our picture of system performance and therefore might affect the discussion on the C-sequestration and resilience potential of ecosystems. PMID:24058632

Gao, Ying Z; Giese, Marcus; Gao, Qiang; Brueck, Holger; Sheng, Lian X; Yang, Hai J

2013-09-18

268

Photosynthetic recovery of foliage after wind disturbance activates ecosystem CO2 uptake in cool temperate forests of northern Japan  

NASA Astrophysics Data System (ADS)

The effects of wind disturbance on forest dynamics and ecosystem CO2 exchange were examined in cool temperate forests of northern Japan during 2004-2008 using eddy covariance (EC) measurements. One site was a young, even-aged, monoculture, deciduous forest; the other was an uneven-aged mixed forest of evergreen and deciduous overstory tree species, including some over 200 years old. On 8 September 2004, a strong typhoon struck the forests, after which leaf and branch amounts decreased in young growth forest, but foliage showed little change in old growth forest. By 2006, foliage at the young-growth forest had recovered to the 2004 pretyphoon state. Average daily accumulated gross primary production (GPPd), terrestrial ecosystem respiration (TERd), and net ecosystem exchange (NEEd) were assessed for six growth stages annually. After the typhoon, large increases in GPPd were found during the growing stage of overstory tree species with high photosynthetic rates compared to that before the typhoon. Pronounced increases in GPPd and corresponding large reductions in NEEd were detected at the young-growth forest, indicating that NEEd was largely regulated by GPPd throughout the growing stages. Although EC measurements contain uncertainty, our continuous EC measurements revealed that interannual variability in meteorological variables and structural changes in foliage have only small impacts on GPP and NEE, while photosynthetic recovery of foliage from typhoon damage has high potential to increase GPP and enhance NEE as compared with those under nondamage conditions.

Toda, Motomu; Kolari, Pasi; Nakai, Taro; Kodama, Yuji; Shibata, Hideaki; Yoshida, Toshiya; Uemura, Shigeru; Sumida, Akihiro; Kato, Kyoko; Ono, Kiyomi; Hara, Toshihiko

2011-06-01

269

Stress responses investigated; application of zinc and heat to Terrestrial Model Ecosystems from heavy metal polluted grassland.  

PubMed

This study tested the hypothesis that soils with a deprived biodiversity due to metal pollution are less stable than non-polluted soils, containing a more diverse community. For this, soils were sampled from specific grasslands in the Netherlands that contain elevated heavy metal concentrations (Cu, Pb and Zn). Soils that showed the largest differences in metal concentrations were incubated in the laboratory using Terrestrial Model Ecosystems (TMEs). This approach enabled simultaneous measurement of structural (bacteria, nematodes, enchytraeids, earthworms) and functional parameters (nitrogen leaching, feeding activity, CO2 production, plant growth). The highest polluted soils showed a lower bacterial growth, and decreased enchytraeid and nematode biomass and diversity, hence a deprived community. More nitrate leached from high polluted soils, while all other functional endpoints did not differ. Additional stress application of zinc and heat was used to test the stability. Zinc treatment caused effects only in the higher polluted soils, observed at several moments in time for enchytraeids, CO2 fluxes and plant growth. Heat stress caused a large reduction in enchytraeid and earthworm biomass. Ammonium leaching was decreased by heat treatments in the most polluted soils, while CO2 was increased by heat in less polluted soils. Most effects were seen in the most polluted systems and it was concluded that they seem less stable. PMID:18701139

Kools, Stefan A E; Berg, Matty P; Boivin, Marie-Elène Y; Kuenen, Frans J A; van der Wurff, André W G; van Gestel, Cornelis A M; van Straalen, Nico M

2008-08-12

270

Scale effects on the controls on mountain grassland leaf stomatal and ecosystem surface conductance to water vapour  

NASA Astrophysics Data System (ADS)

Stomata are the major pathway by which plants exert control on the exchange of trace gases and water vapour with the aerial environment and thus provide a key link between the functioning of terrestrial ecosystems and the state and composition of the atmosphere. Understanding the nature of this control, i.e. how stomatal conductance differs between plant species and ecosystems and how it varies in response to external and internal forcings, is key to predicting feedbacks plants may be providing to changing climatic conditions. Despite a long history of research on stomatal functioning, a fully mechanistic understanding of how stomata function in response to biotic and abiotic controls is still elusive which has led to the development of a large number of (semi-)empirical models of varying complexity. Two of the most widely used models go back to Jarvis (1976) and Ball, Woodrow and Berry (1987), termed J-model and BWB-model, respectively, in the following. The J-model simulates stomatal conductance as some maximal value attenuated by a series of multiplicative functions which are bound between zero and unity, while the BWB-model predicts stomatal conductance as a linear function of photosynthesis, relative humidity and carbon dioxide concentration in the leaf boundary layer. Both models were developed for the prediction of leaf-scale stomatal conductance to water vapour, but have been applied for simulating ecosystem-scale surface conductance as well. The objective of the present paper is to compare leaf- and ecosystem-scale conductances to water vapour and to assess the respective controls using the two above-mentioned models as analysis frameworks. To this end leaf-level stomatal conductance has been measured by means of leaf-gas exchange methods and ecosystem-scale surface conductance by inverting eddy covariance evapotranspiration estimates at a mountain grassland site in Austria. Our major findings are that the proportionality parameter in the BWB-model is scale-consistent, i.e. does not differ significantly between the leaf- and ecosystem scale, while the residual conductance (at zero light) scales with the amount of above-ground transpiring plant area. Among the environmental forcings, air humidity (either relative humidity or vapour pressure deficit) and carbon dioxide concentration in the boundary layer explained most of the variability of stomatal conductance at the leaf level, while the photosynthetic photon flux density was by far the dominant control at the ecosystem-level. References: Ball J.T., Woodrow I.E., Berry J.A., 1987. A model predicting stomatal conductance and its contribution to the control of photosynthesis under different environmental conditions. In: J. Biggens (Editor), Progress in Photosynthesis Research, Vol. IV. Proceedings of the VII International Congress on Photosynthesis. Martinus Nijhoff, Dordrecht, pp. 221-224. Jarvis P.G., 1976. The interpretation of the variations in leaf water potential and stomatal conductance found in canopies in the field. Philosophical Transactions of the Royal Society London 273(B), 593-610.

Haslwanter, Alois; Hammerle, Albin; Wohlfahrt, Georg

2010-05-01

271

Effects of elevated CO2 and N addition on growth and N2 fixation of a legume subshrub (Caragana microphylla Lam.) in temperate grassland in China.  

PubMed

It is well demonstrated that the responses of plants to elevated atmospheric CO(2) concentration are species-specific and dependent on environmental conditions. We investigated the responses of a subshrub legume species, Caragana microphylla Lam., to elevated CO(2) and nitrogen (N) addition using open-top chambers in a semiarid temperate grassland in northern China for three years. Measured variables include leaf photosynthetic rate, shoot biomass, root biomass, symbiotic nitrogenase activity, and leaf N content. Symbiotic nitrogenase activity was determined by the C(2)H(2) reduction method. Elevated CO(2) enhanced photosynthesis and shoot biomass by 83% and 25%, respectively, and the enhancement of shoot biomass was significant only at a high N concentration. In addition, the photosynthetic capacity of C. microphylla did not show down-regulation under elevated CO(2). Elevated CO(2) had no significant effect on root biomass, symbiotic nitrogenase activity and leaf N content. Under elevated CO(2), N addition stimulated photosynthesis and shoot biomass. By contrast, N addition strongly inhibited symbiotic nitrogenase activity and slightly increased leaf N content of C. microphylla under both CO(2) levels, and had no significant effect on root biomass. The effect of elevated CO(2) and N addition on C. microphylla did not show interannual variation, except for the effect of N addition on leaf N content. These results indicate that shoot growth of C. microphylla is more sensitive to elevated CO(2) than is root growth. The stimulation of shoot growth of C. microphylla under elevated CO(2) or N addition is not associated with changes in N(2)-fixation. Additionally, elevated CO(2) and N addition interacted to affect shoot growth of C. microphylla with a stimulatory effect occurring only under combination of these two factors. PMID:22046376

Zhang, Lin; Wu, Dongxiu; Shi, Huiqiu; Zhang, Canjuan; Zhan, Xiaoyun; Zhou, Shuangxi

2011-10-26

272

The likely impact of elevated [CO2], nitrogen deposition, increased temperature, and management on carbon sequestration in temperate and boreal forest ecosystems. A literature review  

Microsoft Academic Search

Temperate and Boreal forest ecosystems contain a large part of the carbon stored on land, both in the form of biomass and soil organic matter. Increasing atmospheric carbon dioxide concentration, increasing temperatures, elevated nitrogen deposition, and intensified management will change this carbon store. We review current literature and conclude that northern forests will acquire extra carbon as a result of

Norby; Richard J; Sune Linder; Tryggve Persson; M. Francesca Cotrufo; Alf Ekblad; Michael Freeman; Achim Grelle; Ivan A. Janssens; Paul G. Jarvis; Seppo Kellomäki; Anders Lindroth; Denis Loustau; Tomas Lundmark; Richard J. Norby; Ram Oren; Kim Pilegaard; Michael G. Ryan; Bjarni D. Sigurdsson; Monika Strömgren; Marcel Van Oijen; Göran Wallin

2007-01-01

273

Spatial and temporal patterns of water-extractable organic carbon (WEOC) of surface mineral soil in a cool temperate forest ecosystem  

Microsoft Academic Search

Water-extractable organic carbon (WEOC) drives the C and N cycles in forest ecosystems via microbial activity. However, few studies have considered both then spatial and temporal patterns of WEOC in forest soils. We investigated the spatial and temporal variation in WEOC along a topographic sequence in a cool temperate deciduous forest. The concentrations of WEOC, carbohydrates, total phenols, and other

Takuo Hishi; Muneto Hirobe; Ryunosuke Tateno; Hiroshi Takeda

2004-01-01

274

Using an ecosystem process model to examine effects of increased atmospheric N deposition on soil carbon storage in northern temperate forests  

Microsoft Academic Search

Although atmospheric nitrogen deposition can increase primary productivity in nitrogen limited northern temperate forests, the potential for nitrogen deposition to increase soil carbon storage through decreased decomposition has gone unexplored in biogeochemical models. We modeled carbon and nitrogen cycling in sugar maple forests along a nitrogen deposition gradient using an ecosystem process model. Our goal was to better understand how

K. A. Whittinghill; W. S. Currie; D. R. Zak

2010-01-01

275

Metagenomic Insights into the Evolution, Function, and Complexity of the Planktonic Microbial Community of Lake Lanier, a Temperate Freshwater Ecosystem  

PubMed Central

Lake Lanier is an important freshwater lake for the southeast United States, as it represents the main source of drinking water for the Atlanta metropolitan area and is popular for recreational activities. Temperate freshwater lakes such as Lake Lanier are underrepresented among the growing number of environmental metagenomic data sets, and little is known about how functional gene content in freshwater communities relates to that of other ecosystems. To better characterize the gene content and variability of this freshwater planktonic microbial community, we sequenced several samples obtained around a strong summer storm event and during the fall water mixing using a random whole-genome shotgun (WGS) approach. Comparative metagenomics revealed that the gene content was relatively stable over time and more related to that of another freshwater lake and the surface ocean than to soil. However, the phylogenetic diversity of Lake Lanier communities was distinct from that of soil and marine communities. We identified several important genomic adaptations that account for these findings, such as the use of potassium (as opposed to sodium) osmoregulators by freshwater organisms and differences in the community average genome size. We show that the lake community is predominantly composed of sequence-discrete populations and describe a simple method to assess community complexity based on population richness and evenness and to determine the sequencing effort required to cover diversity in a sample. This study provides the first comprehensive analysis of the genetic diversity and metabolic potential of a temperate planktonic freshwater community and advances approaches for comparative metagenomics.

Oh, Seungdae; Caro-Quintero, Alejandro; Tsementzi, Despina; DeLeon-Rodriguez, Natasha; Luo, Chengwei; Poretsky, Rachel; Konstantinidis, Konstantinos T.

2011-01-01

276

Net ecosystem CO2 exchange measured by autochambers during the snow-covered season at a temperate peatland  

NASA Astrophysics Data System (ADS)

Net ecosystem exchange of CO2 was measured at a temperate peatland in southeastern New Hampshire. Classified as a mineral-poor fen owing to deep, water-logged peats that are influenced to a limited extent by groundwater, the ecosystem is dominated by plants such as sedges (Carex spp.) and evergreen shrubs. Ten automatic chambers measured fluxes every 3 h by sampling changes in headspace concentration of CO2 from November 2000 through March 2001. The fen was covered in snow for most of this period and CO2 was emitted from the snow pack throughout the winter. The largest fluxes were associated with ground temperatures of 0°C and with declining atmospheric pressure. CO2 effluxes up to 3 µmol m-2 s-1 were recorded when the ground temperature reached the thaw point. Fluxes were lower when the ground temperature rose above 0°C, however, suggesting that the large fluxes were associated with a build up and release of stored CO2 degassing as soon as the ground thawed, or by enhanced microbial activity associated with freeze-thaw dynamics. The large number of thaw events coupled with frequent short-term releases of CO2 suggest that degassing occurred on a regular basis with changes in atmospheric pressure and/or microbial decomposition occurred beneath the snowpack. The extent of soil freezing prior to thaw was also an important factor, with colder soils yielding smaller CO2 emissions upon thaw. Although most of the observed CO2 flux was efflux from the ecosystem, occasional CO2 uptake by the ecosystem of up to 1 µmol m-2 s-1 was also observed, indicating small rates of photosynthesis even during winter. Photosynthesis occurred only when the ground temperature was >0°C. The implications for a warmer climate are unclear. If warmer winter temperatures yield less snow in the temperate region, then soils could freeze more deeply and result in lower CO

Bubier, Jill; Crill, Patrick; Mosedale, Andrew

2002-12-01

277

Mercury bioaccumulation along food webs in temperate aquatic ecosystems colonized by aquatic macrophytes in south western France.  

PubMed

Mercury (Hg) is considered as an important pollutant for aquatic systems as its organic form, methylmercury (MeHg), is easily bioaccumulated and bioamplified along food webs. In various ecosystems, aquatic periphyton associated with macrophyte was identified as an important place for Hg storage and methylation by microorganisms. Our study concerns temperate aquatic ecosystems (South Western France) colonized by invasive macrophytes and characterized by high mercury methylation potentials. This work establishes original data concerning Hg bioaccumulation in organisms (plants, crustaceans, molluscs and fish) from five contrasting ecosystems. For low trophic level species, total Hg (THg) concentrations were low (from 27±2ngTHgg(-1)dw in asiatic clam Corbicula fluminea to 418±114ngTHgg(-1)dw in crayfish Procambarus clarkii). THg concentrations in some carnivorous fish (high trophic level) were close to or exceeded the International Marketing Level (IML) with values ranging from 1049±220ngTHgg(-1)dw in pike perch muscle (Sander lucioperca) to 3910±1307ngTHgg(-1)dw in eel muscle (Anguilla Anguilla). Trophic levels for the individuals were also evaluated through stable isotope analysis, and linked to Hg concentrations of organisms. A significant Hg biomagnification (r(2)= 0.9) was observed in the Aureilhan lake, despite the absence of top predator fish. For this site, Ludwigia sp. periphyton, as an entry point of Hg into food webs, is a serious hypothesis which remains to be confirmed. This study provides a first investigation of Hg transfer in the ecosystems of south western France and allows the assessment of the risk associated with the presence of Hg in aquatic food webs. PMID:23466146

Gentès, Sophie; Maury-Brachet, Régine; Guyoneaud, Rémy; Monperrus, Mathilde; André, Jean-Marc; Davail, Stéphane; Legeay, Alexia

2013-03-05

278

The Janos grassland ecosystem: 20 years of synthesis and experimental research revealing new insights for conservation and management  

Technology Transfer Automated Retrieval System (TEKTRAN)

Janos grasslands are part of the Sky Islands, a unique region of more than 40 isolated mountain ridges surrounded by dry grasslands that straddles the México/Arizona/New Mexico border. It is one of America’s great hotspots for wildlife diversity. It is a transition zone between the Chihuahuan Dese...

279

Predicting the response of a temperate forest ecosystem to atmospheric CO[sub 2] increase  

SciTech Connect

This report summarizes the second year of research progress. Included are progress reports for the following studies: the responses of temperate forest tree to 3 years of exposure to elevated carbon dioxide, and high and low nutrient and light levels; pot-size limitations in carbon dioxide studies, interactive effects of carbon dioxide and soil moisture availability on tree seedling's tissue water relations, growth, and niche characteristics; individual versus population responses to elevated carbon dioxide levels in two species of annual weeds; and the development of gypsy moth larvae raised on gray and yellow birth foliage grown in ambient and elevated carbon dioxide environments.

Bazzaz, F.A.

1993-01-01

280

Carbon input control over soil organic matter dynamics in a temperate grassland exposed to elevated CO2 and warming  

NASA Astrophysics Data System (ADS)

Elevated CO2 generally increases soil C pools. However, greater available C concentrations can potentially stimulate soil organic matter (SOM) decomposition. The effects of climate warming on C storage can also be positive or negative. There is a high degree of uncertainty on the combined effects of climate warming and atmospheric CO2 increase on SOM dynamics and its potential feedbacks to climate change. Semi-arid systems are predicted to show strong ecosystem responses to both factors. Global change factors can have contrasting effects for different SOM pools, thus, to understand the mechanisms underlying the combined effects of multiple factors on soil C storage, effects on individual C pools and their kinetics should be evaluated. We assessed SOM dynamics by conducting long-term laboratory incubations of soils from PHACE (Prairie Heating and CO2 Enrichment experiment), an elevated CO2 and warming field experiment in semi-arid, native northern mixed grass prairie, Wyoming, USA. We measured total C mineralization and estimated the size of the labile pool and the decomposition rates of the labile and resistant SOM pools. To examine the role of plant inputs on SOM dynamics we measured aboveground biomass, root biomass, and soil dissolved organic C (DOC). Greater aboveground productivity under elevated CO2 translated into enlarged pools of readily available C (measured as total mineralized C, labile C pool and DOC). The effects of warming on the labile C only occurred in the first year of warming suggesting a transient effect of the microbial response to increased temperature. Experimental climate change affected the intrinsic decomposability of both the labile and resistant C pools. Positive relationships of the rate of decomposition of the resistant C with aboveground and belowground biomass and dissolved organic C suggested that plant inputs mediated the response by enhancing the degradability of the resistant C. Our results contribute to a growing body of literature suggesting that priming is a ubiquitous phenomenon that should be included in C cycle models.

Carrillo, Y.; Pendall, E.; Dijkstra, F. A.; Morgan, J. A.; Newcomb, J. M.

