Symbiotic N2 fixation activity in relation to C economy of Pisum sativum L. as a function of plant phenology.

PubMed

Voisin, A S; Salon, C; Jeudy, C; Warembourg, F R

2003-12-01

The relationships between symbiotic nitrogen fixation (SNF) activity and C fluxes were investigated in pea plants (Pisum sativum L. cv. Baccara) using simultaneous 13C and 15N labelling. Analysis of the dynamics of labelled CO2 efflux from the nodulated roots allowed the different components associated with SNF activity to be calculated, together with root and nodule synthetic and maintenance processes. The carbon costs for the synthesis of roots and nodules were similar and decreased with time. Carbon lost by turnover, associated with maintenance processes, decreased with time for nodules while it increased in the roots. Nodule turnover remained higher than root turnover until flowering. The effect of the N source on SNF was investigated using plants supplied with nitrate or plants only fixing N2. SNF per unit nodule biomass (nodule specific activity) was linearly related to the amount of carbon allocated to the nodulated roots regardless of the N source, with regression slopes decreasing across the growth cycle. These regression slopes permitted potential values of SNF specific activity to be defined. SNF activity decreased as the plants aged, presumably because of the combined effects of both increasing C costs of SNF (from 4.0 to 6.7 g C g-1 N) and the limitation of C supply to the nodules. SNF activity competed for C against synthesis and maintenance processes within the nodulated roots. Synthesis was the main limiting factor of SNF, but its importance decreased as the plant aged. At seed-filling, SNF was probably more limited by nodule age than by C supply to the nodulated roots.

High potential of nitrogen fixation in pristine, ombrotrophic bogs in Southern Patagonia

NASA Astrophysics Data System (ADS)

Knorr, Klaus-Holger; Horn, Marcus A.; Bahamonde Aguilar, Nelson A.; Borken, Werner

2015-04-01

Nitrogen (N) input in pristine peatlands occurs via natural input of inorganic N through atmospheric deposition or biological dinitrogen (N2) fixation. However, N2 fixation is to date mostly attributed to bacteria and algae associated to Sphagnum and its contribution to plant productivity and peat buildup has been often underestimated in previous studies. Based on net N storage, exceptionally low N deposition, and high abundance of vascular plants at pristine peatlands in Southern Patagonia, we hypothesized that there must be a high potential of non-symbiotic N2 fixation not limited to the occurrence of Sphagnum. To this end, we chose two ombrotrophic bogs with spots that are dominated either by Sphagnum or by vascular, cushion-forming plants and sampled peat from different depths for incubation with 15N2 to determine N2 fixation potentials. Moreover, we analyzed 15N2 fixation by a nodule-forming, endemic conifer inhabiting the peatlands. Results from 15N2 uptake were compared to the conventional approach to study N2 fixation by the acetylene reduction assay (ARA). Using 15N2 as a tracer, high non-symbiotic N2 fixation rates of 0.3-1.4 μmol N g-1 d-1 were found down to 50 cm under micro-oxic conditions (2 vol.%) in samples from both plots either covered by Sphagnum magellanicum or by vascular cushion plants. Peat N concentrations suggested a higher potential of non-symbiotic N2 fixation under cushion plants, likely because of the availability of easily decomposable organic compounds as substrates and oxic conditions in the rhizosphere. In the Sphagnum plots, high N2 fixation below 10 cm depth would rather reflect a potential fixation that may switch on during periods of low water levels when oxygen penetrates deeper into the peat. 15N natural abundance of live Sphagnum from 0-10 cm pointed to N uptake solely from atmospheric deposition and non-symbiotic N2 fixation. 15N signatures of peat from the cushion plant plots indicated additional N supply from N

Nitrogen and Phosphorus Addition Affects Biological N2 Fixation and Sphagnum Moss in an Ombrotrophic Bog

NASA Astrophysics Data System (ADS)

Zivkovic, T.; Ardichvili, A.; Moore, T. R.

2016-12-01

Most of the 18 Pg nitrogen (N) accumulated in northern nutrient-poor and Sphagnum-dominated peatlands (bogs and fens) can be attributed to N2 fixation by diazotrophs either associated with the live Sphagnum or non-symbiotically in the deeper peat. Where atmospheric N deposition is low (< 0.2 g m-2 y-1), ombrotrophic bogs rely on N2 fixation as the primary source of N that sustains primary production. The industrial revolution and anthropogenic impacts in the last 200 years have resulted in larger atmospheric N deposition as ammonium (NH4) and nitrate (NO3). One effect of increased N deposition in Sphagnum is a switch from N to phosphorus (P) limitation suggested by the increase in tissue N:P>16. It is unclear how Sphagnum hosted diazotrophic activity may be affected by N deposition and thus changes in N:P ratio. We investigated the effects of long-term addition of different sources of nitrogen (0, 1.6, 3.2 and 6.4 g N m-2 y-1 as NH4Cl and NaNO3), and phosphorus (5 g P m-2 y-1 as KH2PO4) on Sphagnum nutrient status (N, P and N:P), net primary productivity (NPP) and Sphagnum-associated N2 fixation at Mer Bleue, a temperate ombrotrophic bog. Our study shows that N concentration in Sphagnum tissue increased with larger rates of N addition, with a stronger effect on Sphagnum from NH4 than NO3. The addition of P created a 3.5 fold increase in Sphagnum P content compared to controls. Sphagnum NPP decreased linearly with the rise in N:P ratio, while linear growth declined exponentially with increase in Sphagnum N content. N2 fixation significantly decreased in response to even the smallest addition of both N species. In contrast, the addition of P increased N2 fixation by up to 100 times compared to N treatments and up to 5-30 times compared to controls. The change in N2 fixation was best modeled by the N:P ratio, across all experimental treatments. Although elevated N deposition substantially decreases N2 fixation, the N:P ratio in Sphagnum may be a good predictor, likely

Genotypic Variation for N2-FIXATION in Voandzou (vigna Subterranea) Under P Deficiency and P Sufficiency

NASA Astrophysics Data System (ADS)

Andry, A.; Mahamadou, M.; Lilia, R.; Laurie, A.; Hélène, V.; Dominique, M.; Christian, M.; Jean-Jacques, D.

2011-12-01

Genetic variation associated with N2 fixation exists in numerous legume species (Graham, 2004). High symbiotic N2 fixation under P deficiency is related closely to nodulation which was used in legume selection for N2 fixation (Herridge and Rose, 2000). Until now, study of genetic potential of neglected crops like Vigna subterranea (bambara groundnut or voandzou) is often limited while its agronomic properties is interesting for the farmers of Africa. In order to assess the genotypic variation of voandzou for tolerance to phosphorus deficiency, a physiological approach of cultivar selection was performed with 54 cultivars from Madagascar, Niger and Mali in hydroponic culture under P deficiency and P sufficiency and inoculated with the reference strain of Bradyrhizobium sp. Vigna CB756. The results of nodulation and plant biomass, which are closely related, showed a large dispersion between cultivars (0.05-0.43 g nodule dry weight per plant and 0.50-5.51 g shoot dry weight per plant). The cultivars which presented the maximum growth during the experiment presented a high efficiency in use of the rhizobial symbiosis calculated as the slope of plant biomass regression as a function of nodulation. A large increase in nodulated-root O2 consumption under P deficiency was observed for the two most tolerant cultivars. The microscopic analysis with in situ RT-PCR of the nodule sections showed an increase of a phytase gene expression with tolerance of cultivars to P deficiency. From two most contrasting cultivars, an isotopic exchange method 32P was carried out on rhizosphere soil in rhizotron culture in order to assess the direct effect induced by the roots in terms of phosphorus mobilization. The rhizospheric effect was observed under P deficiency marked by a strong re-supplying capacity of soil solution in the diffusive phosphate ion between solid phase and soil solution leading to great phosphorus nutrition. These results highlight the genotypic variability among voandzou

Medicago truncatula copper transporter 1 (MtCOPT1) delivers copper for symbiotic nitrogen fixation.

PubMed

Senovilla, Marta; Castro-Rodríguez, Rosario; Abreu, Isidro; Escudero, Viviana; Kryvoruchko, Igor; Udvardi, Michael K; Imperial, Juan; González-Guerrero, Manuel

2018-04-01

Copper is an essential nutrient for symbiotic nitrogen fixation. This element is delivered by the host plant to the nodule, where membrane copper (Cu) transporter would introduce it into the cell to synthesize cupro-proteins. COPT family members in the model legume Medicago truncatula were identified and their expression determined. Yeast complementation assays, confocal microscopy and phenotypical characterization of a Tnt1 insertional mutant line were carried out in the nodule-specific M. truncatula COPT family member. Medicago truncatula genome encodes eight COPT transporters. MtCOPT1 (Medtr4g019870) is the only nodule-specific COPT gene. It is located in the plasma membrane of the differentiation, interzone and early fixation zones. Loss of MtCOPT1 function results in a Cu-mitigated reduction of biomass production when the plant obtains its nitrogen exclusively from symbiotic nitrogen fixation. Mutation of MtCOPT1 results in diminished nitrogenase activity in nodules, likely an indirect effect from the loss of a Cu-dependent function, such as cytochrome oxidase activity in copt1-1 bacteroids. These data are consistent with a model in which MtCOPT1 transports Cu from the apoplast into nodule cells to provide Cu for essential metabolic processes associated with symbiotic nitrogen fixation. © 2018 The Authors. New Phytologist © 2018 New Phytologist Trust.

Genome-wide association analysis of symbiotic nitrogen fixation in common bean

USDA-ARS?s Scientific Manuscript database

A genome-wide association study (GWAS) was conducted to explore the genetic basis of variation for symbiotic nitrogen fixation (SNF) and related traits in the Andean diversity panel (ADP) comprised of 259 common bean (Phaseolus vulgaris) genotypes. The ADP was evaluated for SNF and related traits in...

Nitrogen fixation in boreal peatlands: the effects of increased N deposition on N2-fixation

NASA Astrophysics Data System (ADS)

Popma, J. M.; Wieder, R.; Lamers, L.; Vile, M. A.

2013-12-01

Boreal peatlands are of great importance to global carbon and nitrogen cycling. While covering only 3-4 % of the terrestrial surface, they account for 25-30 % of the world's soil C and 9-15 % of the world's soil N. In Western Canada atmospheric dry deposition rates are extremely low: approximately 1 kg N ha-1 yr-1. Though these systems have been functioning as net sinks over the past 11,000 years, natural and anthropogenic disturbances might compromise the historical balance of C and N. Biological N2-fixation has recently been shown to represent a very significant input of N into these systems, contributing to 62% of total N in Western Canada. Interactions between N deposition and biological N2-fixation are as yet, unknown, but the impact of elevated deposition of N-compounds from increased industrial expansion of oil sands mining to peatlands, is concerning. Given that nitrogenase, the enzyme responsible for catalyzing N2-fixation, is energetically costly when active, enhanced inputs of atmospheric N deposition could be a major determinant for enzyme activity and rates of biological N input to these bogs. Understanding interactions between N deposition and N2 fixation in boreal peatlands can aid in predicting the consequences of increased N deposition and setting critical loads. We conducted a field-fertilization experiment in a poor fen in Alberta, Canada, to determine the effects of enhanced N deposition on a dominant fen species Sphagnum angustifolium. The experiment consisted of seven N treatments: Control, 0, 5, 10, 15, 20 and 25 kg N ha-1 y1, n=3. N2-fixation was measured during summer 2012 and 2013 using the acetylene reduction assay (ARA). ARA rates were converted to rates of N2-fixation by calibrating ARA with paired 15N2-incubations. In both 2012 and 2013, with increasing N deposition from 0 kg N ha-1 yr-1 to 25 kg N ha-1 yr-1, rates of N2 fixation decreased, with highest rates in the 0 kg N ha-1 yr-1 treatment mosses (54.2 × 1.40; 48.58 × 7.12 kg N ha

Nutrient feedbacks to soil heterotrophic nitrogen fixation in forests

USGS Publications Warehouse

Perakis, Steven; Pett-Ridge, Julie C.; Catricala, Christina E.

2017-01-01

Multiple nutrient cycles regulate biological nitrogen (N) fixation in forests, yet long-term feedbacks between N-fixation and coupled element cycles remain largely unexplored. We examined soil nutrients and heterotrophic N-fixation across a gradient of 24 temperate conifer forests shaped by legacies of symbiotic N-fixing trees. We observed positive relationships among mineral soil pools of N, carbon (C), organic molybdenum (Mo), and organic phosphorus (P) across sites, evidence that legacies of symbiotic N-fixing trees can increase the abundance of multiple elements important to heterotrophic N-fixation. Soil N accumulation lowered rates of heterotrophic N-fixation in organic horizons due to both N inhibition of nitrogenase enzymes and declines in soil organic matter quality. Experimental fertilization of organic horizon soil revealed widespread Mo limitation of heterotrophic N-fixation, especially at sites where soil Mo was scarce relative to C. Fertilization also revealed widespread absence of P limitation, consistent with high soil P:Mo ratios. Responses of heterotrophic N-fixation to added Mo (positive) and N (negative) were correlated across sites, evidence that multiple nutrient controls of heterotrophic N-fixation were more common than single-nutrient effects. We propose a conceptual model where symbiotic N-fixation promotes coupled N, C, P, and Mo accumulation in soil, leading to positive feedback that relaxes nutrient limitation of overall N-fixation, though heterotrophic N-fixation is primarily suppressed by strong negative feedback from long-term soil N accumulation.

The Sulfate Transporter SST1 Is Crucial for Symbiotic Nitrogen Fixation in Lotus japonicus Root Nodules

PubMed Central

Krusell, Lene; Krause, Katja; Ott, Thomas; Desbrosses, Guilhem; Krämer, Ute; Sato, Shusei; Nakamura, Yasukazu; Tabata, Satoshi; James, Euan K.; Sandal, Niels; Stougaard, Jens; Kawaguchi, Masayoshi; Miyamoto, Ai; Suganuma, Norio; Udvardi, Michael K.

2005-01-01

Symbiotic nitrogen fixation (SNF) by intracellular rhizobia within legume root nodules requires the exchange of nutrients between host plant cells and their resident bacteria. Little is known at the molecular level about plant transporters that mediate such exchanges. Several mutants of the model legume Lotus japonicus have been identified that develop nodules with metabolic defects that cannot fix nitrogen efficiently and exhibit retarded growth under symbiotic conditions. Map-based cloning of defective genes in two such mutants, sst1-1 and sst1-2 (for symbiotic sulfate transporter), revealed two alleles of the same gene. The gene is expressed in a nodule-specific manner and encodes a protein homologous with eukaryotic sulfate transporters. Full-length cDNA of the gene complemented a yeast mutant defective in sulfate transport. Hence, the gene was named Sst1. The sst1-1 and sst1-2 mutants exhibited normal growth and development under nonsymbiotic growth conditions, a result consistent with the nodule-specific expression of Sst1. Data from a previous proteomic study indicate that SST1 is located on the symbiosome membrane in Lotus nodules. Together, these results suggest that SST1 transports sulfate from the plant cell cytoplasm to the intracellular rhizobia, where the nutrient is essential for protein and cofactor synthesis, including nitrogenase biosynthesis. This work shows the importance of plant sulfate transport in SNF and the specialization of a eukaryotic transporter gene for this purpose. PMID:15805486

Root exudates drive interspecific facilitation by enhancing nodulation and N2 fixation

PubMed Central

Li, Bai; Li, Yu-Ying; Wu, Hua-Mao; Zhang, Fang-Fang; Li, Chun-Jie; Li, Xue-Xian; Lambers, Hans; Li, Long

2016-01-01

Plant diversity in experimental systems often enhances ecosystem productivity, but the mechanisms causing this overyielding are only partly understood. Intercropping faba beans (Vicia faba L.) and maize (Zea mays L.) result in overyielding and also, enhanced nodulation by faba beans. By using permeable and impermeable root barriers in a 2-y field experiment, we show that root–root interactions between faba bean and maize significantly increase both nodulation and symbiotic N2 fixation in intercropped faba bean. Furthermore, root exudates from maize promote faba bean nodulation, whereas root exudates from wheat and barley do not. Thus, a decline of soil nitrate concentrations caused by intercropped cereals is not the sole mechanism for maize promoting faba bean nodulation. Intercropped maize also caused a twofold increase in exudation of flavonoids (signaling compounds for rhizobia) in the systems. Roots of faba bean treated with maize root exudates exhibited an immediate 11-fold increase in the expression of chalcone–flavanone isomerase (involved in flavonoid synthesis) gene together with a significantly increased expression of genes mediating nodulation and auxin response. After 35 d, faba beans treated with maize root exudate continued to show up-regulation of key nodulation genes, such as early nodulin 93 (ENOD93), and promoted nitrogen fixation. Our results reveal a mechanism for how intercropped maize promotes nitrogen fixation of faba bean, where maize root exudates promote flavonoid synthesis in faba bean, increase nodulation, and stimulate nitrogen fixation after enhanced gene expression. These results indicate facilitative root–root interactions and provide a mechanism for a positive relationship between species diversity and ecosystem productivity. PMID:27217575

Tropical Dominance of N2 Fixation in the North Atlantic Ocean

NASA Astrophysics Data System (ADS)

Marconi, Dario; Sigman, Daniel M.; Casciotti, Karen L.; Campbell, Ethan C.; Alexandra Weigand, M.; Fawcett, Sarah E.; Knapp, Angela N.; Rafter, Patrick A.; Ward, Bess B.; Haug, Gerald H.

2017-10-01

To investigate the controls on N2 fixation and the role of the Atlantic in the global ocean's fixed nitrogen (N) budget, Atlantic N2 fixation is calculated by combining meridional nitrate fluxes across World Ocean Circulation Experiment sections with observed nitrate 15N/14N differences between northward and southward transported nitrate. N2 fixation inputs of 27.1 ± 4.3 Tg N/yr and 3.0 ± 0.5 Tg N/yr are estimated north of 11°S and 24°N, respectively. That is, 90% of the N2 fixation in the Atlantic north of 11°S occurs south of 24°N in a region with upwelling that imports phosphorus (P) in excess of N relative to phytoplankton requirements. This suggests that, under the modern iron-rich conditions of the equatorial and North Atlantic, N2 fixation occurs predominantly in response to P-bearing, N-poor conditions. We estimate a N2 fixation rate of 30.5 ± 4.9 Tg N/yr north of 30°S, implying only 3 Tg N/yr between 30° and 11°S, despite evidence of P-bearing, N-poor surface waters in this region as well; this is consistent with iron limitation of N2 fixation in the South Atlantic. Since the ocean flows through the Atlantic surface in <2,500 years, similar to the residence time of oceanic fixed N, Atlantic N2 fixation can stabilize the N-to-P ratio of the global ocean. However, the calculated rate of Atlantic N2 fixation is a small fraction of global ocean estimates for either N2 fixation or fixed N loss. This suggests that, in the modern ocean, an approximate balance between N loss and N2 fixation is achieved within the combined Indian and Pacific basins.

Environmental and biogeochemical controls on N2 fixation in ombrotrophic peatlands

NASA Astrophysics Data System (ADS)

Zivkovic, T.; Moore, T. R.

2017-12-01

Northern peatlands have low atmospheric nitrogen (N) inputs and acquire N mostly via biological, microbially-driven N2-fixation. Little is known about rates and controls on N2-fixation in ombrotrophic bogs. We conducted two studies to test environmental and biogeochemical controls on N2-fixation. First, we used acetylene reduction assay (ARA) calibrated with 15N2 tracer to measure N2-fixation rates in three species of Sphagnum mosses along a hydrological gradient (beaver pond, hollow and hummock in bog margin and in bog) at Mer Bleue bog from June-October 2013 and May - November 2014. We tested the following controls: moisture availability, temperature, and PAR. The largest ARA rates throughout both seasons occurred in the pond in floating Sphagnum cuspidatum mats (50.3 ± 12.9 μmol m-2 d-1 Mean ± SE), which were up to 2.5 times larger than the rates found in the driest hummock site. There was a significant seasonal peak in both years in July and early August that coincided with the peak of the air temperature. In fact, 45% of the variance of N2 fixation rates over the two field seasons was explained by rain events, water table fluctuations and the surface peat temperature (multiple regression analysis, n = 539). Our results highlight the potential impact of climate change, namely negative effects due to potential droughts and positive effect of warming, on N2 fixation patterns in ombrotrophic peatlands. Secondly, we tested stoichiometric controls (Sphagnum tissue N and phosphorous (P) ratio) of N2-fixation. In a controlled environment, we selected eight study sites along a latitudinal gradient from temperate, boreal to subarctic zone in eastern Canada. We found that decreasing N:P ratio corresponded to increasing N2-fixation. N:P explained 65% of the variance in N2-fixation in hollows but only 20% in hummocks. Changes in neither N or P concentration alone explained the increase in N2-fixation better than N:P ratio. We interpret that the difference between

Phylogeny of nodulation genes and symbiotic diversity of Acacia senegal (L.) Willd. and A. seyal (Del.) Mesorhizobium strains from different regions of Senegal.

PubMed

Bakhoum, Niokhor; Galiana, Antoine; Le Roux, Christine; Kane, Aboubacry; Duponnois, Robin; Ndoye, Fatou; Fall, Dioumacor; Noba, Kandioura; Sylla, Samba Ndao; Diouf, Diégane

2015-04-01

Acacia senegal and Acacia seyal are small, deciduous legume trees, most highly valued for nitrogen fixation and for the production of gum arabic, a commodity of international trade since ancient times. Symbiotic nitrogen fixation by legumes represents the main natural input of atmospheric N2 into ecosystems which may ultimately benefit all organisms. We analyzed the nod and nif symbiotic genes and symbiotic properties of root-nodulating bacteria isolated from A. senegal and A. seyal in Senegal. The symbiotic genes of rhizobial strains from the two Acacia species were closed to those of Mesorhizobium plurifarium and grouped separately in the phylogenetic trees. Phylogeny of rhizobial nitrogen fixation gene nifH was similar to those of nodulation genes (nodA and nodC). All A. senegal rhizobial strains showed identical nodA, nodC, and nifH gene sequences. By contrast, A. seyal rhizobial strains exhibited different symbiotic gene sequences. Efficiency tests demonstrated that inoculation of both Acacia species significantly affected nodulation, total dry weight, acetylene reduction activity (ARA), and specific acetylene reduction activity (SARA) of plants. However, these cross-inoculation tests did not show any specificity of Mesorhizobium strains toward a given Acacia host species in terms of infectivity and efficiency as stated by principal component analysis (PCA). This study demonstrates that large-scale inoculation of A. senegal and A. seyal in the framework of reafforestation programs requires a preliminary step of rhizobial strain selection for both Acacia species.

Soybean nodulation and symbiotic nitrogen fixation in response to soil compaction and mulching

NASA Astrophysics Data System (ADS)

Siczek, A.; Lipiec, J.

2009-04-01

Symbiotic nitrogen fixation by legume crops such as soybean plays a key role in supplying nitrogen for agricultural systems. In symbiotic associations with Bradyrhizobium japonicum soybean can fix up to 200 kg N ha-1 yr-1. This reduces the need for expensive and often environmentally harmful because of leaching nitrogen fertilization. However both soybean nodulation and nitrogen fixation are sensitive to soil conditions. One of the critical soil constraints is soil compaction. Increasing use of heavy equipment and intensive cropping in modern agriculture leads to excessive soil compaction. Compaction often is found as a result of field operations that have to be performed in a very short period of time and when soils are wet and more susceptible to compaction. This results in unfavourable water content, temperature, aeration, pore size distribution, strength for plant growth and microbial activity. The surface mulching can alleviate the adverse effect of the environmental factors on soil by decreasing fluctuation of soil temperature, increasing moisture by controlling evaporation from the soil surface, decreasing bulk density, preventing soil crusting. The effect of mulch on soil conditions largely depends on soil compaction and weather conditions during growing season. The positive effect of the straw mulch on soil moisture has been seen under seasons with insufficient rainfalls. However thicker layers of mulch can act as diffusion barrier, especially when the mulch is wet. Additionally, low soil temperature prevalent during early spring under mulch can impede development of nodule, nodule size and delay onset of nodulation. The aim of this study was to determine the effect of the straw mulch on nodulation and nitrogen fixation of soybean in variously compacted soil. The experimental field was 192 m2and was divided into three parts composed of 6 micro-plots with area 7 m2. Three degrees of soil compaction obtained in each field part through tractor passes were

Are watershed and lacustrine controls on planktonic N2 fixation hierarchically structured?

PubMed

Scott, J Thad; Doyle, Robert D; Prochnow, Shane J; White, Joseph D

2008-04-01

N2 fixation can be an important source of N to limnetic ecosystems and can influence the structure of phytoplankton communities. However, watershed-scale conditions that favor N2 fixation in lakes and reservoirs have not been well studied. We measured N2 fixation and lacustrine variables monthly over a 19-month period in Waco Reservoir, Texas, USA, and linked these data with nutrient-loading estimates from a physically based watershed model. Readily available topographic, soil, land cover, effluent discharge, and climate data were used in the Soil and Water Assessment Tool (SWAT) to derive watershed nutrient-loading estimates. Categorical and regression tree (CART) analysis revealed that lacustrine and watershed correlates of N2 fixation were hierarchically structured. Lacustrine conditions showed greater predictive capability temporally. For instance, low NO3(-) concentration (<25 microg N/L) and high water temperatures (>27 degrees C) in the reservoir were correlated with the initiation of N2 fixation seasonally. When lacustrine conditions were favorable for N2 fixation, watershed conditions appeared to influence spatial patterns of N2 fixation within the reservoir. For example, spatially explicit patterns of N2 fixation were correlated with the ratio of N:P in nutrient loadings and the N loading rate, which were driven by anthropogenic activity in the watershed and periods of low stream flow, respectively. Although N2 fixation contributed <5% of the annual N load to the reservoir, 37% of the N load was derived from atmospheric N2 fixation during summertime when stream flow in the watershed was low. This study provides evidence that watershed anthropogenic activity can exert control on planktonic N2 fixation, but that temporality is controlled by lacustrine conditions. Furthermore, this study also supports suggestions that reduced inflows may increase the propensity of N2-fixing cyanobacterial blooms in receiving waters of anthropogenically modified landscapes.

In-loop flow [11 C]CO2 fixation and radiosynthesis of N,N'-[11 C]dibenzylurea.

PubMed

Downey, Joseph; Bongarzone, Salvatore; Hader, Stefan; Gee, Antony D

2018-03-01

Cyclotron-produced carbon-11 is a highly valuable radionuclide for the production of positron emission tomography (PET) radiotracers. It is typically produced as relatively unreactive carbon-11 carbon dioxide ([ 11 C]CO 2 ), which is most commonly converted into a more reactive precursor for synthesis of PET radiotracers. The development of [ 11 C]CO 2 fixation methods has more recently enabled the direct radiolabelling of a diverse array of structures directly from [ 11 C]CO 2 , and the advantages afforded by the use of a loop-based system used in 11 C-methylation and 11 C-carboxylation reactions inspired us to apply the [ 11 C]CO 2 fixation "in-loop." In this work, we developed and investigated a new ethylene tetrafluoroethylene (ETFE) loop-based [ 11 C]CO 2 fixation method, enabling the fast and efficient, direct-from-cyclotron, in-loop trapping of [ 11 C]CO 2 using mixed DBU/amine solutions. An optimised protocol was integrated into a proof-of-concept in-loop flow radiosynthesis of N,N'-[ 11 C]dibenzylurea. This reaction exhibited an average 78% trapping efficiency and a crude radiochemical purity of 83% (determined by radio-HPLC), giving an overall nonisolated radiochemical yield of 72% (decay-corrected) within just 3 minutes from end of bombardment. This proof-of-concept reaction has demonstrated that efficient [ 11 C]CO 2 fixation can be achieved in a low-volume (150 μL) ETFE loop and that this can be easily integrated into a rapid in-loop flow radiosynthesis of carbon-11-labelled products. This new in-loop methodology will allow fast radiolabelling reactions to be performed using cheap/disposable ETFE tubing setup (ideal for good manufacturing practice production) thereby contributing to the widespread usage of [ 11 C]CO 2 trapping/fixation reactions for the production of PET radiotracers. © 2017 The Authors. Journal of Labelled Compounds and Radiopharmaceuticals Published by John Wiley & Sons, Ltd.

Genomic features separating ten strains of Neorhizobium galegae with different symbiotic phenotypes.

PubMed

Österman, Janina; Mousavi, Seyed Abdollah; Koskinen, Patrik; Paulin, Lars; Lindström, Kristina

2015-05-02

The symbiotic phenotype of Neorhizobium galegae, with strains specifically fixing nitrogen with either Galega orientalis or G. officinalis, has made it a target in research on determinants of host specificity in nitrogen fixation. The genomic differences between representative strains of the two symbiovars are, however, relatively small. This introduced a need for a dataset representing a larger bacterial population in order to make better conclusions on characteristics typical for a subset of the species. In this study, we produced draft genomes of eight strains of N. galegae having different symbiotic phenotypes, both with regard to host specificity and nitrogen fixation efficiency. These genomes were analysed together with the previously published complete genomes of N. galegae strains HAMBI 540T and HAMBI 1141. The results showed that the presence of an additional rpoN sigma factor gene in the symbiosis gene region is a characteristic specific to symbiovar orientalis, required for nitrogen fixation. Also the nifQ gene was shown to be crucial for functional symbiosis in both symbiovars. Genome-wide analyses identified additional genes characteristic of strains of the same symbiovar and of strains having similar plant growth promoting properties on Galega orientalis. Many of these genes are involved in transcriptional regulation or in metabolic functions. The results of this study confirm that the only symbiosis-related gene that is present in one symbiovar of N. galegae but not in the other is an rpoN gene. The specific function of this gene remains to be determined, however. New genes that were identified as specific for strains of one symbiovar may be involved in determining host specificity, while others are defined as potential determinant genes for differences in efficiency of nitrogen fixation.

Free-air CO2 enrichment (FACE) reduces the inhibitory effect of soil nitrate on N2 fixation of Pisum sativum.

PubMed

Butterly, Clayton R; Armstrong, Roger; Chen, Deli; Tang, Caixian

2016-01-01

Additional carbohydrate supply resulting from enhanced photosynthesis under predicted future elevated CO2 is likely to increase symbiotic nitrogen (N) fixation in legumes. This study examined the interactive effects of atmospheric CO2 and nitrate (NO3(-)) concentration on the growth, nodulation and N fixation of field pea (Pisum sativum) in a semi-arid cropping system. Field pea was grown for 15 weeks in a Vertosol containing 5, 25, 50 or 90 mg NO3(-)-N kg(-1) under either ambient CO2 (aCO2; 390 ppm) or elevated CO2 (eCO2; 550 ppm) using free-air CO2 enrichment (SoilFACE). Under aCO2, field pea biomass was significantly lower at 5 mg NO3(-)-N kg(-1) than at 90 mg NO3(-)-N kg(-1) soil. However, increasing the soil N level significantly reduced nodulation of lateral roots but not the primary root, and nodules were significantly smaller, with 85% less nodule mass in the 90 NO3(-)-N kg(-1) than in the 5 mg NO3(-)-N kg(-1) treatment, highlighting the inhibitory effects of NO3(-). Field pea grown under eCO2 had greater biomass (approx. 30%) than those grown under aCO2, and was not affected by N level. Overall, the inhibitory effects of NO3(-) on nodulation and nodule mass appeared to be reduced under eCO2 compared with aCO2, although the effects of CO2 on root growth were not significant. Elevated CO2 alleviated the inhibitory effect of soil NO3(-) on nodulation and N2 fixation and is likely to lead to greater total N content of field pea growing under future elevated CO2 environments. © The Author 2015. Published by Oxford University Press on behalf of the Annals of Botany Company. All rights reserved. For Permissions, please email: journals.permissions@oup.com.

Genomic resources for identification of the minimal N2 -fixing symbiotic genome.

PubMed

diCenzo, George C; Zamani, Maryam; Milunovic, Branislava; Finan, Turlough M

2016-09-01

The lack of an appropriate genomic platform has precluded the use of gain-of-function approaches to study the rhizobium-legume symbiosis, preventing the establishment of the genes necessary and sufficient for symbiotic nitrogen fixation (SNF) and potentially hindering synthetic biology approaches aimed at engineering this process. Here, we describe the development of an appropriate system by reverse engineering Sinorhizobium meliloti. Using a novel in vivo cloning procedure, the engA-tRNA-rmlC (ETR) region, essential for cell viability and symbiosis, was transferred from Sinorhizobium fredii to the ancestral location on the S. meliloti chromosome, rendering the ETR region on pSymB redundant. A derivative of this strain lacking both the large symbiotic replicons (pSymA and pSymB) was constructed. Transfer of pSymA and pSymB back into this strain restored symbiotic capabilities with alfalfa. To delineate the location of the single-copy genes essential for SNF on these replicons, we screened a S. meliloti deletion library, representing > 95% of the 2900 genes of the symbiotic replicons, for their phenotypes with alfalfa. Only four loci, accounting for < 12% of pSymA and pSymB, were essential for SNF. These regions will serve as our preliminary target of the minimal set of horizontally acquired genes necessary and sufficient for SNF. © 2016 Society for Applied Microbiology and John Wiley & Sons Ltd.

Co-inoculation of a Pea Core-Collection with Diverse Rhizobial Strains Shows Competitiveness for Nodulation and Efficiency of Nitrogen Fixation Are Distinct traits in the Interaction

PubMed Central

Bourion, Virginie; Heulin-Gotty, Karine; Aubert, Véronique; Tisseyre, Pierre; Chabert-Martinello, Marianne; Pervent, Marjorie; Delaitre, Catherine; Vile, Denis; Siol, Mathieu; Duc, Gérard; Brunel, Brigitte; Burstin, Judith; Lepetit, Marc

2018-01-01

Pea forms symbiotic nodules with Rhizobium leguminosarum sv. viciae (Rlv). In the field, pea roots can be exposed to multiple compatible Rlv strains. Little is known about the mechanisms underlying the competitiveness for nodulation of Rlv strains and the ability of pea to choose between diverse compatible Rlv strains. The variability of pea-Rlv partner choice was investigated by co-inoculation with a mixture of five diverse Rlv strains of a 104-pea collection representative of the variability encountered in the genus Pisum. The nitrogen fixation efficiency conferred by each strain was determined in additional mono-inoculation experiments on a subset of 18 pea lines displaying contrasted Rlv choice. Differences in Rlv choice were observed within the pea collection according to their genetic or geographical diversities. The competitiveness for nodulation of a given pea-Rlv association evaluated in the multi-inoculated experiment was poorly correlated with its nitrogen fixation efficiency determined in mono-inoculation. Both plant and bacterial genetic determinants contribute to pea-Rlv partner choice. No evidence was found for co-selection of competitiveness for nodulation and nitrogen fixation efficiency. Plant and inoculant for an improved symbiotic association in the field must be selected not only on nitrogen fixation efficiency but also for competitiveness for nodulation. PMID:29367857

Co-inoculation of a Pea Core-Collection with Diverse Rhizobial Strains Shows Competitiveness for Nodulation and Efficiency of Nitrogen Fixation Are Distinct traits in the Interaction.

PubMed

Bourion, Virginie; Heulin-Gotty, Karine; Aubert, Véronique; Tisseyre, Pierre; Chabert-Martinello, Marianne; Pervent, Marjorie; Delaitre, Catherine; Vile, Denis; Siol, Mathieu; Duc, Gérard; Brunel, Brigitte; Burstin, Judith; Lepetit, Marc

2017-01-01

Pea forms symbiotic nodules with Rhizobium leguminosarum sv. viciae (Rlv). In the field, pea roots can be exposed to multiple compatible Rlv strains. Little is known about the mechanisms underlying the competitiveness for nodulation of Rlv strains and the ability of pea to choose between diverse compatible Rlv strains. The variability of pea-Rlv partner choice was investigated by co-inoculation with a mixture of five diverse Rlv strains of a 104-pea collection representative of the variability encountered in the genus Pisum . The nitrogen fixation efficiency conferred by each strain was determined in additional mono-inoculation experiments on a subset of 18 pea lines displaying contrasted Rlv choice. Differences in Rlv choice were observed within the pea collection according to their genetic or geographical diversities. The competitiveness for nodulation of a given pea-Rlv association evaluated in the multi-inoculated experiment was poorly correlated with its nitrogen fixation efficiency determined in mono-inoculation. Both plant and bacterial genetic determinants contribute to pea-Rlv partner choice. No evidence was found for co-selection of competitiveness for nodulation and nitrogen fixation efficiency. Plant and inoculant for an improved symbiotic association in the field must be selected not only on nitrogen fixation efficiency but also for competitiveness for nodulation.

Short-term N2 fixation kinetics in a moss-associated cyanobacteria.

PubMed

Jean, Marie-Eve; Cassar, Nicolas; Setzer, Cameron; Bellenger, Jean-Philippe

2012-08-21

N(2) fixation by moss-associated cyanobacteria plays an important role in the nitrogen cycling of terrestrial ecosystems. Recent studies have mainly focused on boreal ecosystems; little is known about such association in other ecosystems. Moss-associated cyanobacteria are subject to rapid changes (hourly or less) in environmental conditions that may affect N(2) fixation kinetics. Using a recently developed method (Acetylene Reduction Assays by Cavity ring-down laser Absorption Spectroscopy, ARACAS) with higher sensitivity and sampling frequency than the conventional method, we characterize short-term kinetics of N(2) fixation by cyanobacteria on moss carpets from warm and cold temperate forests. We report the identification of a heretofore unknown multispecies true-moss-cyanobacteria diazotrophic association. We demonstrate that short-term change in abiotic variables greatly influences N(2) fixation. We also show that difference in relative proportion of two epiphytic diazotrophs is consistent with divergent influences of temperature on their N(2) fixation kinetics. Further research is needed to determine whether this difference is consistent with a latitudinal trend.

Identification of an algal carbon fixation-enhancing factor extracted from Paramecium bursaria.

PubMed

Kato, Yutaka; Imamura, Nobutaka

2011-01-01

The green ciliate Paramecium bursaria contains several hundred symbiotic Chlorella species. We previously reported that symbiotic algal carbon fixation is enhanced by P. bursaria extracts and that the enhancing factor is a heat-stable, low-molecular-weight, water-soluble compound. To identify the factor, further experiments were carried out. The enhancing activity remained even when organic compounds in the extract were completely combusted at 700 degrees C, suggesting that the factor is an inorganic substance. Measurement of the major cations, K+, Ca2+, and Mg2+, by an electrode and titration of the extract resulted in concentrations of 0.90 mM, 0.55 mM, and 0.21 mM, respectively. To evaluate the effect of these cations, a mixture of the cations at the measured concentrations was prepared, and symbiotic algal carbon fixation was measured in the solution. The results demonstrated that the fixation was enhanced to the same extent as with the P. bursaria extract, and thus this mixture of K+, Ca2+, and Mg2+ was concluded to be the carbon fixation-enhancing factor. There was no effect of the cation mixture on free-living C. vulgaris. Comparison of the cation concentrations of nonsymbiotic and symbiotic Paramecium extracts revealed that the concentrations of K+ and Mg2+ in nonsymbiotic Paramecium extracts were too low to enhance symbiotic algal carbon fixation, suggesting that symbiotic P. bursaria provide suitable cation conditions for photosynthesis to its symbiotic Chlorella.

Transcriptome analysis of two recombinant inbred lines of common bean contrasting for symbiotic nitrogen fixation

PubMed Central

Kamfwa, Kelvin; Zhao, Dongyan; Kelly, James D.

2017-01-01

Common bean (Phaseolus vulgaris L.) fixes atmospheric nitrogen (N2) through symbiotic nitrogen fixation (SNF) at levels lower than other grain legume crops. An understanding of the genes and molecular mechanisms underlying SNF will enable more effective strategies for the genetic improvement of SNF traits in common bean. In this study, transcriptome profiling was used to identify genes and molecular mechanisms underlying SNF differences between two common bean recombinant inbred lines that differed in their N-fixing abilities. Differential gene expression and functional enrichment analyses were performed on leaves, nodules and roots of the two lines when grown under N-fixing and non-fixing conditions. Receptor kinases, transmembrane transporters, and transcription factors were among the differentially expressed genes identified under N-fixing conditions, but not under non-fixing conditions. Genes up-regulated in the stronger nitrogen fixer, SA36, included those involved in molecular functions such as purine nucleoside binding, oxidoreductase and transmembrane receptor activities in nodules, and transport activity in roots. Transcription factors identified in this study are candidates for future work aimed at understanding the functional role of these genes in SNF. Information generated in this study will support the development of gene-based markers to accelerate genetic improvement of SNF in common bean. PMID:28192540

Nitrogen fixation in the mucus of Red Sea corals.

PubMed

Grover, Renaud; Ferrier-Pagès, Christine; Maguer, Jean-François; Ezzat, Leila; Fine, Maoz

2014-11-15

Scleractinian corals are essential constituents of tropical reef ecological diversity. They live in close association with diazotrophs [dinitrogen (N2)-fixing microbes], which can fix high rates of N2. Whether corals benefit from this extrinsic nitrogen source is still under debate. Until now, N2 fixation rates have been indirectly estimated using the acetylene reduction assay, which does not permit assessment of the amount of nitrogen incorporated into the different compartments of the coral holobiont. In the present study, the (15)N2 technique was applied for the first time on three Red Sea coral species. Significant (15)N enrichment was measured in particles released by corals to the surrounding seawater. N2 fixation rates were species specific and as high as 1.6-2 ng N day(-1) l(-1). However, no significant enrichment was measured in the symbiotic dinoflagellates or the coral host tissues, suggesting that corals do not benefit from diazotrophic N2 fixation. © 2014. Published by The Company of Biologists Ltd.

The Acetylene-Ethylene Assay for N2 Fixation: Laboratory and Field Evaluation 1

PubMed Central

Hardy, R. W. F.; Holsten, R. D.; Jackson, E. K.; Burns, R. C.

1968-01-01

The methodology, characteristics and application of the sensitive C2H2-C2H4 assay for N2 fixation by nitrogenase preparations and bacterial cultures in the laboratory and by legumes and free-living bacteria in situ is presented in this comprehensive report. This assay is based on the N2ase-catalyzed reduction of C2H2 to C2H4, gas chromatographic isolation of C2H2 and C2H4, and quantitative measurement with a H2-flame analyzer. As little as 1 μμmole C2H4 can be detected, providing a sensitivity 103-fold greater than is possible with 15N analysis. A simple, rapid and effective procedure utilizing syringe-type assay chambers is described for the analysis of C2H2-reducing activity in the field. Applications to field samples included an evaluation of N2 fixation by commercially grown soybeans based on over 2000 analyses made during the course of the growing season. Assay values reflected the degree of nodulation of soybean plants and indicated a calculated seasonal N2 fixation rate of 30 to 33 kg N2 fixed per acre, in good agreement with literature estimates based on Kjeldahl analyses. The assay was successfully applied to measurements of N2 fixation by other symbionts and by free living soil microorganisms, and was also used to assess the effects of light and temperature on the N2 fixing activity of soybeans. The validity of measuring N2 fixation in terms of C2H2 reduction was established through extensive comparisons of these activities using defined systems, including purified N2ase preparations and pure cultures of N2-fixing bacteria. With this assay it now becomes possible and practicable to conduct comprehensive surveys of N2 fixation, to make detailed comparisons among different N2-fixing symbionts, and to rapidly evaluate the effects of cultural practices and environmental factors on N2 fixation. The knowledge obtained through extensive application of this assay should provide the basis for efforts leading to the maximum agricultural exploitation of the N2

Phytoplankton plasticity drives large variability in carbon fixation efficiency

NASA Astrophysics Data System (ADS)

Ayata, Sakina-Dorothée.; Lévy, Marina; Aumont, Olivier; Resplandy, Laure; Tagliabue, Alessandro; Sciandra, Antoine; Bernard, Olivier

2014-12-01

Phytoplankton C:N stoichiometry is highly flexible due to physiological plasticity, which could lead to high variations in carbon fixation efficiency (carbon consumption relative to nitrogen). However, the magnitude, as well as the spatial and temporal scales of variability, remains poorly constrained. We used a high-resolution biogeochemical model resolving various scales from small to high, spatially and temporally, in order to quantify and better understand this variability. We find that phytoplankton C:N ratio is highly variable at all spatial and temporal scales (5-12 molC/molN), from mesoscale to regional scale, and is mainly driven by nitrogen supply. Carbon fixation efficiency varies accordingly at all scales (±30%), with higher values under oligotrophic conditions and lower values under eutrophic conditions. Hence, phytoplankton plasticity may act as a buffer by attenuating carbon sequestration variability. Our results have implications for in situ estimations of C:N ratios and for future predictions under high CO2 world.

Basin-wide N2 fixation in the deep waters of the Mediterranean Sea

NASA Astrophysics Data System (ADS)

Benavides, Mar; Bonnet, Sophie; Hernández, Nauzet; Martínez-Pérez, Alba María.; Nieto-Cid, Mar; Álvarez-Salgado, Xosé Antón; Baños, Isabel; Montero, María. F.; Mazuecos, Ignacio P.; Gasol, Josep M.; Osterholz, Helena; Dittmar, Thorsten; Berman-Frank, Ilana; Arístegui, Javier

2016-06-01

Recent findings indicate that N2 fixation is significant in aphotic waters, presumably due to heterotrophic diazotrophs depending on organic matter for their nutrition. However, the relationship between organic matter and heterotrophic N2 fixation remains unknown. Here we explore N2 fixation in the deep chlorophyll maximum and underneath deep waters across the whole Mediterranean Sea and relate it to organic matter composition, characterized by optical and molecular methods. Our N2 fixation rates were in the range of those previously reported for the euphotic zone of the Mediterranean Sea (up to 0.43 nmol N L-1 d-1) and were significantly correlated to the presence of relatively labile organic matter with fluorescence and molecular formula properties representative for peptides and unsaturated aliphatics and associated with the presence of more oxygenated ventilated water masses. Finally, and despite that the aphotic N2 fixation contributes largely to total water column diazotrophic activity (>50%), its contribution to overall nitrogen inputs to the basin is negligible (<0.5%).

N2 fixation as a dominant new N source in the western tropical South Pacific Ocean (OUTPACE cruise)

NASA Astrophysics Data System (ADS)

Caffin, Mathieu; Moutin, Thierry; Foster, Rachel Ann; Bouruet-Aubertot, Pascale; Michelangelo Doglioli, Andrea; Berthelot, Hugo; Guieu, Cécile; Grosso, Olivier; Helias-Nunige, Sandra; Leblond, Nathalie; Gimenez, Audrey; Petrenko, Anne Alexandra; de Verneil, Alain; Bonnet, Sophie

2018-05-01

We performed nitrogen (N) budgets in the photic layer of three contrasting stations representing different trophic conditions in the western tropical South Pacific (WTSP) Ocean during austral summer conditions (February-March 2015). Using a Lagrangian strategy, we sampled the same water mass for the entire duration of each long-duration (5 days) station, allowing us to consider only vertical exchanges for the budgets. We quantified all major vertical N fluxes both entering (N2 fixation, nitrate turbulent diffusion, atmospheric deposition) and leaving the photic layer (particulate N export). The three stations were characterized by a strong nitracline and contrasted deep chlorophyll maximum depths, which were lower in the oligotrophic Melanesian archipelago (MA, stations LD A and LD B) than in the ultra-oligotrophic waters of the South Pacific Gyre (SPG, station LD C). N2 fixation rates were extremely high at both LD A (593 ± 51 µmol N m-2 d-1) and LD B (706 ± 302 µmol N m-2 d-1), and the diazotroph community was dominated by Trichodesmium. N2 fixation rates were lower (59 ± 16 µmol N m-2 d-1) at LD C, and the diazotroph community was dominated by unicellular N2-fixing cyanobacteria (UCYN). At all stations, N2 fixation was the major source of new N (> 90 %) before atmospheric deposition and upward nitrate fluxes induced by turbulence. N2 fixation contributed circa 13-18 % of primary production in the MA region and 3 % in the SPG water and sustained nearly all new primary production at all stations. The e ratio (e ratio = particulate carbon export / primary production) was maximum at LD A (9.7 %) and was higher than the e ratio in most studied oligotrophic regions (< 5 %), indicating a high efficiency of the WTSP to export carbon relative to primary production. The direct export of diazotrophs assessed by qPCR of the nifH gene in sediment traps represented up to 30.6 % of the PC export at LD A, while their contribution was 5 and < 0.1 % at LD B and LD C

Taxonomic identity determines N2 fixation by canopy trees across lowland tropical forests.

PubMed

Wurzburger, Nina; Hedin, Lars O

2016-01-01

Legumes capable of fixing atmospheric N2 are abundant and diverse in many tropical forests, but the factors determining ecological patterns in fixation are unresolved. A long-standing idea is that fixation depends on soil nutrients (N, P or Mo), but recent evidence shows that fixation may also differ among N2-fixing species. We sampled canopy-height trees across five species and one species group of N2-fixers along a landscape P gradient, and manipulated P and Mo to seedlings in a shadehouse. Our results identify taxonomy as the major determinant of fixation, with P (and possibly Mo) only influencing fixation following tree-fall disturbances. While 44% of trees did not fix N2, other trees fixed at high rates, with two species functioning as superfixers across the landscape. Our results raise the possibility that fixation is determined by biodiversity, evolutionary history and species-specific traits (tree growth rate, canopy stature and response to disturbance) in the tropical biome. © 2015 John Wiley & Sons Ltd/CNRS.

Biochemical Approaches to Improved Nitrogen Fixation

USDA-ARS?s Scientific Manuscript database

Improving symbiotic nitrogen fixation by legumes has emerged again as an important topic on the world scene due to the energy crisis and lack of access to nitrogen fertilizer in developing countries. We have taken a biochemical genomics approach to improving symbiotic nitrogen fixation in legumes. L...

Theoretical implications for the estimation of dinitrogen fixation by large perennial plant species using isotope dilution

Treesearch

Dwight D. Baker; Maurice Fried; John A. Parrotta

1995-01-01

Estimation of symbiotic N2 fixation associated with large perennial plant species, especially trees, poses special problems because the process must be followed over a potentially long period of time to integrate the total amount of fixation. Estimations using isotope dilution methodology have begun to be used for trees in field studies. Because...

N2-fixation dynamics during ecosystem recovery in longleaf pine savannas

NASA Astrophysics Data System (ADS)

Tierney, J. A.

2016-12-01

Biological nitrogen fixation (BNF) can alleviate nitrogen (N) deficiencies that inhibit ecosystem recovery. BNF may be particularly important in ecosystems recovering from land-use change and perturbations from fire, as these disturbances can exacerbate N limitation. Here, we investigated how BNF dynamics change throughout ecosystem development in restored longleaf pine savannas, and how BNF responds to fire. We conducted this study in 59 1-ha plots of longleaf pine distributed across gradients of stand age and fire frequency at two sites in the southeastern US. We determined BNF contributions by three functional groups of N2-fixers (herbaceous legumes, biological soil crusts, and asymbiotic N2-fixing bacteria) by quantifying their abundances, assessing nitrogenase activity, and scaling these estimates up to the plot-level. To determine aboveground N demands, we measured tree growth using diameter increments and allometric equations paired with tissue-specific N concentrations. We fit linear models to evaluate the effects of stand age and time since fire on BNF and N demands throughout stand development, and performed separate analyses on mature stands to determine how fire return interval affects BNF. We observed distinct temporal patterns of N2-fixation across stand development among the three groups of N2 fixers. N2-fixation by legumes and asymbiotic bacteria remained low until stands reached maturity, while N2-fixation by biological soil crusts (BSCs) was high in juvenile stands and decreased with stand age. These patterns suggest a compensatory shift in the importance of these functional groups throughout stand development such that contributions from BSCs are critical for meeting N demands when disturbances may hinder the establishment of legumes and asymbiotic bacteria. N2-fixation by BSCs and asymbiotic bacteria throughout stand development was not affected by time since fire, but legume abundance increased the year following fire, suggesting a recovery

Biological Nitrogen Fixation In Tropical Dry Forests Of Costa Rica

NASA Astrophysics Data System (ADS)

Gei, M. G.; Powers, J. S.

2012-12-01

Evidence suggests that tropical dry forests (TDF) are not nitrogen (N) deficient. This evidence includes: high losses of gaseous nitrogen during the rainy season, high ecosystem soil N stocks and high N concentrations in leaves and litterfall. Its been commonly hypothesized that biological nitrogen fixation is responsible for the high availability of N in tropical soils. However, the magnitude of this flux has rarely if ever been measured in tropical dry forests. Because of the high cost of fixing N and the ubiquity of N fixing legume trees in the TDF, at the individual tree level symbiotic fixation should be a strategy down-regulated by the plant. Our main goal was to determine the rates of and controls over symbiotic N fixation. We hypothesized that legume tree species employ a facultative strategy of nitrogen fixation and that this process responds to changes in light availability, soil moisture and nutrient supply. We tested this hypothesis both on naturally established trees in a forest and under controlled conditions in a shade house by estimating the quantities of N fixed annually using the 15N natural abundance method, counting nodules, and quantifying (field) or manipulating (shade house) the variation in important environmental variables (soil nutrients, soil moisture, and light). We found that in both in our shade house experiment and in the forest, nodulation varied among different legume species. For both settings, the 15N natural abundance approach successfully detected differences in nitrogen fixation among species. The legume species that we studied were able to regulate fixation depending on the environmental conditions. They showed to have different strategies of nitrogen fixation that follow a gradient of facultative to obligate fixation. Our data suggest that there exists a continuum of nitrogen fixation strategies among species. Any efforts to define tropical legume trees as a functional group need to incorporate this variation.

Spatially robust estimates of biological nitrogen (N) fixation imply substantial human alteration of the tropical N cycle

USGS Publications Warehouse

Sullivan, Benjamin W.; Smith, William K.; Townsend, Alan R.; Nasto, Megan K.; Reed, Sasha C.; Chazdon, Robin L.; Cleveland, Cory C.

2014-01-01

Biological nitrogen fixation (BNF) is the largest natural source of exogenous nitrogen (N) to unmanaged ecosystems and also the primary baseline against which anthropogenic changes to the N cycle are measured. Rates of BNF in tropical rainforest are thought to be among the highest on Earth, but they are notoriously difficult to quantify and are based on little empirical data. We adapted a sampling strategy from community ecology to generate spatial estimates of symbiotic and free-living BNF in secondary and primary forest sites that span a typical range of tropical forest legume abundance. Although total BNF was higher in secondary than primary forest, overall rates were roughly five times lower than previous estimates for the tropical forest biome. We found strong correlations between symbiotic BNF and legume abundance, but we also show that spatially free-living BNF often exceeds symbiotic inputs. Our results suggest that BNF in tropical forest has been overestimated, and our data are consistent with a recent top-down estimate of global BNF that implied but did not measure low tropical BNF rates. Finally, comparing tropical BNF within the historical area of tropical rainforest with current anthropogenic N inputs indicates that humans have already at least doubled reactive N inputs to the tropical forest biome, a far greater change than previously thought. Because N inputs are increasing faster in the tropics than anywhere on Earth, both the proportion and the effects of human N enrichment are likely to grow in the future.

Bacterial N2-fixation in mangrove ecosystems: insights from a diazotroph-mangrove interaction.

PubMed

Alfaro-Espinoza, Gabriela; Ullrich, Matthias S

2015-01-01

Mangrove forests are highly productive ecosystems but represent low nutrient environments. Nitrogen availability is one of the main factors limiting mangrove growth. Diazotrophs have been identified as key organisms that provide nitrogen to these environments. N2-fixation by such organisms was found to be higher in the mangrove roots than in surrounding rhizosphere. Moreover, previous studies showed that mangroves grew better in the presence of N2-fixers indicating a potentially mutualistic relationship. However, the molecular signals and mechanisms that govern these interactions are still poorly understood. Here we present novel insights in the interaction of a diazotroph with a mangrove species to improve our understanding of the molecular and ecophysiological relationship between these two organisms under controlled conditions. Our results showed that Marinobacterium mangrovicola is a versatile organism capable of competing with other organisms to survive for long periods in mangrove soils. N2-fixation by this bacterium was up-regulated in the presence of mangrove roots, indicating a possible beneficial interaction. The increase in N2-fixation was limited to cells of the exponential growth phase suggesting that N2-fixation differs over the bacterial growth cycle. Bacterial transformants harboring a transcriptional nifH::gusA fusion showed that M. mangrovicola successfully colonized mangrove roots and simultaneously conducted N2-fixation. The colonization process was stimulated by the lack of an external carbon source suggesting a possible mutualistic relationship. M. mangrovicola represents an interesting genetically accessible diazotroph, which colonize mangrove roots and exhibit higher N2-fixation in the presence of mangrove roots. Consequently, we propose this microorganism as a tool to study molecular interactions between N2-fixers and mangrove plants and to better understand how changes in the environment could impact these important and relatively unknown

The role of nitrogen fixation in neotropical dry forests: insights from ecosystem modeling and field data

NASA Astrophysics Data System (ADS)

Trierweiler, A.; Xu, X.; Gei, M. G.; Powers, J. S.; Medvigy, D.

2016-12-01

Tropical dry forests (TDFs) have immense functional diversity and face multiple resource constraints (both water and nutrients). Legumes are abundant and exhibit a wide diversity of N2-fixing strategies in TDFs. The abundance and diversity of legumes and their interaction with N2-fixing bacteria may strongly control the coupled carbon-nitrogen cycle in the biome and influence whether TDFs will be particularly vulnerable or uniquely adapted to projected global change. However, the importance of N2-fixation in TDFs and the carbon cost of acquiring N through symbiotic relationships are not fully understood. Here, we use models along with field measurements to examine the role of legumes, nitrogen fixation, and plant-symbiont nutrient exchanges in TDFs. We use a new version of the Ecosystem Demography (ED2) model that has been recently parameterized for TDFs. The new version incorporates plant-mycorrhizae interactions and multiple resource constraints (carbon, nitrogen, phosphorus, and water). We represent legumes and other functional groups found in TDFs with a range of resource acquisition strategies. In the model, plants then can dynamically adjust their carbon allocation and nutrient acquisition strategies (e.g. N2-fixing bacteria and mycorrhizal fungi) according to the nutrient limitation status. We test (i) the model's performance against a nutrient gradient of field sites in Costa Rica and (ii) the model's sensitivity to the carbon cost to acquire N through fixation and mycorrhizal relationships. We also report on simulated tree community responses to ongoing field nutrient fertilization experiments. We found that the inclusion of the N2-fixation legume plant functional traits were critical to reproducing community dynamics of Costa Rican field TDF sites and have a large impact on forest biomass. Simulated ecosystem fixation rates matched the magnitude and temporal patterns of field measured fixation. Our results show that symbiotic nitrogen fixation plays an

Quantifying nitrogen-fixation in feather moss carpets of boreal forests.

PubMed

DeLuca, Thomas H; Zackrisson, Olle; Nilsson, Marie-Charlotte; Sellstedt, Anita

2002-10-31

Biological nitrogen (N) fixation is the primary source of N within natural ecosystems, yet the origin of boreal forest N has remained elusive. The boreal forests of Eurasia and North America lack any significant, widespread symbiotic N-fixing plants. With the exception of scattered stands of alder in early primary successional forests, N-fixation in boreal forests is considered to be extremely limited. Nitrogen-fixation in northern European boreal forests has been estimated at only 0.5 kg N ha(-1) yr(-1); however, organic N is accumulated in these ecosystems at a rate of 3 kg N ha(-1) yr(-1) (ref. 8). Our limited understanding of the origin of boreal N is unacceptable given the extent of the boreal forest region, but predictable given our imperfect knowledge of N-fixation. Herein we report on a N-fixing symbiosis between a cyanobacterium (Nostoc sp.) and the ubiquitous feather moss, Pleurozium schreberi (Bird) Mitt. that alone fixes between 1.5 and 2.0 kg N ha(-1) yr(-1) in mid- to late-successional forests of northern Scandinavia and Finland. Previous efforts have probably underestimated N-fixation potential in boreal forests.

Influence of tree canopy on N₂ fixation by pasture legumes and soil rhizobial abundance in Mediterranean oak woodlands.

PubMed

Carranca, C; Castro, I V; Figueiredo, N; Redondo, R; Rodrigues, A R F; Saraiva, I; Maricato, R; Madeira, M A V

2015-02-15

Symbiotic N2 fixation is of primordial significance in sustainable agro-forestry management as it allows reducing the use of mineral N in the production of mixed stands and by protecting the soils from degradation. Thereby, on a 2-year basis, N2 fixation was evaluated in four oak woodlands under Mediterranean conditions using a split-plot design and three replicates. (15)N technique was used for determination of N2 fixation rate. Variations in environmental conditions (temperature, rainfall, radiation) by the cork tree canopy as well as the age of stands and pasture management can cause great differences in vegetation growth, legume N2 fixation, and soil rhizobial abundance. In the present study, non-legumes dominated the swards, in particular beneath the tree canopy, and legumes represented only 42% of total herbage. A 2-fold biomass reduction was observed in the oldest sown pasture in relation to the medium-age sward (6 t DW ha(-1)yr(-1)). Overall, competition of pasture growth for light was negligible, but soil rhizobial abundance and symbiotic N2 fixation capacity were highly favored by this environmental factor in the spring and outside the influence of tree canopy. Nitrogen derived from the atmosphere was moderate to high (54-72%) in unsown and sown swards. Inputs of fixed N2 increased from winter to spring due to more favorable climatic conditions (temperature and light intensity) for both rhizobia and vegetation growths. Assuming a constant fixation rate at each seasonal period, N2 fixation capacity increased from about 0.10 kg N ha(-1) per day in the autumn-winter period to 0.15 kg N ha(-1) per day in spring. Belowground plant material contributed to 11% of accumulated N in pasture legumes and was not affected by canopy. Size of soil fixing bacteria contributed little to explain pasture legumes N. Copyright © 2014 Elsevier B.V. All rights reserved.

Drought enhances symbiotic dinitrogen fixation and competitive ability of a temperate forest tree

Treesearch

Nina Wurzburger; Chelcy Ford Miniat

2013-01-01

General circulation models project more intense and frequent droughts over the next century, but many questions remain about how terrestrial ecosystems will respond. Of particular importance, is to understand how drought will alter the species composition of regenerating temperate forests wherein symbiotic dinitrogen (N2)- fixing plants play a...

The NifA-RpoN Regulon of Mesorhizobium loti Strain R7A and Its Symbiotic Activation by a Novel LacI/GalR-Family Regulator

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sullivan, John T.; Brown, Steven D.; Ronson, Clive W.

Mesorhizobium loti is the microsymbiont of Lotus species, including the model legume L. japonicus. M. loti differs from other rhizobia in that it contains two copies of the key nitrogen fixation regulatory gene nifA, nifA1 and nifA2, both of which are located on the symbiosis island ICEMlSymR7A. M. loti R7A also contains two rpoN genes, rpoN1 located on the chromosome outside of ICEMlSymR7A and rpoN2 that is located on ICEMlSymR7A. The aims of the current work were to establish how nifA expression was activated in M. loti and to characterise the NifA-RpoN regulon. The nifA2 and rpoN2 genes were essentialmore » for nitrogen fixation whereas nifA1 and rpoN1 were dispensable. Expression of nifA2 was activated, possibly in response to an inositol derivative, by a novel regulator of the LacI/GalR family encoded by the fixV gene located upstream of nifA2. Other than the well-characterized nif/fix genes, most NifA2-regulated genes were not required for nitrogen fixation although they were strongly expressed in nodules. The NifA-regulated nifZ and fixU genes, along with nifQ which was not NifA-regulated, were required in M. loti for a fully effective symbiosis although they are not present in some other rhizobia. The NifA-regulated gene msi158 that encodes a porin was also required for a fully effective symbiosis. Several metabolic genes that lacked NifA-regulated promoters were strongly expressed in nodules in a NifA2-dependent manner but again mutants did not have an overt symbiotic phenotype. In summary, many genes encoded on ICEMlSymR7A were strongly expressed in nodules but not free-living rhizobia, but were not essential for symbiotic nitrogen fixation. It seems likely that some of these genes have functional homologues elsewhere in the genome and that bacteroid metabolism may be sufficiently plastic to adapt to loss of certain enzymatic functions.« less

The NifA-RpoN Regulon of Mesorhizobium loti Strain R7A and Its Symbiotic Activation by a Novel LacI/GalR-Family Regulator

PubMed Central

Sullivan, John T.; Brown, Steven D.; Ronson, Clive W.