2010-03-01

281

Progressive nitrogen limitation of ecosystem processes under elevated CO2 in a warm-temperate forest.  

PubMed

A hypothesis for progressive nitrogen limitation (PNL) proposes that net primary production (NPP) will decline through time in ecosystems subjected to a step-function increase in atmospheric CO2. The primary mechanism driving this response is a rapid rate of N immobilization by plants and microbes under elevated CO2 that depletes soils of N, causing slower rates of N mineralization. Under this hypothesis, there is little long-term stimulation of NPP by elevated CO2 in the absence of exogenous inputs of N. We tested this hypothesis using data on the pools and fluxes of C and N in tree biomass, microbes, and soils from 1997 through 2002 collected at the Duke Forest free-air CO2 enrichment (FACE) experiment. Elevated CO2 stimulated NPP by 18-24% during the first six years of this experiment. Consistent with the hypothesis for PNL, significantly more N was immobilized in tree biomass and in the O horizon under elevated CO2. In contrast to the PNL hypothesis, microbial-N immobilization did not increase under elevated CO2, and although the rate of net N mineralization declined through time, the decline was not significantly more rapid under elevated CO2. Ecosystem C-to-N ratios widened more rapidly under elevated CO2 than ambient CO2 indicating a more rapid rate of C fixation per unit of N, a processes that could delay PNL in this ecosystem. Mass balance calculations demonstrated a large accrual of ecosystem N capital. Is PNL occurring in this ecosystem and will NPP decline to levels under ambient CO2? The answer depends on the relative strength of tree biomass and O-horizon N immobilization vs. widening C-to-N ratios and ecosystem-N accrual as processes that drive and delay PNL, respectively. Only direct observations through time will definitively answer this question. PMID:16634293

Finzi, Adrien C; Moore, David J P; DeLucia, Evan H; Lichter, John; Hofmockel, Kirsten S; Jackson, Robert B; Kim, Hyun-Seok; Matamala, Roser; McCarthy, Heather R; Oren, Ram; Pippen, Jeffrey S; Schlesinger, William H

2006-01-01

282

Whole-ecosystem labile carbon production in a north temperate deciduous forest  

Microsoft Academic Search

Labile carbon (C), which is principally comprised of non-structural carbohydrates, is an essential intermediary between C assimilation and structural growth in deciduous forests. We developed a new approach that combined meteorological and biometric C cycling data for a mixed deciduous forest in Michigan, USA, to provide novel estimates of whole-ecosystem labile C production and reallocation to structural net primary production

Christopher M. Gough; Charles E. Flower; Christoph S. Vogel; Danilo Dragoni; Peter S. Curtis

2009-01-01

283

Conservation And Management Of Grassland Biodiversity In East Asia  

Microsoft Academic Search

East Asia has various types of grasslands, such as inland arid and semi-arid natural grasslands in China and Mongolia, and\\u000a artificially managed semi-natural grasslands in wet monsoon areas like Japan. Diversified utilization and livestock farming\\u000a are carried out on these grasslands. A variety of grasslands have been maintaining diversified organisms characteristic to\\u000a grassland ecosystems. However, in those grasslands, irrespective of

Hideharu Tsukada; Osamu Imura; Kun Shi

284

Dependency of Ecosystem Respiration in a Cool Temperate Bog on Peat Temperature and Water Table  

NASA Astrophysics Data System (ADS)

We measured ecosystem respiration (ER) from nighttime net ecosystem exchange of carbon dioxide determined from an eddy covariance tower located in a large ombrotrophic bog near Ottawa, Canada. Measurements were made from May to October over 5 years, 1998 to 2002. Ecosystem respiration ranged from <0.05 mg CO2/m2/s in spring (May) and late fall (late October) to 0.10-0.15 mg CO2/m2/s during the summer (July-August). As anticipated, there was a strong relationship between ER and peat temperatures, such as at a depth of 5 cm (r2 = 0.63). Q10 over 5° to 15° C varied from 2.2 to 4.2 depending upon the choice of temperature level and location within a hummock or hollow. Unexpected for a wetland ecosystem, there was only a weak relationship between ER and water table position (r2 = 0.11). Comparison of ER in early and late summer, 2002 with similar surface temperature revealed no significant difference in ER. A laboratory incubation of peat cores at different moisture contents showed that CO2 production was reduced by drying in the surface samples, but there was little decrease in samples from below a depth of 30 cm. We believe that the lack of correlation between ER and water table position in this ecosystem results from an increase in CO2 production at depth compensating a decrease in production of CO2 by heterotrophic respiration in the near surface layers and autotrophic respiration in the moss community.

Moore, T.; Lafleur, P.; Roulet, N.; Frolking, S.

2003-12-01

285

Soil environmental conditions and microbial build-up mediate the effect of plant diversity on soil nitrifying and denitrifying enzyme activities in temperate grasslands.  

PubMed

Random reductions in plant diversity can affect ecosystem functioning, but it is still unclear which components of plant diversity (species number - namely richness, presence of particular plant functional groups, or particular combinations of these) and associated biotic and abiotic drivers explain the observed relationships, particularly for soil processes. We assembled grassland communities including 1 to 16 plant species with a factorial separation of the effects of richness and functional group composition to analyze how plant diversity components influence soil nitrifying and denitrifying enzyme activities (NEA and DEA, respectively), the abundance of nitrifiers (bacterial and archaeal amoA gene number) and denitrifiers (nirK, nirS and nosZ gene number), and key soil environmental conditions. Plant diversity effects were largely due to differences in functional group composition between communities of identical richness (number of sown species), though richness also had an effect per se. NEA was positively related to the percentage of legumes in terms of sown species number, the additional effect of richness at any given legume percentage being negative. DEA was higher in plots with legumes, decreased with increasing percentage of grasses, and increased with richness. No correlation was observed between DEA and denitrifier abundance. NEA increased with the abundance of ammonia oxidizing bacteria. The effect of richness on NEA was entirely due to the build-up of nitrifying organisms, while legume effect was partly linked to modified ammonium availability and nitrifier abundance. Richness effect on DEA was entirely due to changes in soil moisture, while the effects of legumes and grasses were partly due to modified nitrate availability, which influenced the specific activity of denitrifiers. These results suggest that plant diversity-induced changes in microbial specific activity are important for facultative activities such as denitrification, whereas changes in microbial abundance play a major role for non-facultative activities such as nitrification. PMID:23613785

Le Roux, Xavier; Schmid, Bernhard; Poly, Franck; Barnard, Romain L; Niklaus, Pascal A; Guillaumaud, Nadine; Habekost, Maike; Oelmann, Yvonne; Philippot, Laurent; Salles, Joana Falcao; Schloter, Michael; Steinbeiss, Sibylle; Weigelt, Alexandra

2013-04-17

286

Soil Environmental Conditions and Microbial Build-Up Mediate the Effect of Plant Diversity on Soil Nitrifying and Denitrifying Enzyme Activities in Temperate Grasslands  

PubMed Central

Random reductions in plant diversity can affect ecosystem functioning, but it is still unclear which components of plant diversity (species number – namely richness, presence of particular plant functional groups, or particular combinations of these) and associated biotic and abiotic drivers explain the observed relationships, particularly for soil processes. We assembled grassland communities including 1 to 16 plant species with a factorial separation of the effects of richness and functional group composition to analyze how plant diversity components influence soil nitrifying and denitrifying enzyme activities (NEA and DEA, respectively), the abundance of nitrifiers (bacterial and archaeal amoA gene number) and denitrifiers (nirK, nirS and nosZ gene number), and key soil environmental conditions. Plant diversity effects were largely due to differences in functional group composition between communities of identical richness (number of sown species), though richness also had an effect per se. NEA was positively related to the percentage of legumes in terms of sown species number, the additional effect of richness at any given legume percentage being negative. DEA was higher in plots with legumes, decreased with increasing percentage of grasses, and increased with richness. No correlation was observed between DEA and denitrifier abundance. NEA increased with the abundance of ammonia oxidizing bacteria. The effect of richness on NEA was entirely due to the build-up of nitrifying organisms, while legume effect was partly linked to modified ammonium availability and nitrifier abundance. Richness effect on DEA was entirely due to changes in soil moisture, while the effects of legumes and grasses were partly due to modified nitrate availability, which influenced the specific activity of denitrifiers. These results suggest that plant diversity-induced changes in microbial specific activity are important for facultative activities such as denitrification, whereas changes in microbial abundance play a major role for non-facultative activities such as nitrification.

Le Roux, Xavier; Schmid, Bernhard; Poly, Franck; Barnard, Romain L.; Niklaus, Pascal A.; Guillaumaud, Nadine; Habekost, Maike; Oelmann, Yvonne; Philippot, Laurent; Salles, Joana Falcao; Schloter, Michael; Steinbeiss, Sibylle; Weigelt, Alexandra

2013-01-01

287

The Ecological Significance of the Herbaceous Layer in Temperate Forest Ecosystems  

NSDL National Science Digital Library

This peer-reviewed article from the November 2007 issue of BioScience examines the importance of the herbaceous layer of the forest ecosystem. Despite a growing awareness that the herbaceous layer serves a special role in maintaining the structure and function of forests, this stratum remains an underappreciated aspect of forest ecosystems. In this article I review and synthesize information concerning the herb layer's structure, composition, and dynamics to emphasize its role as an integral component of forest ecosystems. Because species diversity is highest in the herb layer among all forest strata, forest biodiversity is largely a function of the herb-layer community. Competitive interactions within the herb layer can determine the initial success of plants occupying higher strata, including the regeneration of dominant overstory tree species. Furthermore, the herb layer and the overstory can become linked through parallel responses to similar environmental gradients. These relationships between strata vary both spatially and temporally. Because the herb layer responds sensitively to disturbance across broad spatial and temporal scales, its dynamics can provide important information regarding the site characteristics of forests, including patterns of past land-use practices. Thus, the herb layer has a significance that belies its diminutive stature.

Frank Gilliam (;)

2007-11-01

288

The role of plants and land management in sequestering soil carbon in temperate arable and grassland ecosystems  

Microsoft Academic Search

Global climate change and concerns about soil quality have led to a widespread interest in the opportunities that are available to sequester carbon in soils. To achieve a better understanding of the changes in C storage, we need to be able to accurately measure and model inputs and losses of C from soils. This in turn requires a thorough understanding

R. M. Rees; I. J. Bingham; J. A. Baddeley; C. A. Watson

2005-01-01

289

Photosynthetic recovery of foliage after wind disturbance activates ecosystem CO2 uptake in cool-temperate forests in northern Japan  

NASA Astrophysics Data System (ADS)

The effects of wind disturbance on forest dynamics and ecosystem CO2 exchange were examined in cool-temperate forests of northern Japan during 2004-2008 using eddy covariance (EC) measurements. One site was a young, even-aged, monoculture, deciduous forest (YGF); the other was an uneven-aged mixed forest of evergreen and deciduous overstory tree species, including some over 200 years old (TGF). On 8 September 2004, a strong typhoon struck the forests, after which leaf and branch amounts decreased in YGF, but foliage showed little change in TGF. By 2006, foliage at YGF had recovered to the 2004 pre-typhoon state. Average daily accumulated GPP (GPPd), terrestrial ecosystem respiration (TERd), and net ecosystem exchange (NEEd) were assessed for six growth stages annually. After the typhoon, large increases in GPPd were found during the growing stage of overstory tree species with high photosynthetic rates compared to that before the typhoon. Pronounced increases in GPPd and corresponding large reductions in NEEd were detected at YGF, indicating that NEEd was largely regulated by GPPd throughout the growing stages. Although EC measurements contain uncertainty, our continuous EC measurements revealed that annual variability in meteorological variables and structural changes in foliage have only small impacts on GPP and NEE, while photosynthetic recovery of foliage from typhoon damage has high potential to enhance annual GPP and reduce NEE as compared with those under non-damage conditions. Plant ecophysiological feedbacks from natural disturbance damage should be considered when predicting annual variability in ecosystem CO2 exchange both at the local scale and when estimating the global carbon budget. The relationship between photosynthetically active radiation (PAR) and GPP for (a1) stage C and (a2) stage D at YGF and for (b1) stage C and (b2) stage D at TGF. Data were obtained at hourly intervals and averaged using the GPP values obtained under u*c = 0.25 m s-1 and u*c = 0.55 m s-1 conditions. Lines in the figures represent the empirical relationship between PAR and GPP expressed in equation (6) for each year from 2004 to 2008.

Toda, M.; Kolari, P.; Nakai, T.; Hara, T.

2010-12-01

290

Ecosystem Manipulation and Restoration on the Basis of Long-Term Conceptions  

Microsoft Academic Search

\\u000a Ecosystems are affected by anthopogenic activities at a global level and, thus, are manipulated world-wide. This chapter addresses\\u000a the impacts of apparent and non-apparent manipulations and restoration by human activities in Europe with a focus on the temperate\\u000a zone. Agricultural management practices induced evident site-specific modification of natural ecosystem structures and functions\\u000a whereas forests and natural grasslands and also aquatic

Oliver Dilly; Seth Nii-Annang; Joachim Schrautzer; Peter Schwartze; Vera Breuer; Eva-Maria Pfeiffer; Werner Gerwin; Wolfgang Schaaf; Dirk Freese; Maik Veste; Reinhard F. Hüttl

291

Use of historical logging patterns to identify disproportionately logged ecosystems within temperate rainforests of southeastern Alaska.  

PubMed

The forests of southeastern Alaska remain largely intact and contain a substantial proportion of Earth's remaining old-growth temperate rainforest. Nonetheless, industrial-scale logging has occurred since the 1950s within a relatively narrow range of forest types that has never been quantified at a regional scale. We analyzed historical patterns of logging from 1954 through 2004 and compared the relative rates of change among forest types, landform associations, and biogeographic provinces. We found a consistent pattern of disproportionate logging at multiple scales, including large-tree stands and landscapes with contiguous productive old-growth forests. The highest rates of change were among landform associations and biogeographic provinces that originally contained the largest concentrations of productive old growth (i.e., timber volume >46.6 m³/ha). Although only 11.9% of productive old-growth forests have been logged region wide, large-tree stands have been reduced by at least 28.1%, karst forests by 37%, and landscapes with the highest volume of contiguous old growth by 66.5%. Within some island biogeographic provinces, loss of rare forest types may place local viability of species dependent on old growth at risk of extirpation. Examination of historical patterns of change among ecological forest types can facilitate planning for conservation of biodiversity and sustainable use of forest resources. PMID:23866037

Albert, David M; Schoen, John W

2013-08-01

292

Quantifying the Role of Water Table Dynamics on Net Ecosystem Exchange of CO2 in a Northern Temperate Shrub Wetland  

NASA Astrophysics Data System (ADS)

Wetlands represent up to a third of the global soil carbon, and so they are a large component of an uncertain terrestrial carbon flux. In the northern temperate forests around the upper Great Lakes of North America forest and shrub stature wetlands cover about one-third of the total land area. In northern Wisconsin lateral subsurface water redistribution associated with hummocky glaciated terrain drives lowland water table heights. A multi-year trend of declining water table height in these areas has been observed throughout this region since year 2000. We examined the effect of this declining water table on net ecosystem exchange (NEE) of carbon measured at the Lost Creek AmeriFlux tower site (46 deg. 49 min. N, 89 deg. 58.7 min. W), which lies within a shrub stature alder and willow wetland. On an inter-annual basis from 2001-2007 there was no significant correlation between annual total NEE and annual mean water table height. There were offsetting increases in both respiration and gross ecosystem production (GEP) as the water table fell through a level of about 20-30 cm below the surface. During an exceptionally dry growing season in 2007 GEP was anomalously low switching the site from a carbon sink to a source for the year. To quantify the role of water table dynamics at shorter timescales and to examine the relative responses of GEP and respiration in more detail we used a coupled water and carbon transport model along with Bayesian analysis. Short-term water table dynamics significantly improved the prediction of NEE, reflecting the importance of seasonal distribution of precipitation on the coupled water and carbon exchanges.

Mackay, S.; Desai, A. R.; Sulman, B. N.; Roberts, D. E.

2009-05-01

293

Light, Soil Temperature, and VPD as controls of flux-tower NEE partitioning into gross photosynthesis and respiration in grassland and agricultural ecosystems  

NASA Astrophysics Data System (ADS)

Partitioning of the flux-tower net CO2 exchange measurements (NEE) into gross photosynthesis (Pg) and ecosystem respiration (Re) components is an essential step in post-processing flux tower data for analysis and modeling. We have developed a method of NEE = Pg - Re partitioning using photosynthetically active radiation (Q), soil temperature at 5 cm depth (Ts), and vapor pressure deficit at 2 m height (VPD) as factors in a nonrectangular hyperbolic model of net CO2 exchange in terrestrial ecosystems (Gilmanov et al. 2003, Bas. Appl. Ecol. 4: 167-183) modified to include the effect of vapor pressure deficit. In contrast to other VPD-based methods of NEE partitioning suggested in the literature, our method (i) describes combined effect of VPD on photosynthetic capacity (Amax) and apparent quantum yield (ALPHA) due to the special functional properties of the nonrectangular hyperbolic equation; (ii) delivers less biased estimates of light-response parameters due to explicit description of the convexity of the light-response compared to rectangular hyperbolic model, and (iii) generates more numerically robust and statistically significant estimates than methods using highly correlated predictors such as incoming radiation, air temperature and VPD. We demonstrate application of the method to flux-tower NEE data sets from grassland and agro-ecosystems of North America as a tool to estimate numerical values and uncertainty characteristics of productivity, respiration, and ecophysiological parameters (apparent quantum yield ALPHA, photosynthetic capacity Amax, gross ecological light-use efficiency LUE, carbon use efficiency CUE, and others). On a representative statistical material our results confirm earlier findings that gross photosynthesis estimates derived through partitioning of flux-tower NEE are significantly closer related to remote sensing indices (e.g., eMODIS NDVI) than variables directly provided by tower measurements such as day-time net CO2 flux totals. We present diagnostic phenomenological models of gross photosynthesis and ecosystem respiration utilizing weekly NDVI data that explain >80% of the seasonal variability of CO2 exchange at a 7-day time scale over the long (up to six years) periods. The light-soil temperature-VPD-based method of tower-NEE data partitioning provides a robust tool to gap-fill flux tower data series to obtain annual totals of GPP and RE of grasslands and agro-ecosystems. Such data for >25 North American flux-tower sites (>50 site-years) plotted on the H. Odum’s RE vs. GPP scatter diagram clearly demonstrate that according to flux-tower data, crop and grassland ecosystems take from the atmosphere significantly more CO2 through gross photosynthesis than return with respiration. Though considerable amount of the CO2 taken up by NEE of these ecosystems may be later returned to the atmosphere in animal feeding facilities, production and consumption of ethanol and human food, etc., it is presently clear that the role of grasslands and agro-ecosystems as sinks for atmospheric CO2 is much higher that estimated previously from non-flux-based (inventory) data (cf.: The First State of the Carbon Cycle Report, 2007).