2013-01-01

Mesorhizobium loti is the microsymbiont of Lotus species, including the model legume L. japonicus. M. loti differs from other rhizobia in that it contains two copies of the key nitrogen fixation regulatory gene nifA, nifA1 and nifA2, both of which are located on the symbiosis island ICEMlSymR7A. M. loti R7A also contains two rpoN genes, rpoN1 located on the chromosome outside of ICEMlSymR7A and rpoN2 that is located on ICEMlSymR7A. The aims of the current work were to establish how nifA expression was activated in M. loti and to characterise the NifA-RpoN regulon. The nifA2 and rpoN2 genes were essential for nitrogen fixation whereas nifA1 and rpoN1 were dispensable. Expression of nifA2 was activated, possibly in response to an inositol derivative, by a novel regulator of the LacI/GalR family encoded by the fixV gene located upstream of nifA2. Other than the well-characterized nif/fix genes, most NifA2-regulated genes were not required for nitrogen fixation although they were strongly expressed in nodules. The NifA-regulated nifZ and fixU genes, along with nifQ which was not NifA-regulated, were required in M. loti for a fully effective symbiosis although they are not present in some other rhizobia. The NifA-regulated gene msi158 that encodes a porin was also required for a fully effective symbiosis. Several metabolic genes that lacked NifA-regulated promoters were strongly expressed in nodules in a NifA2-dependent manner but again mutants did not have an overt symbiotic phenotype. In summary, many genes encoded on ICEMlSymR7A were strongly expressed in nodules but not free-living rhizobia, but were not essential for symbiotic nitrogen fixation. It seems likely that some of these genes have functional homologues elsewhere in the genome and that bacteroid metabolism may be sufficiently plastic to adapt to loss of certain enzymatic functions. PMID:23308282

Woody encroachment impacts on ecosystem nitrogen cycling: fixation, storage and gas loss

NASA Astrophysics Data System (ADS)

Soper, F.; Sparks, J. P.

2016-12-01

Woody encroachment is a pervasive land cover change throughout the tropics and subtropics. Encroachment is frequently catalyzed by nitrogen (N)-fixing trees and the resulting N inputs have the potential to alter whole-ecosystem N cycling, accumulation and loss. In the southern US, widespread encroachment by legume Prosopis glandulosa is associated with increased soil total N storage, inorganic N concentrations, and net mineralization and nitrification rates. To better understand the effects of this process on ecosystem N cycling, we investigated patterns of symbiotic N fixation, N accrual and soil N trace gas and N2 emissions during Prosopis encroachment into the southern Rio Grande Plains. Analyses of d15N in foliage, xylem sap and plant-available soil N suggested that N fixation rates vary seasonally, inter-annually and as a function of plant age and abiotic conditions. Applying a small-scale mass balance model to soil N accrual around individual trees (accounting for atmospheric inputs, and gas and hydrologic losses) generated current fixation estimates of 11 kg N ha-1 yr-1, making symbiotic fixation the largest input of N to the ecosystem. However, soil N accrual and increased cycling rates did not translate into increased N gas losses. Two years of field measurements of a complete suite of N trace gases (ammonia, nitrous oxide, nitric oxide and other oxidized N compounds) found no difference in flux between upland Prosopis groves and adjacent unencroached grasslands. Total emissions average 0.56-0.65 kg N ha-1 yr-1, comparable to other southern US grasslands. Lab incubations suggested that N2 losses are likely to be low, with field oxygen conditions not usually conducive to denitrification. Taken together, results suggest that this ecosystem is currently experiencing a period of significant net N accrual, driven by fixation under ongoing encroachment. Given the large scale of woody legume encroachment in the USA, this process is likely to contribute

Spatially robust estimates of biological nitrogen (N) fixation imply substantial human alteration of the tropical N cycle

PubMed Central

Sullivan, Benjamin W.; Smith, W. Kolby; Townsend, Alan R.; Nasto, Megan K.; Reed, Sasha C.; Chazdon, Robin L.; Cleveland, Cory C.

2014-01-01

Biological nitrogen fixation (BNF) is the largest natural source of exogenous nitrogen (N) to unmanaged ecosystems and also the primary baseline against which anthropogenic changes to the N cycle are measured. Rates of BNF in tropical rainforest are thought to be among the highest on Earth, but they are notoriously difficult to quantify and are based on little empirical data. We adapted a sampling strategy from community ecology to generate spatial estimates of symbiotic and free-living BNF in secondary and primary forest sites that span a typical range of tropical forest legume abundance. Although total BNF was higher in secondary than primary forest, overall rates were roughly five times lower than previous estimates for the tropical forest biome. We found strong correlations between symbiotic BNF and legume abundance, but we also show that spatially free-living BNF often exceeds symbiotic inputs. Our results suggest that BNF in tropical forest has been overestimated, and our data are consistent with a recent top-down estimate of global BNF that implied but did not measure low tropical BNF rates. Finally, comparing tropical BNF within the historical area of tropical rainforest with current anthropogenic N inputs indicates that humans have already at least doubled reactive N inputs to the tropical forest biome, a far greater change than previously thought. Because N inputs are increasing faster in the tropics than anywhere on Earth, both the proportion and the effects of human N enrichment are likely to grow in the future. PMID:24843146

In‐loop flow [11C]CO2 fixation and radiosynthesis of N,N′‐[11C]dibenzylurea

PubMed Central

Downey, Joseph; Bongarzone, Salvatore; Hader, Stefan

2017-01-01

Cyclotron‐produced carbon‐11 is a highly valuable radionuclide for the production of positron emission tomography (PET) radiotracers. It is typically produced as relatively unreactive carbon‐11 carbon dioxide ([11C]CO2), which is most commonly converted into a more reactive precursor for synthesis of PET radiotracers. The development of [11C]CO2 fixation methods has more recently enabled the direct radiolabelling of a diverse array of structures directly from [11C]CO2, and the advantages afforded by the use of a loop‐based system used in 11C‐methylation and 11C‐carboxylation reactions inspired us to apply the [11C]CO2 fixation “in‐loop.” In this work, we developed and investigated a new ethylene tetrafluoroethylene (ETFE) loop‐based [11C]CO2 fixation method, enabling the fast and efficient, direct‐from‐cyclotron, in‐loop trapping of [11C]CO2 using mixed DBU/amine solutions. An optimised protocol was integrated into a proof‐of‐concept in‐loop flow radiosynthesis of N,N′‐[11C]dibenzylurea. This reaction exhibited an average 78% trapping efficiency and a crude radiochemical purity of 83% (determined by radio‐HPLC), giving an overall nonisolated radiochemical yield of 72% (decay‐corrected) within just 3 minutes from end of bombardment. This proof‐of‐concept reaction has demonstrated that efficient [11C]CO2 fixation can be achieved in a low‐volume (150 μL) ETFE loop and that this can be easily integrated into a rapid in‐loop flow radiosynthesis of carbon‐11–labelled products. This new in‐loop methodology will allow fast radiolabelling reactions to be performed using cheap/disposable ETFE tubing setup (ideal for good manufacturing practice production) thereby contributing to the widespread usage of [11C]CO2 trapping/fixation reactions for the production of PET radiotracers. PMID:28977686

Symbiotic N nutrition, bradyrhizobial biodiversity and photosynthetic functioning of six inoculated promiscuous-nodulating soybean genotypes.

PubMed

Pule-Meulenberg, Flora; Gyogluu, Cynthia; Naab, Jesse; Dakora, Felix D

2011-04-15

Six promiscuous soybean genotypes were assessed for their ability to nodulate with indigenous root-nodule bacteria in Ghana, with Bradyrhizobium japonicum WB74 serving as positive control. Although the results revealed free nodulation of all six genotypes in both inoculated and uninoculated plots, there was a marked effect of inoculation on photosynthetic rates and whole-plant C. Inoculation also increased stomatal conductance in TGx1485-1D, TGx1448-2E, TGx1740-2F and TGx1445-3E, leading to significantly elevated transpiration rates in the last two genotypes, and a decrease in TGx1485-1D, TGx1440-1E and Salintuya-1, resulting in reduced leaf transpiration and decreased C accumulation. Nodulation, total plant biomass, plant N concentration and content also increased and ∂(15)N of the six genotypes, except for TGx1448-2E decreased. Significantly higher %Ndfa resulted in all the soybean genotypes tested (except for TGx1485-1D), and the symbiotic N yield in TGx1740-2F and TGx1448-2E doubled. PCR-RFLP revealed 18 distinct IGS types present in root nodules of the six promiscuous soybean genotypes, with IGS type II being isolated from all six genotypes, followed by IGS types X and XI from five out of the six genotypes. Marked differences in strain IGS type symbiotic efficiency were revealed. For example, as sole nodule occupant, IGS type XI produced high symbiotic N in TGx1445-3E, but low amounts in TGx1448-2E. Inoculated Salintuya-1, which trapped nine strain IGS types in its root nodules, was the most promiscuous genotype, but produced less symbiotic N compared to genotypes with fewer strains in their root nodules. Copyright © 2010 Elsevier GmbH. All rights reserved.

Aphotic N2 fixation along an oligotrophic to ultraoligotrophic transect in the western tropical South Pacific Ocean

NASA Astrophysics Data System (ADS)

Benavides, Mar; Shoemaker, Katyanne M.; Moisander, Pia H.; Niggemann, Jutta; Dittmar, Thorsten; Duhamel, Solange; Grosso, Olivier; Pujo-Pay, Mireille; Hélias-Nunige, Sandra; Fumenia, Alain; Bonnet, Sophie

2018-05-01

The western tropical South Pacific (WTSP) Ocean has been recognized as a global hot spot of dinitrogen (N2) fixation. Here, as in other marine environments across the oceans, N2 fixation studies have focused on the sunlit layer. However, studies have confirmed the importance of aphotic N2 fixation activity, although until now only one had been performed in the WTSP. In order to increase our knowledge of aphotic N2 fixation in the WTSP, we measured N2 fixation rates and identified diazotrophic phylotypes in the mesopelagic layer along a transect spanning from New Caledonia to French Polynesia. Because non-cyanobacterial diazotrophs presumably need external dissolved organic matter (DOM) sources for their nutrition, we also identified DOM compounds using Fourier transform ion cyclotron resonance mass spectrometry (FTICRMS) with the aim of searching for relationships between the composition of DOM and non-cyanobacterial N2 fixation in the aphotic ocean. N2 fixation rates were low (average 0.63 ± 0.07 nmol N L-1 d-1) but consistently detected across all depths and stations, representing ˜ 6-88 % of photic N2 fixation. N2 fixation rates were not significantly correlated with DOM compounds. The analysis of nifH gene amplicons revealed a wide diversity of non-cyanobacterial diazotrophs, mostly matching clusters 1 and 3. Interestingly, a distinct phylotype from the major nifH subcluster 1G dominated at 650 dbar, coinciding with the oxygenated Subantarctic Mode Water (SAMW). This consistent pattern suggests that the distribution of aphotic diazotroph communities is to some extent controlled by water mass structure. While the data available are still too scarce to elucidate the distribution and controls of mesopelagic non-cyanobacterial diazotrophs in the WTSP, their prevalence in the mesopelagic layer and the consistent detection of active N2 fixation activity at all depths sampled during our study suggest that aphotic N2 fixation may contribute significantly to fixed

The Genetics of Symbiotic Nitrogen Fixation: Comparative Genomics of 14 Rhizobia Strains by Resolution of Protein Clusters

PubMed Central

Black, Michael; Moolhuijzen, Paula; Chapman, Brett; Barrero, Roberto; Howieson, John; Hungria, Mariangela; Bellgard, Matthew

2012-01-01

The symbiotic relationship between legumes and nitrogen fixing bacteria is critical for agriculture, as it may have profound impacts on lowering costs for farmers, on land sustainability, on soil quality, and on mitigation of greenhouse gas emissions. However, despite the importance of the symbioses to the global nitrogen cycling balance, very few rhizobial genomes have been sequenced so far, although there are some ongoing efforts in sequencing elite strains. In this study, the genomes of fourteen selected strains of the order Rhizobiales, all previously fully sequenced and annotated, were compared to assess differences between the strains and to investigate the feasibility of defining a core ‘symbiome’—the essential genes required by all rhizobia for nodulation and nitrogen fixation. Comparison of these whole genomes has revealed valuable information, such as several events of lateral gene transfer, particularly in the symbiotic plasmids and genomic islands that have contributed to a better understanding of the evolution of contrasting symbioses. Unique genes were also identified, as well as omissions of symbiotic genes that were expected to be found. Protein comparisons have also allowed the identification of a variety of similarities and differences in several groups of genes, including those involved in nodulation, nitrogen fixation, production of exopolysaccharides, Type I to Type VI secretion systems, among others, and identifying some key genes that could be related to host specificity and/or a better saprophytic ability. However, while several significant differences in the type and number of proteins were observed, the evidence presented suggests no simple core symbiome exists. A more abstract systems biology concept of nitrogen fixing symbiosis may be required. The results have also highlighted that comparative genomics represents a valuable tool for capturing specificities and generalities of each genome. PMID:24704847

N2 production and fixation in deep-tier burrows of Squilla empusa in muddy sediments of Great Peconic Bay

NASA Astrophysics Data System (ADS)

Waugh, Stuart; Aller, Robert C.

2017-11-01

Global marine N budgets often show deficits due to dominance of benthic N2 production relative to pelagic N2 fixation. Recent studies have argued that benthic N2 fixation in shallow water environments has been underestimated. In particular, N2 fixation associated with animal burrows may be significant as indicated by high rates of N2 fixation reported in muddy sands populated by the ghost shrimp, Neotrypaea californiensis (Bertics et al., 2010). We investigated whether N2 fixation occurs at higher rates in the burrow-walls of the deep-burrowing ( 0.5-4 m) mantis shrimp, Squilla empusa, compared to ambient, estuarine muds and measured seasonal in-situ N2 concentrations in burrow-water relative to bottom-water. Acetylene reduction assays showed lower N2 fixation in burrow-walls than in un-populated sediments, likely due to inhibitory effects of O2 on ethylene production. Dissolved N2 was higher in burrow-water than proximate bottom-water at all seasons, demonstrating a consistent balance of net N2 production relative to fixation in deep-tier biogenic structures.

Tolerance or avoidance: drought frequency determines the response of an N 2 -fixing tree

Treesearch

Jeffrey M. Minucci; Chelcy Ford Miniat; Robert O. Teskey; Nina Wurzburger

2017-01-01

• Climate change is increasing drought frequency, which may affect symbiotic N2 fixation (SNF), a process that facilitates ecosystem recovery from disturbance. Here, we assessed the effect of drought frequency on the ecophysiology and SNF rate of a common N2-fixing tree in eastern US forests.•We grew Robinia pseudoacacia seedlings under the same mean soil...

The contamination of commercial 15N2 gas stocks with 15N-labeled nitrate and ammonium and consequences for nitrogen fixation measurements.

PubMed

Dabundo, Richard; Lehmann, Moritz F; Treibergs, Lija; Tobias, Craig R; Altabet, Mark A; Moisander, Pia H; Granger, Julie

2014-01-01

We report on the contamination of commercial 15-nitrogen (15N) N2 gas stocks with 15N-enriched ammonium, nitrate and/or nitrite, and nitrous oxide. 15N2 gas is used to estimate N2 fixation rates from incubations of environmental samples by monitoring the incorporation of isotopically labeled 15N2 into organic matter. However, the microbial assimilation of bioavailable 15N-labeled N2 gas contaminants, nitrate, nitrite, and ammonium, is liable to lead to the inflation or false detection of N2 fixation rates. 15N2 gas procured from three major suppliers was analyzed for the presence of these 15N-contaminants. Substantial concentrations of 15N-contaminants were detected in four Sigma-Aldrich 15N2 lecture bottles from two discrete batch syntheses. Per mole of 15N2 gas, 34 to 1900 µmoles of 15N-ammonium, 1.8 to 420 µmoles of 15N-nitrate/nitrite, and ≥21 µmoles of 15N-nitrous oxide were detected. One 15N2 lecture bottle from Campro Scientific contained ≥11 µmoles of 15N-nitrous oxide per mole of 15N2 gas, and no detected 15N-nitrate/nitrite at the given experimental 15N2 tracer dilutions. Two Cambridge Isotopes lecture bottles from discrete batch syntheses contained ≥0.81 µmoles 15N-nitrous oxide per mole 15N2, and trace concentrations of 15N-ammonium and 15N-nitrate/nitrite. 15N2 gas equilibrated cultures of the green algae Dunaliella tertiolecta confirmed that the 15N-contaminants are assimilable. A finite-differencing model parameterized using oceanic field conditions typical of N2 fixation assays suggests that the degree of detected 15N-ammonium contamination could yield inferred N2 fixation rates ranging from undetectable, <0.01 nmoles N L(-1) d(-1), to 530 nmoles N L(-1) d(-1), contingent on experimental conditions. These rates are comparable to, or greater than, N2 fixation rates commonly detected in field assays. These results indicate that past reports of N2 fixation should be interpreted with caution, and demonstrate that the purity of commercial 15N2

Investigating patterns of symbiotic nitrogen fixation during vegetation change from grassland to woodland using fine scale δ(15) N measurements.

PubMed

Soper, Fiona M; Boutton, Thomas W; Sparks, Jed P

2015-01-01

Biological nitrogen fixation (BNF) in woody plants is often investigated using foliar measurements of δ(15) N and is of particular interest in ecosystems experiencing increases in BNF due to woody plant encroachment. We sampled δ(15) N along the entire N uptake pathway including soil solution, xylem sap and foliage to (1) test assumptions inherent to the use of foliar δ(15) N as a proxy for BNF; (2) determine whether seasonal divergences occur between δ(15) Nxylem sap and δ(15) Nsoil inorganic N that could be used to infer variation in BNF; and (3) assess patterns of δ(15) N with tree age as indicators of shifting BNF or N cycling. Measurements of woody N-fixing Prosopis glandulosa and paired reference non-fixing Zanthoxylum fagara at three seasonal time points showed that δ(15) Nsoil inorganic N varied temporally and spatially between species. Fractionation between xylem and foliar δ(15) N was consistently opposite in direction between species and varied on average by 2.4‰. Accounting for these sources of variation caused percent nitrogen derived from fixation values for Prosopis to vary by up to ∼70%. Soil-xylem δ(15) N separation varied temporally and increased with Prosopis age, suggesting seasonal variation in N cycling and BNF and potential long-term increases in BNF not apparent through foliar sampling alone. © 2014 John Wiley & Sons Ltd.

Expression of drought-tolerant N2 fixation in heterogeneous inbred families derived from PI 471938 and Hutcheson soybean

USDA-ARS?s Scientific Manuscript database

Nitrogen fixation of soybean is particularly vulnerable to drought, since, in most genotypes, N2 fixation activity decreases very early in the soil drying cycle. Although a few soybean genotypes, including ‘PI 471938’, have been identified that express N2 fixation tolerance of drought, it is unknown...

N2-fixation, ammonium release and N-transfer to the microbial and classical food web within a plankton community.

PubMed

Adam, Birgit; Klawonn, Isabell; Svedén, Jennie B; Bergkvist, Johanna; Nahar, Nurun; Walve, Jakob; Littmann, Sten; Whitehouse, Martin J; Lavik, Gaute; Kuypers, Marcel M M; Ploug, Helle

2016-02-01

We investigated the role of N2-fixation by the colony-forming cyanobacterium, Aphanizomenon spp., for the plankton community and N-budget of the N-limited Baltic Sea during summer by using stable isotope tracers combined with novel secondary ion mass spectrometry, conventional mass spectrometry and nutrient analysis. When incubated with (15)N2, Aphanizomenon spp. showed a strong (15)N-enrichment implying substantial (15)N2-fixation. Intriguingly, Aphanizomenon did not assimilate tracers of (15)NH4(+) from the surrounding water. These findings are in line with model calculations that confirmed a negligible N-source by diffusion-limited NH4(+) fluxes to Aphanizomenon colonies at low bulk concentrations (<250 nm) as compared with N2-fixation within colonies. No N2-fixation was detected in autotrophic microorganisms <5 μm, which relied on NH4(+) uptake from the surrounding water. Aphanizomenon released about 50% of its newly fixed N2 as NH4(+). However, NH4(+) did not accumulate in the water but was transferred to heterotrophic and autotrophic microorganisms as well as to diatoms (Chaetoceros sp.) and copepods with a turnover time of ~5 h. We provide direct quantitative evidence that colony-forming Aphanizomenon releases about half of its recently fixed N2 as NH4(+), which is transferred to the prokaryotic and eukaryotic plankton forming the basis of the food web in the plankton community. Transfer of newly fixed nitrogen to diatoms and copepods furthermore implies a fast export to shallow sediments via fast-sinking fecal pellets and aggregates. Hence, N2-fixing colony-forming cyanobacteria can have profound impact on ecosystem productivity and biogeochemical processes at shorter time scales (hours to days) than previously thought.

Co-occurrence of methanogenesis and N2 fixation in oil sands tailings.

PubMed

Collins, C E Victoria; Foght, Julia M; Siddique, Tariq

2016-09-15

Oil sands tailings ponds in northern Alberta, Canada have been producing biogenic gases via microbial metabolism of hydrocarbons for decades. Persistent methanogenic activity in tailings ponds without any known replenishment of nutrients such as fixed nitrogen (N) persuaded us to investigate whether N2 fixation or polyacrylamide (PAM; used as a tailings flocculant) could serve as N sources. Cultures comprising mature fine tailings (MFT) plus methanogenic medium supplemented with or deficient in fixed N were incubated under an N2 headspace. Some cultures were further amended with citrate, which is used in oil sands processing, as a relevant carbon source, and/or with PAM. After an initial delay, N-deficient cultures with or without PAM produced methane (CH4) at the same rate as N-containing cultures, indicating a mechanism of overcoming apparent N-deficiency. Acetylene reduction and (15)N2 incorporation in all N-deficient cultures (with or without PAM) suggested active N2 fixation concurrently with methanogenesis but inability to use PAM as a N source. 16S rRNA gene pyrosequencing revealed little difference between archaeal populations regardless of N content. However, bacterial sequences in N-deficient cultures showed enrichment of Hyphomicrobiaceae and Clostridium members that might contain N2-fixing species. The results are important in understanding long-term production of biogenic greenhouse gases in oil sands tailings. Copyright © 2016 Elsevier B.V. All rights reserved.

Revisiting N2 fixation in Guerrero Negro intertidal microbial mats with a functional single-cell approach

PubMed Central

Woebken, Dagmar; Burow, Luke C; Behnam, Faris; Mayali, Xavier; Schintlmeister, Arno; Fleming, Erich D; Prufert-Bebout, Leslie; Singer, Steven W; Cortés, Alejandro López; Hoehler, Tori M; Pett-Ridge, Jennifer; Spormann, Alfred M; Wagner, Michael; Weber, Peter K; Bebout, Brad M

2015-01-01

Photosynthetic microbial mats are complex, stratified ecosystems in which high rates of primary production create a demand for nitrogen, met partially by N2 fixation. Dinitrogenase reductase (nifH) genes and transcripts from Cyanobacteria and heterotrophic bacteria (for example, Deltaproteobacteria) were detected in these mats, yet their contribution to N2 fixation is poorly understood. We used a combined approach of manipulation experiments with inhibitors, nifH sequencing and single-cell isotope analysis to investigate the active diazotrophic community in intertidal microbial mats at Laguna Ojo de Liebre near Guerrero Negro, Mexico. Acetylene reduction assays with specific metabolic inhibitors suggested that both sulfate reducers and members of the Cyanobacteria contributed to N2 fixation, whereas 15N2 tracer experiments at the bulk level only supported a contribution of Cyanobacteria. Cyanobacterial and nifH Cluster III (including deltaproteobacterial sulfate reducers) sequences dominated the nifH gene pool, whereas the nifH transcript pool was dominated by sequences related to Lyngbya spp. Single-cell isotope analysis of 15N2-incubated mat samples via high-resolution secondary ion mass spectrometry (NanoSIMS) revealed that Cyanobacteria were enriched in 15N, with the highest enrichment being detected in Lyngbya spp. filaments (on average 4.4 at% 15N), whereas the Deltaproteobacteria (identified by CARD-FISH) were not significantly enriched. We investigated the potential dilution effect from CARD-FISH on the isotopic composition and concluded that the dilution bias was not substantial enough to influence our conclusions. Our combined data provide evidence that members of the Cyanobacteria, especially Lyngbya spp., actively contributed to N2 fixation in the intertidal mats, whereas support for significant N2 fixation activity of the targeted deltaproteobacterial sulfate reducers could not be found. PMID:25303712

Revisiting N 2 fixation in Guerrero Negro intertidal microbial mats with a functional single-cell approach

DOE PAGES

Woebken, Dagmar; Burow, Luke C.; Behnam, Faris; ...

2014-10-10

Photosynthetic microbial mats are complex, stratified ecosystems in which high rates of primary production create a demand for nitrogen, met partially by N 2 fixation. Dinitrogenase reductase ( nifH) genes and transcripts from Cyanobacteria and heterotrophic bacteria (for example, Deltaproteobacteria) were detected in these mats, yet their contribution to N 2 fixation is poorly understood. We used a combined approach of manipulation experiments with inhibitors, nifH sequencing and single-cell isotope analysis to investigate the active diazotrophic community in intertidal microbial mats at Laguna Ojo de Liebre near Guerrero Negro, Mexico. Acetylene reduction assays with specific metabolic inhibitors suggested that bothmore » sulfate reducers and members of the Cyanobacteria contributed to N 2 fixation, whereas 15N 2 tracer experiments at the bulk level only supported a contribution of Cyanobacteria. Cyanobacterial and nifH Cluster III (including deltaproteobacterial sulfate reducers) sequences dominated the nifH gene pool, whereas the nifH transcript pool was dominated by sequences related to Lyngbya spp. Single-cell isotope analysis of 15N 2-incubated mat samples via high-resolution secondary ion mass spectrometry (NanoSIMS) revealed that Cyanobacteria were enriched in 15N, with the highest enrichment being detected in Lyngbya spp. filaments (on average 4.4 at% 15N), whereas the Deltaproteobacteria (identified by CARD-FISH) were not significantly enriched. We investigated the potential dilution effect from CARD-FISH on the isotopic composition and concluded that the dilution bias was not substantial enough to influence our conclusions. As a result, our combined data provide evidence that members of the Cyanobacteria, especially Lyngbya spp., actively contributed to N 2 fixation in the intertidal mats, whereas support for significant N 2 fixation activity of the targeted deltaproteobacterial sulfate reducers could not be found.« less

CADMIUM EFFECTS ON THE NITROGEN FIXATION SYSTEM OF RED ALDER

EPA Science Inventory

Red alder (Alnus rubra) was grown in sand culture in the greenhouse to obtain data on the effects of cadmium (Cd) on a symbiotic nitrogen (N) fixation system which contributes to the fertility of forest soils. Treatment of red alder seedlings for 11 weeks with 0.545 to 136 microm...

Predictable and efficient carbon sequestration in the North Pacific Ocean supported by symbiotic nitrogen fixation

PubMed Central

Karl, David M.; Church, Matthew J.; Dore, John E.; Letelier, Ricardo M.; Mahaffey, Claire

2012-01-01

The atmospheric and deep sea reservoirs of carbon dioxide are linked via physical, chemical, and biological processes. The last of these include photosynthesis, particle settling, and organic matter remineralization, and are collectively termed the “biological carbon pump.” Herein, we present results from a 13-y (1992–2004) sediment trap experiment conducted in the permanently oligotrophic North Pacific Subtropical Gyre that document a large, rapid, and predictable summertime (July 15–August 15) pulse in particulate matter export to the deep sea (4,000 m). Peak daily fluxes of particulate matter during the summer export pulse (SEP) average 408, 283, 24.1, 1.1, and 67.5 μmol·m−2·d−1 for total carbon, organic carbon, nitrogen, phosphorus (PP), and biogenic silica, respectively. The SEP is approximately threefold greater than mean wintertime particle fluxes and fuels more efficient carbon sequestration because of low remineralization during downward transit that leads to elevated total carbon/PP and organic carbon/PP particle stoichiometry (371:1 and 250:1, respectively). Our long-term observations suggest that seasonal changes in the microbial assemblage, namely, summertime increases in the biomass and productivity of symbiotic nitrogen-fixing cyanobacteria in association with diatoms, are the main cause of the prominent SEP. The recurrent SEP is enigmatic because it is focused in time despite the absence of any obvious predictable stimulus or habitat condition. We hypothesize that changes in day length (photoperiodism) may be an important environmental cue to initiate aggregation and subsequent export of organic matter to the deep sea. PMID:22308450

Predictable and efficient carbon sequestration in the North Pacific Ocean supported by symbiotic nitrogen fixation.

PubMed

Karl, David M; Church, Matthew J; Dore, John E; Letelier, Ricardo M; Mahaffey, Claire

2012-02-07

The atmospheric and deep sea reservoirs of carbon dioxide are linked via physical, chemical, and biological processes. The last of these include photosynthesis, particle settling, and organic matter remineralization, and are collectively termed the "biological carbon pump." Herein, we present results from a 13-y (1992-2004) sediment trap experiment conducted in the permanently oligotrophic North Pacific Subtropical Gyre that document a large, rapid, and predictable summertime (July 15-August 15) pulse in particulate matter export to the deep sea (4,000 m). Peak daily fluxes of particulate matter during the summer export pulse (SEP) average 408, 283, 24.1, 1.1, and 67.5 μmol·m(-2)·d(-1) for total carbon, organic carbon, nitrogen, phosphorus (PP), and biogenic silica, respectively. The SEP is approximately threefold greater than mean wintertime particle fluxes and fuels more efficient carbon sequestration because of low remineralization during downward transit that leads to elevated total carbon/PP and organic carbon/PP particle stoichiometry (371:1 and 250:1, respectively). Our long-term observations suggest that seasonal changes in the microbial assemblage, namely, summertime increases in the biomass and productivity of symbiotic nitrogen-fixing cyanobacteria in association with diatoms, are the main cause of the prominent SEP. The recurrent SEP is enigmatic because it is focused in time despite the absence of any obvious predictable stimulus or habitat condition. We hypothesize that changes in day length (photoperiodism) may be an important environmental cue to initiate aggregation and subsequent export of organic matter to the deep sea.

Loss of the nodule-specific cysteine rich peptide, NCR169, abolishes symbiotic nitrogen fixation in the Medicago truncatula dnf7 mutant.

PubMed

Horváth, Beatrix; Domonkos, Ágota; Kereszt, Attila; Szűcs, Attila; Ábrahám, Edit; Ayaydin, Ferhan; Bóka, Károly; Chen, Yuhui; Chen, Rujin; Murray, Jeremy D; Udvardi, Michael K; Kondorosi, Éva; Kaló, Péter

2015-12-08

Host compatible rhizobia induce the formation of legume root nodules, symbiotic organs within which intracellular bacteria are present in plant-derived membrane compartments termed symbiosomes. In Medicago truncatula nodules, the Sinorhizobium microsymbionts undergo an irreversible differentiation process leading to the development of elongated polyploid noncultivable nitrogen fixing bacteroids that convert atmospheric dinitrogen into ammonia. This terminal differentiation is directed by the host plant and involves hundreds of nodule specific cysteine-rich peptides (NCRs). Except for certain in vitro activities of cationic peptides, the functional roles of individual NCR peptides in planta are not known. In this study, we demonstrate that the inability of M. truncatula dnf7 mutants to fix nitrogen is due to inactivation of a single NCR peptide, NCR169. In the absence of NCR169, bacterial differentiation was impaired and was associated with early senescence of the symbiotic cells. Introduction of the NCR169 gene into the dnf7-2/NCR169 deletion mutant restored symbiotic nitrogen fixation. Replacement of any of the cysteine residues in the NCR169 peptide with serine rendered it incapable of complementation, demonstrating an absolute requirement for all cysteines in planta. NCR169 was induced in the cell layers in which bacteroid elongation was most pronounced, and high expression persisted throughout the nitrogen-fixing nodule zone. Our results provide evidence for an essential role of NCR169 in the differentiation and persistence of nitrogen fixing bacteroids in M. truncatula.