Gilmanov, T. G.

2010-12-01

294

Scale-Dependent Effects of Grazing on Plant C: N: P Stoichiometry and Linkages to Ecosystem Functioning in the Inner Mongolia Grassland  

PubMed Central

Background Livestock grazing is the most prevalent land use of grasslands worldwide. The effects of grazing on plant C, N, P contents and stoichiometry across hierarchical levels, however, have rarely been studied; particularly whether the effects are mediated by resource availability and the underpinning mechanisms remain largely unclear. Methodology/Principal Findings Using a multi-organization-level approach, we examined the effects of grazing on the C, N, and P contents and stoichiometry in plant tissues (leaves and roots) and linkages to ecosystem functioning across three vegetation types (meadow, meadow steppe, and typical steppe) in the Inner Mongolia grassland, China. Our results showed that the effects of grazing on the C, N, and P contents and stoichiometry in leaves and roots differed substantially among vegetation types and across different hierarchical levels (species, functional group, and vegetation type levels). The magnitude of positive effects of grazing on leaf N and P contents increased progressively along the hierarchy of organizational levels in the meadow, whereas its negative effect on leaf N content decreased considerably along hierarchical levels in both the typical and meadow steppes. Grazing increased N and P allocation to aboveground in the meadow, while greater N and P allocation to belowground was found in the typical and meadow steppes. The differences in soil properties, plant trait-based resource use strategies, tolerance or defense strategies to grazing, and shifts in functional group composition are likely to be the key mechanisms for the observed patterns among vegetation types. Conclusions/Significance Our findings suggest that the enhanced vegetation-type-level N contents by grazing and species compensatory feedbacks may be insufficient to prevent widespread declines in primary productivity in the Inner Mongolia grassland. Hence, it is essential to reduce the currently high stocking rates and restore the vast degraded steppes for sustainable development of arid and semiarid grasslands.

Zheng, Shuxia; Ren, Haiyan; Li, Wenhuai; Lan, Zhichun

2012-01-01

295

Impacts of clearing invasive alien plants from 1995 to 2005 on vegetation structure, invasion intensity and ground cover in a temperate to subtropical riparian ecosystem  

Microsoft Academic Search

The impacts of invasive alien plants (IAP) and their subsequent clearing by the Working for Water Programme (WfW) on (a) overstorey (woody plant) vegetation structure, (b) invasion intensity (overstorey aerial cover of woody alien plants) and (c) ground cover, in a temperate to subtropical riparian ecosystem were studied in 1996\\/7 and again in 2005, in order to provide a longer-term

M. M. T. Beater; R. D. Garner; E. T. F. Witkowski

2008-01-01

296

Gnawing damage by rodents to the seedlings of Fagus crenata and Quercus mongolica var. grosseserrata in a temperate Sasa grassland-deciduous forest series in southwestern Japan  

Microsoft Academic Search

The effects of dwarf bamboo,Sasa, cover on the initial morrality of hardwood seedlings were investigated by transplanting 1-year-old beech (Fagus crenata) and current-year oak (Quercus mongolica var.grosseserrata) seedling to three different stands; old-growth beech and secondary oak forests withSasa undergrowth, and aSasa grassland in a grassland-forest series near the top of Mt Jippo, southwestern Japan. The most frequent cause of

Hideyuki Ida; Nobukazu Nakagoshi

1996-01-01

297

The Spatial Factor, Rather than Elevated CO2, Controls the Soil Bacterial Community in a Temperate Forest Ecosystem? †  

PubMed Central

The global atmospheric carbon dioxide (CO2) concentration is expected to increase continuously over the next century. However, little is known about the responses of soil bacterial communities to elevated CO2 in terrestrial ecosystems. This study aimed to partition the relative influences of CO2, nitrogen (N), and the spatial factor (different sampling plots) on soil bacterial communities at the free-air CO2 enrichment research site in Duke Forest, North Carolina, by two independent techniques: an entirely sequencing-based approach and denaturing gradient gel electrophoresis. Multivariate regression tree analysis demonstrated that the spatial factor could explain more than 70% of the variation in soil bacterial diversity and 20% of the variation in community structure, while CO2 or N treatment explains less than 3% of the variation. For the effects of soil environmental heterogeneity, the diversity estimates were distinguished mainly by the total soil N and C/N ratio. Bacterial diversity estimates were positively correlated with total soil N and negatively correlated with C/N ratio. There was no correlation between the overall bacterial community structures and the soil properties investigated. This study contributes to the information about the effects of elevated CO2 and soil fertility on soil bacterial communities and the environmental factors shaping the distribution patterns of bacterial community diversity and structure in temperate forest soils.

Ge, Yuan; Chen, Chengrong; Xu, Zhihong; Oren, Ram; He, Ji-Zheng

2010-01-01

298

Applicability of the flood-pulse concept in a temperate floodplain river ecosystem: Thermal and temporal components  

USGS Publications Warehouse

Annual growth increments were calculated for blue catfish (Ictalurus furcatus) and flathead catfish (Pylodictis olivaris) from the lower Mississippi River (LMR) to assess hypothesized relationships between fish growth and floodplain inundation as predicted by the Flood-Pulse Concept. Variation in catfish growth increment was high for all age classes of both species, and growth increments were not consistently related to various measures of floodplain inundation. However, relationships became stronger, and usually direct, when water temperature was integrated with area and duration of floodplain inundation. Relationships were significant for four of six age classes for blue catfish, a species known to utilize floodplain habitats. Though similar in direction, relationships were weaker for flathead catfish, which is considered a more riverine species. Our results indicate the Flood-Pulse Concept applies more strongly to temperate floodplain-river ecosystems when thermal aspects of flood pulses are considered. We recommend that future management of the LMR should consider ways to 'recouple' the annual flood and thermal cycles. An adaptive management approach will allow further determination of important processes affecting fisheries production in the LMR. Copyright ?? John Wiley & Sons, Ltd.

Schramm, Jr. , H. L.; Eggleton, M. A.

2006-01-01

299

Contribution of Root and Microbial Respiration to Soil CO 2 Efflux and Their Environmental Controls in a Humid Temperate Grassland of Japan *1 *1 Project supported by the National Natural Science Foundation of China (Nos. 30670342 and 30870408) and the Jilin Provincial Natural Science Funds for Distinguished Young Scholars of China (No. 20060105)  

Microsoft Academic Search

Soil CO2 efflux, root mass, and root production were investigated in a humid temperate grassland of Japan over a growing season (Apr. to Sep.) of 2005 to reveal seasonal changes of soil CO2 efflux, to separate the respective contributions of root and microbial respiration to the total soil CO2 efflux, and to determine the environmental factors that control soil respiration.

Wei WANG; Jiang FENG; T. OIKAWA

2009-01-01

300

Interactive effects of elevated CO2, warming, and drought on photosynthesis of Deschampsia flexuosa in a temperate heath ecosystem  

PubMed Central

Global change factors affect plant carbon uptake in concert. In order to investigate the response directions and potential interactive effects, and to understand the underlying mechanisms, multifactor experiments are needed. The focus of this study was on the photosynthetic response to elevated CO2 [CO2; free air CO2 enrichment (FACE)], drought (D; water-excluding curtains), and night-time warming (T; infrared-reflective curtains) in a temperate heath. A/Ci curves were measured, allowing analysis of light-saturated net photosynthesis (Pn), light- and CO2-saturated net photosynthesis (Pmax), stomatal conductance (gs), the maximal rate of Rubisco carboxylation (Vcmax), and the maximal rate of ribulose bisphosphate (RuBP) regeneration (Jmax) along with leaf ?13C, and carbon and nitrogen concentration on a monthly basis in the grass Deschampsia flexuosa. Seasonal drought reduced Pn via gs, but severe (experimental) drought decreased Pn via a reduction in photosynthetic capacity (Pmax, Jmax, and Vcmax). The effects were completely reversed by rewetting and stimulated Pn via photosynthetic capacity stimulation. Warming increased early and late season Pn via higher Pmax and Jmax. Elevated CO2 did not decrease gs, but stimulated Pn via increased Ci. The T×CO2 synergistically increased plant carbon uptake via photosynthetic capacity up-regulation in early season and by better access to water after rewetting. The effects of the combination of drought and elevated CO2 depended on soil water availability, with additive effects when the soil water content was low and D×CO2 synergistic stimulation of Pn after rewetting. The photosynthetic responses appeared to be highly influenced by growth pattern. The grass has opportunistic water consumption, and a biphasic growth pattern allowing for leaf dieback at low soil water availability followed by rapid re-growth of active leaves when rewetted and possibly a large resource allocation capability mediated by the rhizome. This growth characteristic allowed for the photosynthetic capacity up-regulations that mediated the T×CO2 and D×CO2 synergistic effects on photosynthesis. These are clearly advantageous characteristics when exposed to climate changes. In conclusion, after 1 year of experimentation, the limitations by low soil water availability and stimulation in early and late season by warming clearly structure and interact with the photosynthetic response to elevated CO2 in this grassland species.

Albert, K. R.; Ro-Poulsen, H.; Mikkelsen, T. N.; Michelsen, A.; van der Linden, L.; Beier, C.

2011-01-01

301

Interactive effects of elevated CO2, warming, and drought on photosynthesis of Deschampsia flexuosa in a temperate heath ecosystem.  

PubMed

Global change factors affect plant carbon uptake in concert. In order to investigate the response directions and potential interactive effects, and to understand the underlying mechanisms, multifactor experiments are needed. The focus of this study was on the photosynthetic response to elevated CO(2) [CO2; free air CO(2) enrichment (FACE)], drought (D; water-excluding curtains), and night-time warming (T; infrared-reflective curtains) in a temperate heath. A/C(i) curves were measured, allowing analysis of light-saturated net photosynthesis (P(n)), light- and CO(2)-saturated net photosynthesis (P(max)), stomatal conductance (g(s)), the maximal rate of Rubisco carboxylation (V(cmax)), and the maximal rate of ribulose bisphosphate (RuBP) regeneration (J(max)) along with leaf ?(13)C, and carbon and nitrogen concentration on a monthly basis in the grass Deschampsia flexuosa. Seasonal drought reduced P(n) via g(s), but severe (experimental) drought decreased P(n) via a reduction in photosynthetic capacity (P(max), J(max), and V(cmax)). The effects were completely reversed by rewetting and stimulated P(n) via photosynthetic capacity stimulation. Warming increased early and late season P(n) via higher P(max) and J(max). Elevated CO(2) did not decrease g(s), but stimulated P(n) via increased C(i). The T×CO2 synergistically increased plant carbon uptake via photosynthetic capacity up-regulation in early season and by better access to water after rewetting. The effects of the combination of drought and elevated CO(2) depended on soil water availability, with additive effects when the soil water content was low and D×CO2 synergistic stimulation of P(n) after rewetting. The photosynthetic responses appeared to be highly influenced by growth pattern. The grass has opportunistic water consumption, and a biphasic growth pattern allowing for leaf dieback at low soil water availability followed by rapid re-growth of active leaves when rewetted and possibly a large resource allocation capability mediated by the rhizome. This growth characteristic allowed for the photosynthetic capacity up-regulations that mediated the T×CO2 and D×CO2 synergistic effects on photosynthesis. These are clearly advantageous characteristics when exposed to climate changes. In conclusion, after 1 year of experimentation, the limitations by low soil water availability and stimulation in early and late season by warming clearly structure and interact with the photosynthetic response to elevated CO(2) in this grassland species. PMID:21586430

Albert, K R; Ro-Poulsen, H; Mikkelsen, T N; Michelsen, A; van der Linden, L; Beier, C

2011-05-16

302

Inter-annual Variability in Net Ecosystem Exchange of Carbon Dioxide and Methane Emissions in a Temperate Freshwater Marsh  

NASA Astrophysics Data System (ADS)

There exists very little information on greenhouse gas (GHG) exchange in marsh wetlands, especially in temperate climates. Measurements of carbon dioxide (CO2) and methane (CH4) fluxes were made from May 2005 to June 2008 in a temperate freshwater cattail marsh in Eastern Ontario, Canada. The net ecosystem exchange (NEE) of CO2 was measured continuously using the eddy covariance technique, and closed chambers were used to measure CH4 emissions from open water, soil, and vegetated portions of the marsh. Based on NEE, we found that the marsh accumulated 264 g C m-2 from May 2005 to April 2006 and 185 g C m-2 and 308 g C m-2 in 2006-2007 and 2007-2008, respectively. Lower spring temperature in 2005 seems to have delayed the initial growth of cattails and therefore led to a later switchover time from a net CO2 source to a net CO2 sink compared to spring 2006 and 2007. The lower cumulative NEE measured in 2006-2007 is mainly due to the cloudy conditions (i.e. low average incoming photosynthetically active radiation) that occurred through late summer and early fall 2006, which greatly decreased cattail photosynthesis and induced an earlier death of the pants, which in turn resulted in a lower average CO2 uptake compared to the other years. During the 2005, 2006 and 2007 growing seasons, the carbon uptake period was 109, 104, and 116 days in length, which is consistent with the inter-annual variability in NEE observed. The results suggest that the timing of the fall switchover from a net CO2 sink to a net CO2 source is probably the main factor influencing the annual CO2 accumulation. The average CH4 flux measured from open water was 658 mg CH4 m-2 d-1 in 2005, 381 mg CH4 m-2 d-1 in 2006, and 352 mg CH4 m-2 d-1 in 2008. The average CH4 flux from vegetation was 1001 mg CH4 m-2 d-1 in 2005, 1640 mg CH4 m-2 d-1 in 2006, and 1260 mg CH4 m-2 d-1 in 2008. The CH4 flux from soil was only measured in 2006 (255 mg CH4 m-2 d-1) and 2008 (224 mg CH4 m-2 d-1). It is known that the presence of the aerenchyma tissue that runs through the cattail's roots, stem and leaves facilitates the transport of gases such as CH4 from the production site (i.e. soil) to the atmosphere, which explains the higher fluxes measured from vegetated portions of the marsh. Knowing that CH4 is produced under anaerobic waterlogged conditions, the higher CH4 fluxes measured from plants in 2006 may be related to the higher rainfall observed during that year. This long-term record of CO2 and CH4 fluxes combined with continuous measurements of meteorological and ecosystem properties allows us to investigate the overall carbon budget of this marsh wetland as well as the major controls on the GHG fluxes for this type of ecosystem. This study provides valuable knowledge that can complement the existing information on other wetlands types and may be useful for predicting the impacts of climate change on CO2 and CH4 fluxes and for estimating national carbon stocks.

Bonneville, M.; Strachan, I.

2009-05-01

303

Medium-term fertilization of grassland plant communities masks plant species-linked effects on soil microbial community structure  

Microsoft Academic Search

According to the singular hypothesis of plant diversity, different plant species are expected to make unique contributions\\u000a to ecosystem functioning. Hence, individual species would support distinct microbial communities. It was hypothesized that\\u000a microbial community dynamics in the respective rhizospheres of, two floristically divergent species, Agrostis capillaris and Prunella vulgaris that were dominant in a temperate, upland grassland in northern Greece,

Stavros D. Veresoglou; Andreas P. Mamolos; Barry Thornton; Olga K. Voulgari; Robin Sen; Demetrios S. Veresoglou

2011-01-01

304

Disentangling leaf area and environmental effects on the response of the net ecosystem CO2 exchange to diffuse radiation  

NASA Astrophysics Data System (ADS)

There is an ongoing discussion about why the net ecosystem CO2 exchange (NEE) of some ecosystems is less sensitive to diffuse radiation than others and about the role other environmental factors play in determining the response of NEE to diffuse radiation. Using a six-year data set from a temperate mountain grassland in Austria we show that differences between ecosystems may be reconciled based on their green area index (GAI; square meter green plant area per square meter ground area) - the sensitivity to diffuse radiation increasing with GAI. Our data suggest diffuse radiation to have a negligible influence on NEE below a GAI of 2 m2 m-2. Changes in air/soil temperature and air humidity concurrent with the fraction of diffuse radiation were found to amplify the sensitivity of the investigated temperate mountain grassland ecosystem to diffuse radiation.

Wohlfahrt, Georg; Hammerle, Albin; Haslwanter, Alois; Bahn, Michael; Tappeiner, Ulrike; Cernusca, Alexander

2008-08-01

305

Deposition fluxes of terpenes over grassland  

NASA Astrophysics Data System (ADS)

Eddy covariance flux measurements were carried out for two subsequent vegetation periods above a temperate mountain grassland in an alpine valley using a proton-transfer-reaction-mass spectrometer (PTR-MS) and a PTR time-of-flight-mass spectrometer (PTR-TOF). In 2008 and during the first half of the vegetation period 2009 the volume mixing ratios (VMRs) for the sum of monoterpenes (MTs) were typically well below 1 ppbv and neither MT emission nor deposition was observed. After a hailstorm in July 2009 an order of magnitude higher amount of terpenes was transported to the site from nearby coniferous forests causing elevated VMRs. As a consequence, deposition fluxes of terpenes to the grassland, which continued over a time period of several weeks without significant reemission, were observed. For days without precipitation the deposition occurred at velocities close to the aerodynamic limit. In addition to monoterpene uptake, deposition fluxes of the sum of sesquiterpenes (SQTs) and the sum of oxygenated terpenes (OTs) were detected. Considering an entire growing season for the grassland (i.e., 1 April to 1 November 2009), the cumulative carbon deposition of monoterpenes reached 276 mg C m-2. This is comparable to the net carbon emission of methanol (329 mg C m-2), which is the dominant nonmethane volatile organic compound (VOC) emitted from this site, during the same time period. It is suggested that deposition of monoterpenes to terrestrial ecosystems could play a more significant role in the reactive carbon budget than previously assumed.

Bamberger, I.; HöRtnagl, L.; Ruuskanen, T. M.; Schnitzhofer, R.; Müller, M.; Graus, M.; Karl, T.; Wohlfahrt, G.; Hansel, A.

2011-07-01

306

Testing mechanisms of N-enrichment-induced species loss in a semiarid Inner Mongolia grassland: critical thresholds and implications for long-term ecosystem responses.  

PubMed

The increase in nutrient availability as a consequence of elevated nitrogen (N) deposition is an important component of global environmental change. This is likely to substantially affect the functioning and provisioning of ecosystem services by drylands, where water and N are often limited. We tested mechanisms of chronic N-enrichment-induced plant species loss in a 10-year field experiment with six levels of N addition rate. Our findings on a semi-arid grassland in Inner Mongolia demonstrated that: (i) species richness (SR) declined by 16 per cent even at low levels of additional N (1.75 g N m(-2) yr(-1)), and 50-70% species were excluded from plots which received high N input (10.5-28 g N m(-2) yr(-1)); (ii) the responses of SR and above-ground biomass (AGB) to N were greater in wet years than dry years; (iii) N addition increased the inter-annual variations in AGB, reduced the drought resistance of production and hence diminished ecosystem stability; (iv) the critical threshold for chronic N-enrichment-induced reduction in SR differed between common and rare species, and increased over the time of the experiment owing to the loss of the more sensitive species. These results clearly indicate that both abundance and functional trait-based mechanisms operate simultaneously on N-induced species loss. The low initial abundance and low above-ground competitive ability may be attributable to the loss of rare species. However, shift from below-ground competition to above-ground competition and recruitment limitation are likely to be the key mechanisms for the loss of abundant species, with soil acidification being less important. Our results have important implications for understanding the impacts of N deposition and global climatic change (e.g. change in precipitation regimes) on biodiversity and ecosystem services of the Inner Mongolian grassland and beyond. PMID:23045710

Lan, Zhichun; Bai, Yongfei

2012-11-19

307

Habitat requirements of weasels Mustela nivalis constrain their impact on prey populations in complex ecosystems of the temperate zone.  

PubMed

Differences in habitat use by prey and predator may lead to a shift of occupied niches and affect dynamics of their populations. The weasel Mustela nivalis specializes in hunting rodents, therefore habitat preferences of this predator may have important consequences for the population dynamics of its prey. We investigated habitat selection by weasels in the Bia?owieza Forest in different seasons at the landscape and local scales, and evaluated possible consequences for the population dynamics of their prey. At the landscape scale, weasels preferred open habitats (both dry and wet) and avoided forest. In open areas they selected habitats with higher prey abundance, except during the low-density phase of the vole cycle, when the distribution of these predators was more uniform. Also in winter, the distribution of weasels at the landscape scale was proportional to available resources. In summer, within open dry and wet habitats, weasels preferred areas characterised by dense vegetation, but avoided poor plant cover. In winter, weasels used wet open areas proportionally to availability of habitats when hunting, but in contrast to summer, they rested only in habitats characterized by a lower water level, which offered better thermal conditions. At the local scale, the abundance of voles was a less important factor affecting the distribution of these predators. Although we were not able to provide direct evidence for the existence of refuges for voles, our results show that they may be located within habitat patches, where availability of dense plant cover and physiological constraints limit the activity of weasels. Our results indicate that in complex ecosystems of the temperate zone, characterized by a mosaic pattern of vegetation types and habitat specific dynamics of rodents, impact of weasels on prey populations might be limited. PMID:18629542

Zub, K; Sönnichsen, L; Szafra?ska, P A

2008-07-16

308

Elevated CO2 and warming influence ecosystem carbon dynamics and evapotranspiration in a semi-arid grassland  

Technology Transfer Automated Retrieval System (TEKTRAN)

Ecosystem carbon dynamics are sensitive to rising CO2 concentrations and warming, but the combined effects of these global change drivers on ecosystem carbon uptake and loss remain a critical uncertainty. Northern mixed grass prairie is expected to be among the most responsive ecosystems to the effe...

309

Upscaling Carbon Fluxes Over Grasslands of the U.S. Great Plains and Northern China: A Comparative Study  

NASA Astrophysics Data System (ADS)

Grassland ecosystems cover a vast area of the Earth's terrestrial surface, comprising about 40% of total non-permafrost land area. These ecosystems have been found to be highly susceptible to climate changes. Previous studies suggest that the grasslands are carbon sinks or near equilibrium, and often shift between carbon sources in drought years and carbon sinks in other years. It is important to understand the responses of net ecosystem production (NEP) to various climatic conditions across grasslands. Recently we developed a data-driven piecewise regression model and mapped the grassland NEP at 250-m resolution over the Great Plains from 2000 to 2008 based on 15 flux towers. Our results showed the Great Plains was a net sink with an average annual NEP of 24 ± 14 g C/m2/yr, ranging from 0.3 g C/m2/yr in 2002 to 47.7 g C/m2/yr in 2005. The droughts in 2000, 2002, 2006, and 2008 resulted in increased carbon losses over the drought-affected areas, and the Great Plains grasslands turned into a relatively low sink with NEP values of 15.8, 0.3, 20.1, and 10.2 g C/m2/yr for the four years, respectively. The temperate grasslands in the northern China are distributed in the same latitude zone as the U.S. Great Plains and have similar vegetation types and climatic conditions. We will develop a piecewise regression model to estimate the grassland NEP for 2000-2010 over northern China based on grassland flux towers, remotely sensed data (vegetation indices and phonological metrics), and climate data. Our secondary goal in the study is to conduct a comparative study between the U.S. Great Plains and northern China with regard to the carbon sink and source activities under various geographic and climate conditions.

Zhang, L.; Wylie, B. K.; Yuan, W.; Ji, L.; Xiao, J.; Howard, D. M.; Gilmanov, T. G.

2011-12-01

310

Population size and conservation of the last eastern remnants of the regal fritillary, Speyeria idalia (Drury) [Lepidoptera, Nymphalidae]; implications for temperate grassland restoration  

Microsoft Academic Search

We monitored the last remaining Pennsylvania population of the regal fritillary butterfly (Speyeria idalia) for 8 years (1997–2005) at Fort Indiantown Gap, a National Guard training facility located in south-central Pennsylvania,\\u000a USA. We observed demes of this population in five grassland areas, four of which received limited protection from anthropogenic\\u000a military activities (i.e., motorized vehicles were prohibited). The Pollard walk technique

Betty Ferster; Kevina Vulinec

2010-01-01

311

Effects of time-since-fire on the tussock dynamics of a dominant grass ( Themeda triandra) in a temperate Australian grassland  

Microsoft Academic Search

Changes in tussock attributes and sward structure with time-since-fire were documented for the dominant tussock grass, Themeda triandra, at the Derrimut Grassland Reserve in southern Victoria, Australia. When the inter-fire interval exceeded 6 yr, the number of tillers per tussock and the total number of tussocks declined, and by 11 yr, few live tillers or tussocks remained in the sward.

John W Morgan; Ian D Lunt

1999-01-01

312

Predicting the response of a temperate forest ecosystem to atmospheric CO(sub 2) increase. Final report, 1984--1995.  

National Technical Information Service (NTIS)

This document describes the most recent progress made in several areas of the project. Details of individual experiments in the following areas are provided: (1) the impact of soil volume on the physiological acclimation of temperate deciduous trees in el...

F. A. Bazzaz

1995-01-01

313

Elevated carbon dioxide alters impacts of precipitation pulses on ecosystem photosynthesis and respiration in a semi-arid grassland  

Technology Transfer Automated Retrieval System (TEKTRAN)

Predicting net carbon (C) balance under future global change scenarios requires a comprehensive understanding of photosynthetic (GPP) and ecosystem respiration (Re) responses to atmospheric CO2 concentration and water availability. We measured net ecosystem exchange of CO2 (NEE), GPP and Re prior to...

314

Community structure, trophic position and reproductive mode of soil and bark-living oribatid mites in an alpine grassland ecosystem.  

PubMed

The community structure, stable isotope ratios ((15)N/(14)N, (13)C/(12)C) and reproductive mode of oribatid mites (Acari, Oribatida) were investigated in four habitats (upper tree bark, lower tree bark, dry grassland soil, forest soil) at two sites in the Central Alps (Tyrol, Austria). We hypothesized that community structure and trophic position of oribatid mites of dry grassland soils and bark of trees are similar since these habitats have similar abiotic characteristics (open, dry) compared with forest soil. Further, we hypothesized that derived taxa of oribatid mites reproducing sexually dominate on the bark of trees since species in this habitat consume living resources such as lichens. In contrast to our hypothesis, the community structure of oribatid mites differed among grassland, forest and bark indicating the existence of niche differentiation in the respective oribatid mite species. In agreement with our hypothesis, sexually reproducing taxa of oribatid mites dominated on the bark of trees whereas parthenogenetic species were more frequent in soil. Several species of bark-living oribatid mites had stable isotope signatures that were similar to lichens indicating that they feed on lichens. However, nine species that frequently occurred on tree bark did not feed on lichens according to their stable isotope signatures. No oribatid mite species could be ascribed to moss feeding. We conclude that sexual reproduction served as preadaptation for oribatid mites allowing them to exploit new habitats and new resources on the bark of trees. Abiotic factors likely are of limited importance for bark-living oribatid mites since harsh abiotic conditions are assumed to favor parthenogenesis. PMID:20490626

Fischer, Barbara M; Schatz, Heinrich; Maraun, Mark

2010-05-21

315

Elevated carbon dioxide alters impacts of precipitation pulses on ecosystem photosynthesis and respiration in a semi-arid grassland  

Microsoft Academic Search

Predicting net C balance under future global change scenarios requires a comprehensive understanding of how ecosystem photosynthesis\\u000a (gross primary production; GPP) and respiration (Re) respond to elevated atmospheric [CO2] and altered water availability. We measured net ecosystem exchange of CO2 (NEE), GPP and Re under ambient and elevated [CO2] in a northern mixed-grass prairie (Wyoming, USA) during dry intervals and

Sarah Bachman; Jana L. Heisler-White; Elise Pendall; David G. Williams; Jack A. Morgan; Joanne Newcomb

2010-01-01

316

Controls on the fate, structure and function of dissolved organic carbon and nitrogen in a California grassland, oak woodland and conifer ecosystem  

NASA Astrophysics Data System (ADS)

In California, oak woodlands and grasslands, have been expanding their geographic range over the past 100 years, and are projected to extend upward along the western slopes of the Sierra Nevada foothills in response to climate change. Since vegetation type plays a large role in soil formation and carbon (C) and nitrogen (N) cycling, shifts in vegetation distribution could impact C and N storage and processing. This study was designed to determine if dissolved organic carbon (DOC) and nitrogen (DON) production, composition, biodegradation and sorption in the mineral soil of a grassland, oak woodland and conifer ecosystem is related to the type of plant material from which it is derived and how these processes are correlated with temperature. A field experiment where leachates from transplanted soil columns were collected over two rainy seasons at a grassland, oak woodland and conifer field location was combined with laboratory batch adsorption and biodegradation using litter and soil from the same sites. Specific ultra-violet absorbance at 254 nm (SUVA 254), 13C nuclear magnetic resonance (13C NMR) and fractionation of dissolved organic matter (DOM) into hydrophilic and hydrophobic factions was used to determine the structural composition of the DOC solutions. In the laboratory, surface litter from the grass, oak and a conifer site were incubated with de-ionized water for 5, 15 or 96 hours at 4, 20 or 30oC. Incubation time had little effect on DOC structure while vegetation type and temperature had significant effects on DOC functional groups. Increased incubation time and temperature significantly increased DOC and DON concentration. Percent biodegradable DOC was positively correlated to increasing heteroaliphatic functional groups. Since grass, oak and pine DOM solutions had the highest levels of biodegradation using soil inoculums from the sites where the surface litter originated, biodegradation appears to be related to site microbial activity. In batch adsorption studies, an increase in incubation temperature is related to an increase in sorption and biodegradation. There were no significant correlations between adsorption and DOC functional groups. Soil iron and aluminum content were found to play a larger role in DOC adsorption than DOC functional group concentration. Therefore, sorption appears to be primarily controlled by ecosystem soil characteristics and a thermodynamic relationship with temperature rather than surface litter type. In the field experiment, neither DOC, DON nor SUVA 254 values of column leachates differed significantly with surface litter or soil type. However, the 15 month incubation of the soil columns containing all three soil types at all three field locations resulted in several significant changes in soil C and N parameters. Percent C, water extractable DOC and soil C:N all increased in the soil from the pine location that was incubated at the oak and grass location. These changes indicate that the soils at mixed conifer sites in the Sierra Nevada foothills could store increased levels of soil C if grassland and oak woodland vegetation shift into the areas currently dominated by mixed conifers.

Pittiglio, S. L.; Zasoski, R.

2010-12-01

317

Representing agro-pastoral sahelian ecosystems in the global land surface model ORCHIDEE: in situ validation and comparison between croplands and grasslands.  

NASA Astrophysics Data System (ADS)

In a effort to improve the representation of tropical agro-ecosystems in the global terrestrial biosphere model ORCHIDEE, recent model developments have been made in order to better account for tropical croplands and savannahs. Here we compare the simulations performed with these new versions with in situ data from the AMMA-Niger Wankama "local site". Indeed, since 2005, soil moisture, vegetation (biomass, LAI) and eddy-covariance flux tower measurements have been conducted at Wankama over both a millet and a fallow site, resulting in a unique dataset of carbon and energy fluxes over two different agricultural land-cover types and for several climatically-contrasted years in the sahelian zone. Thus, we performed on-site simulations with ORCHIDEE forced with local meteorological data over 2005-2007: we assess the ability of the two land-use specific versions of the model (croplands and grasslands) to capture the respective observed characteristics of vegetation, water balance and energy fluxes over time scales ranging from diurnal to inter-annual. We also discuss the ability of the model to account for the relative differences between crops and fallow in terms of land/atmosphere interactions - for on a large scale these differences may feed back on the atmosphere as grasslands are gradually converted to croplands. We finally attempt to discriminate between the validated features and deficiencies that are most likely to be site-specific and the ones that may impair the representation of the contrast between these two land cover types at larger scale.

Berg, Alexis; Brender, Pierre; Boulain, Nicolas; Ramier, David; Sultan, Benjamin; de Noblet, Nathalie; Ciais, Philippe; Ottlé, Catherine; Cappelaere, Bernard; Demarty, Jerome

2010-05-01

318

Quantifying nitrous oxide emissions from Chinese grasslands with a process-based model  

NASA Astrophysics Data System (ADS)

As one of the largest land cover types, grassland can potentially play an important role in the ecosystem services of natural resources in China. Nitrous oxide (N2O) is a major greenhouse gas emitted from grasslands. Current N2O inventory at regional or national level in China relies on the emission factor method, and is based on limited measurements. To improve inventory accuracy and capture the spatial variability of the N2O emissions under the diverse climate, soil and management conditions across China, we adopted an approach that uses a process-based biogeochemical model, DeNitrification-DeComposition (DNDC) in this study, to map the N2O emissions from China's grasslands. The DNDC was linked to a GIS database of spatially distributed information of climate, soil, vegetation and management at county-level for all grasslands in China. Daily weather data from 2000-2007 based on the national network of 670 meteorological stations were utilized in the model simulations. The results were validated against observations from several grasslands in China and from other countries. The modelled results showed a clear geographic pattern of N2O emissions from China's grasslands. A high-emission strip was found that stretched from northeast to central China, along the eastern boundary of the temperate grassland region adjacent to the major agricultural regions. The grasslands in the western mountain regions, however, emitted much less N2O. The regional average of N2O emission rates was 0.23, 0.11 and 0.39 kg N ha-1y-1 for the temperate, montane and tropical/subtropical grasslands, respectively. The national N2O emission was 76.5 Gg N from the 337 million ha of grasslands in China. The modelled results were in good agreement with observations (R2=0.64 for 11 datasets), suggesting that the process-based model can be used to capture the spatial dynamics of N2O emissions as an effective alternative to statistical method currently used in China.

Zhang, F.; Qi, J.; Li, F. M.; Li, C. S.; Li, C. B.

2010-03-01

319

Effects of an increase in summer precipitation on leaf, soil, and ecosystem fluxes of CO 2 and H 2 O in a sotol grassland in Big Bend National Park, Texas  

Microsoft Academic Search

Global climate models predict that in the next century precipitation in desert regions of the USA will increase, which is\\u000a anticipated to affect biosphere\\/atmosphere exchanges of both CO2 and H2O. In a sotol grassland ecosystem in the Chihuahuan Desert at Big Bend National Park, we measured the response of leaf-level\\u000a fluxes of CO2 and H2O 1 day before and up to

Lisa Patrick; Jessica Cable; Daniel Potts; Danielle Ignace; Greg Barron-Gafford; Alden Griffith; Holly Alpert; Natasja Van Gestel; Traesha Robertson; Travis E. Huxman; John Zak; Michael E. Loik; David Tissue

2007-01-01

320

Fire effects on ecosystem nitrogen cycling in a Californian bishop pine forest  

Microsoft Academic Search

Fire can cause severe nitrogen (N) losses from grassland, chaparral, and temperate and boreal forest ecosystems. Paradoxically,\\u000a soil ammonium levels are markedly increased by fire, resulting in high rates of primary production in re-establishing plant\\u000a communities. In a manipulative experiment, we examined the influence of wild-fire ash residues on soil, microbial and plant\\u000a N pools in a recently burned Californian

P. Grogan; T. D. Burns; F. S. Chapin III

2000-01-01

321

Predicting the response of a temperate forest ecosystem to atmospheric CO(sub 2) increase. Annual report, 1992--1993.  

National Technical Information Service (NTIS)

This report summarizes the second year of research progress. Included are progress reports for the following studies: the responses of temperate forest tree to 3 years of exposure to elevated carbon dioxide, and high and low nutrient and light levels; pot...

F. A. Bazzaz

1993-01-01

322

Quantifying the Role of Water Table Dynamics on Net Ecosystem Exchange of CO2 in a Northern Temperate Shrub Wetland  

Microsoft Academic Search

Wetlands represent up to a third of the global soil carbon, and so they are a large component of an uncertain terrestrial carbon flux. In the northern temperate forests around the upper Great Lakes of North America forest and shrub stature wetlands cover about one-third of the total land area. In northern Wisconsin lateral subsurface water redistribution associated with hummocky

S. Mackay; A. R. Desai; B. N. Sulman; D. E. Roberts

2009-01-01

323

8. Protected area planning and management for eastern Australian temperate forests and woodland ecosystems under climate change - a landscape approach  

Microsoft Academic Search

The ecological effects of rapid global warming are predicted to be dramatic with mass species extinctions worldwide. For temperate eastern Australia, a drier and warmer environment will affect survival, distribution and abundance of species, including exotics, and ecological processes within and outside reserves. Ecological connectivity and fragmentation, already major conservation issues, will be exacerbated by climate change and migration will

Ian Mansergh; David Cheal

324

Effects of grazing on leaf traits and ecosystem functioning in Inner Mongolia grasslands: scaling from species to community  

Microsoft Academic Search

More attention has focused on using some easily measured plant functional traits to predict grazing influence on plant growth and ecosystem functioning. However, there has been much controversy on leaf traits response to grazing, thus more research should be conducted at the species level. Here we investigated the leaf area, leaf mass and specific leaf area (SLA) of 263 species

S. X. Zheng; H. Y. Ren; Z. C. Lan; W. H. Li; Y. F. Bai

2009-01-01

325

Increasing diurnal and seasonal amplitudes in carbon and water fluxes after conversion from arable to grassland  

NASA Astrophysics Data System (ADS)

Land-use change is a topical scientific and political issue due to its potential to affect atmospheric greenhouse gas concentrations. Conversion of arable land to permanent grassland has been proposed as a strategy to sequester atmospheric CO2 into soil organic matter. In this context, eddy covariance measurements were recorded over grazed grassland at a site in the temperate region of southern Germany (annual precipitation 775 mm, annual temperature 9°C) from 2002 to 2008. The site had been arable farm land for decades but from 2000 it became grassland grazed by cattle (Bos taurus). Over the study period the total ecosystem respiration (TER), gross primary production (GPP) and evapotranspiration (ET) increased during the growing season and, therefore, in annual totals (by about 80%, 85%, and 33%, respectively, during seven-year period). A similar trend could not be found for net ecosystem exchange (NEE) of carbon in the daily to annual sums, but was evident in the separated day and night fluxes of NEE. There was no trend in the meteorological conditions (temperature, precipitation) causing the trends. The main effect of the land use change was not a change in C sequestration but an increase in temperature sensitivity; in grassland the C distribution within the soil is closer to the surface than in arable systems, which causes the daily and yearly variations in C balance to increase.