Loss of the nodule-specific cysteine rich peptide, NCR169, abolishes symbiotic nitrogen fixation in the Medicago truncatula dnf7 mutant

PubMed Central

Horváth, Beatrix; Domonkos, Ágota; Szűcs, Attila; Ábrahám, Edit; Ayaydin, Ferhan; Bóka, Károly; Chen, Yuhui; Chen, Rujin; Murray, Jeremy D.; Udvardi, Michael K.; Kondorosi, Éva; Kaló, Péter

2015-01-01

Host compatible rhizobia induce the formation of legume root nodules, symbiotic organs within which intracellular bacteria are present in plant-derived membrane compartments termed symbiosomes. In Medicago truncatula nodules, the Sinorhizobium microsymbionts undergo an irreversible differentiation process leading to the development of elongated polyploid noncultivable nitrogen fixing bacteroids that convert atmospheric dinitrogen into ammonia. This terminal differentiation is directed by the host plant and involves hundreds of nodule specific cysteine-rich peptides (NCRs). Except for certain in vitro activities of cationic peptides, the functional roles of individual NCR peptides in planta are not known. In this study, we demonstrate that the inability of M. truncatula dnf7 mutants to fix nitrogen is due to inactivation of a single NCR peptide, NCR169. In the absence of NCR169, bacterial differentiation was impaired and was associated with early senescence of the symbiotic cells. Introduction of the NCR169 gene into the dnf7-2/NCR169 deletion mutant restored symbiotic nitrogen fixation. Replacement of any of the cysteine residues in the NCR169 peptide with serine rendered it incapable of complementation, demonstrating an absolute requirement for all cysteines in planta. NCR169 was induced in the cell layers in which bacteroid elongation was most pronounced, and high expression persisted throughout the nitrogen-fixing nodule zone. Our results provide evidence for an essential role of NCR169 in the differentiation and persistence of nitrogen fixing bacteroids in M. truncatula. PMID:26401023

N2 Fixation by Unicellular Bacterioplankton from the Atlantic and Pacific Oceans: Phylogeny and In Situ Rates

PubMed Central

Falcón, Luisa I.; Carpenter, Edward J.; Cipriano, Frank; Bergman, Birgitta; Capone, Douglas G.

2004-01-01

N2-fixing proteobacteria (α and γ) and unicellular cyanobacteria are common in both the tropical North Atlantic and Pacific oceans. In near-surface waters proteobacterial nifH transcripts were present during both night and day while unicellular cyanobacterial nifH transcripts were present during the nighttime only, suggesting separation of N2 fixation and photosynthesis by unicellular cyanobacteria. Phylogenetic relationships among unicellular cyanobacteria from both oceans were determined after sequencing of a conserved region of 16S ribosomal DNA (rDNA) of cyanobacteria, and results showed that they clustered together, regardless of the ocean of origin. However, sequencing of nifH transcripts of unicellular cyanobacteria from both oceans showed that they clustered separately. This suggests that unicellular cyanobacteria from the tropical North Atlantic and subtropical North Pacific share a common ancestry (16S rDNA) and that potential unicellular N2 fixers have diverged (nifH). N2 fixation rates for unicellular bacterioplankton (including small cyanobacteria) from both oceans were determined in situ according to the acetylene reduction and 15N2 protocols. The results showed that rates of fixation by bacterioplankton can be almost as high as those of fixation by the colonial N2-fixing marine cyanobacteria Trichodesmium spp. in the tropical North Atlantic but that rates are much lower in the subtropical North Pacific. PMID:14766553

Estimation of phenotypic variability in symbiotic nitrogen fixation ability of common bean under drought stress using 15N natural abundance in grain.

PubMed

Polania, Jose; Poschenrieder, Charlotte; Rao, Idupulapati; Beebe, Stephen

2016-09-01

Common bean ( Phaseolus vulgaris L.) is the most important food legume, cultivated by small farmers and is usually exposed to unfavorable conditions with minimum use of inputs. Drought and low soil fertility, especially phosphorus and nitrogen (N) deficiencies, are major limitations to bean yield in smallholder systems. Beans can derive part of their required N from the atmosphere through symbiotic nitrogen fixation (SNF). Drought stress severely limits SNF ability of plants. The main objectives of this study were to: (i) test and validate the use of 15 N natural abundance in grain to quantify phenotypic differences in SNF ability for its implementation in breeding programs of common bean with bush growth habit aiming to improve SNF, and (ii) quantify phenotypic differences in SNF under drought to identify superior genotypes that could serve as parents. Field studies were conducted at CIAT-Palmira, Colombia using a set of 36 bean genotypes belonging to the Middle American gene pool for evaluation in two seasons with two levels of water supply (irrigated and drought stress). We used 15 N natural abundance method to compare SNF ability estimated from shoot tissue sampled at mid-pod filling growth stage vs. grain tissue sampled at harvest. Our results showed positive and significant correlation between nitrogen derived from the atmosphere (%Ndfa) estimated using shoot tissue at mid-pod filling and %Ndfa estimated using grain tissue at harvest. Both methods showed phenotypic variability in SNF ability under both drought and irrigated conditions and a significant reduction in SNF ability was observed under drought stress. We suggest that the method of estimating Ndfa using grain tissue (Ndfa-G) could be applied in bean breeding programs to improve SNF ability. Using this method of Ndfa-G, we identified four bean lines (RCB 593, SEA 15, NCB 226 and BFS 29) that combine greater SNF ability with greater grain yield under drought stress and these could serve as potential

Regional constraints to biological nitrogen fixation in post-fire forest communities

USGS Publications Warehouse

Yelenik, Stephanie; Perakis, Steven S.; Hibbs, David

2013-01-01

Biological nitrogen fixation (BNF) is a key ecological process that can restore nitrogen (N) lost in wildfire and shape the pace and pattern of post-fire forest recovery. To date, there is limited information on how climate and soil fertility interact to influence different pathways of BNF in early forest succession. We studied asymbiotic (forest floor and soil) and symbiotic (the shrub Ceanothus integerrimus) BNF rates across six sites in the Klamath National Forest, California, USA. We used combined gradient and experimental phosphorus (P) fertilization studies to explore cross-site variation in BNF rates and then related these rates to abiotic and biotic variables. We estimate that our measured BNF rates 22 years after wildfire (6.1–12.1 kg N·ha-1·yr-1) are unlikely to fully replace wildfire N losses. We found that asymbiotic BNF is P limited, although this is not the case for symbiotic BNF in Ceanothus. In contrast, Ceanothus BNF is largely driven by competition from other vegetation: in high-productivity sites with high potential evapotranspiration (Et), shrub biomass is suppressed as tree biomass increases. Because shrub biomass governed cross-site variation in Ceanothus BNF, this competitive interaction led to lower BNF in sites with high productivity and Et. Overall, these results suggest that the effects of nutrients play a larger role in driving asymbiotic than symbiotic fixation across our post-fire sites. However, because symbiotic BNF is 8–90x greater than asymbiotic BNF, it is interspecific plant competition that governs overall BNF inputs in these forests.

Symbiotic Efficiency of Native Rhizobia Nodulating Common Bean (Phaseolus vulgaris L.) in Soils of Western Kenya

PubMed Central

Kawaka, Fanuel; Dida, Mathews M.; Opala, Peter A.; Ombori, Omwoyo; Maingi, John; Osoro, Newton; Muthini, Morris; Amoding, Alice; Mukaminega, Dative; Muoma, John

2014-01-01

This study was conducted to determine the abundance and symbiotic efficiency of native rhizobia nodulating common bean in Kisumu and Kakamega, Kenya. Soil sampling was carried out in three farms that had been used for growing common bean for at least two seasons and one fallow land with no known history of growing common bean or inoculation. Abundance of soil rhizobia and symbiotic efficiency (SE) were determined in a greenhouse experiment. Native rhizobia populations ranged from 3.2 × 101 to 3.5 × 104 cells per gram of soil. Pure bacterial cultures isolated from fresh and healthy root nodules exhibited typical characteristics of Rhizobium sp. on yeast extract mannitol agar media supplemented with Congo red. Bean inoculation with the isolates significantly (p < 0.05) increased the shoot dry weight and nitrogen (N) concentration and content. The SE of all the native rhizobia were higher when compared to a reference strain, CIAT 899 (67%), and ranged from 74% to 170%. Four isolates had SE above a second reference strain, Strain 446 (110%). Our results demonstrate the presence of native rhizobia that are potentially superior to the commercial inoculants. These can be exploited to enhance bean inoculation programmes in the region. PMID:27355005

The Contamination of Commercial 15N2 Gas Stocks with 15N–Labeled Nitrate and Ammonium and Consequences for Nitrogen Fixation Measurements

PubMed Central

Dabundo, Richard; Lehmann, Moritz F.; Treibergs, Lija; Tobias, Craig R.; Altabet, Mark A.; Moisander, Pia H.; Granger, Julie

2014-01-01

We report on the contamination of commercial 15-nitrogen (15N) N2 gas stocks with 15N-enriched ammonium, nitrate and/or nitrite, and nitrous oxide. 15N2 gas is used to estimate N2 fixation rates from incubations of environmental samples by monitoring the incorporation of isotopically labeled 15N2 into organic matter. However, the microbial assimilation of bioavailable 15N-labeled N2 gas contaminants, nitrate, nitrite, and ammonium, is liable to lead to the inflation or false detection of N2 fixation rates. 15N2 gas procured from three major suppliers was analyzed for the presence of these 15N-contaminants. Substantial concentrations of 15N-contaminants were detected in four Sigma-Aldrich 15N2 lecture bottles from two discrete batch syntheses. Per mole of 15N2 gas, 34 to 1900 µmoles of 15N-ammonium, 1.8 to 420 µmoles of 15N-nitrate/nitrite, and ≥21 µmoles of 15N-nitrous oxide were detected. One 15N2 lecture bottle from Campro Scientific contained ≥11 µmoles of 15N-nitrous oxide per mole of 15N2 gas, and no detected 15N-nitrate/nitrite at the given experimental 15N2 tracer dilutions. Two Cambridge Isotopes lecture bottles from discrete batch syntheses contained ≥0.81 µmoles 15N-nitrous oxide per mole 15N2, and trace concentrations of 15N-ammonium and 15N-nitrate/nitrite. 15N2 gas equilibrated cultures of the green algae Dunaliella tertiolecta confirmed that the 15N-contaminants are assimilable. A finite-differencing model parameterized using oceanic field conditions typical of N2 fixation assays suggests that the degree of detected 15N-ammonium contamination could yield inferred N2 fixation rates ranging from undetectable, <0.01 nmoles N L−1 d−1, to 530 nmoles N L−1 d−1, contingent on experimental conditions. These rates are comparable to, or greater than, N2 fixation rates commonly detected in field assays. These results indicate that past reports of N2 fixation should be interpreted with caution, and demonstrate that the purity of commercial 15N2

Molecular Determinants of a Symbiotic Chronic Infection

PubMed Central

Gibson, Katherine E.; Kobayashi, Hajime

2009-01-01

Rhizobial bacteria colonize legume roots for the purpose of biological nitrogen fixation. A complex series of events, coordinated by host and bacterial signal molecules, underlie the development of this symbiotic interaction. Rhizobia elicit de novo formation of a novel root organ within which they establish a chronic intracellular infection. Legumes permit rhizobia to invade these root tissues while exerting control over the infection process. Once rhizobia gain intracellular access to their host, legumes also strongly influence the process of bacterial differentiation that is required for nitrogen fixation. Even so, symbiotic rhizobia play an active role in promoting their goal of host invasion and chronic persistence by producing a variety of signal molecules that elicit changes in host gene expression. In particular, rhizobia appear to advocate for their access to the host by producing a variety of signal molecules capable of suppressing a general pathogen defense response. PMID:18983260

Pesticides reduce symbiotic efficiency of nitrogen-fixing rhizobia and host plants

PubMed Central

Fox, Jennifer E.; Gulledge, Jay; Engelhaupt, Erika; Burow, Matthew E.; McLachlan, John A.

2007-01-01

Unprecedented agricultural intensification and increased crop yield will be necessary to feed the burgeoning world population, whose global food demand is projected to double in the next 50 years. Although grain production has doubled in the past four decades, largely because of the widespread use of synthetic nitrogenous fertilizers, pesticides, and irrigation promoted by the “Green Revolution,” this rate of increased agricultural output is unsustainable because of declining crop yields and environmental impacts of modern agricultural practices. The last 20 years have seen diminishing returns in crop yield in response to increased application of fertilizers, which cannot be completely explained by current ecological models. A common strategy to reduce dependence on nitrogenous fertilizers is the production of leguminous crops, which fix atmospheric nitrogen via symbiosis with nitrogen-fixing rhizobia bacteria, in rotation with nonleguminous crops. Here we show previously undescribed in vivo evidence that a subset of organochlorine pesticides, agrichemicals, and environmental contaminants induces a symbiotic phenotype of inhibited or delayed recruitment of rhizobia bacteria to host plant roots, fewer root nodules produced, lower rates of nitrogenase activity, and a reduction in overall plant yield at time of harvest. The environmental consequences of synthetic chemicals compromising symbiotic nitrogen fixation are increased dependence on synthetic nitrogenous fertilizer, reduced soil fertility, and unsustainable long-term crop yields. PMID:17548832

Characterization of the Symbiotic Nitrogen-Fixing Common Bean Low Phytic Acid (lpa1) Mutant Response to Water Stress.

PubMed

Chiozzotto, Remo; Ramírez, Mario; Talbi, Chouhra; Cominelli, Eleonora; Girard, Lourdes; Sparvoli, Francesca; Hernández, Georgina

2018-02-15

The common bean ( Phaseolus vulgaris L.) low phytic acid ( lpa1 ) biofortified genotype produces seeds with improved nutritional characteristics and does not display negative pleiotropic effects. Here we demonstrated that lpa1 plants establish an efficient nitrogen-fixing symbiosis with Rhizobium etli CE3. The lpa1 nodules showed a higher expression of nodule-function related genes than the nodules of the parental wild type genotype (BAT 93). We analyzed the response to water stress of lpa1 vs. BAT 93 plants grown under fertilized or under symbiotic N₂-fixation conditions. Water stress was induced by water withholding (up to 14% soil moisture) to fertilized or R. etli nodulated plants previously grown with normal irrigation. The fertilized lpa1 plants showed milder water stress symptoms during the water deployment period and after the rehydration recovery period when lpa1 plants showed less biomass reduction. The symbiotic water-stressed lpa1 plants showed decreased nitrogenase activity that coincides with decreased sucrose synthase gene expression in nodules; lower turgor weight to dry weight (DW) ratio, which has been associated with higher drought resistance index; downregulation of carbon/nitrogen (C/N)-related and upregulation of stress-related genes. Higher expression of stress-related genes was also observed in bacteroids of stressed lpa1 plants that also displayed very high expression of the symbiotic cbb ₃ oxidase ( fixN d).

CO2 and soil water potential as regulators of the growth and N fraction derived from fixation of a legume in tallgrass prairie communities

USDA-ARS?s Scientific Manuscript database

CO2 enrichment may increase N input to ecosystems by increasing N2 fixation, but the fixation-CO2 response depends on factors such as soil water availability that are influenced by both CO2 and soil properties. We used the d15N natural abundance method to determine N2 fixation by the legume Desmant...

Plant, Microbiome, and Biogeochemistry: Quantifying moss-associated N fixation in Alaska

NASA Astrophysics Data System (ADS)

Stuart, J.; Mack, M. C.; Holland Moritz, H.; Fierer, N.; McDaniels, S.; Lewis, L.

2017-12-01

The future carbon (C) sequestration potential of the Arctic and boreal zones, currently the largest terrestrial C sink globally, is linked to nitrogen (N) cycling and N availability vis-a-vis C accumulation and plant species composition. Pristine environments in Alaska have low anthropogenic N deposition (<1 kg N ha-1 yr-1), and the main source of new N to these ecosystems is through previously overlooked N-fixation from microbial communities on mosses. Despite the importance of moss associated N-fixation, the relationship between moss species, microbial communities, and fixation rates remains ambiguous. In the summer of 2016, the fixation rates of 20 moss species from sites around both Fairbanks and Toolik Lake were quantified using 15N2 incubations. Subsequently, the microbial community and moss genome of the samples were also analyzed by collaborators. The most striking result is that all sampled moss genera fixed N, including well-studied feather mosses such as Hylocomium splendens and Pleurozium schreberi as well as less common but ecologically relevant mosses such as Aulacomnium spp., Dicranum spp., Ptilium crista-castrensis, and Tomentypnum nitens. Across all samples, preliminary fixation rates ranged from 0.004-19.994 µg N g-1 moss d-1. Depending upon percent cover, moss-associated N fixation is the largest input of new N to the ecosystem. Given this, linking variation in N-fixation rates to microbial and moss community structures can be helpful in predicting future trends of C and N cycling in northern latitudes. Vegetation changes, alterations in downstream biogeochemical N processes, and anthropogenic N deposition could all interact with or alter moss associated N-fixation, thereby changing ecosystem N inputs. Further elucidation of the species level signal in N-fixation rates and microbial community will augment our knowledge of N cycling in northern latitudes, both current and future.

Comparative Genomic Analysis of N2-Fixing and Non-N2-Fixing Paenibacillus spp.: Organization, Evolution and Expression of the Nitrogen Fixation Genes

PubMed Central

Xie, Jian-Bo; Du, Zhenglin; Bai, Lanqing; Tian, Changfu; Zhang, Yunzhi; Xie, Jiu-Yan; Wang, Tianshu; Liu, Xiaomeng; Chen, Xi; Cheng, Qi; Chen, Sanfeng; Li, Jilun

2014-01-01

We provide here a comparative genome analysis of 31 strains within the genus Paenibacillus including 11 new genomic sequences of N2-fixing strains. The heterogeneity of the 31 genomes (15 N2-fixing and 16 non-N2-fixing Paenibacillus strains) was reflected in the large size of the shell genome, which makes up approximately 65.2% of the genes in pan genome. Large numbers of transposable elements might be related to the heterogeneity. We discovered that a minimal and compact nif cluster comprising nine genes nifB, nifH, nifD, nifK, nifE, nifN, nifX, hesA and nifV encoding Mo-nitrogenase is conserved in the 15 N2-fixing strains. The nif cluster is under control of a σ70-depedent promoter and possesses a GlnR/TnrA-binding site in the promoter. Suf system encoding [Fe–S] cluster is highly conserved in N2-fixing and non-N2-fixing strains. Furthermore, we demonstrate that the nif cluster enabled Escherichia coli JM109 to fix nitrogen. Phylogeny of the concatenated NifHDK sequences indicates that Paenibacillus and Frankia are sister groups. Phylogeny of the concatenated 275 single-copy core genes suggests that the ancestral Paenibacillus did not fix nitrogen. The N2-fixing Paenibacillus strains were generated by acquiring the nif cluster via horizontal gene transfer (HGT) from a source related to Frankia. During the history of evolution, the nif cluster was lost, producing some non-N2-fixing strains, and vnf encoding V-nitrogenase or anf encoding Fe-nitrogenase was acquired, causing further diversification of some strains. In addition, some N2-fixing strains have additional nif and nif-like genes which may result from gene duplications. The evolution of nitrogen fixation in Paenibacillus involves a mix of gain, loss, HGT and duplication of nif/anf/vnf genes. This study not only reveals the organization and distribution of nitrogen fixation genes in Paenibacillus, but also provides insight into the complex evolutionary history of nitrogen fixation. PMID:24651173

Nitrogen fixation rates associated with the invasive macroalgae Sargassum horneri around Catalina Island, CA

NASA Astrophysics Data System (ADS)

DeLiberto, A.

2016-02-01

Nitrogen fixation is an important process which allows organisms access to biologically unavailable dinitrogen gas. Bacteria, known as diazotrophs use the enzyme nitrogenase to convert N2 to NH3. These bacteria, including certain species of heterotrophic bacteria and cyanobacteria, can be symbiotically associated with marine macroalgae, facilitating nutrient cycling in oligotrophic regions. As many species within the genera Sargassum are associated with nitrogen fixation, this study hypothesized that nitrogenase activity would be associated with the benthic invasive Sargassum horneri on Catalina Island. In the past decade, Sargassum horneri, an invasive from Japan, has spread throughout the waters around Catalina Island. Using the acetylene reduction procedure using flame ionization detection, initial nitrogenase activity of S. horneri sampled from Indian Rock was observed. Nitrogen fixation rates increased with decomposition, particularly in dark/anaerobic treatments, suggesting the presence of heterotrophic bacteria. In addition, acetate additions greatly increase nitrogen fixation rates, once again indicating heterotrophic nitrogen fixing bacteria.

Epiphytic Cyanobacteria on Chara vulgaris Are the Main Contributors to N2 Fixation in Rice Fields

PubMed Central

Ariosa, Yoanna; Quesada, Antonio; Aburto, Juan; Carrasco, David; Carreres, Ramón; Leganés, Francisco; Fernández Valiente, Eduardo

2004-01-01

The distribution of nitrogenase activity in the rice-soil system and the possible contribution of epiphytic cyanobacteria on rice plants and other macrophytes to this activity were studied in two locations in the rice fields of Valencia, Spain, in two consecutive crop seasons. The largest proportion of photodependent N2 fixation was associated with the macrophyte Chara vulgaris in both years and at both locations. The nitrogen fixation rate associated with Chara always represented more than 45% of the global nitrogenase activity measured in the rice field. The estimated average N2 fixation rate associated with Chara was 27.53 kg of N ha−1 crop−1. The mean estimated N2 fixation rates for the other parts of the system for all sampling periods were as follows: soil, 4.07 kg of N ha−1 crop−1; submerged parts of rice plants, 3.93 kg of N ha−1 crop−1; and roots, 0.28 kg of N ha−1 crop−1. Micrographic studies revealed the presence of epiphytic cyanobacteria on the surface of Chara. Three-dimensional reconstructions by confocal scanning laser microscopy revealed no cyanobacterial cells inside the Chara structures. Quantification of epiphytic cyanobacteria by image analysis revealed that cyanobacteria were more abundant in nodes than in internodes (on average, cyanobacteria covered 8.4% ± 4.4% and 6.2% ± 5.0% of the surface area in the nodes and internodes, respectively). Epiphytic cyanobacteria were also quantified by using a fluorometer. This made it possible to discriminate which algal groups were the source of chlorophyll a. Chlorophyll a measurements confirmed that cyanobacteria were more abundant in nodes than in internodes (on average, the chlorophyll a concentrations were 17.2 ± 28.0 and 4.0 ± 3.8 μg mg [dry weight] of Chara−1 in the nodes and internodes, respectively). These results indicate that this macrophyte, which is usually considered a weed in the context of rice cultivation, may help maintain soil N fertility in the rice field

Biological N2-FIXATION and Mineral N-Fertilization Effects on Soybean (Glicine max L. Merr.) Yield Under Temperate Climate Conditions

NASA Astrophysics Data System (ADS)

László Phd, M., ,, Dr.

2009-04-01

continues to increase) and allewiate world hunger is to increase the intensity of production in those ecosystems that lend themselves to sustainable intensification while decreasing the intensity of production in the more fragile ecologies (Reeves 1998). Most plants depend entirely for growth on fixed nitrogen absorbed from the soil, mainly as nitrate but also as ammonium. Therefore to the methods of crop production now dominant in the agricultural systems of many developed countries strongly depend upon a sustained input of N. Economic and environmental considerations surrounding fertilizer use then empasize the need to increase the efficiency of N- utilization by plants. On the other hand the biological nitrogen fixation (BNF) is important under all imput conditions to ensure an optimal supply of nitrogen to the farming system. A well-founded understanding of the mechanistic interactions between BNF and N limitations is presently lacking. Synbiotic nitrogen fixation by legumes makes a valuable contribution to N-inputs, especially in countries like Hungary where effective rhizobia-inoculation techniques have been developed in the context of the new sustainable agricultural system. It is widely known that soya bean -Glycine max (L.) Merr.-, is an important legume. This plant able to fix the atmospheric nitrogen (N2) it needs for growth through the agency of specific bacteria Rhizobium japonicum. Under field conditions fixation usually accounts for only 25-30% of the total nitrogen accumulated by these plants at harvest. Therefore to marginal yield have to optimalise the nitrogen supply of these legume by N-fertilization. Objectives for our experiments were to (1.) comparisons of the plant nutrition performance of different soil nitrogen supply levels by N- fertilization and N- fixation under Mediterranean climate conditions at Hungary, (2.) evaluates the potential for N2 fixation imputs by grain legume based on the soya bean as a means of improving soil fertility, (3

The importance of regulation of nitrogen fixation

NASA Astrophysics Data System (ADS)

Menge, D. N.

2012-12-01

I am not a proponent of including more detail in models simply because it makes them more realistic. More complexity increases the difficulty of model interpretation, so it only makes sense to include complexity if its benefit exceeds its costs. Biological nitrogen (N) fixation (BNF) is one process for which I feel the benefits of including greater complexity far outweigh the costs. I don't think that just because I work on BNF; I work on BNF because I think that. BNF, a microbial process carried out by free-living and symbiotic microbes, is the dominant N input to many ecosystems, the primary mechanism by which N deficiency can feed back to N inputs, and a main mechanism by which N surplus can develop. The dynamics of BNF, therefore, have huge implications for the rate of carbon uptake and the extent of CO2 fertilization, as well as N export to waterways and N2O emissions to the atmosphere. Unfortunately, there are serious deficiencies in our understanding of BNF. One main deficiency in our understanding is the extent to which various symbiotic N fixing organisms respond to imbalanced nutrition. Theory suggests that these responses, which I will call "strategies," have fundamental consequences for N fixer niches and ecosystem-level N and C cycling. Organisms that fix N regardless of whether they need it, a strategy that I will call "obligate," occupy post-disturbance niches and rapidly lead to N surplus. On the contrary, organisms that only fix as much N as they need, a "facultative" strategy, can occupy a wider range of successional niches, do not produce surplus N, and respond more rapidly to increased atmospheric CO2. In this talk I will show new results showing that consideration of these strategies could on its own explain the latitudinal distribution of symbiotic N fixing trees in North America. Specifically, the transition in N-fixing tree abundance from ~10% of basal area south of 35° latitude to ~1% of basal area north of 35° latitude that we observe

Fluorescent excitation of Fe 2, Mn 2, Ti 2, N 1 lines by V 4, N 5, O 6: Emission lines in the spectra of symbiotic stars and Seyfert galaxies

NASA Technical Reports Server (NTRS)

Gilra, D. P.

1984-01-01

Analysis of the published IUE and ground based high resolution spectra of symbiotic stars, particularly RR Tel, shows that the dominant excitation mechanism of Fe II, Mn II, Ti II, and N I lines is the selective fluorescent excitation of some levels by the strong C IV, N V, and O VI emission lines. The same mechanism should work for the excitation of Fe II lines in the spectra of Seyfert galaxies and Q60's whose emission spectra are quite similar to those of symbiotic stars. The similarities and differences between the fluroescent excitation mechanism reported herein and the Bowen's mechanism is analyzed.

Rhizobium-Legume Symbiosis and Nitrogen Fixation under Severe Conditions and in an Arid Climate

PubMed Central

Zahran, Hamdi Hussein

1999-01-01

Biological N2 fixation represents the major source of N input in agricultural soils including those in arid regions. The major N2-fixing systems are the symbiotic systems, which can play a significant role in improving the fertility and productivity of low-N soils. The Rhizobium-legume symbioses have received most attention and have been examined extensively. The behavior of some N2-fixing systems under severe environmental conditions such as salt stress, drought stress, acidity, alkalinity, nutrient deficiency, fertilizers, heavy metals, and pesticides is reviewed. These major stress factors suppress the growth and symbiotic characteristics of most rhizobia; however, several strains, distributed among various species of rhizobia, are tolerant to stress effects. Some strains of rhizobia form effective (N2-fixing) symbioses with their host legumes under salt, heat, and acid stresses, and can sometimes do so under the effect of heavy metals. Reclamation and improvement of the fertility of arid lands by application of organic (manure and sewage sludge) and inorganic (synthetic) fertilizers are expensive and can be a source of pollution. The Rhizobium-legume (herb or tree) symbiosis is suggested to be the ideal solution to the improvement of soil fertility and the rehabilitation of arid lands and is an important direction for future research. PMID:10585971

Levels of daily light doses under changed day-night cycles regulate temporal segregation of photosynthesis and N2 Fixation in the cyanobacterium Trichodesmium erythraeum IMS101.

PubMed

Cai, Xiaoni; Gao, Kunshan

2015-01-01

While the diazotrophic cyanobacterium Trichodesmium is known to display inverse diurnal performances of photosynthesis and N2 fixation, such a phenomenon has not been well documented under different day-night (L-D) cycles and different levels of light dose exposed to the cells. Here, we show differences in growth, N2 fixation and photosynthetic carbon fixation as well as photochemical performances of Trichodesmium IMS101 grown under 12L:12D, 8L:16D and 16L:8D L-D cycles at 70 μmol photons m-2 s-1 PAR (LL) and 350 μmol photons m-2 s-1 PAR (HL). The specific growth rate was the highest under LL and the lowest under HL under 16L:8D, and it increased under LL and decreased under HL with increased levels of daytime light doses exposed under the different light regimes, respectively. N2 fixation and photosynthetic carbon fixation were affected differentially by changes in the day-night regimes, with the former increasing directly under LL with increased daytime light doses and decreased under HL over growth-saturating light levels. Temporal segregation of N2 fixation from photosynthetic carbon fixation was evidenced under all day-night regimes, showing a time lag between the peak in N2 fixation and dip in carbon fixation. Elongation of light period led to higher N2 fixation rate under LL than under HL, while shortening the light exposure to 8 h delayed the N2 fixation peaking time (at the end of light period) and extended it to night period. Photosynthetic carbon fixation rates and transfer of light photons were always higher under HL than LL, regardless of the day-night cycles. Conclusively, diel performance of N2 fixation possesses functional plasticity, which was regulated by levels of light energy supplies either via changing light levels or length of light exposure.

SPARCHS: Symbiotic, Polymorphic, Automatic, Resilient, Clean-Slate, Host Security

DTIC Science & Technology

2016-03-01

SPARCHS: SYMBIOTIC , POLYMORPHIC, AUTOMATIC, RESILIENT, CLEAN-SLATE, HOST SECURITY COLUMBIA UNIVERSITY MARCH 2016 FINAL... SYMBIOTIC , POLYMORPHIC, AUTOTOMIC, RESILIENT, CLEAN-SLATE, HOST SECURITY 5a. CONTRACT NUMBER N/A 5b. GRANT NUMBER FA8750-10-2-0253 5c. PROGRAM...17 4.2.3 SYMBIOTIC EMBEDDED MACHINES

Construction and simulation of the Bradyrhizobium diazoefficiens USDA110 metabolic network: a comparison between free-living and symbiotic states.

PubMed

Yang, Yi; Hu, Xiao-Pan; Ma, Bin-Guang

2017-02-28

Bradyrhizobium diazoefficiens is a rhizobium able to convert atmospheric nitrogen into ammonium by establishing mutualistic symbiosis with soybean. It has been recognized as an important parent strain for microbial agents and is widely applied in agricultural and environmental fields. In order to study the metabolic properties of symbiotic nitrogen fixation and the differences between a free-living cell and a symbiotic bacteroid, a genome-scale metabolic network of B. diazoefficiens USDA110 was constructed and analyzed. The metabolic network, iYY1101, contains 1031 reactions, 661 metabolites, and 1101 genes in total. Metabolic models reflecting free-living and symbiotic states were determined by defining the corresponding objective functions and substrate input sets, and were further constrained by high-throughput transcriptomic and proteomic data. Constraint-based flux analysis was used to compare the metabolic capacities and the effects on the metabolic targets of genes and reactions between the two physiological states. The results showed that a free-living rhizobium possesses a steady state flux distribution for sustaining a complex supply of biomass precursors while a symbiotic bacteroid maintains a relatively condensed one adapted to nitrogen-fixation. Our metabolic models may serve as a promising platform for better understanding the symbiotic nitrogen fixation of this species.

Importance of N2-Fixation on the Productivity at the North-Western Azores Current/Front System, and the Abundance of Diazotrophic Unicellular Cyanobacteria.

PubMed

Riou, Virginie; Fonseca-Batista, Debany; Roukaerts, Arnout; Biegala, Isabelle C; Prakya, Shree Ram; Magalhães Loureiro, Clara; Santos, Mariana; Muniz-Piniella, Angel E; Schmiing, Mara; Elskens, Marc; Brion, Natacha; Martins, M Ana; Dehairs, Frank

2016-01-01

To understand the impact of the northwestern Azores Current Front (NW-AzC/AzF) system on HCO3--and N2-fixation activities and unicellular diazotrophic cyanobacteria (UCYN) distribution, we combined geochemical and biological approaches from the oligotrophic surface to upper mesopelagic waters. N2-fixation was observed to sustain 45-85% of the HCO3--fixation in the picoplanktonic fraction performing 47% of the total C-fixation at the deep chlorophyll maximum north and south of the AzF. N2-fixation rates as high as 10.9 μmol N m-3 d-1 and surface nitrate δ15N as low as 2.7‰ were found in the warm (18-24°C), most saline (36.5-37.0) and least productive waters south of the AzF, where UCYN were the least abundant. However, picoplanktonic UCYN abundances up to 55 cells mL-1 were found at 45-200m depths in the coolest nutrient-rich waters north of the AzF. In this area, N2-fixation rates up to 4.5 μmol N m-3 d-1 were detected, associated with depth-integrated H13CO3--fixation rates at least 50% higher than observed south of the AzF. The numerous eddies generated at the NW-AzC/AzF seem to enhance exchanges of plankton between water masses, as well as vertical and horizontal diapycnal diffusion of nutrients, whose increase probably enhances the growth of diazotrophs and the productivity of C-fixers.

Influence of arbuscular mycorrhizae on biomass production and nitrogen fixation of berseem clover plants subjected to water stress.

PubMed

Saia, Sergio; Amato, Gaetano; Frenda, Alfonso Salvatore; Giambalvo, Dario; Ruisi, Paolo

2014-01-01

Several studies, performed mainly in pots, have shown that arbuscular mycorrhizal symbiosis can mitigate the negative effects of water stress on plant growth. No information is available about the effects of arbuscular mycorrhizal symbiosis on berseem clover growth and nitrogen (N) fixation under conditions of water shortage. A field experiment was conducted in a hilly area of inner Sicily, Italy, to determine whether symbiosis with AM fungi can mitigate the detrimental effects of drought stress (which in the Mediterranean often occurs during the late period of the growing season) on forage yield and symbiotic N2 fixation of berseem clover. Soil was either left under water stress (i.e., rain-fed conditions) or the crop was well-watered. Mycorrhization treatments consisted of inoculation of berseem clover seeds with arbuscular mycorrhizal spores or suppression of arbuscular mycorrhizal symbiosis by means of fungicide treatments. Nitrogen biological fixation was assessed using the 15N-isotope dilution technique. Arbuscular mycorrhizal symbiosis was able to mitigate the negative effect of water stress on berseem clover grown in a typical semiarid Mediterranean environment. In fact, under water stress conditions, arbuscular mycorrhizal symbiosis resulted in increases in total biomass, N content, and N fixation, whereas no effect of crop mycorrhization was observed in the well-watered treatment.

Iron availability influences 15N-isotope fractionation during nitrogen fixation by aerobic chemoheterotroph Azotobacter vinelandii

NASA Astrophysics Data System (ADS)

Zhang, X.; Kopf, S.; Lee, A. C.

2016-12-01

The N stable isotope composition (δ15N) of biomass provides a powerful tool for reconstructing present and past N cycling, but its interpretation hinges on a complete understanding of the isotopic signature of biological nitrogen fixation, which sets the δ15N of newly fixed N. All biological nitrogen fixation is catalyzed by the metalloenzyme nitrogenase in a complex reaction that reduces inert atmospheric N2 gas into bioavailable ammonium. Recent investigations into the metal cofactor variants of nitrogenase revealed that the canonical Mo-, and alternative V-, and Fe-only isoforms of nitrogenase impart different isotope fractionations during N2 fixation in vivo, challenging the traditional view that N2 fixation only imparts small, invariable isotope effects of 0-2‰. However, the mechanistic basis for the fractionation of N2 fixation remains largely unknown. To better understand mechanisms underlying fractionation, we varied Fe availability and measured in vivo fractionations for the aerobic chemoheterotroph Azotobacter vinelandii utilizing Mo- or V-nitrogenase under batch culture conditions. Under all iron conditions, N2 fixation based on Mo-nitrogenase yielded lower fractionations (heavier biomasss δ15N) compared to V-nitrogenase. For fractionations associated with a single metalloenzyme, higher Fe concentrations, which correlated with faster growth rates, yielded small but systematically larger fractionations ( 1 ‰ increase for Mo- and V- nitrogenases). To directly determine the effect of growth rate on fractionation, we grew Mo-nitrogenase expressing A. vinelandii in Fe-replete medium at different growth rates using chemostats and found that growth rate alone does not alter fractionation. The results indicate that Fe availability, in addition to the type of nitrogenase metalloenzyme, controls 15N fractionation during N2 fixation by A. vinelandii.

Alfalfa (Medicago sativa L.) forage production, tissue and soil nutrient concentration under three N based broiler litter regimes

USDA-ARS?s Scientific Manuscript database

Alfalfa (Medicago sativa L.) is considered as most important forage legume grown in Kentucky. Alfalfa supports many livestock production systems including the beef, dairy, and horse industries in Kentucky. Being a legume, alfalfa typically meets its N requirement through symbiotic N2 fixation, but h...

The impact of simulated chronic nitrogen deposition on the biomass and N2-fixation activity of two boreal feather moss–cyanobacteria associations

PubMed Central

Gundale, Michael J.; Bach, Lisbet H.; Nordin, Annika

2013-01-01

Bryophytes achieve substantial biomass and play several key functional roles in boreal forests that can influence how carbon (C) and nitrogen (N) cycling respond to atmospheric deposition of reactive nitrogen (Nr). They associate with cyanobacteria that fix atmospheric N2, and downregulation of this process may offset anthropogenic Nr inputs to boreal systems. Bryophytes also promote soil C accumulation by thermally insulating soils, and changes in their biomass influence soil C dynamics. Using a unique large-scale (0.1 ha forested plots), long-term experiment (16 years) in northern Sweden where we simulated anthropogenic Nr deposition, we measured the biomass and N2-fixation response of two bryophyte species, the feather mosses Hylocomium splendens and Pleurozium schreberi. Our data show that the biomass declined for both species; however, N2-fixation rates per unit mass and per unit area declined only for H. splendens. The low and high treatments resulted in a 29% and 54% reduction in total feather moss biomass, and a 58% and 97% reduction in total N2-fixation rate per unit area, respectively. These results help to quantify the sensitivity of feather moss biomass and N2 fixation to chronic Nr deposition, which is relevant for modelling ecosystem C and N balances in boreal ecosystems. PMID:24196519

Adaptation of the symbiotic Mesorhizobium-chickpea relationship to phosphate deficiency relies on reprogramming of whole-plant metabolism.

PubMed

Nasr Esfahani, Maryam; Kusano, Miyako; Nguyen, Kien Huu; Watanabe, Yasuko; Ha, Chien Van; Saito, Kazuki; Sulieman, Saad; Herrera-Estrella, Luis; Tran, L S

2016-08-09

Low inorganic phosphate (Pi) availability is a major constraint for efficient nitrogen fixation in legumes, including chickpea. To elucidate the mechanisms involved in nodule acclimation to low Pi availability, two Mesorhizobium-chickpea associations exhibiting differential symbiotic performances, Mesorhizobium ciceri CP-31 (McCP-31)-chickpea and Mesorhizobium mediterranum SWRI9 (MmSWRI9)-chickpea, were comprehensively studied under both control and low Pi conditions. MmSWRI9-chickpea showed a lower symbiotic efficiency under low Pi availability than McCP-31-chickpea as evidenced by reduced growth parameters and down-regulation of nifD and nifK These differences can be attributed to decline in Pi level in MmSWRI9-induced nodules under low Pi stress, which coincided with up-regulation of several key Pi starvation-responsive genes, and accumulation of asparagine in nodules and the levels of identified amino acids in Pi-deficient leaves of MmSWRI9-inoculated plants exceeding the shoot nitrogen requirement during Pi starvation, indicative of nitrogen feedback inhibition. Conversely, Pi levels increased in nodules of Pi-stressed McCP-31-inoculated plants, because these plants evolved various metabolic and biochemical strategies to maintain nodular Pi homeostasis under Pi deficiency. These adaptations involve the activation of alternative pathways of carbon metabolism, enhanced production and exudation of organic acids from roots into the rhizosphere, and the ability to protect nodule metabolism against Pi deficiency-induced oxidative stress. Collectively, the adaptation of symbiotic efficiency under Pi deficiency resulted from highly coordinated processes with an extensive reprogramming of whole-plant metabolism. The findings of this study will enable us to design effective breeding and genetic engineering strategies to enhance symbiotic efficiency in legume crops.

Regulation of respiration and the oxygen diffusion barrier in soybean protect symbiotic nitrogen fixation from chilling-induced inhibition and shoots from premature senescence.

PubMed

van Heerden, Philippus D R; Kiddle, Guy; Pellny, Till K; Mokwala, Phatlane W; Jordaan, Anine; Strauss, Abram J; de Beer, Misha; Schlüter, Urte; Kunert, Karl J; Foyer, Christine H

2008-09-01

Symbiotic nitrogen fixation is sensitive to dark chilling (7 degrees C-15 degrees C)-induced inhibition in soybean (Glycine max). To characterize the mechanisms that cause the stress-induced loss of nodule function, we examined nodule structure, carbon-nitrogen interactions, and respiration in two soybean genotypes that differ in chilling sensitivity: PAN809 (PAN), which is chilling sensitive, and Highveld Top (HT), which is more chilling resistant. Nodule numbers were unaffected by dark chilling, as was the abundance of the nitrogenase and leghemoglobin proteins. However, dark chilling decreased nodule respiration rates, nitrogenase activities, and NifH and NifK mRNAs and increased nodule starch, sucrose, and glucose in both genotypes. Ureide and fructose contents decreased only in PAN nodules. While the chilling-induced decreases in nodule respiration persisted in PAN even after return to optimal temperatures, respiration started to recover in HT by the end of the chilling period. The area of the intercellular spaces in the nodule cortex and infected zone was greatly decreased in HT after three nights of chilling, an acclimatory response that was absent from PAN. These data show that HT nodules are able to regulate both respiration and the area of the intercellular spaces during chilling and in this way control the oxygen diffusion barrier, which is a key component of the nodule stress response. We conclude that chilling-induced loss of symbiotic nitrogen fixation in PAN is caused by the inhibition of respiration coupled to the failure to regulate the oxygen diffusion barrier effectively. The resultant limitations on nitrogen availability contribute to the greater chilling-induced inhibition of photosynthesis in PAN than in HT.

Effect of light intensity and nitrogen starvation on CO2 fixation and lipid/carbohydrate production of an indigenous microalga Scenedesmus obliquus CNW-N.

PubMed

Ho, Shih-Hsin; Chen, Chun-Yen; Chang, Jo-Shu

2012-06-01

Engineering strategies were applied to improve the CO(2) fixation rate and carbohydrate/lipid production of a Scenedesmus obliquus CNW-N isolate. The light intensity that promotes cell growth, carbohydrate/lipid productivity, and CO(2) fixation efficiency was identified. Nitrogen starvation was also employed to trigger the accumulation of lipid and carbohydrate. The highest productivity of biomass, lipid, and carbohydrate was 840.57 mg L(-1)d(-1), 140.35 mg L(-1)d(-1). The highest lipid and carbohydrate content was 22.4% (5-day N-starvation) and 46.65% (1-day N-starvation), respectively. The optimal CO(2) consumption rate was 1420.6 mg L(-1)d(-1). This performance is better than that reported in most other studies. Under nitrogen starvation, the microalgal lipid was mainly composed of C16/C18 fatty acid (around 90%), which is suitable for biodiesel synthesis. The carbohydrate present in the biomass was mainly glucose, accounting for 77-80% of total carbohydrates. This carbohydrate composition is also suitable for fermentative biofuels production (e.g., bioethanol and biobutanol). Copyright © 2011 Elsevier Ltd. All rights reserved.

Symbiotic potential and survival of native rhizobia kept on different carriers

PubMed Central

Ruíz-Valdiviezo, Víctor Manuel; Canseco, Lucía María Cristina Ventura; Suárez, Luis Antonio Castillo; Gutiérrez-Miceli, Federico Antonio; Dendooven, Luc; Rincón-Rosales, Reiner

2015-01-01

Native rhizobia are ideal for use as commercial legume inoculants. The characteristics of the carrier used to store the inoculants are important for the survival and symbiotic potential of the rhizobia. The objective of this study was to investigate the effects of peat (PEAT), perlite sugarcane bagasse (PSB), carboxymethyl cellulose plus starch (CMCS), and yeast extract mannitol supplemented with mannitol (YEMM) on the survival, nodulation potential and N2 fixation capacity of the native strains Sinorhizobium mexicanum ITTG R7T and Rhizobium calliandrae LBP2-1T and of the reference strain Rhizobium etli CFN42T. A factorial design (4 × 3) with four repetitions was used to determine the symbiotic potential of the rhizobial strains. The survival of the strains was higher for PEAT (46% for strain LBP2-1T, 167% for strain CFN42T and 219% for strain ITTG R7T) than for the other carriers after 240 days, except for CFN42T kept on CMCS (225%). All the strains kept on the different carriers effectively nodulated common bean, with the lowest number of nodules found (5 nodules) when CFN42T was kept on CMCS and with the highest number of nodules found (28 nodules) when ITTG R7T was kept on PSB. The nitrogenase activity was the highest for ITTG R7T kept on PEAT (4911 μmol C2H4 per fresh weight nodule h−1); however, no activity was found when the strains were kept on YEMM. Thus, the survival and symbiotic potential of the rhizobia depended on the carrier used to store them. PMID:26413054

A proteomic network for symbiotic nitrogen fixation efficiency in Bradyrhizobium elkanii

USDA-ARS?s Scientific Manuscript database

Rhizobia bacteroids colonize legumes and reduce N2 to NH3 in root nodules. The current model is that bacteroids avoid assimilating this NH3. Instead, the legume forms glutamine from it, the nitrogen of which is returned to the bacteroid as leucine, isoleucine, valine, dicarboxylates, and peptides. I...

Arbuscular Mycorrhiza Stimulates Biological Nitrogen Fixation in Two Medicago spp. through Improved Phosphorus Acquisition

PubMed Central

Püschel, David; Janoušková, Martina; Voříšková, Alena; Gryndlerová, Hana; Vosátka, Miroslav; Jansa, Jan

2017-01-01

Legumes establish root symbioses with rhizobia that provide plants with nitrogen (N) through biological N fixation (BNF), as well as with arbuscular mycorrhizal (AM) fungi that mediate improved plant phosphorus (P) uptake. Such complex relationships complicate our understanding of nutrient acquisition by legumes and how they reward their symbiotic partners with carbon along gradients of environmental conditions. In order to disentangle the interplay between BNF and AM symbioses in two Medicago species (Medicago truncatula and M. sativa) along a P-fertilization gradient, we conducted a pot experiment where the rhizobia-treated plants were either inoculated or not inoculated with AM fungus Rhizophagus irregularis ‘PH5’ and grown in two nutrient-poor substrates subjected to one of three different P-supply levels. Throughout the experiment, all plants were fertilized with 15N-enriched liquid N-fertilizer to allow for assessment of BNF efficiency in terms of the fraction of N in the plants derived from the BNF (%NBNF). We hypothesized (1) higher %NBNF coinciding with higher P supply, and (2) higher %NBNF in mycorrhizal as compared to non-mycorrhizal plants under P deficiency due to mycorrhiza-mediated improvement in P nutrition. We found a strongly positive correlation between total plant P content and %NBNF, clearly documenting the importance of plant P nutrition for BNF efficiency. The AM symbiosis generally improved P uptake by plants and considerably stimulated the efficiency of BNF under low P availability (below 10 mg kg-1 water extractable P). Under high P availability (above 10 mg kg-1 water extractable P), the AM symbiosis brought no further benefits to the plants with respect to P nutrition even as the effects of P availability on N acquisition via BNF were further modulated by the environmental context (plant and substrate combinations). As a response to elevated P availability in the substrate, the extent of root length colonization by AM fungi was

Phytoestrogen signaling and symbiotic gene activation are disrupted by endocrine-disrupting chemicals.

PubMed Central

Fox, Jennifer E; Starcevic, Marta; Jones, Phillip E; Burow, Matthew E; McLachlan, John A

2004-01-01

Some organochlorine pesticides and other synthetic chemicals mimic hormones in representatives of each vertebrate class, including mammals, reptiles, amphibians, birds, and fish. These compounds are called endocrine-disrupting chemicals (EDCs). Similarly, hormonelike signaling has also been observed when vertebrates are exposed to plant chemicals called phytoestrogens. Previous research has shown the mechanism of action for EDCs and phytoestrogens is as unintended ligands for the estrogen receptor (ER). Although pesticides have been synthesized to deter insects and weeds, plants produce phytoestrogens to deter herbivores, as attractant cues for insects, and as recruitment signals for symbiotic soil bacteria. Our data present the first evidence that some of the same organochlorine pesticides and EDCs known to disrupt endocrine signaling through ERs in exposed wildlife and humans also disrupt the phytoestrogen signaling that leguminous plants use to recruit Sinorhizobium meliloti soil bacteria for symbiotic nitrogen fixation. Here we report that a variety of EDCs and pesticides commonly found in agricultural soils interfere with the symbiotic signaling necessary for nitrogen fixation, suggesting that the principles underlying endocrine disruption may have more widespread biological and ecological importance than had once been thought. PMID:15121509

Reverse Dynamization: Influence of Fixator Stiffness on the Mode and Efficiency of Large-Bone-Defect Healing at Different Doses of rhBMP-2.

PubMed

Glatt, Vaida; Bartnikowski, Nicole; Quirk, Nicholas; Schuetz, Michael; Evans, Christopher

2016-04-20

Reverse dynamization is a technology for enhancing the healing of osseous defects. With use of an external fixator, the axial stiffness across the defect is initially set low and subsequently increased. The purpose of the study described in this paper was to explore the efficacy of reverse dynamization under different conditions. Rat femoral defects were stabilized with external fixators that allowed the stiffness to be modulated on living animals. Recombinant human bone morphogenetic protein-2 (rhBMP-2) was implanted into the defects on a collagen sponge. Following a dose-response experiment, 5.5 μg of rhBMP-2 was placed into the defect under conditions of very low (25.4-N/mm), low (114-N/mm), medium (185-N/mm), or high (254-N/mm) stiffness. Reverse dynamization was evaluated with 2 different starting stiffnesses: low (114 N/mm) and very low (25.4 N/mm). In both cases, high stiffness (254 N/mm) was imposed after 2 weeks. Healing was assessed with radiographs, micro-computed tomography (μCT), histological analysis, and mechanical testing. In the absence of dynamization, the medium-stiffness fixators provided the best healing. Reverse dynamization starting with very low stiffness was detrimental to healing. However, with low initial stiffness, reverse dynamization considerably improved healing with minimal residual cartilage, enhanced cortication, increased mechanical strength, and smaller callus. Histological analysis suggested that, in all cases, healing provoked by rhBMP-2 occurred by endochondral ossification. These data confirm the potential utility of reverse dynamization as a way of improving bone healing but indicate that the stiffness parameters need to be selected carefully. Reverse dynamization may reduce the amount of rhBMP-2 needed to induce healing of recalcitrant osseous lesions, reduce the time to union, and decrease the need for prolonged external fixation. Copyright © 2016 by The Journal of Bone and Joint Surgery, Incorporated.

Heterotrophic N2-fixation contributes to nitrogen economy of a common wetland sedge, Schoenoplectus californicus.

PubMed

Rejmánková, Eliška; Sirová, Dagmara; Castle, Stephanie T; Bárta, Jiří; Carpenter, Heather

2018-01-01

A survey of the ecological variability within 52 populations of Schoenoplectus californicus (C.A. Mey.) Soják across its distributional range revealed that it is commonly found in nitrogen (N) limited areas, but rarely in phosphorus limited soils. We explored the hypothesis that S. californicus supplements its nitrogen demand by bacterial N2-fixation processes associated with its roots and rhizomes. We estimated N2-fixation of diazotrophs associated with plant rhizomes and roots from several locations throughout the species' range and conducted an experiment growing plants in zero, low, and high N additions. Nitrogenase activity in rhizomes and roots was measured using the acetylene reduction assay. The presence of diazotrophs was verified by the detection of the nifH gene. Nitrogenase activity was restricted to rhizomes and roots and it was two orders of magnitude higher in the latter plant organs (81 and 2032 nmol C2H4 g DW-1 d-1, respectively). Correspondingly, 40x more nifH gene copies were found on roots compared to rhizomes. The proportion of the nifH gene copies in total bacterial DNA was positively correlated with the nitrogenase activity. In the experiment, the contribution of fixed N to the plant N content ranged from 13.8% to 32.5% among clones from different locations. These are relatively high values for a non-cultivated plant and justify future research on the link between N-fixing bacteria and S. californicus production.

Global climate change will increase the abundance of symbiotic nitrogen-fixing trees in much of North America.

PubMed

Liao, Wenying; Menge, Duncan N L; Lichstein, Jeremy W; Ángeles-Pérez, Gregorio

2017-11-01

Symbiotic nitrogen (N)-fixing trees can drive N and carbon cycling and thus are critical components of future climate projections. Despite detailed understanding of how climate influences N-fixation enzyme activity and physiology, comparatively little is known about how climate influences N-fixing tree abundance. Here, we used forest inventory data from the USA and Mexico (>125,000 plots) along with climate data to address two questions: (1) How does the abundance distribution of N-fixing trees (rhizobial, actinorhizal, and both types together) vary with mean annual temperature (MAT) and precipitation (MAP)? (2) How will changing climate shift the abundance distribution of N-fixing trees? We found that rhizobial N-fixing trees were nearly absent below 15°C MAT, but above 15°C MAT, they increased in abundance as temperature rose. We found no evidence for a hump-shaped response to temperature throughout the range of our data. Rhizobial trees were more abundant in dry than in wet ecosystems. By contrast, actinorhizal trees peaked in abundance at 5-10°C MAT and were least abundant in areas with intermediate precipitation. Next, we used a climate-envelope approach to project how N-fixing tree relative abundance might change in the future. The climate-envelope projection showed that rhizobial N-fixing trees will likely become more abundant in many areas by 2080, particularly in the southern USA and western Mexico, due primarily to rising temperatures. Projections for actinorhizal N-fixing trees were more nuanced due to their nonmonotonic dependence on temperature and precipitation. Overall, the dominant trend is that warming will increase N-fixing tree abundance in much of the USA and Mexico, with large increases up to 40° North latitude. The quantitative link we provide between climate and N-fixing tree abundance can help improve the representation of symbiotic N fixation in Earth System Models. © 2017 John Wiley & Sons Ltd.

Comparative transcriptome analysis of nodules of two Mesorhizobium-chickpea associations with differential symbiotic efficiency under phosphate deficiency.

PubMed

Nasr Esfahani, Maryam; Inoue, Komaki; Chu, Ha Duc; Nguyen, Kien Huu; Van Ha, Chien; Watanabe, Yasuko; Burritt, David J; Herrera-Estrella, Luis; Mochida, Keiichi; Tran, Lam-Son Phan

2017-09-01

Phosphate (Pi) deficiency is known to be a major limitation for symbiotic nitrogen fixation (SNF), and hence legume crop productivity globally. However, very little information is available on the adaptive mechanisms, particularly in the important legume crop chickpea (Cicer arietinum L.), which enable nodules to respond to low-Pi availability. Thus, to elucidate these mechanisms in chickpea nodules at molecular level, we used an RNA sequencing approach to investigate transcriptomes of the nodules in Mesorhizobium mediterraneum SWRI9-(MmSWRI9)-chickpea and M. ciceri CP-31-(McCP-31)-chickpea associations under Pi-sufficient and Pi-deficient conditions, of which the McCP-31-chickpea association has a better SNF capacity than the MmSWRI9-chickpea association during Pi starvation. Our investigation revealed that more genes showed altered expression patterns in MmSWRI9-induced nodules than in McCP-31-induced nodules (540 vs. 225) under Pi deficiency, suggesting that the Pi-starvation-more-sensitive MmSWRI9-induced nodules required expression change in a larger number of genes to cope with low-Pi stress than the Pi-starvation-less-sensitive McCP-31-induced nodules. The functional classification of differentially expressed genes (DEGs) was examined to gain an understanding of how chickpea nodules respond to Pi starvation, caused by soil Pi deficiency. As a result, more DEGs involved in nodulation, detoxification, nutrient/ion transport, transcriptional factors, key metabolic pathways, Pi remobilization and signalling were found in Pi-starved MmSWRI9-induced nodules than in Pi-starved McCP-31-induced nodules. Our findings have enabled the identification of molecular processes that play important roles in the acclimation of nodules to Pi deficiency, ultimately leading to the development of Pi-efficient chickpea symbiotic associations suitable for Pi-deficient soils. © 2017 The Authors The Plant Journal © 2017 John Wiley & Sons Ltd.

Host-secreted antimicrobial peptide enforces symbiotic selectivity in Medicago truncatula.

PubMed

Wang, Qi; Yang, Shengming; Liu, Jinge; Terecskei, Kata; Ábrahám, Edit; Gombár, Anikó; Domonkos, Ágota; Szűcs, Attila; Körmöczi, Péter; Wang, Ting; Fodor, Lili; Mao, Linyong; Fei, Zhangjun; Kondorosi, Éva; Kaló, Péter; Kereszt, Attila; Zhu, Hongyan

2017-06-27

Legumes engage in root nodule symbioses with nitrogen-fixing soil bacteria known as rhizobia. In nodule cells, bacteria are enclosed in membrane-bound vesicles called symbiosomes and differentiate into bacteroids that are capable of converting atmospheric nitrogen into ammonia. Bacteroid differentiation and prolonged intracellular survival are essential for development of functional nodules. However, in the Medicago truncatula - Sinorhizobium meliloti symbiosis, incompatibility between symbiotic partners frequently occurs, leading to the formation of infected nodules defective in nitrogen fixation (Fix - ). Here, we report the identification and cloning of the M. truncatula NFS2 gene that regulates this type of specificity pertaining to S. meliloti strain Rm41. We demonstrate that NFS2 encodes a nodule-specific cysteine-rich (NCR) peptide that acts to promote bacterial lysis after differentiation. The negative role of NFS2 in symbiosis is contingent on host genetic background and can be counteracted by other genes encoded by the host. This work extends the paradigm of NCR function to include the negative regulation of symbiotic persistence in host-strain interactions. Our data suggest that NCR peptides are host determinants of symbiotic specificity in M. truncatula and possibly in closely related legumes that form indeterminate nodules in which bacterial symbionts undergo terminal differentiation.

Exploring the symbiotic pangenome of the nitrogen-fixing bacterium Sinorhizobium meliloti

PubMed Central

2011-01-01

Background Sinorhizobium meliloti is a model system for the studies of symbiotic nitrogen fixation. An extensive polymorphism at the genetic and phenotypic level is present in natural populations of this species, especially in relation with symbiotic promotion of plant growth. AK83 and BL225C are two nodule-isolated strains with diverse symbiotic phenotypes; BL225C is more efficient in promoting growth of the Medicago sativa plants than strain AK83. In order to investigate the genetic determinants of the phenotypic diversification of S. meliloti strains AK83 and BL225C, we sequenced the complete genomes for these two strains. Results With sizes of 7.14 Mbp and 6.97 Mbp, respectively, the genomes of AK83 and BL225C are larger than the laboratory strain Rm1021. The core genome of Rm1021, AK83, BL225C strains included 5124 orthologous groups, while the accessory genome was composed by 2700 orthologous groups. While Rm1021 and BL225C have only three replicons (Chromosome, pSymA and pSymB), AK83 has also two plasmids, 260 and 70 Kbp long. We found 65 interesting orthologous groups of genes that were present only in the accessory genome, consequently responsible for phenotypic diversity and putatively involved in plant-bacterium interaction. Notably, the symbiosis inefficient AK83 lacked several genes required for microaerophilic growth inside nodules, while several genes for accessory functions related to competition, plant invasion and bacteroid tropism were identified only in AK83 and BL225C strains. Presence and extent of polymorphism in regulons of transcription factors involved in symbiotic interaction were also analyzed. Our results indicate that regulons are flexible, with a large number of accessory genes, suggesting that regulons polymorphism could also be a key determinant in the variability of symbiotic performances among the analyzed strains. Conclusions In conclusions, the extended comparative genomics approach revealed a variable subset of genes and

Ultraviolet Observations of M-Type Symbiotic Stars

NASA Astrophysics Data System (ADS)

Michalitsianos, Andrew G.

The significant differences revealed in high dispersion short wavelength spectra of two M-type symbiotic stars RW Hya (gM2 + pec) and RX Pup (M5 + pec) observed previously with IUE emphasizes the need for high resolution observations of a wide range of similar objects. The anomalies observed in high excitation lines in RX Pup of He II, N III], N IV], O III], C III], C IV and Si III] that show split line profiles, multiple component Doppler displaced components, and broadened blue wing emission structure in N III] and N IV] suggest motion in circumstellar material. In contrast, high dispersion UV spectra of RW Hya reveal narrow high excitation emission lines that give no suggestion of macroscopic motions in the circumstellar gas. We wish to extend observations of a selected number of symbiotic stars observed previously but in low resolution, to high dispersion in order to determine if particular M-type symbiotic stars exhibit anomalies in their line profile. As such, symbiotic stars exhibiting velocity structure in emission lines may form a subset of objects that are characterized by mass motions in their circumstellar envelops that create high excitation emission. UV line and continuum emission from other M-type symbiotics may arise from mainly photo-excitation processes that results from the intense radiation field associated with the hot secondary companion.

Intracellular pH and its response to CO2-driven seawater acidification in symbiotic versus non-symbiotic coral cells.

PubMed

Gibbin, Emma M; Putnam, Hollie M; Davy, Simon K; Gates, Ruth D

2014-06-01

Regulating intracellular pH (pHi) is critical for optimising the metabolic activity of corals, yet the mechanisms involved in pH regulation and the buffering capacity within coral cells are not well understood. Our study investigated how the presence of symbiotic dinoflagellates affects the response of pHi to PCO2-driven seawater acidification in cells isolated from Pocillopora damicornis. Using the fluorescent dye BCECF-AM, in conjunction with confocal microscopy, we simultaneously characterised the pHi response in host coral cells and their dinoflagellate symbionts, in symbiotic and non-symbiotic states under saturating light, with and without the photosynthetic inhibitor DCMU. Each treatment was run under control (pH 7.8) and CO2-acidified seawater conditions (decreasing pH from 7.8 to 6.8). After 105 min of CO2 addition, by which time the external pH (pHe) had declined to 6.8, the dinoflagellate symbionts had increased their pHi by 0.5 pH units above control levels when in the absence of DCMU. In contrast, in both symbiotic and non-symbiotic host coral cells, 15 min of CO2 addition (0.2 pH unit drop in pHe) led to cytoplasmic acidosis equivalent to 0.3-0.4 pH units irrespective of whether DCMU was present. Despite further seawater acidification over the duration of the experiment, the pHi of non-symbiotic coral cells did not change, though in host cells containing a symbiont cell the pHi recovered to control levels when photsynthesis was not inhibited. This recovery was negated when cells were incubated with DCMU. Our results reveal that photosynthetic activity of the endosymbiont is tightly coupled with the ability of the host cell to recover from cellular acidosis after exposure to high CO2/low pH. © 2014. Published by The Company of Biologists Ltd.