Vetter, S. H.; Auerswald, K.; Bernhofer, C.

2012-04-01

326

[Spatiotemporal characteristics of MODIS NDVI in Hulunber Grassland].  

PubMed

Time-series MODIS NDVI datasets from 2000 to 2008 were used to study the spatial change trend, fluctuation degree, and occurrence time of the annual NDVImax of four typical grassland types, i.e., lowland meadow, temperate steppe, temperate meadow steppe, and upland meadow, in Hulunber Grassland. In 2000-2008, the vegetation in Hulunber Grassland presented an obvious deterioration trend. The mean annual NDVImax of the four grassland types had a great fluctuation, especially in temperate steppe where the maximum change in the mean value of annual NDVImax approximated to 50%. As for the area change of different grade grasslands, the areas with NDVImax between 0.4 and 1 accounted for about 91% of the total grassland area, which suggested the good vegetation coverage in the Grassland. However, though the areas with NDVImax values in (0.4, 0.8) showed an increasing trend, the areas with NDVImax values in (0.2, 0.4) and (0.8, 1) decreased greatly in the study period. Overall, the deteriorating grassland took up about 66.25% of the total area, and the restoring grassland took the rest. There was about 62.85% of the grassland whose NDVImax occurred between the 193rd day and the 225th day in each year, indicating that this period was the most important vegetation growth season in Hulunber Grassland. PMID:20136010

Zhang, Hong-Bin; Yang, Gui-Xia; Wu, Wen-Bin; Li, Gang; Chen, Bao-Rui; Xin, Xiao-Ping

2009-11-01

327

Herbivore influence on soil microbial biomass and nitrogen mineralization in a northern grassland ecosystem: Yellowstone National Park  

Microsoft Academic Search

Microorganisms are largely responsible for soil nutrient cycling and energy flow in terrestrial ecosystems. Although soil\\u000a microorganisms are affected by topography and grazing, little is known about how these two variables may interact to influence\\u000a microbial processes. Even less is known about how these variables influence microorganisms in systems that contain large populations\\u000a of free-roaming ungulates. In this study, we

Benjamin F. Tracy; Douglas A. Frank

1998-01-01

328

Source components and interannual variability of soil CO2 efflux under experimental warming and clipping in a grassland ecosystem  

Microsoft Academic Search

Partitioning soil CO2 efflux into autotrophic (RA) and heterotrophic (RH) components is crucial for understanding their differential responses to climate change. We conducted a long-term experiment (2000-2005) to investigate effects of warming 21C and yearly clipping on soil CO2 efflux and its components (i.e. RA and RH) in a tallgrass prairie ecosystem. Interannual variability of these fluxes was also examined.

XUHUI Z HOU

329

Effects of Increased Nitrogen Deposition and Precipitation on Seed and Seedling Production of Potentilla tanacetifolia in a Temperate Steppe Ecosystem  

Microsoft Academic Search

BackgroundThe responses of plant seeds and seedlings to changing atmospheric nitrogen (N) deposition and precipitation regimes determine plant population dynamics and community composition under global change.Methodology\\/Principal FindingsIn a temperate steppe in northern China, seeds of P. tanacetifolia were collected from a field-based experiment with N addition and increased precipitation to measure changes in their traits (production, mass, germination). Seedlings germinated

Yang Li; Haijun Yang; Jianyang Xia; Wenhao Zhang; Shiqiang Wan; Linghao Li

2011-01-01

330

Gross primary production and net ecosystem exchange of a cool-temperate deciduous forest estimated by the eddy covariance method  

Microsoft Academic Search

An eddy covariance measurement system was installed to measure long-term turbulent fluxes of heat, water vapor, and CO2 over a cool-temperate deciduous forest in the central part of Japan. Previous to a long-term measurement, a comparison of flux measurements using open- and closed-path type infrared gas analyzers was conducted for CO2 and water vapor. The closure of the energy budget

Nobuko Saigusa; Susumu Yamamoto; Shohei Murayama; Hiroaki Kondo; Noboru Nishimura

2002-01-01

331

Effects of Air Pollutants on Mediterranean and Temperate Forest Ecosystems, June 22-27, 1980, Riverside, California.  

National Technical Information Service (NTIS)

These proceedings papers and poster summaries discuss the influence of air pollution on terrestrial and related aquatic ecosystems. They describe single species-single pollutant relationships; interactions of producers, consumers, and decomposers under po...

P. R. Miller

1980-01-01

332

Evaluation of grassland dynamics in the northern-tibet plateau of china using remote sensing and climate data  

USGS Publications Warehouse

The grassland ecosystem in the Northern-Tibet Plateau (NTP) of China is very sensitive to weather and climate conditions of the region. In this study, we investigate the spatial and temporal variations of the grassland ecosystem in the NTP using the NOAA/AVHRR ten-day maximum NDVI composite data of 1981-2001. The relationships among Vegetation Peak-Normalized Difference Vegetation Index (VP-NDVI) and climate variables were quantified for six counties within the NTP. The notable and uneven alterations of the grassland in response to variation of climate and human impact in the NTP were revealed. Over the last two decades of the 20th century, the maximum greenness of the grassland has exhibited high increase, slight increase, no-change, slight decrease and high decrease, each occupies 0.27%, 8.71%, 77.27%, 13.06% and 0.69% of the total area of the NTP, respectively. A remarkable increase (decrease) in VP-NDVI occurred in the central-eastern (eastern) NTP whereas little change was observed in the western and northwestern NTP. A strong negative relationship between VP-NDVI and ET 0 was found in sub-frigid, semi-arid and frigid- arid regions of the NTP (i.e., Nakchu, Shantsa, Palgon and Amdo counties), suggesting that the ETo is one limiting factor affecting grassland degradation. In the temperate-humid, sub-frigid and sub-humid regions of the NTP (Chali and Sokshan counties), a significant inverse correlation between VP-NDVI and population indicates that human activities have adversely affected the grassland condition as was previously reported in the literature. Results from this research suggest that the alteration and degradation of the grassland in the lower altitude of the NTP over the last two decades of the 20th century are likely caused by variations of climate and anthropogenic activities. ?? 2007 by MDPI.

Zhang, J.; Yao, F.; Zheng, L.; Yang, L.

2007-01-01

333

Predicting the response of a temperate forest ecosystem to atmospheric CO{sub 2} increase. Annual report, 1992--1993  

SciTech Connect

This report summarizes the second year of research progress. Included are progress reports for the following studies: the responses of temperate forest tree to 3 years of exposure to elevated carbon dioxide, and high and low nutrient and light levels; pot-size limitations in carbon dioxide studies, interactive effects of carbon dioxide and soil moisture availability on tree seedling`s tissue water relations, growth, and niche characteristics; individual versus population responses to elevated carbon dioxide levels in two species of annual weeds; and the development of gypsy moth larvae raised on gray and yellow birth foliage grown in ambient and elevated carbon dioxide environments.

Bazzaz, F.A.

1993-03-01

334

Effects of elevated atmospheric carbon dioxide on amino acid and NH4 1 -N cycling in a temperate pine ecosystem  

Microsoft Academic Search

Rising atmospheric carbon dioxide (CO2) is expected to increase forest productivity, resulting in greater carbon (C) storage in forest ecosystems. Because elevated atmo- spheric CO2 does not increase nitrogen (N) use efficiency in many forest tree species, additional N inputs will be required to sustain increased net primary productivity (NPP) under elevated atmospheric CO2. We investigated the importance of free

KIRSTEN S. H OFMOCKEL; W ILLIAM H. S CHLESINGER; R O B E RT

335

Using an ecosystem process model to examine effects of increased atmospheric N deposition on soil carbon storage in northern temperate forests  

NASA Astrophysics Data System (ADS)

Although atmospheric nitrogen deposition can increase primary productivity in nitrogen limited northern temperate forests, the potential for nitrogen deposition to increase soil carbon storage through decreased decomposition has gone unexplored in biogeochemical models. We modeled carbon and nitrogen cycling in sugar maple forests along a nitrogen deposition gradient using an ecosystem process model. Our goal was to better understand how elevated atmospheric nitrogen deposition is affecting decomposition in forest soils and how such an effect integrates with other aspects of forest C and N cycling, potentially altering ecosystem C storage. Previous field research in four Michigan forests dominated by sugar maple demonstrates greater soil carbon storage under simulated increased nitrogen deposition;. however, this response did not occur via greater above- or belowground litter production. The accumulation of soil organic matter in forest floor and surface soil coincided with declines in soil respiration, the activity of microbial extracellular enzymes mediating lignocellulose degradation, and forest floor turnover rates. To explore ecosystem feedbacks and interactions mediating these responses, we used the TRACE (Tracer Redistributions Among Compartments in Ecosystems) ecosystem process model. TRACE was developed to examine fluxes of carbon and nitrogen (including nitrogen stable isotopes) and currently allows for interactions between climate and litter lignin content to control decomposition rates. For the present research, we parameterized TRACE using field data from four sugar maple dominated forest stands along a gradient of nitrogen deposition in Michigan. We calibrated carbon and nitrogen cycling within the model using field data from one of the four stands. We then compared modeled biogeochemical processes within all four stands to field data for control stands and stands with simulated elevated nitrogen deposition. Model results from sites with higher nitrogen deposition stored proportionally more carbon in vegetation and proportionally less carbon in organic and mineral soil carbon pools for both treatments than model results from sites with relatively low nitrogen deposition. For the control treatment, TRACE accurately modeled vegetation production as well as carbon storage in vegetation and soil carbon pools. However TRACE overestimates foliar and fine root nitrogen concentrations. Unlike field results, modeled results did not show increased soil carbon storage with experimentally elevated nitrogen deposition. However, experimentally elevated nitrogen deposition decreased C:N ratios in modeled forest floor organic matter from all stands. In future, we will alter TRACE to allow atmospheric nitrogen deposition to interact with lignin decomposition.

Whittinghill, K. A.; Currie, W. S.; Zak, D. R.

2010-12-01

336

Spatial and temporal dynamics of biotic and abiotic features of temperate coastal ecosystems as revealed by a combination of ecological indicators  

NASA Astrophysics Data System (ADS)

Coastal ecosystems exhibit complex spatio-temporal patterns due to their position at the interface between land and sea. This is particularly the case of temperate ecosystems where exploitation of coastal resources (fisheries and aquaculture) and intensive agricultural use of watersheds further complicate our understanding of their dynamics. The aim of the present study was to unravel the spatio-temporal dynamics of contrasted megatidal coastal ecosystems located at the same regional scale (i.e. under the same regional climate), but under different kinds of human pressure. Two kinds of ecological indicators were assessed over a period of four years at 11 locations along the coast of the Cotentin peninsula (Normandy, France). A first set of hydrobiological variables (dissolved nutrients, Chl a, temperature, salinity, etc.) was measured fortnightly in the water column. These data were analysed by principal components analysis (PCA). A second set of variables were the carbon and nitrogen stable isotope ratios of the adductor muscles of cultured Crassostrea gigas introduced every year to typify the bentho-pelagic coupling at each location. Food sources were also investigated using a mixing model with data on the isotopic composition of the food sources obtained previously. To identify which environmental variables played a significant role in determining the oyster diet, the contributions of oyster food sources were combined with environmental variables in a canonical correspondence analysis (CCA). Isotopic values of adductor muscles varied significantly between -20.12‰ and -16.79‰ for ?13C and between 8.28‰ and 11.87‰ for ?15N. The PCA distinguished two groups of coastal ecosystems that differed in their coastal hydrology, nutrient inputs, and the size of their respective watershed, irrespective of the year. In each zone, different spatial patterns in the measured variables were observed depending on the year showing that local impacts differed temporally. As revealed by CCA, food sources used by the oysters were mainly explained by salinity suggesting regional differences between ecosystems. On the west coast of the peninsula, climatic factors act in synergy with anthropogenic factors (i.e. nutrient enrichment) whereas on the east coast, climatic factors appear to be dampened by anthropogenic factors.

Grangeré, K.; Lefebvre, S.; Blin, J.-L.

2012-08-01

337

Algal biomass and primary production within a temperate zone sandstone  

SciTech Connect

The use of dimethyl sulfoxide (DMSO) to extract chlorophyll a and {sup 14}C-labelled photosynthate from endolithic algae of sparsely vegetated, cold temperate grasslands on the Colorado Plateau in Arizona has yielded the first estimates of biomass and photosynthesis for this unusual community. These subsurface microorganisms are found widespread in exposed Coconino Sandstone, a predominant formation in this cold temperate region. The endolithic community in Coconino Sandstone, composed primarily of coccoid blue-green and coccoid/sarcinoid green algae, yielded a biomass value (as chlorophyll a content) of 87 mg m{sup {minus}2} rock surface area and a photosynthetic rate of 0.37 mg CO{sub 2} dm{sup {minus}2} hr{sup {minus}1} or 0.48 mg CO{sub 2} mg{sup {minus}1} chl a hr{sup {minus}1}. The endolithic algal community contributes moderate biomass (5-10%) and substantial photosynthesis (20-80%) to the sparse grassland ecosystem.

Bell, R.A.; Sommerfeld, M.R. (Arizona State Univ., Tempe (USA))

1987-02-01

338

Effects of an increase in summer precipitation on leaf, soil, and ecosystem fluxes of CO2 and H2O in a sotol grassland in Big Bend National Park, Texas.  

PubMed

Global climate models predict that in the next century precipitation in desert regions of the USA will increase, which is anticipated to affect biosphere/atmosphere exchanges of both CO(2) and H(2)O. In a sotol grassland ecosystem in the Chihuahuan Desert at Big Bend National Park, we measured the response of leaf-level fluxes of CO(2) and H(2)O 1 day before and up to 7 days after three supplemental precipitation pulses in the summer (June, July, and August 2004). In addition, the responses of leaf, soil, and ecosystem fluxes of CO(2) and H(2)O to these precipitation pulses were also evaluated in September, 1 month after the final seasonal supplemental watering event. We found that plant carbon fixation responded positively to supplemental precipitation throughout the summer. Both shrubs and grasses in watered plots had increased rates of photosynthesis following pulses in June and July. In September, only grasses in watered plots had higher rates of photosynthesis than plants in the control plots. Soil respiration decreased in supplementally watered plots at the end of the summer. Due to these increased rates of photosynthesis in grasses and decreased rates of daytime soil respiration, watered ecosystems were a sink for carbon in September, assimilating on average 31 mmol CO(2) m(-2) s(-1) ground area day(-1). As a result of a 25% increase in summer precipitation, watered plots fixed eightfold more CO(2) during a 24-h period than control plots. In June and July, there were greater rates of transpiration for both grasses and shrubs in the watered plots. In September, similar rates of transpiration and soil water evaporation led to no observed treatment differences in ecosystem evapotranspiration, even though grasses transpired significantly more than shrubs. In summary, greater amounts of summer precipitation may lead to short-term increased carbon uptake by this sotol grassland ecosystem. PMID:17180661

Patrick, Lisa; Cable, Jessica; Potts, Daniel; Ignace, Danielle; Barron-Gafford, Greg; Griffith, Alden; Alpert, Holly; Van Gestel, Natasja; Robertson, Traesha; Huxman, Travis E; Zak, John; Loik, Michael E; Tissue, David

2006-12-20

339

Seasonal contribution of C 3 and C 4 species to ecosystem respiration and photosynthesis estimated from isotopic measurements of atmospheric CO 2 at a grassland in Japan  

Microsoft Academic Search

Measurements of ?13C in atmospheric CO2 and plant samples were made in 2003, along with CO2 flux measurements, at a grassland site in Tsukuba in central Japan. The objective of the study was to obtain estimates of relative seasonal contributions of C3 and C4 plants to the net CO2 flux over a C3\\/C4 grassland area influenced by the Asian monsoon.

Seiji Shimoda; Shohei Murayama; Wenhong Mo; Takehisa Oikawa

2009-01-01

340

Equilibrium carbon storage in North American ecosystems as estimated by the Terrestruak Ecosystem Model for pre-industrial CO[sub 2]: Soil C storage along gradients of temperature, moisture, and texture  

SciTech Connect

The Terrestrial Ecosystem Model (TEM), a process-based model, estimates a total C storage of 410 PgC (10[sup 15] gC) for undisturbed North American ecosystems at preindustrial CO[sub 2], of which soil C is 59%. Conifer forests and moist tundra account for the most vegetation and soil C storage, 31% and 18%, respectively. Along a temperature gradient in eastern North America, soil C storage decreases from 16200 to 6200 gC m[sup [minus]2] between the northern limit of moist tundra and the southern limit of temperate forest. Along a moisture gradient at 40[degrees]N, soil C storage increases from 3000 to 11000 gC m[sup [minus]2] between the western end of temperate grasslands and the eastern end of temperate forests. The model estimates that finer textured soils store more carbon under the same climatic conditions.

McGuire, A.D.; Melillo, J.M.; Joyce, L.A.; Kicklighter, D.W. (The Ecosystems Center, Woods Hole, MA (United States) Rocky Mountain Forest and Range Experiment Station, Ft. Colling, CO (United States))

1993-06-01

341

Biomass production in experimental grasslands of different species richness during three years of climate warming  

NASA Astrophysics Data System (ADS)

Here we report on the single and combined impacts of climate warming and species richness on the biomass production in experimental grassland communities. Projections of a future warmer climate have stimulated studies on the response of terrestrial ecosystems to this global change. Experiments have likewise addressed the importance of species numbers for ecosystem functioning. There is, however, little knowledge on the interplay between warming and species richness. During three years, we grew experimental plant communities containing one, three or nine grassland species in 12 sunlit, climate-controlled chambers in Wilrijk, Belgium. Half of these chambers were exposed to ambient air temperatures (unheated), while the other half were warmed by 3°C (heated). Equal amounts of water were added to heated and unheated communities, so that warming would imply drier soils if evapotranspiration was higher. Biomass production was decreased due to warming, both aboveground (-29%) and belowground (-25%), as negative impacts of increased heat and drought stress in summer prevailed. Complementarity effects, likely mostly through both increased aboveground spatial complementarity and facilitative effects of legumes, led to higher shoot and root biomass in multi-species communities, regardless of the induced warming. Surprisingly, warming suppressed productivity the most in 9-species communities, which may be attributed to negative impacts of intense interspecific competition for resources under conditions of high abiotic stress. Our results suggest that warming and the associated soil drying could reduce primary production in many temperate grasslands, and that this will not necessarily be mitigated by efforts to maintain or increase species richness.

de Boeck, H. J.; Lemmens, C. M. H. M.; Zavalloni, C.; Gielen, B.; Malchair, S.; Carnol, M.; Merckx, R.; van den Berge, J.; Ceulemans, R.; Nijs, I.

2008-04-01

342

Biomass production in experimental grasslands of different species richness during three years of climate warming  

NASA Astrophysics Data System (ADS)

Here we report on the single and combined impacts of climate warming and species richness on the biomass production in experimental grassland communities. Projections of a future warmer climate have stimulated studies on the response of terrestrial ecosystems to this global change. Experiments have likewise addressed the importance of species numbers for ecosystem functioning. There is, however, little knowledge on the interplay between warming and species richness. During three years, we grew experimental plant communities containing one, three or nine grassland species in 12 sunlit, climate-controlled chambers in Wilrijk, Belgium. Half of these chambers were exposed to ambient air temperatures (unheated), while the other half were warmed by 3°C (heated). Equal amounts of water were added to heated and unheated communities, so that warming would imply drier soils if evapotranspiration was higher. Biomass production was decreased due to warming, both aboveground (-29%) and belowground (-25%), as negative impacts of increased heat and drought stress in summer prevailed. Increased resource partitioning, likely mostly through spatial complementarity, led to higher shoot and root biomass in multi-species communities, regardless of the induced warming. Surprisingly, warming suppressed productivity the most in 9-species communities, which may be attributed to negative impacts of intense interspecific competition for resources under conditions of high abiotic stress. Our results suggest that warming and the associated soil drying could reduce primary production in many temperate grasslands, and that this will not necessarily be mitigated by efforts to maintain or increase species richness.

de Boeck, H. J.; Lemmens, C. M. H. M.; Gielen, B.; Malchair, S.; Carnol, M.; Merckx, R.; van den Berge, J.; Ceulemans, R.; Nijs, I.

2007-12-01

343

Effects of Increased Nitrogen Deposition and Precipitation on Seed and Seedling Production of Potentilla tanacetifolia in a Temperate Steppe Ecosystem  

PubMed Central

Background The responses of plant seeds and seedlings to changing atmospheric nitrogen (N) deposition and precipitation regimes determine plant population dynamics and community composition under global change. Methodology/Principal Findings In a temperate steppe in northern China, seeds of P. tanacetifolia were collected from a field-based experiment with N addition and increased precipitation to measure changes in their traits (production, mass, germination). Seedlings germinated from those seeds were grown in a greenhouse to examine the effects of improved N and water availability in maternal and offspring environments on seedling growth. Maternal N-addition stimulated seed production, but it suppressed seed mass, germination rate and seedling biomass of P. tanacetifolia. Maternal N-addition also enhanced responses of seedlings to N and water addition in the offspring environment. Maternal increased-precipitation stimulated seed production, but it had no effect on seed mass and germination rate. Maternal increased-precipitation enhanced seedling growth when grown under similar conditions, whereas seedling responses to offspring N- and water-addition were suppressed by maternal increased-precipitation. Both offspring N-addition and increased-precipitation stimulated growth of seedlings germinated from seeds collected from the maternal control environment without either N or water addition. Our observations indicate that both maternal and offspring environments can influence seedling growth of P. tanacetifolia with consequent impacts on the future population dynamics of this species in the study area. Conclusion/Significance The findings highlight the importance of the maternal effects on seed and seedling production as well as responses of offspring to changing environmental drivers in mechanistic understanding and projecting of plant population dynamics under global change.

Li, Yang; Yang, Haijun; Xia, Jianyang; Zhang, Wenhao; Wan, Shiqiang; Li, Linghao

2011-01-01

344

Multisource data complex classification of grassland: case study of Inner Mongolia grassland  

NASA Astrophysics Data System (ADS)

Based on daily MODIS Enhanced Vegetation Index (EVI), monthly MODIS EVI was calculated, and was analyzed by Principal Component Analysis (PCA) further, whose first three components were inputted as the first three parameters for classification. The fourth, fifth classification parameters were obtained by applying kriging interpolation, principal component analysis, and data re-sampling to temperature, precipitation, bio-temperature and DEM data. Based on these five parameters, the Inner Mongolia grassland was classified by using ISODATA. The results showed that the grassland classification of MODIS EVI provided more information than that of AVHRR NDVI and MODIS NDVI. This method could identify five classes of Inner Mongolia grassland clearly, and sub-classes of temperate meadow, temperate steppe and temperate desert steppe were also distinguished.

Zhao, Bingru; Wang, Hui

2011-11-01

345

Community structure and dynamics in desert ecosystems: potential implications for insecticide risk assessment.  

PubMed

Insecticides are increasingly being used in hot arid ecosystems. The evaluation of the ecological risk these insecticides may pose, however, is based largely on data derived from temperate organisms and ecosystems. The major differences in the composition, structure, and functioning of desert animal communities when compared to temperate terrestrial ecosystems are discussed. Desert communities are characterized by a high fraction of ectotherms (both vertebrates and invertebrates);rodents and insectivores appear to dominate the mammalian fauna; and detritivores make up a very large part of the arthropod fauna. Presently available toxicity data cover these groups only to a very limited extent. It is not known if the ranges of insecticide susceptibility observed in temperate species are representative of those in arid organisms. Thus, it is not certain that ecotoxicological assessments based on such data sets adequately protect desert animal communities. It is shown that food web connectance is higher in desert ecosystems than in temperate grasslands or forests. This may to a large extent be due to the high degree of omnivory among desert organisms. Population regulation between predators and prey appears to be weaker in deserts. The same is often, though not always, the case for competition among desert organisms. It is argued that such characteristics will reduce the chance that strong indirect effects of insecticide perturbations will occur. In spite of the fact that many desert organisms are well adapted to cope with high temporal and spatial environmental variability, there is no reason to believe that they will always recover more rapidly from population perturbations caused by insecticides. The relatively large physiological and life-history plasticity encountered in many desert animals may increase tolerance to insecticide stress. Food chains are longer in deserts than in temperate grasslands and forests. The implications of this observation for the risk of biomagnification of contaminants are discussed. PMID:9002430

van der Valk, H C

1997-01-01

346

Biometric and Eddy-Covariance Based Estimates of Ecosystem Carbon Exchange in an Age-Sequence of Temperate Pine Forests  

NASA Astrophysics Data System (ADS)

We determined and compared annual carbon (C) exchanges from biometric and eddy-covariance (EC) measurements in an age-sequence (6-, 19-, 34-, 69-years old) of managed pine (Pinus strobus L.) forests in southern Ontario from 2005-2007. The biometric approach determined annual above- and belowground tree biomass production from site-specific allometric biomass equations depending on either tree diameter at breast height (DBH) only (method B1) or on DBH with tree height as additional variable (method B2). In addition, detritus production and heterotrophic soil respiration were determined. Data from continuous closed- path measurements at the oldest site and from a roving open-path system among the three younger sites provided EC-based estimates of C exchanges (method EC). The contribution of individual net primary productivity (NPP) components varied considerably with stand age, suggesting different dominant fluxes and uncertainty levels occurring at various forest development stages. All methods produced similar patterns for inter-annual variations with highest (lowest) C fluxes in 2006 (2005). While on an annual basis, differences between methods ranged from ± 4-67% for estimates of annual net ecosystem productivity (NEP), the differences were within ± 15% when averaged over three years, except for the 34-year old stand. Mean annual NEP was estimated by the biometric method B1 (B2) as 1 (N.A.), 394 (634), 134 (265), and 124 (272) g C m-2 y-1 compared to 47, 724, 408, and 119 g C m-2 y-1 by the EC method for the 6-, 19-, 34-, 69-years old stands, respectively. The biometric method B1 agreed best with the EC estimates in the youngest and the oldest stand, but estimated considerably lower productivity rates than the EC method in the two middle-age stands in which method B2 showed a better agreement with method EC by accounting for the vigorous height growth in these stands. Thus, our comparison study shows that the use of inadequate allometric equations may considerably hamper the agreement between biometric and EC estimates. We also observed a strong correlation between annual NEP and tree stem production which suggests that large-scale estimates of annual NEP could be efficiently derived from tree diameter measurements in existing permanent sample plots. Cross-validation of different methodologies is an important tool to define uncertainties around individual method outputs and to improve estimates of C exchange processes in managed forest ecosystems.

Peichl, M.; Arain, M. A.; Brodeur, J. J.; Khomik, M.

2009-05-01

347

Trace Gas and Carbon Sequestration Dynamics in Temperate Croplands and Successional Ecosystems: A Full-Cost Accounting  

NASA Astrophysics Data System (ADS)

Agriculture is responsible for 21-25% of the global anthropic CO2 flux, 55-60% of the anthropic CH4 flux, and 65-80% of the anthopic flux of N2O. A number of CO2 stabilization strategies target agricultural production practices, and the potential for simultaneously abating fluxes of the non-CO2 greenhouse gases is substantial. But so is the potential for creating greenhouse gas (GHG) liabilities, the unintentional increase in one or more GHGs by activities that mitigate another. Whole-system accounting provides a means for including all GHG-contributing processes in the same cropping system analysis in order to illuminate major liabilities and synergies. We contrast a field crop system in the upper U.S. midwest with unmanaged successional ecosystems in the same landscape, and provide evidence that N2O flux - the major contributor to radiative forcing in row-crop systems - can be abated with little loss of crop productivity.

Robertson, G. P.; McSwiney, C. P.

2003-12-01

348

Biological soil crusts are the main contributor to winter soil respiration in a temperate desert ecosystem of China  

NASA Astrophysics Data System (ADS)

Aims Biological soil crusts (BSCs) are a key biotic component of desert ecosystems worldwide. However, most studies carried out to date on carbon (fluxes) in these ecosystems, such as soil respiration (RS), have neglected them. Also, winter RS is reported to be a significant component of annual carbon budget in other ecosystems, however, we have less knowledge about winter RS of BSCs in winter and its contribution to carbon cycle in desert regions. Therefore, the specific objectives of this study were to: (i) quantify the effects of different BSCs types (moss crust, algae crust, physical crust) on the winter RS; (ii) explore relationships of RS against soil temperature and water content for different BSCs, and (iii) assess the relative contribution of BSCs to the annual amount of C released by RS at desert ecosystem level. Methods Site Description The study sites are located at the southeast fringe of the Tengger Desert in the Shapotou region of the Ningxia Hui Autonomous Region [37°32'N and 105°02'E, at 1340 m above mean sea level (a.m.s.l.)], western China. The mean daily temperature in January is -6.9°C , while it is 24.3°C in July. The mean annual precipitation is 186 mm, approximately 80% of which falls between May and September. The annual potential evaporation is 2800 mm. The landscape of the Shapotou region is characterized by large and dense reticulate barchans chains of sand dunes that migrate south-eastward at a velocity of 3-6 m per year. The soil is loose, infertile and mobile and can thus be classified as orthic sierozem and Aeolian sandy soil. Additionally, the soil has a consistent gravimetric water content that ranges from 3 to 4%. The groundwater in the study area is too deep (>60 m) to support large areas of the native vegetation cover; therefore, precipitation is usually the only source of freshwater. The predominant native plants are Hedysarum scoparium Fisch. and Agriophyllum squarrosum Moq., Psammochloa cillosa Bor, which scattered distribute with cover about 1% of the entire study area. Prior to revegetation, straw-checkerboards approximately 1×1 m2 in area were constructed using wheat or rice straw to stabilize the dune surface and allow time for the planted xerophytic shrubs to adapt to the new environment. In 1956, the following 2-year-old xerophytic shrub seedlings were planted within the checkerboard at a density of 16 individuals per 100 m2 and grown without irrigation: Artemisia ordosica Krasch, H. scoparium Fisch, Calligonum mongolicum Turc'z, Caragana microphylla Lam., Caragana korshinskii Kom, Salix gordejevii and Atraphaxis bracteata A.Los. The stabilized area was then expanded to parallel areas in 1964 and 1982 using the same method and species. As a result, the initial stages of change that have occurred at these sites were similar. After more than fifties years succession, the predominant plants are semi-shrubs, shrubs, forbs, and grasses at present and BSCs formed. The common BSCs in the region may be dominated by cyanobacteria, algae, lichens and mosses, or any combination of these organisms. Cyanobacteria species include Microcolous vaginatus Gom., Hydrocoleus violacens Gom., Lyngbya crytoraginatus Schk., Phormidium amblgum Gom., P. autumnale (Ag.) Gom., P. foveolarum (Mont.) Gom. and Phormidium luridum (Kutz) Gom. etc; algal species mainly include Anabaena azotica Ley, Euglena sp., Hantzschia amphioxys var capitata Grum, Oscillatoria obscura Gom., O. pseudogeminate G. Schm. And Scytonema javanicum (Kutz) Bornet Flash etc; lichen species include Collema tenax (Sw.) Ach., Endocarpon pusillum Hedw.; and moss species are dominated by Bryum argenteum Hedw., Didymodon constrictus (Mitt.) Saito., Tortula bidentata Bai Xue Liang and T. desertorum Broth.. Experimental Design and Rs measurements On October 2010, We selected the moss-dominated BSCs at four revegetation sites and natural vegetation sites, in which 3 replicated plots were selected randomly. In each plot, olyvinyl chloride (PVC) collar (lenth 10 cm, internal diameter 10cm ) were inserted 7 cm into the soil. During the

He, M. Z.

2012-04-01

349

Algal biomass and primary production within a temperate zone sandstone  

Microsoft Academic Search

The use of dimethyl sulfoxide (DMSO) to extract chlorophyll a and ¹⁴C-labelled photosynthate from endolithic algae of sparsely vegetated, cold temperate grasslands on the Colorado Plateau in Arizona has yielded the first estimates of biomass and photosynthesis for this unusual community. These subsurface microorganisms are found widespread in exposed Coconino Sandstone, a predominant formation in this cold temperate region. The

Robert A. Bell; Milton R. Sommerfeld

1987-01-01

350

Tree species richness promotes productivity in temperate forests through strong complementarity between species.  

PubMed

Understanding the link between biodiversity and ecosystem functioning (BEF) is pivotal in the context of global biodiversity loss. Yet, long-term effects have been explored only weakly, especially for forests, and no clear evidence has been found regarding the underlying mechanisms. We explore the long-term relationship between diversity and productivity using a forest succession model. Extensive simulations show that tree species richness promotes productivity in European temperate forests across a large climatic gradient, mostly through strong complementarity between species. We show that this biodiversity effect emerges because increasing species richness promotes higher diversity in shade tolerance and growth ability, which results in forests responding faster to small-scale mortality events. Our study generalises results from short-term experiments in grasslands to forest ecosystems and demonstrates that competition for light alone induces a positive effect of biodiversity on productivity, thus providing a new angle for explaining BEF relationships. PMID:21955682

Morin, Xavier; Fahse, Lorenz; Scherer-Lorenzen, Michael; Bugmann, Harald

2011-09-29

351

An examination of songbird avian diversity, abundance trends, and community composition in two endangered temperate ecosystems: riparian willow habitat of the Greater Yellowstone Ecosystem and a restored tallgrass prairie ecosystem, Neal Smith National Wildlife Refuge  

Microsoft Academic Search

One of the central issues in avian community ecology is an understanding of diversity patterns. The diversity of birds is especially important in endangered ecosystems because birds are good indicator species, and their presence could give conservation biologists and wildlife managers clues about the overall health of these systems. I studied the richness, abundance, and community composition of songbirds in

Brian Frederick Olechnowski

2009-01-01

352

Comparative analysis of SPOT, Landsat, MODIS, and AVHRR normalized difference vegetation index data on the estimation of leaf area index in a mixed grassland ecosystem  

NASA Astrophysics Data System (ADS)

Many grassland studies have depended on or are currently depending on the Landsat series of satellite sensors for monitoring work. However, given the identified gaps in Landsat data, alternatives to Landsat imagery need to be tested in an operational environment. In this study, normalized difference vegetation index (NDVI) values are derived from a Système Pour l'Observation de la Terre (SPOT), Moderate Resolution Imaging Spectroradiometer (MODIS), and Advanced Very High Resolution Radiometer (AVHRR) image and compared to the NDVI values from a Landsat image for LAI estimation in a semi-arid heterogeneous grassland. Results indicate a high agreement between Landsat and SPOT data with R2 over 85% at all buffer levels (100, 250, and 1000 m), and a significant but lower agreement between MODIS and Landsat with R2 around 28% at 250 m buffer level to 37% at 100 m buffer level. Based on in situ measurements of LAI in 22 homogeneous sites, the relationships established between LAI and NDVI show that SPOT and Landsat could predict LAI with acceptable accuracy, but MODIS and AVHRR cannot quantify the spatial variation in LAI measurements. Data fusion or blending techniques that combine the spectral information of high spatial/low temporal resolution data with low spatial/high temporal resolution data may be considered to study semi-arid heterogeneous grasslands.