The influence of woody encroachment on the nitrogen cycle: fixation, storage and gas loss

NASA Astrophysics Data System (ADS)

Soper, F.; Sparks, J. P.

2015-12-01

Woody encroachment is a pervasive land cover change throughout the tropics and subtropics. Encroachment is frequently catalyzed by nitrogen (N)-fixing trees and the resulting N inputs potentially alter whole-ecosystem N cycling, accumulation and loss. In the southern US, widespread encroachment by legume Prosopis glandulosa is associated with increased soil total N storage, inorganic N concentrations, and net mineralization and nitrification rates. To better understand the effects of this process on ecosystem N cycling, we investigated patterns of symbiotic N fixation, N accrual and soil N trace gas and N2 emissions during Prosopis encroachment into the southern Rio Grande Plains. Analyses of d15N in foliage, xylem sap and plant-available soil N suggested that N fixation rates increase with tree age and are influenced by abiotic conditions. A model of soil N accrual around individual trees, accounting for atmospheric inputs and gas losses, generates lifetimes N fixation estimates of up to 9 kg for a 100-year-old tree and current rates of 7 kg N ha-1 yr-1. However, these N inputs and increased soil cycling rates do not translate into increased N gas losses. Two years of field measurements of a complete suite of N trace gases (ammonia, nitrous oxide, nitric oxide and other oxidized N compounds) found no difference in flux between upland Prosopis groves and adjacent unencroached grasslands. Total emissions for both land cover types average 0.56-0.65 kg N ha-1 yr-1, comparable to other southern US grasslands. Additional lab experiments suggested that N2 losses are low and that field oxygen conditions are not usually conducive to denitrification. Taken together, results suggest that this ecosystem is currently experiencing a period of net N accrual under ongoing encroachment.

Symbiotic Optimization of Behavior

DTIC Science & Technology

2015-05-01

SYMBIOTIC OPTIMIZATION OF BEHAVIOR UNIVERSITY OF WASHINGTON MAY 2015 FINAL TECHNICAL REPORT APPROVED FOR PUBLIC RELEASE; DISTRIBUTION UNLIMITED...2014 4. TITLE AND SUBTITLE SYMBIOTIC OPTIMIZATION OF BEHAVIOR 5a. CONTRACT NUMBER FA8750-12-1-0304 5b. GRANT NUMBER N/A 5c. PROGRAM ELEMENT

Simple approach for the preparation of (15-15)N2-enriched water for nitrogen fixation assessments: evaluation, application and recommendations.

PubMed

Klawonn, Isabell; Lavik, Gaute; Böning, Philipp; Marchant, Hannah K; Dekaezemacker, Julien; Mohr, Wiebke; Ploug, Helle

2015-01-01

Recent findings revealed that the commonly used (15)N2 tracer assay for the determination of dinitrogen (N2) fixation can underestimate the activity of aquatic N2-fixing organisms. Therefore, a modification to the method using pre-prepared (15-15)N2-enriched water was proposed. Here, we present a rigorous assessment and outline a simple procedure for the preparation of (15-15)N2-enriched water. We recommend to fill sterile-filtered water into serum bottles and to add (15-15)N2 gas to the water in amounts exceeding the standard N2 solubility, followed by vigorous agitation (vortex mixing ≥ 5 min). Optionally, water can be degassed at low-pressure (≥950 mbar) for 10 min prior to the (15-15)N2 gas addition to indirectly enhance the (15-15)N2 concentration. This preparation of (15-15)N2-enriched water can be done within 1 h using standard laboratory equipment. The final (15)N-atom% excess was 5% after replacing 2-5% of the incubation volume with (15-15)N2-enriched water. Notably, the addition of (15-15)N2-enriched water can alter levels of trace elements in the incubation water due to the contact of (15-15)N2-enriched water with glass, plastic and rubber ware. In our tests, levels of trace elements (Fe, P, Mn, Mo, Cu, Zn) increased by up to 0.1 nmol L(-1) in the final incubation volume, which may bias rate measurements in regions where N2 fixation is limited by trace elements. For these regions, we tested an alternative way to enrich water with (15-15)N2. The (15-15)N2 was injected as a bubble directly to the incubation water, followed by gentle shaking. Immediately thereafter, the bubble was replaced with water to stop the (15-15)N2 equilibration. This approach achieved a (15)N-atom% excess of 6.6 ± 1.7% when adding 2 mL (15-15)N2 per liter of incubation water. The herein presented methodological tests offer guidelines for the (15)N2 tracer assay and thus, are crucial to circumvent methodological draw-backs for future N2 fixation assessments.

Regulation of Respiration and the Oxygen Diffusion Barrier in Soybean Protect Symbiotic Nitrogen Fixation from Chilling-Induced Inhibition and Shoots from Premature Senescence1[W][OA

PubMed Central

van Heerden, Philippus D.R.; Kiddle, Guy; Pellny, Till K.; Mokwala, Phatlane W.; Jordaan, Anine; Strauss, Abram J.; de Beer, Misha; Schlüter, Urte; Kunert, Karl J.; Foyer, Christine H.

2008-01-01

Symbiotic nitrogen fixation is sensitive to dark chilling (7°C–15°C)-induced inhibition in soybean (Glycine max). To characterize the mechanisms that cause the stress-induced loss of nodule function, we examined nodule structure, carbon-nitrogen interactions, and respiration in two soybean genotypes that differ in chilling sensitivity: PAN809 (PAN), which is chilling sensitive, and Highveld Top (HT), which is more chilling resistant. Nodule numbers were unaffected by dark chilling, as was the abundance of the nitrogenase and leghemoglobin proteins. However, dark chilling decreased nodule respiration rates, nitrogenase activities, and NifH and NifK mRNAs and increased nodule starch, sucrose, and glucose in both genotypes. Ureide and fructose contents decreased only in PAN nodules. While the chilling-induced decreases in nodule respiration persisted in PAN even after return to optimal temperatures, respiration started to recover in HT by the end of the chilling period. The area of the intercellular spaces in the nodule cortex and infected zone was greatly decreased in HT after three nights of chilling, an acclimatory response that was absent from PAN. These data show that HT nodules are able to regulate both respiration and the area of the intercellular spaces during chilling and in this way control the oxygen diffusion barrier, which is a key component of the nodule stress response. We conclude that chilling-induced loss of symbiotic nitrogen fixation in PAN is caused by the inhibition of respiration coupled to the failure to regulate the oxygen diffusion barrier effectively. The resultant limitations on nitrogen availability contribute to the greater chilling-induced inhibition of photosynthesis in PAN than in HT. PMID:18667725

Taxonomically Different Co-Microsymbionts of a Relict Legume, Oxytropis popoviana, Have Complementary Sets of Symbiotic Genes and Together Increase the Efficiency of Plant Nodulation.

PubMed

Safronova, Vera I; Belimov, Andrey A; Sazanova, Anna L; Chirak, Elizaveta R; Verkhozina, Alla V; Kuznetsova, Irina G; Andronov, Evgeny E; Puhalsky, Jan V; Tikhonovich, Igor A

2018-06-20

Ten rhizobial strains were isolated from root nodules of a relict legume Oxytropis popoviana Peschkova. For identification of the isolates, sequencing of rrs, the internal transcribed spacer region, and housekeeping genes recA, glnII, and rpoB was used. Nine fast-growing isolates were Mesorhizobium-related; eight strains were identified as M. japonicum and one isolate belonged to M. kowhaii. The only slow-growing isolate was identified as a Bradyrhizobium sp. Two strains, M. japonicum Opo-242 and Bradyrhizobium sp. strain Opo-243, were isolated from the same nodule. Symbiotic genes of these isolates were searched throughout the whole-genome sequences. The common nodABC genes and other symbiotic genes required for plant nodulation and nitrogen fixation were present in the isolate Opo-242. Strain Opo-243 did not contain the principal nod, nif, and fix genes; however, five genes (nodP, nodQ, nifL, nolK, and noeL) affecting the specificity of plant-rhizobia interactions but absent in isolate Opo-242 were detected. Strain Opo-243 could not induce nodules but significantly accelerated the root nodule formation after coinoculation with isolate Opo-242. Thus, we demonstrated that taxonomically different strains of the archaic symbiotic system can be co-microsymbionts infecting the same nodule and promoting the nodulation process due to complementary sets of symbiotic genes.

Photosynthesis, N(2) fixation and taproot reserves during the cutting regrowth cycle of alfalfa under elevated CO(2) and temperature.

PubMed

Erice, G; Sanz-Sáez, A; Aranjuelo, I; Irigoyen, J J; Aguirreolea, J; Avice, J-C; Sánchez-Díaz, M

2011-11-15

Future climatic conditions, including rising atmospheric CO(2) and temperature may increase photosynthesis and, consequently, plant production. A larger knowledge of legume performance under the predicted growth conditions will be crucial for safeguarding crop management and extending the area under cultivation with these plants in the near future. N(2) fixation is a key process conditioning plant responsiveness to varying growth conditions. Moreover, it is likely to increase under future environments, due to the higher photosynthate availability, as a consequence of the higher growth rate under elevated CO(2). However, as described in the literature, photosynthesis performance is frequently down-regulated (acclimated) under long-term exposure to CO(2), especially when affected by stressful temperature and water availability conditions. As growth responses to elevated CO(2) are dependent on sink-source status, it is generally accepted that down-regulation occurs in situations with insufficient plant C sink capacity. Alfalfa management involves the cutting of shoots, which alters the source-sink relationship and thus the photosynthetic behaviour. As the growth rate decreases at the end of the pre-cut vegetative growth period, nodulated alfalfa plants show photosynthetic down-regulation, but during regrowth following defoliation, acclimation to elevated CO(2) disappears. The shoot harvest also leads to a drop in mineral N uptake and C translocation to the roots, resulting in a reduction in N(2) fixation due to the dependence on photosynthate supply to support nodule function. Therefore, the production of new shoots during the first days following cutting requires the utilization of reduced C and N compounds that have been stored previously in reserve organs. The stored reserves are mediated by phytohormones such as methyl jasmonate and abscisic acid and in situations where water stress reduces shoot production this potentially enables the enhancement of taproot

He 2-104 - A symbiotic proto-planetary nebula?

NASA Technical Reports Server (NTRS)

Schwarz, Hugo E.; Aspin, Colin; Lutz, Julie H.

1989-01-01

CCD observations are presented for He 2-104, an object previously classified as both PN and symbiotic star, which show that this is in fact a protoplanetary nebula (PPN) with a dynamical age of about 800 yr. The presence of highly collimated jets, extending over 75 arcsec on the sky, combined with an energy distribution showing a hot as well as a cool component, indicates that He 2-104 is a binary PPN. Since the primary is probably a Mira with a 400-d period (as reported by Whitelock, 1988), it is proposed that the system is a symbiotic PPN.

Healing at the Interface Between Autologous Block Bone Grafts and Recipient Sites Using n-Butyl-2-Cyanoacrylate Adhesive as Fixation: Histomorphometric Study in Rabbits.

PubMed

De Santis, Enzo; Silva, Erick Ricardo; Martins, Evandro Neto Carneiro; Favero, Riccardo; Botticelli, Daniele; Xavier, Samuel Porfirio

2017-12-01

The aim of the present split-mouth (split-plot) study was to describe the sequential healing in the interface between autologous bone grafts and recipient parent bone, fixed using an n-butyl-2-cyanoacrylate adhesive with or without an additional titanium fixation screw. Bone grafts were collected from the calvaria and fixed to the lateral aspect of the mandible in 24 rabbits. The cortical layers of the recipient sites were perforated, and the grafts were randomly fixed using an n-butyl-2-cyanocrylate adhesive, either alone or in conjunction with a 1.5 mm × 6.0 mm titanium fixation screw. The animals were sacrificed after 3, 7, 20, and 40 days, and histomorphometric evaluations of the interface between graft and parent bone were performed. Only 2 of 6 grafts in each group were partially incorporated to the parent bone after 40 days of healing. The remaining grafts were separated from the parent bone by adhesive and connective tissue. It was concluded that the use of n-butyl-2-cyanoacrylate as fixation of an autologous bone graft to the lateral aspect of the mandible was able to maintain the fixation over time but did not incorporate the graft to the recipient sites. Use of fixation screws did not improve the healing.

Global metabolic rewiring for improved CO2 fixation and chemical production in cyanobacteria

NASA Astrophysics Data System (ADS)

Kanno, Masahiro; Carroll, Austin L.; Atsumi, Shota

2017-03-01

Cyanobacteria have attracted much attention as hosts to recycle CO2 into valuable chemicals. Although cyanobacteria have been engineered to produce various compounds, production efficiencies are too low for commercialization. Here we engineer the carbon metabolism of Synechococcus elongatus PCC 7942 to improve glucose utilization, enhance CO2 fixation and increase chemical production. We introduce modifications in glycolytic pathways and the Calvin Benson cycle to increase carbon flux and redirect it towards carbon fixation. The engineered strain efficiently uses both CO2 and glucose, and produces 12.6 g l-1 of 2,3-butanediol with a rate of 1.1 g l-1 d-1 under continuous light conditions. Removal of native regulation enables carbon fixation and 2,3-butanediol production in the absence of light. This represents a significant step towards industrial viability and an excellent example of carbon metabolism plasticity.

Transcriptomic dissection of Bradyrhizobium sp. strain ORS285 in symbiosis with Aeschynomene spp. inducing different bacteroid morphotypes with contrasted symbiotic efficiency.

PubMed

Lamouche, Florian; Gully, Djamel; Chaumeret, Anaïs; Nouwen, Nico; Verly, Camille; Pierre, Olivier; Sciallano, Coline; Fardoux, Joël; Jeudy, Christian; Szücs, Attila; Mondy, Samuel; Salon, Christophe; Nagy, István; Kereszt, Attila; Dessaux, Yves; Giraud, Eric; Mergaert, Peter; Alunni, Benoit

2018-06-19

To circumvent the paucity of nitrogen sources in the soil legume plants establish a symbiotic interaction with nitrogen-fixing soil bacteria called rhizobia. During symbiosis, the plants form root organs called nodules, where bacteria are housed intracellularly and become active nitrogen fixers known as bacteroids. Depending on their host plant, bacteroids can adopt different morphotypes, being either unmodified (U), elongated (E) or spherical (S). E- and S-type bacteroids undergo a terminal differentiation leading to irreversible morphological changes and DNA endoreduplication. Previous studies suggest that differentiated bacteroids display an increased symbiotic efficiency (E>U and S>U). In this study, we used a combination of Aeschynomene species inducing E- or S-type bacteroids in symbiosis with Bradyrhizobium sp. ORS285 to show that S-type bacteroids present a better symbiotic efficiency than E-type bacteroids. We performed a transcriptomic analysis on E- and S-type bacteroids formed by Aeschynomene afraspera and Aeschynomene indica nodules and identified the bacterial functions activated in bacteroids and specific to each bacteroid type. Extending the expression analysis in E- and S-type bacteroids in other Aeschynomene species by qRT-PCR on selected genes from the transcriptome analysis narrowed down the set of bacteroid morphotype-specific genes. Functional analysis of a selected subset of 31 bacteroid-induced or morphotype-specific genes revealed no symbiotic phenotypes in the mutants. This highlights the robustness of the symbiotic program but could also indicate that the bacterial response to the plant environment is partially anticipatory or even maladaptive. Our analysis confirms the correlation between differentiation and efficiency of the bacteroids and provides a framework for the identification of bacterial functions that affect the efficiency of bacteroids. This article is protected by copyright. All rights reserved. © 2018 Society for Applied

Exploring the symbiotic pangenome of the nitrogen-fixing bacterium Sinorhizobium meliloti

DOE Office of Scientific and Technical Information (OSTI.GOV)

Galardini, Marco; Mengoni, Alessio; Brilli, Matteo

Background: Sinorhizobium meliloti is a model system for the studies of symbiotic nitrogen fixation. An extensive polymorphism at the genetic and phenotypic level is present in natural populations of this species, especially in relation with symbiotic promotion of plant growth. AK83 and BL225C are two nodule-isolated strains with diverse symbiotic phenotypes; BL225C is more efficient in promoting growth of the Medicago sativa plants than strain AK83. In order to investigate the genetic determinants of the phenotypic diversification of S. meliloti strains AK83 and BL225C, we sequenced the complete genomes for these two strains. Results: With sizes of 7.14 Mbp andmore » 6.97 Mbp, respectively, the genomes of AK83 and BL225C are larger than the laboratory strain Rm1021. The core genome of Rm1021, AK83, BL225C strains included 5124 orthologous groups, while the accessory genome was composed by 2700 orthologous groups. While Rm1021 and BL225C have only three replicons (Chromosome, pSymA and pSymB), AK83 has also two plasmids, 260 and 70 Kbp long. We found 65 interesting orthologous groups of genes that were present only in the accessory genome, consequently responsible for phenotypic diversity and putatively involved in plant-bacterium interaction. Notably, the symbiosis inefficient AK83 lacked several genes required for microaerophilic growth inside nodules, while several genes for accessory functions related to competition, plant invasion and bacteroid tropism were identified only in AK83 and BL225C strains. Presence and extent of polymorphism in regulons of transcription factors involved in symbiotic interaction were also analyzed. Our results indicate that regulons are flexible, with a large number of accessory genes, suggesting that regulons polymorphism could also be a key determinant in the variability of symbiotic performances among the analyzed strains.« less

Genetic diversity and symbiotic effectiveness of Bradyrhizobium strains nodulating selected annual grain legumes growing in Ethiopia.

PubMed

Degefu, Tulu; Wolde-Meskel, Endalkachew; Rasche, Frank

2018-01-01

Vigna unguiculata, Vigna radiata and Arachis hypogaea growing in Ethiopia are nodulated by a genetically diverse group of Bradyrhizobium strains. To determine the genetic identity and symbiotic effectiveness of these bacteria, a collection of 36 test strains originating from the root nodules of the three hosts was investigated using multilocus sequence analyses (MLSA) of core genes including 16S rRNA, recA, glnII, gyrB, atpD and dnaK. Sequence analysis of nodA and nifH genes along with tests for symbiotic effectiveness using δ 15 N analysis were also carried out. The phylogenetic trees derived from the MLSA grouped most test strains into four well-supported distinct positions designated as genospecies I-IV. The maximum likelihood (ML) tree that was constructed based on the nodA gene sequences separated the entire test strains into two lineages, where the majority of the test strains were clustered on one of a well-supported large branch that comprise Bradyrhizobium species from the tropics. This clearly suggested the monophyletic origin of the nodA genes within the bradyrhizobia of tropical origin. The δ 15 N-based symbiotic effectiveness test of seven selected strains revealed that strains GN100 (δ 15 N=0.73) and GN102 (δ 15 N=0.79) were highly effective nitrogen fixers when inoculated to cowpea, thus can be considered as inoculants in cowpea production. It was concluded that Ethiopian soils are a hotspot for rhizobial diversity. This calls for further research to unravel as yet unknown bradyrhizobia nodulating legume host species growing in the country. In this respect, prospective research should also address the mechanisms of symbiotic specificity that could lead to high nitrogen fixation in target legumes.

AUTORADIOGRAPHIC LOCALIZATION OF 13N AFTER FIXATION OF 13N-LABELED NITROGEN GAS BY A HETEROCYST-FORMING BLUE-GREEN ALGA

PubMed Central

Wolk, C. Peter; Austin, Sam M.; Bortins, John; Galonsky, Aaron

1974-01-01

13N, generated by proton bombardment of 13C powder, is rapidly and easily converted to 13N-N2, 0.01 atm pressure, ca. 10 mCi/ml, by automated Dumas combustion. 13N fixed (as 13N-N2) by algal filaments was localized by an autoradiographic technique which permits track autoradiography with isotopes having short half-lives. Our findings show directly that a minimum of about 25% of the N2 fixation by intact, aerobically grown filaments of Anabaena cylindrica is carried out by the heterocysts. If all of the N2 fixation takes place in the heterocysts, then the movement of nitrogen along the filaments can be characterized by a constant τ < ca. 5 s (cell-2). PMID:4208073

Global metabolic rewiring for improved CO2 fixation and chemical production in cyanobacteria.

PubMed

Kanno, Masahiro; Carroll, Austin L; Atsumi, Shota

2017-03-13

Cyanobacteria have attracted much attention as hosts to recycle CO 2 into valuable chemicals. Although cyanobacteria have been engineered to produce various compounds, production efficiencies are too low for commercialization. Here we engineer the carbon metabolism of Synechococcus elongatus PCC 7942 to improve glucose utilization, enhance CO 2 fixation and increase chemical production. We introduce modifications in glycolytic pathways and the Calvin Benson cycle to increase carbon flux and redirect it towards carbon fixation. The engineered strain efficiently uses both CO 2 and glucose, and produces 12.6 g l -1 of 2,3-butanediol with a rate of 1.1 g l -1  d -1 under continuous light conditions. Removal of native regulation enables carbon fixation and 2,3-butanediol production in the absence of light. This represents a significant step towards industrial viability and an excellent example of carbon metabolism plasticity.

Evolutionary Dynamics of Nitrogen Fixation in the Legume–Rhizobia Symbiosis

PubMed Central

Fujita, Hironori; Aoki, Seishiro; Kawaguchi, Masayoshi

2014-01-01

The stabilization of host–symbiont mutualism against the emergence of parasitic individuals is pivotal to the evolution of cooperation. One of the most famous symbioses occurs between legumes and their colonizing rhizobia, in which rhizobia extract nutrients (or benefits) from legume plants while supplying them with nitrogen resources produced by nitrogen fixation (or costs). Natural environments, however, are widely populated by ineffective rhizobia that extract benefits without paying costs and thus proliferate more efficiently than nitrogen-fixing cooperators. How and why this mutualism becomes stabilized and evolutionarily persists has been extensively discussed. To better understand the evolutionary dynamics of this symbiosis system, we construct a simple model based on the continuous snowdrift game with multiple interacting players. We investigate the model using adaptive dynamics and numerical simulations. We find that symbiotic evolution depends on the cost–benefit balance, and that cheaters widely emerge when the cost and benefit are similar in strength. In this scenario, the persistence of the symbiotic system is compatible with the presence of cheaters. This result suggests that the symbiotic relationship is robust to the emergence of cheaters, and may explain the prevalence of cheating rhizobia in nature. In addition, various stabilizing mechanisms, such as partner fidelity feedback, partner choice, and host sanction, can reinforce the symbiotic relationship by affecting the fitness of symbionts in various ways. This result suggests that the symbiotic relationship is cooperatively stabilized by various mechanisms. In addition, mixed nodule populations are thought to encourage cheater emergence, but our model predicts that, in certain situations, cheaters can disappear from such populations. These findings provide a theoretical basis of the evolutionary dynamics of legume–rhizobia symbioses, which is extendable to other single-host, multiple

Long-term 15N tracking from biological N fixation across different plant and humus components of the boreal forest

NASA Astrophysics Data System (ADS)

Arroniz-Crespo, Maria; Jones, David L.; Zackrisson, Olle; Nilsson, Marie-Charlotte; DeLuca, Thomas H.

2014-05-01

Biological N2 fixation by cyanobacteria associated with feather mosses is an important cog in the nitrogen (N) cycle of boreal forests; still, our understanding of the turnover and fate of N fixed by this association remains greatly incomplete. The 15N signature of plants and soil serves as a powerful tool to explore N dynamics in forest ecosystems. In particular, in the present study we aimed to investigate the contribution of N2 fixation to δ15N signatures of plants and humus component of the boreal forest. Here we present results from a long-term (7 years) tacking of labelled 15N2 across the humus layer, seedlings of the tree species Pinus sylvestris, two common dwarf shrub species (Empetrum hermaphroditum and Vaccinium vitis-idaea) and the feather moss Pleurozium schreibery. The enriched experiment was conducted in 2005 in a natural boreal forest in northern Sweden. Two different treatments (10% 15N2 headspace enrichment and control) were setup in nine different plots (0.5 x 0.5 m) within the forest. We observed a significant reduction of δ15N signature of the 15N-enriched moss that could be explained by a growth dilution effect. Nevertheless, after 5 years since 15N2 enrichment some of the label 15N was still detected on the moss and in particular in the dead tissue. We could not detect a clear transfer of the labelled 15N2 from the moss-cyanobacteria system to other components of the ecosystem. However, we found consistence relationship through time between increments of δ15N signature of some of the forest components in plots which exhibited higher N fixation rates in the moss. In particular, changes in natural abundance δ15N that could be associated with N fixation were more apparent in the humus layer, the dwarf shrub Vaccinium vitis-idaea and the pine seedlings when comparing across plots and years.

Methanotrophy induces nitrogen fixation during peatland development

PubMed Central

Larmola, Tuula; Leppänen, Sanna M.; Tuittila, Eeva-Stiina; Aarva, Maija; Merilä, Päivi; Fritze, Hannu; Tiirola, Marja

2014-01-01

Nitrogen (N) accumulation rates in peatland ecosystems indicate significant biological atmospheric N2 fixation associated with Sphagnum mosses. Here, we show that the linkage between methanotrophic carbon cycling and N2 fixation may constitute an important mechanism in the rapid accumulation of N during the primary succession of peatlands. In our experimental stable isotope enrichment study, previously overlooked methane-induced N2 fixation explained more than one-third of the new N input in the younger peatland stages, where the highest N2 fixation rates and highest methane oxidation activities co-occurred in the water-submerged moss vegetation. PMID:24379382

Demography of Symbiotic Nitrogen-Fixing Trees Explains Their Rarity and Successional Decline in Temperate Forests in the United States.

PubMed

Liao, Wenying; Menge, Duncan N L

2016-01-01

Symbiotic nitrogen (N) fixation is the major N input to many ecosystems. Although temperate forests are commonly N limited, symbiotic N-fixing trees ("N fixers") are rare and decline in abundance as succession proceeds-a challenging paradox that remains unexplained. Understanding demographic processes that underlie N fixers' rarity and successional decline would provide a proximate answer to the paradox. Do N fixers grow slower, die more frequently, or recruit less in temperate forests? We quantified demographic rates of N-fixing and non-fixing trees across succession using U.S. forest inventory data. We used an individual-based model to evaluate the relative contribution of each demographic process to community dynamics. Compared to non-fixers, N fixers had lower growth rates, higher mortality rates, and lower recruitment rates throughout succession. The mortality effect contributed more than the growth effect to N fixers' successional decline. Canopy and understory N fixers experienced these demographic disadvantages, indicating that factors in addition to light limitation likely contribute to N fixers' successional decline. We show that the rarity and successional decline of N-fixing trees in temperate forests is due more to their survival disadvantage than their growth disadvantage, and a recruitment disadvantage might also play a large role.

Demography of Symbiotic Nitrogen-Fixing Trees Explains Their Rarity and Successional Decline in Temperate Forests in the United States

PubMed Central

Liao, Wenying; Menge, Duncan N. L.

2016-01-01

Symbiotic nitrogen (N) fixation is the major N input to many ecosystems. Although temperate forests are commonly N limited, symbiotic N-fixing trees (“N fixers”) are rare and decline in abundance as succession proceeds–a challenging paradox that remains unexplained. Understanding demographic processes that underlie N fixers’ rarity and successional decline would provide a proximate answer to the paradox. Do N fixers grow slower, die more frequently, or recruit less in temperate forests? We quantified demographic rates of N-fixing and non-fixing trees across succession using U.S. forest inventory data. We used an individual-based model to evaluate the relative contribution of each demographic process to community dynamics. Compared to non-fixers, N fixers had lower growth rates, higher mortality rates, and lower recruitment rates throughout succession. The mortality effect contributed more than the growth effect to N fixers’ successional decline. Canopy and understory N fixers experienced these demographic disadvantages, indicating that factors in addition to light limitation likely contribute to N fixers’ successional decline. We show that the rarity and successional decline of N-fixing trees in temperate forests is due more to their survival disadvantage than their growth disadvantage, and a recruitment disadvantage might also play a large role. PMID:27780268

Simple approach for the preparation of 15−15N2-enriched water for nitrogen fixation assessments: evaluation, application and recommendations

PubMed Central

Klawonn, Isabell; Lavik, Gaute; Böning, Philipp; Marchant, Hannah K.; Dekaezemacker, Julien; Mohr, Wiebke; Ploug, Helle

2015-01-01

Recent findings revealed that the commonly used 15N2 tracer assay for the determination of dinitrogen (N2) fixation can underestimate the activity of aquatic N2-fixing organisms. Therefore, a modification to the method using pre-prepared 15−15N2-enriched water was proposed. Here, we present a rigorous assessment and outline a simple procedure for the preparation of 15−15N2-enriched water. We recommend to fill sterile-filtered water into serum bottles and to add 15−15N2 gas to the water in amounts exceeding the standard N2 solubility, followed by vigorous agitation (vortex mixing ≥ 5 min). Optionally, water can be degassed at low-pressure (≥950 mbar) for 10 min prior to the 15−15N2 gas addition to indirectly enhance the 15−15N2 concentration. This preparation of 15−15N2-enriched water can be done within 1 h using standard laboratory equipment. The final 15N-atom% excess was 5% after replacing 2–5% of the incubation volume with 15−15N2-enriched water. Notably, the addition of 15−15N2-enriched water can alter levels of trace elements in the incubation water due to the contact of 15−15N2-enriched water with glass, plastic and rubber ware. In our tests, levels of trace elements (Fe, P, Mn, Mo, Cu, Zn) increased by up to 0.1 nmol L−1 in the final incubation volume, which may bias rate measurements in regions where N2 fixation is limited by trace elements. For these regions, we tested an alternative way to enrich water with 15−15N2. The 15−15N2 was injected as a bubble directly to the incubation water, followed by gentle shaking. Immediately thereafter, the bubble was replaced with water to stop the 15−15N2 equilibration. This approach achieved a 15N-atom% excess of 6.6 ± 1.7% when adding 2 mL 15−15N2 per liter of incubation water. The herein presented methodological tests offer guidelines for the 15N2 tracer assay and thus, are crucial to circumvent methodological draw-backs for future N2 fixation assessments. PMID:26300853

Variable Nitrogen Fixation in Wild Populus

PubMed Central

Doty, Sharon L.; Sher, Andrew W.; Fleck, Neil D.; Khorasani, Mahsa; Bumgarner, Roger E.; Khan, Zareen; Ko, Andrew W. K.; Kim, Soo-Hyung; DeLuca, Thomas H.

2016-01-01

The microbiome of plants is diverse, and like that of animals, is important for overall health and nutrient acquisition. In legumes and actinorhizal plants, a portion of essential nitrogen (N) is obtained through symbiosis with nodule-inhabiting, N2-fixing microorganisms. However, a variety of non-nodulating plant species can also thrive in natural, low-N settings. Some of these species may rely on endophytes, microorganisms that live within plants, to fix N2 gas into usable forms. Here we report the first direct evidence of N2 fixation in the early successional wild tree, Populus trichocarpa, a non-leguminous tree, from its native riparian habitat. In order to measure N2 fixation, surface-sterilized cuttings of wild poplar were assayed using both 15N2 incorporation and the commonly used acetylene reduction assay. The 15N label was incorporated at high levels in a subset of cuttings, suggesting a high level of N-fixation. Similarly, acetylene was reduced to ethylene in some samples. The microbiota of the cuttings was highly variable, both in numbers of cultured bacteria and in genetic diversity. Our results indicated that associative N2-fixation occurred within wild poplar and that a non-uniformity in the distribution of endophytic bacteria may explain the variability in N-fixation activity. These results point to the need for molecular studies to decipher the required microbial consortia and conditions for effective endophytic N2-fixation in trees. PMID:27196608

Free amino acids exhibit anthozoan "host factor" activity: they induce the release of photosynthate from symbiotic dinoflagellates in vitro.