Tong, Alexander; He, Yuhong

2013-01-01

353

Regional variability of grassland CO2 fluxes in Tyrol/Austria  

NASA Astrophysics Data System (ADS)

The FLUXNET project [1] aims at quantifying the magnitude and controls on the CO2, H2O and energy exchange of terrestrial ecosystems. Ideally, the various biomes of the Earth would be sampled in proportion to their spatial extent - in reality, however, study site selection is usually based on other (more practical) criteria so that a bias exists towards certain biomes and ecosystem types. This may be problematic because FLUXNET data are used to calibrate/parameterize models at various scales - if certain ecosystems are poorly replicated this may bias model predictions. Here we present data from a project in Tyrol/Austria where we have been investigating the CO2, H2O and energy exchange of five grassland sites during 2005-2007. The five permanent grassland sites were exposed to similar climate, but differed slightly in management. In a FLUXNET style approach, any of these sites might have been selected for making long-term flux measurements - the aim of this project was to examine the representativeness of these sites and, if evident, elucidate the causes for and controls on differences between sites. To this end we conducted continuous eddy covariance flux measurements at one (anchor) site [2, 3], and episodic, month long flux measurements at the four additional sites using a roving eddy covariance tower. These data were complemented by measurements of environmental drivers, the amount of above ground phytomass and basic data on vegetation and soil type, as well as management. Data are subject to a rigorous statistical analysis in order to quantify significant differences in the CO2, H2O and energy exchange between the sites and to identify the factors which are responsible for these differences. In the present contribution we report results on CO2 fluxes. Our major findings are that (i) site-identity of the surveyed grassland ecosystems was a significant factor for the net ecosystem CO2 exchange (NEE), somewhat less for gross primary production (GPP) and not for ecosystem respiration (RECO), (ii) GPP depended mainly on the amount of incident photosynthetically active radiation and the amount of green plant matter, the scale of influence of these two factors varying fourfold between the sites, and not so much on the available water, (iii) RECO was mainly affected by the soil temperature, but some evidence for priming effects was also found, (iv) the NEE was mainly influenced by GPP and to a lower extent by RECO. Taken together our results indicate that even within the same ecosystem type exposed to similar climate and land use, site selection may strongly affect the resulting NEE estimates. References: [1] D.D. Baldocchi, "Breathing of the terrestrial biosphere: lessons learned from a global network of carbon dioxide flux measurement systems", Australian Journal of Botany vol.56 (2008) pp. 1-26. [2] A. Hammerle, A. Haslwanter, U. Tappeiner, A. Cernusca, G. Wohlfahrt, "Leaf area controls on energy partitioning of a temperate mountain grassland", Biogeosciences vol.5 (2008) pp. 421 431. [3] G. Wohlfahrt, A. Hammerle, A. Haslwanter, M. Bahn, U. Tappeiner, A. Cernusca, "Seasonal and inter-annual variability of the net ecosystem CO2 exchange of a temperate mountain grassland: effects of weather and management", Journal of Geophysical Research 113 (2008) D08110, doi:10.1029/2007JD009286.

Irschick, Christoph; Hammerle, Albin; Haslwanter, Alois; Wohlfahrt, Georg

2010-05-01

354

Carbon storage potential of a managed mountain grassland - Inverse modelling and uncertainty analysis  

NASA Astrophysics Data System (ADS)

Biogeochemical models are often difficult to calibrate due to their complex structure and/or their large number of parameters. To provide reliable results as well as defensible estimations of uncertainty any data-fusion approach has to account for and quantify all errors consisting of input, model structural and parameter errors. Here we present a study of the carbon cycling of a managed temperate mountain grassland in the Austrian Alps. A ten year data set of measured carbon dioxide fluxes and aboveground biomass are combined with the grassland-adapted DALEC model and a big-leaf photosynthesis model. Parameter estimation of these models is done using a Bayesian inversion scheme. A vital part of this study is the correct residual handling and representation in the inverse parameter estimation scheme in order to provide a robust parameter- and predictive uncertainty estimation. This is achieved by using a generalized likelihood function that, in contrast to the formal approach, does not rely on independent and identically distributed errors according to a normal distribution, with zero mean and constant variance, which does not hold in many ecological applications. After successful calibration these models are used to explore the carbon storage potential of the managed grassland ecosystem under different future management and climate scenarios. To evaluate interactive effects of future climate conditions and management strategies different likely climate scenarios are calculated and prescribed and management strategies (cutting dates and frequency) are optimized in regard to carbon storage and/or yield.

Liener, T.; Hammerle, A.; Williams, M.; Scharnagl, B.; Themeßl, M.; Gobiet, A.; Wohlfahrt, G.

2012-04-01

355

Parallel Computing for Terrestrial Ecosystem Carbon Modeling  

SciTech Connect

Terrestrial ecosystems are a primary component of research on global environmental change. Observational and modeling research on terrestrial ecosystems at the global scale, however, has lagged behind their counterparts for oceanic and atmospheric systems, largely because the unique challenges associated with the tremendous diversity and complexity of terrestrial ecosystems. There are 8 major types of terrestrial ecosystem: tropical rain forest, savannas, deserts, temperate grassland, deciduous forest, coniferous forest, tundra, and chaparral. The carbon cycle is an important mechanism in the coupling of terrestrial ecosystems with climate through biological fluxes of CO{sub 2}. The influence of terrestrial ecosystems on atmospheric CO{sub 2} can be modeled via several means at different timescales. Important processes include plant dynamics, change in land use, as well as ecosystem biogeography. Over the past several decades, many terrestrial ecosystem models (see the 'Model developments' section) have been developed to understand the interactions between terrestrial carbon storage and CO{sub 2} concentration in the atmosphere, as well as the consequences of these interactions. Early TECMs generally adapted simple box-flow exchange models, in which photosynthetic CO{sub 2} uptake and respiratory CO{sub 2} release are simulated in an empirical manner with a small number of vegetation and soil carbon pools. Demands on kinds and amount of information required from global TECMs have grown. Recently, along with the rapid development of parallel computing, spatially explicit TECMs with detailed process based representations of carbon dynamics become attractive, because those models can readily incorporate a variety of additional ecosystem processes (such as dispersal, establishment, growth, mortality etc.) and environmental factors (such as landscape position, pest populations, disturbances, resource manipulations, etc.), and provide information to frame policy options for climate change impact analysis.

Wang, Dali [ORNL; Post, Wilfred M [ORNL; Ricciuto, Daniel M [ORNL; Berry, Michael [University of Tennessee, Knoxville (UTK)

2011-01-01

356

Grassland birds: An overview of threats and recommended management strategies  

USGS Publications Warehouse

Grassland ecosystems are dependent on periodic disturbance for habitat maintenance. Historically, grazing by native herbivores and prairie fires were the agents principally responsible for maintaining grassland areas. However, elimination of native herbivores, wide-spread fire suppression, and conversion for agriculture have greatly altered grasslands in the United States and Canada. Because of these landscape changes, many grassland birds are increasingly dependent on land managers for habitat creation, maintenance, and health. Grazing, prescribed burning, and mowing/haying are the most frequently used, and versatile, grassland management techniques. Grassland birds prefer a wide range of grass heights and densities, with some species preferring short sparse vegetation, and others preferring taller, more dense vegetation. Due to differences in species habitat preferences and regional differences in soils and floristics, the responses of individual grassland species to specific grassland management practices can be variable and often are regionally dependent. As a result, management of grassland areas is best directed toward the creation of a mosaic of grassland habitat types. This habitat mosaic is probably best maintained through some type of rotational management system in which sections of large grassland areas receive management on a regular schedule. Such a rotational system would provide a variety of habitat types in every year, would ensure the availability of suitable habitat for birds at either end of the grassland management spectrum, and also would provide habitat for birds whose preferences lie between these extremes.

Vickery, P.D.; Herkert, J.R.; Knopf, F.L.; Ruth, J.; Keller, C.E.

2000-01-01

357

Spatial and temporal CO2 exchanges measured by Eddy Covariance over a temperate intertidal flat and their relationships to net ecosystem production  

NASA Astrophysics Data System (ADS)

Measurements of carbon dioxide fluxes were performed over a temperate intertidal mudflat in southwestern France using the micrometeorological Eddy Covariance (EC) technique. EC measurements were carried out in two contrasting sites of the Arcachon flat during four periods and in three different seasons (autumn 2007, summer 2008, autumn 2008 and spring 2009). In addition, satellite images of the tidal flat at low tide were used to link the net ecosystem CO2 exchange (NEE) with the occupation of the mudflat by primary producers, particularly by Zostera noltii meadows. CO2 fluxes during the four deployments showed important spatial and temporal variations, with the flat rapidly shifting from sink to source with the tide. Absolute CO2 fluxes showed generally small negative (influx) and positive (efflux) values, with larger values up to -13 ?mol m-2 s-1 for influxes and 19 ?mol m-2 s-1 for effluxes. Low tide during the day was mostly associated with a net uptake of atmospheric CO2. In contrast, during immersion and during low tide at night, CO2 fluxes where positive, negative or close to zero, depending on the season and the site. During the autumn of 2007, at the innermost station with a patchy Zostera noltii bed (cover of 22 ± 14% in the wind direction of measurements), CO2 influx was -1.7 ± 1.7 ?mol m-2 s-1 at low tide during the day, and the efflux was 2.7 ± 3.7 ?mol m-2 s-1 at low tide during the night. A gross primary production (GPP) of 4.4 ± 4.1 ?mol m-2 s-1 during emersion could be attributed to microphytobenthic communities. During the summer and autumn of 2008, at the central station with a dense eelgrass bed (92 ± 10%), CO2 uptakes at low tide during the day were -1.5 ± 1.2 and -0.9 ± 1.7 ?mol m-2 s-1, respectively. Night time effluxes of CO2 were 1.0 ± 0.9 and 0.2 ± 1.1 ?mol m-2 s-1 in summer and autumn, respectively, resulting in a GPP during emersion of 2.5 ± 1.5 and 1.1 ± 2.0 ?mol m-2 s-1, respectively, attributed primarily to the seagrass community. At the same station in April 2009, before Zostera noltii started to grow, the CO2 uptake at low tide during the day was the highest (-2.7 ± 2.0 ?mol m-2 s-1). Influxes of CO2 were also observed during immersion at the central station in spring and early autumn and were apparently related to phytoplankton blooms occurring at the mouth of the flat, followed by the advection of CO2-depleted water with the flooding tide. Although winter data as well as water carbon measurements would be necessary to determine a precise CO2 budget for the flat, our results suggest that tidal flat ecosystems are a modest contributor to the CO2 budget of the coastal ocean.

Polsenaere, P.; Lamaud, E.; Lafon, V.; Bonnefond, J.-M.; Bretel, P.; Delille, B.; Deborde, J.; Loustau, D.; Abril, G.

2012-01-01

358

Spatial and temporal CO2 exchanges measured by Eddy Correlation over a temperate intertidal flat and their relationships to net ecosystem production  

NASA Astrophysics Data System (ADS)

Measurements of carbon dioxide fluxes were performed over a temperate intertidal mudflat in southwestern France using the micrometeorological Eddy Correlation (EC) technique. EC measurements were carried out in two contrasting sites of the Arcachon lagoon during four periods and in three different seasons (autumn 2007, summer 2008, autumn 2008 and spring 2009). In this paper, spatial and temporal variations in vertical CO2 exchanges at the diurnal, tidal and seasonal scales are presented and discussed. In addition, satellite images of the tidal flat at low tide were used to link the net ecosystem exchange (NEE) with the occupation of the mudflat by primary producers, particularly by Zostera noltii meadows. CO2 fluxes during the four deployments showed important spatial and temporal variations, with the lagoon rapidly shifting from a sink to a source of CO2. CO2 fluxes showed generally low negative (influx) and positive (efflux) values and ranged from -13 to 19 ?mol m-2 s-1 at maximum. Low tide and daytime conditions were always characterised by an uptake of atmospheric CO2. In contrast, during immersion and during low tide at night, CO2 fluxes where positive, negative or close to zero, depending on the season and the site. During the autumn of 2007, at the innermost station with a patchy Zostera noltii bed (cover of 22 ± 14 % in the wind direction of measurements), CO2 influx was -1.7 ± 1.7 ?mol m-2 s-1 at low tide during the day, and the efflux was 2.7 ± 3.7 ?mol m-2 s-1 at low tide during the night. A gross primary production (GPP) of 4.4 ?mol m-2 s-1 during emersion could be attributed mostly to microphytobenthic communities. During immersion, the water was a source of CO2 to the atmosphere, suggesting strong heterotrophy or resuspension of microphytobenthic cells. During the summer and autumn of 2008, at the central station with a dense eelgrass bed (92 ± 10 %), CO2 uptakes at low tide during the day were -1.5 ± 1.2 and -0.9 ± 1.7 ?mol m-2 s-1, respectively. Nighttime effluxes of CO2 were 1.0 ± 0.9 and 0.2 ± 1.1 ?mol m-2 s-1 in summer and autumn, respectively, resulting in a GPP during emersion of 2.5 and 1.1 ?mol m-2 s-1, respectively, attributed primarily to the seagrass community. At the same station in April 2009, before Zostera noltii started to grow, the CO2 uptake at low tide during the day was the highest (-2.7 ± 2.0 ?mol m-2 s-1) and could be attributed to microphytobenthos dominance on NEP in this case. NEE versus PAR relationships for data ranked by wind directions were generally negative where and when Zostera noltii was dominant and positive when this community was minor. The latter relationship suggests important processes of photo-acclimatisation by the microphytobenthos, such as migration through the sediment. Influxes of CO2 were also observed during immersion at the central station in spring and early autumn and were apparently related to phytoplankton blooms occurring at the mouth of the lagoon, followed by the advection of CO2-depleted water with the tide. Although winter data would be necessary to determine a precise CO2 budget for the lagoon, our results suggest that tidal flat ecosystems are a modest contributor to the CO2 budget of the coastal ocean.

Polsenaere, P.; Lamaud, E.; Lafon, V.; Bonnefond, J.-M.; Bretel, P.; Delille, B.; Deborde, J.; Loustau, D.; Abril, G.

2011-06-01

359

Biodiversity and stability in grasslands  

Microsoft Academic Search

ONE of the ecological tenets justifying conservation of biodiversity is that diversity begets stability. Impacts of biodiversity on population dynamics and ecosystem functioning have long been debated1-7, however, with many theoretical explorations2-6,8-11 but few field studies12-15. Here we describe a long-term study of grasslands16,17 which shows that primary productivity in more diverse plant communities is more resistant to, and recovers

David Tilman; John A. Downing

1994-01-01

360

Our current understanding of lake ecosystem response to climate change: What have we really learned from the north temperate deep lakes?  

Microsoft Academic Search

Climatic change is recognized as an important factor capable of influencing the structural properties of aquatic ecosystems. Lake ecosystems are particularly sensitive to climate change. Several long time-series studies have shown close coupling between climate, lake thermal properties and individual organism physiology, population abundance, community structure, and food-web structure. Understanding the complex interplay between climate, hydrological variability, and ecosystem structure

Yuko Shimoda; M. Ekram Azim; Gurbir Perhar; Maryam Ramin; Melissa A. Kenney; Somayeh Sadraddini; Alex Gudimov; George B. Arhonditsis

2011-01-01

361

Shrub establishment under experimental global changes in a California grassland  

Microsoft Academic Search

Accelerating invasion of grasslands by woody species is a widespread global phenomenon. The native shrub Baccharis pilularis has recently increased in abundance in some California grasslands, with large local community and ecosystem effects. I investigated potential contributions of (1) future global climate and atmospheric changes and (2) variation in moisture and nutrient availability to increased Baccharis germination and early establishment

Erika S. Zavaleta

2006-01-01

362

SURVEY OF CRP AND OTHER GRASSLANDS IN THE NORTHEASTERN USA  

Technology Transfer Automated Retrieval System (TEKTRAN)

Grassland ecosystems are important wildlife habitat and have the potential to be a significant component of the new biobased economy. Most currently established grasslands in the northeastern USA are on land with marginal crop production potential. Little is known about the plant composition or amou...

363

Predicting Sustained Fire Spread in Tasmanian Native Grasslands  

Microsoft Academic Search

Fire is widely used in conservation management of native grasslands. Burning is often carried out under conditions that are\\u000a marginal for sustained fire spread, and therefore it would be useful to be able to predict fire sustainability. There is currently\\u000a no model allowing such prediction in temperate grasslands. This study aims to identify the environmental variables that determine\\u000a whether fires

Steven Leonard

2009-01-01

364

Seed production, seed bank dynamics, resprouting and long-term response to clearing of the alien invasive Solanum mauritianum in a temperate to subtropical riparian ecosystem  

Microsoft Academic Search

Solanum mauritianum Scopoli (Solanaceae; ‘bugweed’) is a major weed of natural vegetation and plantations in the eastern higher rainfall regions of South Africa. This study assessed the aerial cover and density of S. mauritianum, prior to and after Working for Water (WfW) clearing on the Sabie River, in both higher altitude grassland and lower altitude savanna reaches, using 40, 50×20 m

E. T. F. Witkowski; R. D. Garner

2008-01-01

365

Long-term reactions of plants and macroinvertebrates to extreme floods in floodplain grasslands.  

PubMed

Extreme summertime flood events are expected to become more frequent in European rivers due to climate change. In temperate areas, where winter floods are common, extreme floods occurring in summer, a period of high physiological activity, may seriously impact floodplain ecosystems. Here we report on the effects of the 2002 extreme summer flood on flora and fauna of the riverine grasslands of the Middle Elbe (Germany), comparing pre- and post-flooding data collected by identical methods. Plants, mollusks, and carabid beetles differed considerably in their response in terms of abundance and diversity. Plants and mollusks, displaying morphological and behavioral adaptations to flooding, showed higher survival rates than the carabid beetles, the adaptation strategies of which were mainly linked to life history. Our results illustrate the complexity of responses of floodplain organisms to extreme flood events. They demonstrate that the efficiency of resistance and resilience strategies is widely dependent on the mode of adaptation. PMID:18831159

Ilg, Christiane; Dziock, Frank; Foeckler, Francis; Follner, Klaus; Gerisch, Michael; Glaeser, Judith; Rink, Anke; Schanowski, Arno; Scholz, Mathias; Deichner, Oskar; Henle, Klaus

2008-09-01

366

Invasion by Aegilops triuncialis (Barb Goatgrass) Slows Carbon and Nutrient Cycling in a Serpentine Grassland  

Microsoft Academic Search

Invasive plant species alter plant community composition and ecosystem function. In the United States, California native grasslands\\u000a have been displaced almost completely by invasive annual grasses, with serpentine grasslands being one of the few remaining\\u000a refugia for California grasslands. This study examined how the invasive annual grass, Aegilops triuncialis, has altered decomposition processes in a serpentine annual grassland. Our objectives

Rebecca E. Drenovsky; Katharine M. Batten

2007-01-01

367

Tempered glass  

SciTech Connect

This document describes a demonstration for making tempered glass using minimal equipment. The demonstration is intended for a typical student of materials science, at the high school level or above. (JL)

Bunnell, L.R.