PubMed Central

Gates, R D; Hoegh-Guldberg, O; McFall-Ngai, M J; Bil, K Y; Muscatine, L

1995-01-01

Reef-building corals and other tropical anthozoans harbor endosymbiotic dinoflagellates. It is now recognized that the dinoflagellates are fundamental to the biology of their hosts, and their carbon and nitrogen metabolisms are linked in important ways. Unlike free living species, growth of symbiotic dinoflagellates is unbalanced and a substantial fraction of the carbon fixed daily by symbiont photosynthesis is released and used by the host for respiration and growth. Release of fixed carbon as low molecular weight compounds by freshly isolated symbiotic dinoflagellates is evoked by a factor (i.e., a chemical agent) present in a homogenate of host tissue. We have identified this "host factor" in the Hawaiian coral Pocillopora damicornis as a set of free amino acids. Synthetic amino acid mixtures, based on the measured free amino acid pools of P. damicornis tissues, not only elicit the selective release of 14C-labeled photosynthetic products from isolated symbiotic dinoflagellates but also enhance total 14CO2 fixation. Images Fig. 2 PMID:11607567

Reverse Anterior Cruciate Ligament Reconstruction Fixation: A Biomechanical Comparison Study of Tibial Cross-Pin and Femoral Interference Screw Fixation.

PubMed

Lawley, Richard J; Klein, Samuel E; Chudik, Steven C

2017-03-01

To evaluate the biomechanical performance of tibial cross-pin (TCP) fixation relative to femoral cross-pin (FCP), femoral interference screw (FIS), and tibial interference screw (TIS) fixation. We randomized 40 porcine specimens (20 tibias and 20 femurs) to TIS fixation (group 1, n = 10), FIS fixation (group 2, n = 10), TCP fixation (group 3, n = 10), or FCP fixation (group 4, n = 10) and performed biomechanical testing to compare ultimate load, stiffness, yield load, cyclic displacement, and load at 5-mm displacement. We performed cross-pin fixation of the looped end and interference screw fixation of the free ends of 9-mm-diameter bovine extensor digitorum communis tendon grafts. Graft fixation constructs were cyclically loaded and then loaded to failure in line with the tunnels. Regarding yield load, FIS was superior to TIS (704 ± 125 N vs 504 ± 118 N, P = .002), TCP was superior to TIS (1,449 ± 265 N vs 504 ± 118 N, P < .001), and TCP was superior to FCP (1,449 ± 265 N vs 792 ± 397 N, P < .001). Cyclic displacement for FCP was superior to TCP. Cyclic displacement for TIS versus FIS showed no statistically significant difference (2.5 ± 1.0 mm vs 2.2 ± 0.6 mm, P = .298). Interference screw fixation consistently failed by graft slippage, whereas TCP fixation failed by tibial bone failure. FCP fixation failed by either femoral bone failure or failure elsewhere in the testing apparatus. Regarding yield load, TCP fixation performed biomechanically superior to the clinically proven FCP at time zero. Because TIS fixation shows the lowest yield strength, it represents the weak link, and combined TCP-FIS fixation theoretically would be biomechanically superior relative to combined FCP-TIS fixation with regard to yield load. Cyclic displacement showed a small difference in favor of FCP over TCP fixation and no difference between TIS and FIS. Time-zero biomechanics of TCP fixation paired with FIS fixation show that this method of fixation can be

Analysis of the Symbiotic Performance of Bradyrhizobium japonicum USDA 110 and Its Derivative I-110 and Discovery of a New Mannitol-Utilizing, Nitrogen-Fixing USDA 110 Derivative.

PubMed

Mathis, J N; Israel, D W; Barbour, W M; Jarvis, B D; Elkan, G H

1986-07-01

Previously, Bradyrhizobium japonicum USDA 110 was shown to contain colony morphology variants which differed in nitrogen-fixing ability. Mannitol-utilizing derivatives L1-110 and L2-110 have been shown to be devoid of symbiotic nitrogen fixation ability, and non-mannitol-utilizing derivatives I-110 and S-110 have been shown to be efficient at nitrogen fixation. The objectives of this study were to determine the effect of media carbon sources on the symbiotic N(2)-fixing ability of strain USDA 110 and to compare the effectiveness of strain USDA 110 and derivative I-110. Based on acetylene reduction activity and the nitrogen content of 41-day-old soybean plants, neither derivative I-110 nor cultures of USDA 110 grown in media favoring non-mannitol-using derivatives had symbiotic nitrogen fixation that was statistically superior to that of cultures of USDA 110 grown in media favoring mannitol-using derivatives. In another experiment 200 individual nodules formed by strain USDA 110 grown in yeast extract gluconate were screened for colony morphology of occupying variant(s) and acetylene reduction activity. Nodules occupied by mannitol-using derivatives (large colony type on 0.1% yeast extract-0.05% K(2)HPO(4)-0.08% MgSO(4) . 7H(2)O-0.02% NaCl-0.001% FeCl(3) . 6H(2)O [pH 6.7] with 1% mannitol [YEM] plates) had a mean acetylene reduction activity equal to that of nodules occupied by non-mannitol-using derivatives (small colony type on YEM plates). A total of 20 large colonial derivatives and 10 small colonial derivatives (I-110-like) were isolated and purified by repeated culture in YEM and YEG (same as YEM except 1% gluconate instead of 1% mannitol) media, respectively, followed by dilution in solutions containing 0.05% Tween 40. After 25 days of growth, soybean plants inoculated with the large colony isolates had mean whole-plant acetylene reduction activity, whole-plant dry weight, and whole-plant nitrogen contents equal to or better than those of plants inoculated

Genome evolution and nitrogen fixation in bacterial ectosymbionts of a protist inhabiting wood-feeding cockroaches

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tai, Vera; Carpenter, Kevin J.; Weber, Peter K.

By combining genomics and isotope imaging analysis using high-resolution secondary ion mass spectrometry (NanoSIMS), we examined the function and evolution of Bacteroidales ectosymbionts of the protistBarbulanymphafrom the hindguts of the wood-eating cockroachCryptocercus punctulatus. In particular, we investigated the structure of ectosymbiont genomes, which, in contrast to those of endosymbionts, has been little studied to date, and tested the hypothesis that these ectosymbionts fix nitrogen. Unlike with most obligate endosymbionts, genome reduction has not played a major role in the evolution of the Barbulanympha ectosymbionts. Instead, interaction with the external environment has remained important for this symbiont as genes for synthesismore » of transporters, outer membrane proteins, lipopolysaccharides, and lipoproteins have been retained. The ectosymbiont genome carried two complete operons for nitrogen fixation, a urea transporter, and a urease, indicating the availability of nitrogen as a driving force behind the symbiosis. NanoSIMS analysis ofC. punctulatushindgut symbionts exposedin vivoto 15N 2 supports the hypothesis thatBarbulanymphaectosymbionts are capable of nitrogen fixation. This genomic andin vivofunctional investigation of protist ectosymbionts highlights the diversity of evolutionary forces and trajectories that shape symbiotic interactions. The ecological and evolutionary importance of symbioses is increasingly clear, but the overall diversity of symbiotic interactions remains poorly explored. Here in this study, we investigated the evolution and nitrogen fixation capabilities of ectosymbionts attached to the protist Barbulanympha from the hindgut of the wood-eating cockroach Cryptocercus punctulatus. In addressing genome evolution of protist ectosymbionts, our data suggest that the ecological pressures influencing the evolution of extracellular symbionts clearly differ from intracellular symbionts and organelles. Using NanoSIMS analysis

Genome evolution and nitrogen fixation in bacterial ectosymbionts of a protist inhabiting wood-feeding cockroaches

DOE PAGES

Tai, Vera; Carpenter, Kevin J.; Weber, Peter K.; ...

2016-05-27

By combining genomics and isotope imaging analysis using high-resolution secondary ion mass spectrometry (NanoSIMS), we examined the function and evolution of Bacteroidales ectosymbionts of the protistBarbulanymphafrom the hindguts of the wood-eating cockroachCryptocercus punctulatus. In particular, we investigated the structure of ectosymbiont genomes, which, in contrast to those of endosymbionts, has been little studied to date, and tested the hypothesis that these ectosymbionts fix nitrogen. Unlike with most obligate endosymbionts, genome reduction has not played a major role in the evolution of the Barbulanympha ectosymbionts. Instead, interaction with the external environment has remained important for this symbiont as genes for synthesismore » of transporters, outer membrane proteins, lipopolysaccharides, and lipoproteins have been retained. The ectosymbiont genome carried two complete operons for nitrogen fixation, a urea transporter, and a urease, indicating the availability of nitrogen as a driving force behind the symbiosis. NanoSIMS analysis ofC. punctulatushindgut symbionts exposedin vivoto 15N 2 supports the hypothesis thatBarbulanymphaectosymbionts are capable of nitrogen fixation. This genomic andin vivofunctional investigation of protist ectosymbionts highlights the diversity of evolutionary forces and trajectories that shape symbiotic interactions. The ecological and evolutionary importance of symbioses is increasingly clear, but the overall diversity of symbiotic interactions remains poorly explored. Here in this study, we investigated the evolution and nitrogen fixation capabilities of ectosymbionts attached to the protist Barbulanympha from the hindgut of the wood-eating cockroach Cryptocercus punctulatus. In addressing genome evolution of protist ectosymbionts, our data suggest that the ecological pressures influencing the evolution of extracellular symbionts clearly differ from intracellular symbionts and organelles. Using NanoSIMS analysis

Screw fixation versus arthroplasty versus plate fixation for 3-part radial head fractures.

PubMed

Wu, P H; Shen, L; Chee, Y H

2016-04-01

To compare the outcome following headless compression screw fixation versus radial head arthroplasty versus plate fixation for 3-part Mason types III or IV radial head fracture. Records of 25 men and 16 women aged 21 to 80 (mean, 43.3) years who underwent fixation using 2 to 3 2-mm cannulated headless compression screws (n=16), radial head arthroplasty (n=13), or fixation with a 2-mm Synthes plate (n=12) for 3-part Mason types III or IV radial head and neck fracture were reviewed. Treatment option was decided by the surgeon based on the presence of associated injury, neurovascular deficit, and the Mason classification. Bone union, callus formation, and complications (such as heterotopic ossification, malunion, and nonunion) were assessed by an independent registrar or consultant using radiographs. The Mayo Elbow Performance Score and range of motion were assessed by an independent physiotherapist. The median age of the 3 groups were comparable. Associated injuries were most common in patients with arthroplasty, followed by screw fixation and plate fixation (61.5% vs. 50% vs. 33%, p=0.54). The median time to bone union was shorter after screw fixation than plate fixation (55 vs. 86 days, p=0.05). No patient with screw fixation had nonunion, but 4 patients with plate fixation had nonunion. The 3 groups were comparable in terms of the mean Mayo Elbow Performance Score (p=0.56) and the mean range of motion (p=0.45). The complication rate was highest after plate fixation, followed by screw fixation and arthroplasty (50% vs. 18.8% vs. 15.4%, p=0.048). Excluding 20 patients with associated injuries (8 in screw fixation, 8 in arthroplasty, and 4 in plate fixation), the 3 groups were comparable in terms of the median time to bone union (p=0.109), mean Mayo Elbow Performance Score (p=0.260), mean range of motion (p=0.162), and complication rate (p=0.096). Headless compression screw fixation is a viable option for 3-part radial head fracture. It achieves earlier bone union

Comparative symbiotic plasmid analysis indicates that symbiosis gene ancestor type affects plasmid genetic evolution.

PubMed

Wang, X; Zhao, L; Zhang, L; Wu, Y; Chou, M; Wei, G

2018-07-01

Rhizobial symbiotic plasmids play vital roles in mutualistic symbiosis with legume plants by executing the functions of nodulation and nitrogen fixation. To explore the gene composition and genetic constitution of rhizobial symbiotic plasmids, comparison analyses of 24 rhizobial symbiotic plasmids derived from four rhizobial genera was carried out. Results illustrated that rhizobial symbiotic plasmids had higher proportion of functional genes participating in amino acid transport and metabolism, replication; recombination and repair; carbohydrate transport and metabolism; energy production and conversion and transcription. Mesorhizobium amorphae CCNWGS0123 symbiotic plasmid - pM0123d had similar gene composition with pR899b and pSNGR234a. All symbiotic plasmids shared 13 orthologous genes, including five nod and eight nif/fix genes which participate in the rhizobia-legume symbiosis process. These plasmids contained nod genes from four ancestors and fix genes from six ancestors. The ancestral type of pM0123d nod genes was similar with that of Rhizobium etli plasmids, while the ancestral type of pM0123d fix genes was same as that of pM7653Rb. The phylogenetic trees constructed based on nodCIJ and fixABC displayed different topological structures mainly due to nodCIJ and fixABC ancestral type discordance. The study presents valuable insights into mosaic structures and the evolution of rhizobial symbiotic plasmids. This study compared 24 rhizobial symbiotic plasmids that included four genera and 11 species, illuminating the functional gene composition and symbiosis gene ancestor types of symbiotic plasmids from higher taxonomy. It provides valuable insights into mosaic structures and the evolution of symbiotic plasmids. © 2018 The Society for Applied Microbiology.

Role of antimicrobial peptides in controlling symbiotic bacterial populations.

PubMed

Mergaert, P

2018-04-25

Covering: up to 2018 Antimicrobial peptides (AMPs) have been known for well over three decades as crucial mediators of the innate immune response in animals and plants, where they are involved in the killing of infecting microbes. However, AMPs have now also been found to be produced by eukaryotic hosts during symbiotic interactions with bacteria. These symbiotic AMPs target the symbionts and therefore have a more subtle biological role: not eliminating the microbial symbiont population but rather keeping it in check. The arsenal of AMPs and the symbionts' adaptations to resist them are in a careful balance, which contributes to the establishment of the host-microbe homeostasis. Although in many cases the biological roles of symbiotic AMPs remain elusive, for a number of symbiotic interactions, precise functions have been assigned or proposed to the AMPs, which are discussed here. The microbiota living on epithelia in animals, from the most primitive ones to the mammals, are challenged by a cocktail of AMPs that determine the specific composition of the bacterial community as well as its spatial organization. In the symbiosis of legume plants with nitrogen-fixing rhizobium bacteria, the host deploys an extremely large panel of AMPs - called nodule-specific cysteine-rich (NCR) peptides - that drive the bacteria into a terminally differentiated state and manipulate the symbiont physiology to maximize the benefit for the host. The NCR peptides are used as tools to enslave the bacterial symbionts, limiting their reproduction but keeping them metabolically active for nitrogen fixation. In the nutritional symbiotic interactions of insects and protists that have vertically transmitted bacterial symbionts with reduced genomes, symbiotic AMPs could facilitate the integration of the endosymbiont and host metabolism by favouring the flow of metabolites across the symbiont membrane through membrane permeabilization.

Origin and Evolution of Nitrogen Fixation Genes on Symbiosis Islands and Plasmid in Bradyrhizobium

PubMed Central

Okubo, Takashi; Piromyou, Pongdet; Tittabutr, Panlada; Teaumroong, Neung; Minamisawa, Kiwamu

2016-01-01

The nitrogen fixation (nif) genes of nodule-forming Bradyrhizobium strains are generally located on symbiosis islands or symbiosis plasmids, suggesting that these genes have been transferred laterally. The nif genes of rhizobial and non-rhizobial Bradyrhizobium strains were compared in order to infer the evolutionary histories of nif genes. Based on all codon positions, the phylogenetic tree of concatenated nifD and nifK sequences showed that nifDK on symbiosis islands formed a different clade from nifDK on non-symbiotic loci (located outside of symbiosis islands and plasmids) with elongated branches; however, these genes were located in close proximity, when only the 1st and 2nd codon positions were analyzed. The guanine (G) and cytosine (C) content of the 3rd codon position of nifDK on symbiosis islands was lower than that on non-symbiotic loci. These results suggest that nif genes on symbiosis islands were derived from the non-symbiotic loci of Bradyrhizobium or closely related strains and have evolved toward a lower GC content with a higher substitution rate than the ancestral state. Meanwhile, nifDK on symbiosis plasmids clustered with nifDK on non-symbiotic loci in the tree representing all codon positions, and the GC content of symbiotic and non-symbiotic loci were similar. These results suggest that nif genes on symbiosis plasmids were derived from the non-symbiotic loci of Bradyrhizobium and have evolved with a similar evolutionary pattern and rate as the ancestral state. PMID:27431195

St 2-22 - Another Symbiotic Star with High-Velocity Bipolar Jets

NASA Astrophysics Data System (ADS)

Tomov, T.; Zamanov, R.; Gałan, C.; Pietrukowicz, P.

2017-09-01

We report the detection of high-velocity components in the wings of Hα emission line in spectra of symbiotic binary star St 2-22 obtained in 2005. This finding encouraged us to start the present investigation in order to show that this poorly-studied object is a jet-producing system. We have used high-resolution optical and low-resolution near-infrared spectra, as well as available optical and infrared photometry, to evaluate some physical parameters of the St 2-22 components and characteristics of the jets. We confirm that St 2-22 is a S-type symbiotic star. Our results demonstrate that an unnoticed outburst, similar to those in classical symbiotic systems, occurred in the first half of 2005. During the outburst, collimated bipolar jets were ejected by the hot component of St 2-22 with an average velocity of about 1700 km/s.

Genome-wide association analysis of diverse soybean genotypes reveals novel markers for nitrogen traits

USDA-ARS?s Scientific Manuscript database

Nitrogen is a primary plant nutrient that plays a major role in achieving maximum economic yield. Insufficient availability most often limits soybean crop growth. Symbiotic N2 fixation in soybean is highly sensitive to limited water availability, and breeding for reduced N2 fixation sensitivity to ...

Sugar enrichment provides evidence for a role of nitrogen fixation in coral bleaching.

PubMed

Pogoreutz, Claudia; Rädecker, Nils; Cárdenas, Anny; Gärdes, Astrid; Voolstra, Christian R; Wild, Christian

2017-09-01

The disruption of the coral-algae symbiosis (coral bleaching) due to rising sea surface temperatures has become an unprecedented global threat to coral reefs. Despite decades of research, our ability to manage mass bleaching events remains hampered by an incomplete mechanistic understanding of the processes involved. In this study, we induced a coral bleaching phenotype in the absence of heat and light stress by adding sugars. The sugar addition resulted in coral symbiotic breakdown accompanied by a fourfold increase of coral-associated microbial nitrogen fixation. Concomitantly, increased N:P ratios by the coral host and algal symbionts suggest excess availability of nitrogen and a disruption of the nitrogen limitation within the coral holobiont. As nitrogen fixation is similarly stimulated in ocean warming scenarios, here we propose a refined coral bleaching model integrating the cascading effects of stimulated microbial nitrogen fixation. This model highlights the putative role of nitrogen-fixing microbes in coral holobiont functioning and breakdown. © 2017 The Authors. Global Change Biology Published by John Wiley & Sons Ltd.

The symbiotic relationship between dominant canopy trees and soil microbes affects the nitrogen source utilization of co-existing understory trees

NASA Astrophysics Data System (ADS)

Iwaoka, C.; Hyodo, F.; Taniguchi, T.; Shi, W.; Du, S.; Yamanaka, N.; Tateno, R.

2017-12-01

The symbiotic relationship between dominant canopy trees and soil microbes such as mycorrhiza or nitrogen (N) fixer are important determinants of soil N dynamics of a forest. However, it is not known how and to what extent the symbiotic relationship of dominant canopy trees with soil microbes affect the N source of co-existing trees in forest. We measured the δ15N of surface soils (0-10 cm), leaves, and roots of the dominant canopy trees and common understory trees in an arbuscular mycorrhizal N-fixing black locust (Robinia pseudoacacia) plantation and an ectomycorrhizal oak (Quercus liaotungensis) natural forest in a China dryland. We also analyzed the soil dissolved N content in soil extracts and absorbed by ion exchange resin, and soil ammonia-oxidizer abundance using real-time PCR. The δ15N of soil and leaves were higher in the black locust forest than in the oak forest, although the δ15N of fine roots was similar in the two forests, in co-existing understory trees as well as dominant canopy trees. Accordingly, the δ15N of leaves was similar to or higher than that of fine roots in the black locust forest, whereas it was consistently lower than that of fine roots in the oak forest. In the black locust forest, the soil dissolved organic N and ammonium N contents were less abundant but the nitrate N contents in soils and absorbed by the ion exchange resin and ammonia-oxidizer abundance were greater, due to N fixation or less uptake of organic N from arbuscular mycorrhiza. In contrast, the soil dissolved organic N and ammonium N contents were more abundant in the oak forest, whereas the N content featured very low nitrate, due to ectomycorrhizal ability to access organic N. These results suggest that the main N source is nitrate N in the black locust forest, but dissolved organic N or ammonium N in the oak forest. N fixation or high N loss due to high N availability would cause high δ15N in soil and leaves in black locust forest. On the other hand, low soil N

A conserved α-proteobacterial small RNA contributes to osmoadaptation and symbiotic efficiency of rhizobia on legume roots.

PubMed

Robledo, Marta; Peregrina, Alexandra; Millán, Vicenta; García-Tomsig, Natalia I; Torres-Quesada, Omar; Mateos, Pedro F; Becker, Anke; Jiménez-Zurdo, José I

2017-07-01

Small non-coding RNAs (sRNAs) are expected to have pivotal roles in the adaptive responses underlying symbiosis of nitrogen-fixing rhizobia with legumes. Here, we provide primary insights into the function and activity mechanism of the Sinorhizobium meliloti trans-sRNA NfeR1 (Nodule Formation Efficiency RNA). Northern blot probing and transcription tracking with fluorescent promoter-reporter fusions unveiled high nfeR1 expression in response to salt stress and throughout the symbiotic interaction. The strength and differential regulation of nfeR1 transcription are conferred by a motif, which is conserved in nfeR1 promoter regions in α-proteobacteria. NfeR1 loss-of-function compromised osmoadaptation of free-living bacteria, whilst causing misregulation of salt-responsive genes related to stress adaptation, osmolytes catabolism and membrane trafficking. Nodulation tests revealed that lack of NfeR1 affected competitiveness, infectivity, nodule development and symbiotic efficiency of S. meliloti on alfalfa roots. Comparative computer predictions and a genetic reporter assay evidenced a redundant role of three identical NfeR1 unpaired anti Shine-Dalgarno motifs for targeting and downregulation of translation of multiple mRNAs from transporter genes. Our data provide genetic evidence of the hyperosmotic conditions of the endosymbiotic compartments. NfeR1-mediated gene regulation in response to this cue could contribute to coordinate nutrient uptake with the metabolic reprogramming concomitant to symbiotic transitions. © 2017 Society for Applied Microbiology and John Wiley & Sons Ltd.

Acetogenesis from H2 plus CO2 and nitrogen fixation by an endosymbiotic spirochete of a termite-gut cellulolytic protist

PubMed Central

Ohkuma, Moriya; Noda, Satoko; Hattori, Satoshi; Iida, Toshiya; Yuki, Masahiro; Starns, David; Inoue, Jun-ichi; Darby, Alistair C.; Hongoh, Yuichi

2015-01-01

Symbiotic associations of cellulolytic eukaryotic protists and diverse bacteria are common in the gut microbial communities of termites. Besides cellulose degradation by the gut protists, reductive acetogenesis from H2 plus CO2 and nitrogen fixation by gut bacteria play crucial roles in the host termites’ nutrition by contributing to the energy demand of termites and supplying nitrogen poor in their diet, respectively. Fractionation of these activities and the identification of key genes from the gut community of the wood-feeding termite Hodotermopsis sjoestedti revealed that substantial activities in the gut—nearly 60% of reductive acetogenesis and almost exclusively for nitrogen fixation—were uniquely attributed to the endosymbiotic bacteria of the cellulolytic protist in the genus Eucomonympha. The rod-shaped endosymbionts were surprisingly identified as a spirochete species in the genus Treponema, which usually exhibits a characteristic spiral morphology. The endosymbionts likely use H2 produced by the protist for these dual functions. Although H2 is known to inhibit nitrogen fixation in some bacteria, it seemed to rather stimulate this important mutualistic process. In addition, the single-cell genome analyses revealed the endosymbiont's potentials of the utilization of sugars for its energy requirement, and of the biosynthesis of valuable nutrients such as amino acids from the fixed nitrogen. These metabolic interactions are suitable for the dual functions of the endosymbiont and reconcile its substantial contributions in the gut. PMID:25979941

Efficient Nitrogen Fixation via a Redox-Flexible Single-Iron Site with Reverse-Dative Iron → Boron σ Bonding.

PubMed

Lu, Jun-Bo; Ma, Xue-Lu; Wang, Jia-Qi; Liu, Jin-Cheng; Xiao, Hai; Li, Jun

2018-05-10

Model systems of the FeMo cofactor of nitrogenase have been explored extensively in catalysis to gain insights into their ability for nitrogen fixation that is of vital importance to the human society. Here we investigate the trigonal pyramidal borane-ligand Fe complex by first-principles calculations, and find that the variation of oxidation state of Fe along the reaction path correlates with that of the reverse-dative Fe → B bonding. The redox-flexibility of the reverse-dative Fe → B bonding helps to provide an electron reservoir that buffers and stabilizes the evolution of Fe oxidation state, which is essential for forming the key intermediates of N 2 activation. Our work provides insights for understanding and optimizing homogeneous and surface single-atom catalysts with reverse-dative donating ligands for efficient dinitrogen fixation. The extension of this kind of molecular catalytic active center to heterogeneous catalysts with surface single-clusters is also discussed.

Searching for New Yellow Symbiotic Stars: Positive Identification of StHα63

NASA Astrophysics Data System (ADS)

Baella, N. O.; Pereira, C. B.; Miranda, L. F.; Alvarez-Candal, A.

2016-04-01

Yellow symbiotic stars are useful targets for probing whether mass transfer has happened in their binary systems. However, the number of known yellow symbiotic stars is very scarce. We report spectroscopic observations of five candidate yellow symbiotic stars that were selected by their positions in the 2MASS (J - H) versus (H - Ks) diagram and which were included in some emission-line catalogs. Among the five candidates, only StHα63 is identified as a new yellow symbiotic star because of its spectrum and its position in the [TiO]1-[TiO]2 diagram, which indicates a K4-K6 spectral type. In addition, the derived electron density (˜108.4 cm-3) and several emission-line intensity ratios provide further support for that classification. The other four candidates are rejected as symbiotic stars because three of them actually do not show emission lines and the fourth one only Balmer emission lines. We also found that the WISE W3-W4 index clearly separates normal K-giants from yellow symbiotic stars and therefore can be used as an additional tool for selecting candidate yellow symbiotic stars. Based on observations collected at the Centro Astronómico Hispano-Alemán, Calar Alto, jointly operated by the Max-Planck-Institut für Astronomie (Heidelberg) and the Instituto de Astrofísica de Andalucía (CSIC), and at the 4.1 m telescope at Cerro Pachón Observatory, Chile.

Free amino acids exhibit anthozoan "host factor" activity: they induce the release of photosynthate from symbiotic dinoflagellates in vitro.

PubMed

Gates, R D; Hoegh-Guldberg, O; McFall-Ngai, M J; Bil, K Y; Muscatine, L

1995-08-01

Reef-building corals and other tropical anthozoans harbor endosymbiotic dinoflagellates. It is now recognized that the dinoflagellates are fundamental to the biology of their hosts, and their carbon and nitrogen metabolisms are linked in important ways. Unlike free living species, growth of symbiotic dinoflagellates is unbalanced and a substantial fraction of the carbon fixed daily by symbiont photosynthesis is released and used by the host for respiration and growth. Release of fixed carbon as low molecular weight compounds by freshly isolated symbiotic dinoflagellates is evoked by a factor (i.e., a chemical agent) present in a homogenate of host tissue. We have identified this "host factor" in the Hawaiian coral Pocillopora damicornis as a set of free amino acids. Synthetic amino acid mixtures, based on the measured free amino acid pools of P. damicornis tissues, not only elicit the selective release of 14C-labeled photosynthetic products from isolated symbiotic dinoflagellates but also enhance total 14CO2 fixation.

Synthetic biology for CO2 fixation.

PubMed

Gong, Fuyu; Cai, Zhen; Li, Yin

2016-11-01

Recycling of carbon dioxide (CO 2 ) into fuels and chemicals is a potential approach to reduce CO 2 emission and fossil-fuel consumption. Autotrophic microbes can utilize energy from light, hydrogen, or sulfur to assimilate atmospheric CO 2 into organic compounds at ambient temperature and pressure. This provides a feasible way for biological production of fuels and chemicals from CO 2 under normal conditions. Recently great progress has been made in this research area, and dozens of CO 2 -derived fuels and chemicals have been reported to be synthesized by autotrophic microbes. This is accompanied by investigations into natural CO 2 -fixation pathways and the rapid development of new technologies in synthetic biology. This review first summarizes the six natural CO 2 -fixation pathways reported to date, followed by an overview of recent progress in the design and engineering of CO 2 -fixation pathways as well as energy supply patterns using the concept and tools of synthetic biology. Finally, we will discuss future prospects in biological fixation of CO 2 .

Namib Desert primary productivity is driven by cryptic microbial community N-fixation.

PubMed

Ramond, Jean-Baptiste; Woodborne, Stephan; Hall, Grant; Seely, Mary; Cowan, Don A

2018-05-02

Carbon exchange in drylands is typically low, but during significant rainfall events (wet anomalies) drylands act as a C sink. During these anomalies the limitation on C uptake switches from water to nitrogen. In the Namib Desert of southern Africa, the N inventory in soil organic matter available for mineralisation is insufficient to support the observed increase in primary productivity. The C4 grasses that flourish after rainfall events are not capable of N fixation, and so there is no clear mechanism for adequate N fixation in dryland ecosystems to support rapid C uptake. Here we demonstrate that N fixation by photoautotrophic hypolithic communities forms the basis for the N budget for plant productivity events in the Namib Desert. Stable N isotope (δ 15 N) values of Namib Desert hypolithic biomass, and surface and subsurface soils were measured over 3 years across dune and gravel plain biotopes. Hypoliths showed significantly higher biomass and lower δ 15 N values than soil organic matter. The δ 15 N values of hypoliths approach the theoretical values for nitrogen fixation. Our results are strongly indicative that hypolithic communities are the foundation of productivity after rain events in the Namib Desert and are likely to play similar roles in other arid environments.

Carbon sequestration in soybean crop soils: the role of hydrogen-coupled CO2 fixation

NASA Astrophysics Data System (ADS)

Graham, A.; Layzell, D. B.; Scott, N. A.; Cen, Y.; Kyser, T. K.

2011-12-01

Conversion of native vegetation to agricultural land in order to support the world's growing population is a key factor contributing to global climate change. However, the extent to which agricultural activities contribute to greenhouse gas emissions compared to carbon storage is difficult to ascertain, especially for legume crops, such as soybeans. Soybean establishment often leads to an increase in N2O emissions because N-fixation leads to increased soil available N during decomposition of the low C:N legume biomass. However, soybean establishment may also reduce net greenhouse gas emissions by increasing soil fertility, plant growth, and soil carbon storage. The mechanism behind increased carbon storage, however, remains unclear. One explanation points to hydrogen coupled CO2 fixation; the process by which nitrogen fixation releases H2 into the soil system, thereby promoting chemoautotrophic carbon fixation by soil microbes. We used 13CO2 as a tracer to track the amount and fate of carbon fixed by hydrogen coupled CO2 fixation during one-year field and laboratory incubations. The objectives of the research are to 1) quantify rates of 13CO2 fixation in soil collected from a field used for long-term soybean production 2) examine the impact of H2 gas concentration on rates of 13CO2 fixation, and 3) measure changes in δ13C signature over time in 3 soil fractions: microbial biomass, light fraction, and acid stable fraction. If this newly-fixed carbon is incorporated into the acid-stable soil C fraction, it has a good chance of contributing to long-term soil C sequestration under soybean production. Soil was collected in the field both adjacent to root nodules (nodule soil) and >3cm away (root soil) and labelled with 13CO2 (1% v/v) in the presence and absence of H2 gas. After a two week labelling period, δ13C signatures already revealed differences in the four treatments of bulk soil: -17.1 for root, -17.6 for nodule, -14.2 for root + H2, and -6.1 for nodule + H2

Regulation of nif gene expression and the energetics of N2 fixation over the diel cycle in a hot spring microbial mat.