1991-11-01

368

Spatial and temporal CO2 exchanges measured by Eddy Correlation over a temperate intertidal flat and their relationships to net ecosystem production  

Microsoft Academic Search

Measurements of carbon dioxide fluxes were performed over a temperate intertidal mudflat in southwestern France using the micrometeorological Eddy Correlation (EC) technique. EC measurements were carried out in two contrasting sites of the Arcachon lagoon during four periods and in three different seasons (autumn 2007, summer 2008, autumn 2008 and spring 2009). In this paper, spatial and temporal variations in

P. Polsenaere; E. Lamaud; V. Lafon; J.-M. Bonnefond; P. Bretel; B. Delille; J. Deborde; D. Loustau; G. Abril

2011-01-01

369

Coupling Imaging Spectroscopy and Ecosystem Process Modelling - The Importance of Spatially Distributed Foliar Biochemical Concentration Estimates for Modelling NPP of Grassland Habitats  

Microsoft Academic Search

Information on canopy chemical concentrations is of great importance for the study of nutrient cycling, productivity and for input to ecosystem process models. In particular, foliar Carbon to Nitrogen ratio (C:N) drives terrestrial biogeochemical processes such as decomposition and mineralization, and thus strongly influences soil organic matter concentrations and turnover rates. This study evaluated the effects of using spatial estimates

Achilleas Psomas; Niklaus E. Zimmermann; Mathias Kneubühler; Silvia Huber; Klaus I. Itten

2008-01-01

370

Scaling-up knowledge of growing-season net ecosystem exchange for long-term assessment of North Dakota grasslands under the Conservation Reserve Program  

Technology Transfer Automated Retrieval System (TEKTRAN)

Scaling-up knowledge of land-atmosphere net ecosystem exchange (NEE) from a single experimental site to numerous perennial grass fields in the Northern Great Plains (NGP) requires appropriate scaling protocols. We addressed this problem using synoptic data available from the Landsat sensor for ten ...

371

A geomorphic perspective on terrain-modulated organization of vegetation productivity: Analysis in two semiarid grassland ecosystems in Southwestern United States  

Technology Transfer Automated Retrieval System (TEKTRAN)

Spatial patterns of ecosystem productivity arise from the terrain-modulated wetting and drying of the landscape. Using a daily relative greenness (rG) index we explore the relations between spatial variability of plant productivity and landscape morphology, and how these relations change over time...

372

Estimation of nitrous oxide emissions from US grasslands  

SciTech Connect

Nitrous oxide (N{sub 2}O) emissions from temperate grasslands are poorly quantified and may be an important part of the atmospheric N{sub 2}O budget. In this study N{sub 2}O emissions were simulated for 1,052 grassland sites in the US using the NGAS model of Parton and others (1996) coupled with an organic matter decomposition model. N{sub 2}O flux was calculated for each site using soil and land use data obtained from the National Resource Inventory (NRI) database and weather data obtained from NASA. The estimates were regionalized based upon temperature and moisture isotherms. Annual N{sub 2}O emissions for each region were based on the grassland area of each region and the mean estimated annual N{sub 2}O flux from NRI grassland sites in the region. The regional fluxes ranged from 0.18 to 1.02 kg N{sub 2}O N/ha/yr with the mean flux for all regions being 0.29 kg N{sub 2}O N/ha/yr. Even though fluxes from the western regions were relatively low, these regions made the largest contribution to total emissions due to their large grassland area. Total US grassland N{sub 2}O emissions were estimated to be about 67 Gg N{sub 2}O N/yr. Emissions from the Great Plains states, which contain the largest expanse of natural grassland in the US, were estimated to average 0.24 kg N{sub 2}O N/ha/yr. Using the annual flux estimate for the temperate Great Plains, the authors estimate that temperate grasslands worldwide may potentially produce 0.27 Tg N{sub 2}O N/yr. Even though the estimate for global temperate grassland N{sub 2}O emissions is less than published estimates for other major temperate grasslands are a significant part of both United States and global atmospheric N{sub 2}O budgets. This study demonstrates the utility of models for regional N{sub 2}O budgets. This study demonstrates the utility of models for regional N{sub 2}O flux estimation although additional data from carefully designed field studies is needed to further validate model results.

Mummey, D.L.; Smith, J.L.; Bluhm, G.

2000-02-01

373

Woody Plant Invasion in Relictual Grasslands  

Microsoft Academic Search

Invasion by alien plants is one of the greatest and most widely distributed causes of man-made changes in ecosystems. One of its most conspicuous variants is the invasion of natural grasslands by exotic trees, which not only means the addition of new taxa to the native biota, but also the introduction of completely new life-forms. In Argentina, the Pampean plain

S. M. Zalba; C. B. Villamil

2002-01-01

374

The greenhouse gas balance of European grasslands  

NASA Astrophysics Data System (ADS)

The long-term carbon balance (NBP) of grasslands is estimated by combining scarce multi-year eddy-covariance observations at ecosystem observation sites where information on carbon inputs and harvesting removals is available. Following accounting for carbon leached to rivers, we estimated grasslands to be net carbon sinks of 74±10 g C m-2 yr-1. Uncertainties arise from the small number of sites and the short measurement period. Only 11 sites, out of a total of 20 grassland sites in Europe where eddy covariance systems are installed, were set-up for estimating NBP. These 11 selected sites are representative of intensive management practice and we lack information on disturbance history, such as plowing. This suggests that the grassland NBP estimate is likely biased towards overestimating the sink, compared to the European average. Direct measurements of Net Primary Productivity (NPP) are not possible in grasslands given permanent biomass removal by grazing and mowing, uncertainties in rhizodeposition and production of volatile organic carbon compounds lost to the atmosphere. Therefore, the grassland process-based ecosystem model PASIM was used to estimate the spatial-temporal distribution of NPP, providing a European average value of 750±150 g C across extensively grazed, intensively grazed pastures, and forage production systems. In Europe the NPP of grasslands seems higher than that of croplands and forests. The carbon sequestration efficiency of grasslands, defined as the ratio of NBP to NPP, amounts to 0.09±0.10. Therefore, per unit of carbon input, grasslands sequester 3-4 times more carbon in the soil than forests do, making them a good candidate for managing onsite carbon sinks. When using the 100 yr greenhouse warming potential for CH4 and N2O, their emissions due to management of grasslands together offset roughly 70-80% of the carbon sink. Uncertainties on the European grassland greenhouse gas balance, including CO2, CH4 and N2O fluxes are likely to be reduced in the near future, with data being collected from more sites, and improved up-scaling methods.

Ciais, P.; Soussana, J. F.; Vuichard, N.; Luyssaert, S.; Don, A.; Janssens, I. A.; Piao, S. L.; Dechow, R.; Lathière, J.; Maignan, F.; Wattenbach, M.; Smith, P.; Ammann, C.; Freibauer, A.; Schulze, E. D.; Carboeurope Synthesis Team

2010-08-01

375

Carbon Sequestration Rates and the Energy Balance of Turf in the Denver Urban Ecosystem and in an Adjacent Native Grassland Under Contrasting Management Practices  

NASA Astrophysics Data System (ADS)

Although urban areas occupy just a few percent of US land area, they are expanding rapidly and are expected to maintain this trend for the foreseeable future. Within these domains is the largest irrigated crop in the US - lawns. Utilizing eddy covariance instruments, surface chambers, and destructive leaf sampling, well watered, fertilized lawns in metropolitan Denver were found to sequester substantially more carbon (1.3 T C ha-1 yr-1) than adjacent native grassland (0.6 T C ha-1 yr-1) over a growing season. Due to the semi-arid environment, contrasts in lawn management (irrigation and fertilization) led to wide variation in carbon sequestration rates, evapotranspiration, and the sensible and latent heat partitioning of the energy balance. Measured leaf area was correlated with remotely sensed vegetation indices obtained from aircraft and satellite hyperspectral instruments to quantify spatial variability in leaf area over contrasting land surfaces and lawn management practices. These relations applied to continuing acquisition of remotely sensed data provide us with a means to assess potential variability in carbon sequestration in space and time domains.

Anderson, D. E.; Powell, K.; Szanko, G.; Mladinich, C.; Curry, S.; Griebel, A.

2010-12-01

376

Productivity, Respiration, CO2 Sink Potential, and Light-Response Parameters of World Grasslands Derived From Flux-Tower Data Partitioning  

NASA Astrophysics Data System (ADS)

Net CO2 flux (Fc) data from 52 grassland flux tower sites in North America, Europe, and Asia representing 101 years of measurements were partitioned into gross primary productivity (Pg) and ecosystem respiration (Re) components using light-temperature-response functions method (Bas. Appl. Ecol. 2003, 4:167-183). This sample of sites encompasses a wide climatic range (mean annual temperatures 0.5 to 20° C and precipitation 190 to 1500 mm/yr) and includes unmanaged and extensively or intensively managed grasslands. Highest values of daily gross primary productivity (Pg,max = 64 g CO2/m2/d) were found in intensively managed grasslands of W. Europe with Atlantic climate, while lowest Pg,max (<10 g CO2/m2/d) were recorded in mixed prairies and shortgragss steppes of the Great Plains, shrubsteppes of the Intermountain West, and dry steppes of Mongolia. Maximum values of gross primary production (GPP) were achieved in intensively managed European grasslands with Atlantic climate (GPP=6900 g CO2/m2/yr), and lowest GPP values (<500 g CO2/m2/yr) were estimated for grazed mixed prairies under drought. Highest annual ecosystem respiration (RE) were recorded for warm-temperate and low montane W.European grasslands (RE > 5000 g CO2/m2/yr), and lowest RE were characteristic for shrubsteppes and grazed dry steppes (RE < 1000 g CO2/m2/yr). In 62 out of 101 site-years, the grasslands were net CO2 sinks, with average net annual CO2 exchange NEE = 250, maximum NEE = 2400 (uptake), and minimum NEE = -1350 g CO2/m2/yr (release). Maximum mean weekly values of the apparent quantum yield (? >70 mmol CO2/mol photons) were recorded in intensively managed Atlantic grasslands, the lowest weekly quantum efficiencies were observed in grazed mixed prairies of N.America and dry steppes of Central Asia (? <10 mmol/mol). The maximum values of the gross photosynthesis parameter (mean weekly Amax>2 mg CO2/m2/s) were estimated for intensively managed C3 grasslands of W.Europe and for unmanaged tallgrass (C3/C4) prairies. Maximum daytime respiration (rDay) were determined in intensively managed warm-temperate grasslands of W.Europe and E.North America (mean weekly rDay > 0.4 mg CO2/m2/s), while lowest rDay values are characteristic for semiarid mixed prairies and shrubsteppes (rDay<0.1 mg CO2/m2/s). Gross ecological light-use efficiency (?=daily gross photosynthesis/daily income of photosynthetically active radiation) achieves maximum in intensively managed European grasslands with Atlantic climate (mean weekly ? >35 mmol/mol), and has lowest values in semiarid short- and mixed prairies and shrubsteppes of N. America and dry steppes of Central Asia (mean weekly ? <5 mmol/mol). Our data show significant allometric relationships between light-response parameters: ?(Amax) and rDay(Amax), with allometry exponent <1 in both cases. Both the CO2 exchange characteristics (Pg,max, Re,max, GPP, RE, NEE), and the light-response parameters (?, Amax, rDay, ?) demonstrate significant relationships to climate (growing season length, sum of temperatures above 5° C, hydrologic year precipitation). These relationships become even stronger after stratification with respect to management (e.g., unmanaged vs. managed grasslands).

Gilmanov, T. G.; Contributors, W. D.

2007-12-01

377

From fronds to fish: the use of indicators for ecological monitoring in marine benthic ecosystems, with case studies from temperate Western Australia  

Microsoft Academic Search

Ecological indicators are used for monitoring in marine habitats the world over. With the advent of Ecosystem Based Fisheries\\u000a Management (EBFM), the need for cost effective indicators of environmental impacts and ecosystem condition has intensified.\\u000a Here, we review the development, utilisation and analysis of indicators for monitoring in marine benthic habitats, and outline\\u000a important advances made in recent years. We

Dan A. Smale; Timothy J. Langlois; Gary A. Kendrick; Jessica J. Meeuwig; Euan S. Harvey

378

Quantifying Grassland-to-Woodland Transitions and the Implications for Carbon and Nitrogen Dynamics in the Southwest United States.  

National Technical Information Service (NTIS)

Replacement of grasslands and savannas by shrublands and woodlands has been widely reported in tropical, temperate and high-latitude rangelands worldwide (Archer 1994). These changes in vegetation structure may reflect historical shifts in climate and lan...

C. A. Wessman S. R. Archer G. P. Asner C. A. Bateson

2004-01-01

379

Taming Tempers  

MedlinePLUS

... You're having a conversation instead of an argument. Praise your child for talking about it instead of slamming the door, for instance. See that kids get a lot of physical activity. Active play can really help kids who have big tempers. Encourage outside play and sports your ...

380

Contribution of root to soil respiration and carbon balance in disturbed and undisturbed grassland communities, northeast China.  

PubMed

Changes in the composition of plant species induced by grassland degradation may alter soil respiration rates and decrease carbon sequestration; however, few studies in this area have been conducted. We used net primary productivity (NPP),microbial biomass carbon (MBC), and soil organic carbon (SOC)to examine the changes in soil respiration and carbon balance in two Chinese temperate grassland communities dominated by Leymus chinensis (undisturbed community; Community 1)and Puccinellia tenuiflora (degraded community; Community 2), respectively. Soil respiration varied from 2.5 to 11.9 g CO 2 m ;-2 d;-1 and from 1.5 to 9.3 g CO2 m;-2 d;-1, and the contribution of root respiration to total soil respiration from 38% to 76% and from 25% to 72% in Communities 1 and 2,respectively. During the growing season (May-September), soil respiration, shoot biomass, live root biomass, MBC and SOC in Community 2 decreased by 28%,39%,45%,55% and 29%,respectively, compared to those in Community 1.The considerably lower net ecosystem productivity in Community 2 than in Community 1 (104.56 vs. 224.73 g C m;-2 yr;-1) suggests that the degradation has significantly decreased carbon sequestration of the ecosystems. PMID:17435328

Wang, Wei; Guo, Jixun; Oikawa, Takehisa

2007-03-01

381

Sensitivity of temperate desert steppe carbon exchange to seasonal droughts and precipitation variations in Inner Mongolia, China.  

PubMed

Arid grassland ecosystems have significant interannual variation in carbon exchange; however, it is unclear how environmental factors influence carbon exchange in different hydrological years. In this study, the eddy covariance technique was used to investigate the seasonal and interannual variability of CO? flux over a temperate desert steppe in Inner Mongolia, China from 2008 to 2010. The amounts and times of precipitation varied significantly throughout the study period. The precipitation in 2009 (186.4 mm) was close to the long-term average (183.9±47.6 mm), while the precipitation in 2008 (136.3 mm) and 2010 (141.3 mm) was approximately a quarter below the long-term average. The temperate desert steppe showed carbon neutrality for atmospheric CO? throughout the study period, with a net ecosystem carbon dioxide exchange (NEE) of -7.2, -22.9, and 26.0 g C m?² yr?¹ in 2008, 2009, and 2010, not significantly different from zero. The ecosystem gained more carbon in 2009 compared to other two relatively dry years, while there was significant difference in carbon uptake between 2008 and 2010, although both years recorded similar annual precipitation. The results suggest that summer precipitation is a key factor determining annual NEE. The apparent quantum yield and saturation value of NEE (NEE(sat)) and the temperature sensitivity coefficient of ecosystem respiration (R(eco)) exhibited significant variations. The values of NEE(sat) were -2.6, -2.9, and -1.4 µmol CO? m?² s?¹ in 2008, 2009, and 2010, respectively. Drought suppressed both the gross primary production (GPP) and R(eco), and the drought sensitivity of GPP was greater than that of R(eco). The soil water content sensitivity of GPP was high during the dry year of 2008 with limited soil moisture availability. Our results suggest the carbon balance of this temperate desert steppe was not only sensitive to total annual precipitation, but also to its seasonal distribution. PMID:23393576

Yang, Fulin; Zhou, Guangsheng

2013-02-05

382

Measurement of soil nitrogen oxide emissions at three North American ecosystems  

SciTech Connect

Results from measurements of emission of nitrogen oxides from soils at three North American ecosystems are presented. These measurements were conducted during the summer and fall of 1988 at (1) a grassland site near Nunn, Colorado, (2) a coastal marine environment at North Inlet, South Carolina and (3) a deciduous forest near Oak Ridge, Tennessee. Emission of NO was highest from the grassland soil (mean: 10.0 ng N m{sup {minus}2}s{sup {minus}1}), intermediate at the forest area (mean: 0.28 ng N m{sup {minus}2}s{sup {minus}1}) and lowest at the coastal site (mean: 0.034 ng N m{sup {minus}2}s{sup {minus}1}). A comparison of the results from the present study with previous measurements indicates that NO{sub x} (NO + NO{sub 2}) emission from grasslands and temperate forests are similar within each ecosystem independent of location. This suggests that simple approaches may be used to estimate soil emissions over wide areas.

Williams, E.J.; Fehsenfeld, F.C. (National Oceanic and Atmospheric Administration, Boulder, CO (USA) Univ. of Colorado, Boulder (USA))

1991-01-20

383

Interannual Variation in Root Production in Grasslands Affected by Artificially Modified Amount of Rainfall  

PubMed Central

The effect of different amounts of rainfall on the below-ground plant biomass was studied in three grassland ecosystems. Responses of the lowland (dry Festuca grassland), highland (wet Cirsium grassland), and mountain (Nardus grassland) grasslands were studied during five years (2006–2010). A field experiment based on rainout shelters and gravity irrigation simulated three climate scenarios: rainfall reduced by 50% (dry), rainfall increased by 50% (wet), and the natural rainfall of the current growing season (ambient). The interannual variation in root increment and total below-ground biomass reflected the experimentally manipulated amount of precipitation and also the amount of current rainfall of individual years. The effect of year on these below-ground parameters was found significant in all studied grasslands. In comparison with dry Festuca grassland, better adapted to drought, submontane wet Cirsium grassland was more sensitive to the different water inputs forming rather lower amount of below-ground plant matter at reduced precipitation.

Fiala, Karel; Tuma, Ivan; Holub, Petr

2012-01-01

384

Long-term resistance to simulated climate change in an infertile grassland.  

PubMed

Climate shifts over this century are widely expected to alter the structure and functioning of temperate plant communities. However, long-term climate experiments in natural vegetation are rare and largely confined to systems with the capacity for rapid compositional change. In unproductive, grazed grassland at Buxton in northern England (U.K.), one of the longest running experimental manipulations of temperature and rainfall reveals vegetation highly resistant to climate shifts maintained over 13 yr. Here we document this resistance in the form of: (i) constancy in the relative abundance of growth forms and maintained dominance by long-lived, slow-growing grasses, sedges, and small forbs; (ii) immediate but minor shifts in the abundance of several species that have remained stable over the course of the experiment; (iii) no change in productivity in response to climate treatments with the exception of reduction from chronic summer drought; and (iv) only minor species losses in response to drought and winter heating. Overall, compositional changes induced by 13-yr exposure to climate regime change were less than short-term fluctuations in species abundances driven by interannual climate fluctuations. The lack of progressive compositional change, coupled with the long-term historical persistence of unproductive grasslands in northern England, suggests the community at Buxton possesses a stabilizing capacity that leads to long-term persistence of dominant species. Unproductive ecosystems provide a refuge for many threatened plants and animals and perform a diversity of ecosystem services. Our results support the view that changing land use and overexploitation rather than climate change per se constitute the primary threats to these fragile ecosystems. PMID:18606995

Grim