PubMed

Steunou, Anne-Soisig; Jensen, Sheila I; Brecht, Eric; Becraft, Eric D; Bateson, Mary M; Kilian, Oliver; Bhaya, Devaki; Ward, David M; Peters, John W; Grossman, Arthur R; Kühl, Michael

2008-04-01

Nitrogen fixation, a prokaryotic, O2-inhibited process that reduces N2 gas to biomass, is of paramount importance in biogeochemical cycling of nitrogen. We analyzed the levels of nif transcripts of Synechococcus ecotypes, NifH subunit and nitrogenase activity over the diel cycle in the microbial mat of an alkaline hot spring in Yellowstone National Park. The results showed a rise in nif transcripts in the evening, with a subsequent decline over the course of the night. In contrast, immunological data demonstrated that the level of the NifH polypeptide remained stable during the night, and only declined when the mat became oxic in the morning. Nitrogenase activity was low throughout the night; however, it exhibited two peaks, a small one in the evening and a large one in the early morning, when light began to stimulate cyanobacterial photosynthetic activity, but O2 consumption by respiration still exceeded the rate of O2 evolution. Once the irradiance increased to the point at which the mat became oxic, the nitrogenase activity was strongly inhibited. Transcripts for proteins associated with energy-producing metabolisms in the cell also followed diel patterns, with fermentation-related transcripts accumulating at night, photosynthesis- and respiration-related transcripts accumulating during the day and late afternoon, respectively. These results are discussed with respect to the energetics and regulation of N2 fixation in hot spring mats and factors that can markedly influence the extent of N2 fixation over the diel cycle.

Characterization of a heat-tolerant Chlorella sp. GD mutant with enhanced photosynthetic CO2 fixation efficiency and its implication as lactic acid fermentation feedstock.

PubMed

Lee, Tse-Min; Tseng, Yu-Fei; Cheng, Chieh-Lun; Chen, Yi-Chuan; Lin, Chih-Sheng; Su, Hsiang-Yen; Chow, Te-Jin; Chen, Chun-Yen; Chang, Jo-Shu

2017-01-01

Fermentative production of lactic acid from algae-based carbohydrates devoid of lignin has attracted great attention for its potential as a suitable alternative substrate compared to lignocellulosic biomass. A Chlorella sp. GD mutant with enhanced thermo-tolerance was obtained by mutagenesis using N -methyl- N '-nitro- N -nitrosoguanidine to overcome outdoor high-temperature inhibition and it was used as a feedstock for fermentative lactic acid production. The indoor experiments showed that biomass, reducing sugar content, photosynthetic O 2 evolution rate, photosystem II activity ( F v / F m and F v '/ F m '), and chlorophyll content increased as temperature, light intensity, and CO 2 concentration increased. The mutant showed similar DIC affinity and initial slope of photosynthetic light response curve (α) as that of the wild type but had higher dissolved inorganic carbon (DIC) utilization capacity and maximum photosynthesis rate ( P max ). Moreover, the PSII activity ( F v '/ F m ') in the mutant remained normal without acclimation process after being transferred to photobioreactor. This suggests that efficient utilization of incident high light and enhanced carbon fixation with its subsequent flux to carbohydrates accumulation in the mutant contributes to higher sugar and biomass productivity under enriched CO 2 condition. The mutant was cultured outdoors in a photobioreactor with 6% CO 2 aeration in hot summer season in southern Taiwan. The harvested biomass was subjected to separate hydrolysis and fermentation (SHF) for lactic acid production with carbohydrate concentration equivalent to 20 g/L glucose using the lactic acid-producing bacterium Lactobacillus plantarum 23. The conversion rate and yield of lactic acid were 80% and 0.43 g/g Chlorella biomass, respectively. These results demonstrated that the thermo-tolerant Chlorella mutant with high photosynthetic efficiency and biomass productivity under hot outdoor condition is an efficient fermentative

DT2008: A Promising New Genetic Resource for Improved Drought Tolerance in Soybean When Solely Dependent on Symbiotic N2 Fixation

PubMed Central

Sulieman, Saad; Ha, Chien Van; Nasr Esfahani, Maryam; Watanabe, Yasuko; Nishiyama, Rie; Pham, Chung Thi Bao; Nguyen, Dong Van; Tran, Lam-Son Phan

2015-01-01

Water deficit is one of the major constraints for soybean production in Vietnam. The soybean breeding research efforts conducted at the Agriculture Genetics Institute (AGI) of Vietnam resulted in the development of promising soybean genotypes, suitable for the drought-stressed areas in Vietnam and other countries. Such a variety, namely, DT2008, was recommended by AGI and widely used throughout the country. The aim of this work was to assess the growth of shoots, roots, and nodules of DT2008 versus Williams 82 (W82) in response to drought and subsequent rehydration in symbiotic association as a means to provide genetic resources for genomic research. Better shoot, root, and nodule growth and development were observed in the cultivar DT2008 under sufficient, water deficit, and recovery conditions. Our results represent a good foundation for further comparison of DT2008 and W82 at molecular levels using high throughput omic technologies, which will provide huge amounts of data, enabling us to understand the genetic network involved in regulation of soybean responses to water deficit and increasing the chances of developing drought-tolerant cultivars. PMID:25685802

The relationship between dissolved hydrogen and nitrogen fixation in ocean waters

NASA Astrophysics Data System (ADS)

Moore, Robert M.; Punshon, Stephen; Mahaffey, Claire; Karl, David

2009-09-01

Fixed nitrogen is a key nutrient involved in regulating global marine productivity and hence the global oceanic carbon cycle. Oceanic nitrogen (N 2) fixation is estimated to supply 8×10 12 moles N y -1 to the ocean, approximately equal to current riverine and the atmospheric inputs of fixed N, and between 50 and 100% of current estimates of oceanic denitrification. However, the spatial and temporal variability of N 2 fixation remains uncertain, mostly because of the normal low resolution sampling for diazotroph distribution and fixation rates. It is well established that N 2 fixation, mediated by the enzyme nitrogenase, is a source of hydrogen (H 2), but the extent to which it leads to supersaturation of H 2 in oceanic waters is unresolved. Here, we present simultaneous measurements of upper ocean dissolved H 2 concentration (nmol L -1), and rates of N 2 fixation (μmol N m -3 d -1), determined using 15N 2 tracer techniques (at 7 or 15 m), on a transect from Fiji to Hawaii. We find a significant correlation ( r=0.98) between dissolved H 2 and rates of N 2 fixation, with the greatest supersaturation of H 2 and highest rates of N 2 fixation being observed in the subtropical gyres at the southern (˜18°S) and northern (18°N) reaches of the transect. The lowest H 2 saturation and N 2 fixation were observed in the equatorial region between 8°S and 14°N. We propose that an empirical relationship between H 2 supersaturations and N 2 fixation measurements could be used to guide sampling for 15N fixation measurements or to aid the spatial interpolation of such measurements.

Radiological evaluation of ankle arthrodesis with Ilizarov fixation compared to internal fixation.

PubMed

Morasiewicz, Piotr; Dejnek, Maciej; Urbański, Wiktor; Dragan, Szymon Łukasz; Kulej, Mirosław; Dragan, Szymon Feliks

2017-07-01

We asked whether the type of ankle joint arthrodesis stabilization will affect: (1) rate of union, (2) rate of adjacted-joint arthritis, (3) malalignment of the ankle joint. We retrospectively radiological studied 62 patients who underwent ankle arthrodesis with Ilizarov external fixator stabilization (group 1,n=29) or internal stabilization (group 2,n=33) from 2006 to 2015. Radiologic outcomes were mesure by: (1) rate of union, (2) rate of adjacent-joint arthritis, (3) malalignment of the ankle joint. The Levene's test,Mann-Whitney U test and Students t-test were used to the statistical analyses. Ankle fusion was achieved in 100% of patients treated with external fixation and in 88% with internal stabilization. Desired frontal plane alignment was achieved in 100% of patients with external fixation and 76% with internal stabilization. Desired sagittal plane alignment was achieved in 100% of external fixation and 85% of internal stabilization. A total of 14 (48.3%) patients from group 1 showed a radiographic evidence of pre-existing adjacent-joint OA. The radiographic evidence of pre-existing adjacent-joint OA was also found in 27(81.8%) subjects from group 2. Alterations of adjacent joints were also found on postoperative radiograms of 19 (65.5%) patients subjected to Ilizarov fixation and in all 33 patients from group 2. Ilizarov fixation of ankle arthrodesis is associated with lower prevalence of adjacent-joint OA and ankle joint misalignment,and with higher fusion rates than after internal fixation.Although achieving a complex ankle fusion is generally challenging,radiological outcomes after fixation with the Ilizarov apparatus are better than after internal stabilization. Copyright © 2017 Elsevier Ltd. All rights reserved.

N-fixation in legumes--An assessment of the potential threat posed by ozone pollution.

PubMed

Hewitt, D K L; Mills, G; Hayes, F; Norris, D; Coyle, M; Wilkinson, S; Davies, W

2016-01-01

The growth, development and functioning of legumes are often significantly affected by exposure to tropospheric ozone (O3) pollution. However, surprisingly little is known about how leguminous Nitrogen (N) fixation responds to ozone, with a scarcity of studies addressing this question in detail. In the last decade, ozone impacts on N-fixation in soybean, cowpea, mung bean, peanut and clover have been shown for concentrations which are now commonly recorded in ambient air or are likely to occur in the near future. We provide a synthesis of the existing literature addressing this issue, and also explore the effects that may occur on an agroecosystem scale by predicting reductions in Trifolium (clovers) root nodule biomass in United Kingdom (UK) pasture based on ozone concentration data for a "high" (2006) and "average" ozone year (2008). Median 8% and 5% reductions in clover root nodule biomass in pasture across the UK were predicted for 2006 and 2008 respectively. Seasonal exposure to elevated ozone, or short-term acute concentrations >100 ppb, are sufficient to reduce N-fixation and/or impact nodulation, in a range of globally-important legumes. However, an increasing global burden of CO2, the use of artificial fertiliser, and reactive N-pollution may partially mitigate impacts of ozone on N-fixation. Copyright © 2015 Elsevier Ltd. All rights reserved.

Comparisons of external fixator combined with limited internal fixation and open reduction and internal fixation for Sanders type 2 calcaneal fractures: Finite element analysis and clinical outcome.

PubMed

Pan, M; Chai, L; Xue, F; Ding, L; Tang, G; Lv, B

2017-07-01

The aim of this study was to compare the biomechanical stability and clinical outcome of external fixator combined with limited internal fixation (EFLIF) and open reduction and internal fixation (ORIF) in treating Sanders type 2 calcaneal fractures. Two types of fixation systems were selected for finite element analysis and a dual cohort study. Two fixation systems were simulated to fix the fracture in a finite element model. The relative displacement and stress distribution were analysed and compared. A total of 71 consecutive patients with closed Sanders type 2 calcaneal fractures were enrolled and divided into two groups according to the treatment to which they chose: the EFLIF group and the ORIF group. The radiological and clinical outcomes were evaluated and compared. The relative displacement of the EFLIF was less than that of the plate (0.1363 mm to 0.1808 mm). The highest von Mises stress value on the plate was 33% higher than that on the EFLIF. A normal restoration of the Böhler angle was achieved in both groups. No significant difference was found in the clinical outcome on the American Orthopedic Foot and Ankle Society Ankle Hindfoot Scale, or on the Visual Analogue Scale between the two groups (p > 0.05). Wound complications were more common in those who were treated with ORIF (p = 0.028). Both EFLIF and ORIF systems were tested to 160 N without failure, showing the new construct to be mechanically safe to use. Both EFLIF and ORIF could be effective in treating Sanders type 2 calcaneal fractures. The EFLIF may be superior to ORIF in achieving biomechanical stability and less blood loss, shorter surgical time and hospital stay, and fewer wound complications. Cite this article : M. Pan, L. Chai, F. Xue, L. Ding, G. Tang, B. Lv. Comparisons of external fixator combined with limited internal fixation and open reduction and internal fixation for Sanders type 2 calcaneal fractures: Finite element analysis and clinical outcome. Bone Joint Res 2017

Effects of ultraviolet radiation on photosynthetic performance and N2 fixation in Trichodesmium erythraeum IMS 101

NASA Astrophysics Data System (ADS)

Cai, Xiaoni; Hutchins, David A.; Fu, Feixue; Gao, Kunshan

2017-10-01

Biological effects of ultraviolet radiation (UVR; 280-400 nm) on marine primary producers are of general concern, as oceanic carbon fixers that contribute to the marine biological CO2 pump are being exposed to increasing UV irradiance due to global change and ozone depletion. We investigated the effects of UV-B (280-320 nm) and UV-A (320-400 nm) on the biogeochemically critical filamentous marine N2-fixing cyanobacterium Trichodesmium (strain IMS101) using a solar simulator as well as under natural solar radiation. Short exposure to UV-B, UV-A, or integrated total UVR significantly reduced the effective quantum yield of photosystem II (PSII) and photosynthetic carbon and N2 fixation rates. Cells acclimated to low light were more sensitive to UV exposure compared to high-light-grown ones, which had more UV-absorbing compounds, most likely mycosporine-like amino acids (MAAs). After acclimation under natural sunlight, the specific growth rate was lower (by up to 44 %), MAA content was higher, and average trichome length was shorter (by up to 22 %) in the full spectrum of solar radiation with UVR, than under a photosynthetically active radiation (PAR) alone treatment (400-700 nm). These results suggest that prior shipboard experiments in UV-opaque containers may have substantially overestimated in situ nitrogen fixation rates by Trichodesmium, and that natural and anthropogenic elevation of UV radiation intensity could significantly inhibit this vital source of new nitrogen to the current and future oligotrophic oceans.

Outbursts in Symbiotic Binaries

NASA Technical Reports Server (NTRS)

Sonneborn, George (Technical Monitor); Keyes, Charles

2005-01-01

A major question for symbiotic stars concerns the nature and cause of their outbursts. A small subset of symbiotics, the slow novae are fairly well established as thermonuclear events that last on the order of decades. The several symbiotic recurrent novae, which are much shorter and last on the order of months, are also thought to be thermonuclear runaways. Yet the majority of symbiotics are neither slow novae nor recurrent novae. These are the so-called classical symbiotics, many of which show outbursts whose cause is not well understood. In some cases, jets are produced in association with an outburst, therefore an investigation into the causes of outbursts will yield important insights into the production of collimated outflows. To investigate the cause and nature of classical symbiotic outbursts, we initiated a program of multiwavelength observations of these events. In FUSE Cycle 2, we obtained six observational epochs of the 2000-2002 classic symbiotic outburst in the first target of our campaign - class prototype, Z Andromedae. That program was part of a coordinated multi-wavelength Target-of-Opportunity (TOO) campaign with FUSE, XMM, Chandra, MERLIN, the VLA, and ground-based spectroscopic and high time-resolution photometric observations. Our campaign proved the concept, utility, and need for coordinated multi-wavelength observations in order to make progress in understanding the nature of the outburst mechanisms in symbiotic stars. Indeed, the FUSE data were the cornerstone of this project

Low rates of nitrogen fixation in eastern tropical South Pacific surface waters

PubMed Central

Knapp, Angela N.; Casciotti, Karen L.; Berelson, William M.; Prokopenko, Maria G.; Capone, Douglas G.

2016-01-01

An extensive region of the Eastern Tropical South Pacific (ETSP) Ocean has surface waters that are nitrate-poor yet phosphate-rich. It has been proposed that this distribution of surface nutrients provides a geochemical niche favorable for N2 fixation, the primary source of nitrogen to the ocean. Here, we present results from two cruises to the ETSP where rates of N2 fixation and its contribution to export production were determined with a suite of geochemical and biological measurements. N2 fixation was only detectable using nitrogen isotopic mass balances at two of six stations, and rates ranged from 0 to 23 µmol N m−2 d−1 based on sediment trap fluxes. Whereas the fractional importance of N2 fixation did not change, the N2-fixation rates at these two stations were several-fold higher when scaled to other productivity metrics. Regardless of the choice of productivity metric these N2-fixation rates are low compared with other oligotrophic locations, and the nitrogen isotope budgets indicate that N2 fixation supports no more than 20% of export production regionally. Although euphotic zone-integrated short-term N2-fixation rates were higher, up to 100 µmol N m−2 d−1, and detected N2 fixation at all six stations, studies of nitrogenase gene abundance and expression from the same cruises align with the geochemical data and together indicate that N2 fixation is a minor source of new nitrogen to surface waters of the ETSP. This finding is consistent with the hypothesis that, despite a relative abundance of phosphate, iron may limit N2 fixation in the ETSP. PMID:26976587

NAD1 Controls Defense-Like Responses in Medicago truncatula Symbiotic Nitrogen Fixing Nodules Following Rhizobial Colonization in a BacA-Independent Manner

PubMed Central

Domonkos, Ágota; Kovács, Szilárd; Gombár, Anikó; Kiss, Ernő; Horváth, Beatrix; Kováts, Gyöngyi Z.; Farkas, Attila; Tóth, Mónika T.; Ayaydin, Ferhan; Bóka, Károly; Fodor, Lili; Endre, Gabriella; Kaló, Péter

2017-01-01

Legumes form endosymbiotic interaction with host compatible rhizobia, resulting in the development of nitrogen-fixing root nodules. Within symbiotic nodules, rhizobia are intracellularly accommodated in plant-derived membrane compartments, termed symbiosomes. In mature nodule, the massively colonized cells tolerate the existence of rhizobia without manifestation of visible defense responses, indicating the suppression of plant immunity in the nodule in the favur of the symbiotic partner. Medicago truncatula DNF2 (defective in nitrogen fixation 2) and NAD1 (nodules with activated defense 1) genes are essential for the control of plant defense during the colonization of the nitrogen-fixing nodule and are required for bacteroid persistence. The previously identified nodule-specific NAD1 gene encodes a protein of unknown function. Herein, we present the analysis of novel NAD1 mutant alleles to better understand the function of NAD1 in the repression of immune responses in symbiotic nodules. By exploiting the advantage of plant double and rhizobial mutants defective in establishing nitrogen-fixing symbiotic interaction, we show that NAD1 functions following the release of rhizobia from the infection threads and colonization of nodule cells. The suppression of plant defense is self-dependent of the differentiation status of the rhizobia. The corresponding phenotype of nad1 and dnf2 mutants and the similarity in the induction of defense-associated genes in both mutants suggest that NAD1 and DNF2 operate close together in the same pathway controlling defense responses in symbiotic nodules. PMID:29240711

NAD1 Controls Defense-Like Responses in Medicago truncatula Symbiotic Nitrogen Fixing Nodules Following Rhizobial Colonization in a BacA-Independent Manner.

PubMed

Domonkos, Ágota; Kovács, Szilárd; Gombár, Anikó; Kiss, Ernő; Horváth, Beatrix; Kováts, Gyöngyi Z; Farkas, Attila; Tóth, Mónika T; Ayaydin, Ferhan; Bóka, Károly; Fodor, Lili; Ratet, Pascal; Kereszt, Attila; Endre, Gabriella; Kaló, Péter

2017-12-14

Legumes form endosymbiotic interaction with host compatible rhizobia, resulting in the development of nitrogen-fixing root nodules. Within symbiotic nodules, rhizobia are intracellularly accommodated in plant-derived membrane compartments, termed symbiosomes. In mature nodule, the massively colonized cells tolerate the existence of rhizobia without manifestation of visible defense responses, indicating the suppression of plant immunity in the nodule in the favur of the symbiotic partner. Medicago truncatula DNF2 (defective in nitrogen fixation 2) and NAD1 (nodules with activated defense 1) genes are essential for the control of plant defense during the colonization of the nitrogen-fixing nodule and are required for bacteroid persistence. The previously identified nodule-specific NAD1 gene encodes a protein of unknown function. Herein, we present the analysis of novel NAD1 mutant alleles to better understand the function of NAD1 in the repression of immune responses in symbiotic nodules. By exploiting the advantage of plant double and rhizobial mutants defective in establishing nitrogen-fixing symbiotic interaction, we show that NAD1 functions following the release of rhizobia from the infection threads and colonization of nodule cells. The suppression of plant defense is self-dependent of the differentiation status of the rhizobia. The corresponding phenotype of nad1 and dnf2 mutants and the similarity in the induction of defense-associated genes in both mutants suggest that NAD1 and DNF2 operate close together in the same pathway controlling defense responses in symbiotic nodules.

Electrochemical Reduction of N2 under Ambient Conditions for Artificial N2 Fixation and Renewable Energy Storage Using N2 /NH3 Cycle.

PubMed

Bao, Di; Zhang, Qi; Meng, Fan-Lu; Zhong, Hai-Xia; Shi, Miao-Miao; Zhang, Yu; Yan, Jun-Min; Jiang, Qing; Zhang, Xin-Bo

2017-01-01

Using tetrahexahedral gold nanorods as a heterogeneous electrocatalyst, an electrocatalytic N 2 reduction reaction is shown to be possible at room temperature and atmospheric pressure, with a high Faradic efficiency up to 4.02% at -0.2 V vs reversible hydrogen electrode (1.648 µg h -1 cm -2 and 0.102 µg h -1 cm -2 for NH 3 and N 2 H 4 ·H 2 O, respectively). © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

RNA-seq transcriptome profiling reveals that Medicago truncatula nodules acclimate N2 fixation before emerging P deficiency reaches the nodules

PubMed Central

Cabeza, Ricardo A.; Liese, Rebecca; Lingner, Annika; von Stieglitz, Ilsabe; Neumann, Janice; Salinas-Riester, Gabriela; Pommerenke, Claudia; Dittert, Klaus; Schulze, Joachim

2014-01-01

Legume nodules are plant tissues with an exceptionally high concentration of phosphorus (P), which, when there is scarcity of P, is preferentially maintained there rather than being allocated to other plant organs. The hypothesis of this study was that nodules are affected before the P concentration in the organ declines during whole-plant P depletion. Nitrogen (N2) fixation and P concentration in various organs were monitored during a whole-plant P-depletion process in Medicago truncatula. Nodule gene expression was profiled through RNA-seq at day 5 of P depletion. Until that point in time P concentration in leaves reached a lower threshold but was maintained in nodules. N2-fixation activity per plant diverged from that of fully nourished plants beginning at day 5 of the P-depletion process, primarily because fewer nodules were being formed, while the activity of the existing nodules was maintained for as long as two weeks into P depletion. RNA-seq revealed nodule acclimation on a molecular level with a total of 1140 differentially expressed genes. Numerous genes for P remobilization from organic structures were increasingly expressed. Various genes involved in nodule malate formation were upregulated, while genes involved in fermentation were downregulated. The fact that nodule formation was strongly repressed with the onset of P deficiency is reflected in the differential expression of various genes involved in nodulation. It is concluded that plants follow a strategy to maintain N2 fixation and viable leaf tissue as long as possible during whole-plant P depletion to maintain their ability to react to emerging new P sources (e.g. through active P acquisition by roots). PMID:25151618

A mechanistic, globally-applicable model of plant nitrogen uptake, retranslocation and fixation

NASA Astrophysics Data System (ADS)

Fisher, J. B.; Tan, S.; Malhi, Y.; Fisher, R. A.; Sitch, S.; Huntingford, C.

2008-12-01

Nitrogen is one of the nutrients that can most limit plant growth, and nitrogen availability may be a controlling factor on biosphere responses to climate change. We developed a plant nitrogen assimilation model based on a) advective transport through the transpiration stream, b) retranslocation whereby carbon is expended to resorb nitrogen from leaves, c) active uptake whereby carbon is expended to acquire soil nitrogen, and d) biological nitrogen fixation whereby carbon is expended for symbiotic nitrogen fixers. The model relies on 9 inputs: 1) net primary productivity (NPP), 2) plant C:N ratio, 3) available soil nitrogen, 4) root biomass, 5) transpiration rate, 6) saturated soil depth,7) leaf nitrogen before senescence, 8) soil temperature, and 9) ability to fix nitrogen. A carbon cost of retranslocation is estimated based on leaf nitrogen and compared to an active uptake carbon cost based on root biomass and available soil nitrogen; for nitrogen fixers both costs are compared to a carbon cost of fixation dependent on soil temperature. The NPP is then allocated to optimize growth while maintaining the C:N ratio. The model outputs are total plant nitrogen uptake, remaining NPP available for growth, carbon respired to the soil and updated available soil nitrogen content. We test and validate the model (called FUN: Fixation and Uptake of Nitrogen) against data from the UK, Germany and Peru, and run the model under simplified scenarios of primary succession and climate change. FUN is suitable for incorporation into a land surface scheme of a General Circulation Model and will be coupled with a soil model and dynamic global vegetation model as part of a land surface model (JULES).

Novel European free-living, non-diazotrophic Bradyrhizobium isolates from contrasting soils that lack nodulation and nitrogen fixation genes - a genome comparison

NASA Astrophysics Data System (ADS)

Jones, Frances Patricia; Clark, Ian M.; King, Robert; Shaw, Liz J.; Woodward, Martin J.; Hirsch, Penny R.

2016-05-01

The slow-growing genus Bradyrhizobium is biologically important in soils, with different representatives found to perform a range of biochemical functions including photosynthesis, induction of root nodules and symbiotic nitrogen fixation and denitrification. Consequently, the role of the genus in soil ecology and biogeochemical transformations is of agricultural and environmental significance. Some isolates of Bradyrhizobium have been shown to be non-symbiotic and do not possess the ability to form nodules. Here we present the genome and gene annotations of two such free-living Bradyrhizobium isolates, named G22 and BF49, from soils with differing long-term management regimes (grassland and bare fallow respectively) in addition to carbon metabolism analysis. These Bradyrhizobium isolates are the first to be isolated and sequenced from European soil and are the first free-living Bradyrhizobium isolates, lacking both nodulation and nitrogen fixation genes, to have their genomes sequenced and assembled from cultured samples. The G22 and BF49 genomes are distinctly different with respect to size and number of genes; the grassland isolate also contains a plasmid. There are also a number of functional differences between these isolates and other published genomes, suggesting that this ubiquitous genus is extremely heterogeneous and has roles within the community not including symbiotic nitrogen fixation.

Methanotrophy Induces Nitrogen Fixation in Boreal Mosses

NASA Astrophysics Data System (ADS)

Tiirola, M. A.

2014-12-01

Many methanotrophic bacterial groups fix nitrogen in laboratory conditions. Furthermore, nitrogen (N) is a limiting nutrient in many environments where methane concentrations are highest. Despite these facts, methane-induced N fixation has previously been overlooked, possibly due to methodological problems. To study the possible link between methanotrophy and diazotrophy in terrestrial and aquatic habitats, we measured the co-occurrence of these two processes in boreal forest, peatland and stream mosses using a stable isotope labeling approach (15 N2 and 13 CH4 double labeling) and sequencing of the nifH gene marker. N fixation associated with forest mosses was dependent on the annual N deposition, whereas methane stimulate N fixation neither in high (>3 kg N ha -1 yr -1) nor low deposition areas, which was in accordance with the nifH gene sequencing showing that forest mosses (Pleurozium schreberi and Hylocomium splendens ) carried mainly cyanobacterial N fixers. On the other extreme, in stream mosses (Fontinalis sp.) methane was actively oxidized throughout the year, whereas N fixation showed seasonal fluctuation. The co-occurrence of the two processes in single cell level was proven by co-localizing both N and methane-carbon fixation with the secondary ion mass spectrometry (SIMS) approach. Methanotrophy and diazotrophy was also studied in peatlands of different primary successional stages in the land-uplift coast of Bothnian Bay, in the Siikajoki chronosequence, where N accumulation rates in peat profiles indicate significant N fixation. Based on experimental evidence it was counted that methane-induced N fixation explained over one-third of the new N input in the younger peatland successional stages, where the highest N fixation rates and highest methane oxidation activities co-occurred in the water-submerged Sphagnum moss vegetation. The linkage between methanotrophic carbon cycling and N fixation may therefore constitute an important mechanism in the rapid

Rhizobial peptidase HrrP cleaves host-encoded signaling peptides and mediates symbiotic compatibility

PubMed Central

Price, Paul A.; Tanner, Houston R.; Dillon, Brett A.; Shabab, Mohammed; Walker, Graham C.; Griffitts, Joel S.

2015-01-01

Legume–rhizobium pairs are often observed that produce symbiotic root nodules but fail to fix nitrogen. Using the Sinorhizobium meliloti and Medicago truncatula symbiotic system, we previously described several naturally occurring accessory plasmids capable of disrupting the late stages of nodule development while enhancing bacterial proliferation within the nodule. We report here that host range restriction peptidase (hrrP), a gene found on one of these plasmids, is capable of conferring both these properties. hrrP encodes an M16A family metallopeptidase whose catalytic activity is required for these symbiotic effects. The ability of hrrP to suppress nitrogen fixation is conditioned upon the genotypes of both the host plant and the hrrP-expressing rhizobial strain, suggesting its involvement in symbiotic communication. Purified HrrP protein is capable of degrading a range of nodule-specific cysteine-rich (NCR) peptides encoded by M. truncatula. NCR peptides are crucial signals used by M. truncatula for inducing and maintaining rhizobial differentiation within nodules, as demonstrated in the accompanying article [Horváth B, et al. (2015) Proc Natl Acad Sci USA, 10.1073/pnas.1500777112]. The expression pattern of hrrP and its effects on rhizobial morphology are consistent with the NCR peptide cleavage model. This work points to a symbiotic dialogue involving a complex ensemble of host-derived signaling peptides and bacterial modifier enzymes capable of adjusting signal strength, sometimes with exploitative outcomes. PMID:26401024

Rhizobial peptidase HrrP cleaves host-encoded signaling peptides and mediates symbiotic compatibility.

PubMed

Price, Paul A; Tanner, Houston R; Dillon, Brett A; Shabab, Mohammed; Walker, Graham C; Griffitts, Joel S

2015-12-08

Legume-rhizobium pairs are often observed that produce symbiotic root nodules but fail to fix nitrogen. Using the Sinorhizobium meliloti and Medicago truncatula symbiotic system, we previously described several naturally occurring accessory plasmids capable of disrupting the late stages of nodule development while enhancing bacterial proliferation within the nodule. We report here that host range restriction peptidase (hrrP), a gene found on one of these plasmids, is capable of conferring both these properties. hrrP encodes an M16A family metallopeptidase whose catalytic activity is required for these symbiotic effects. The ability of hrrP to suppress nitrogen fixation is conditioned upon the genotypes of both the host plant and the hrrP-expressing rhizobial strain, suggesting its involvement in symbiotic communication. Purified HrrP protein is capable of degrading a range of nodule-specific cysteine-rich (NCR) peptides encoded by M. truncatula. NCR peptides are crucial signals used by M. truncatula for inducing and maintaining rhizobial differentiation within nodules, as demonstrated in the accompanying article [Horváth B, et al. (2015) Proc Natl Acad Sci USA, 10.1073/pnas.1500777112]. The expression pattern of hrrP and its effects on rhizobial morphology are consistent with the NCR peptide cleavage model. This work points to a symbiotic dialogue involving a complex ensemble of host-derived signaling peptides and bacterial modifier enzymes capable of adjusting signal strength, sometimes with exploitative outcomes.

Global assessment of limitation to symbiotic nitrogen fixation by phosphorus availability in terrestrial ecosystems using a meta-analysis approach

NASA Astrophysics Data System (ADS)

Augusto, Laurent; Delerue, Florian; Gallet-Budynek, Anne; Achat, David L.

2013-09-01

nitrogen fixation (SNF) is the main natural source of nitrogen (N) in terrestrial ecosystems worldwide. Previous studies have shown that fixation of N by plants can be limited by the availability of phosphorus (P) in soils. We used global meta-analysis to investigate how P availability controls SNF. In experiments in which plants were grown in an artificial medium, severe P deficiencies in the nutritive solution ([PO4] < 5-42 μM) depressed SNF flux through both a direct decrease in the plant fixation rate (i.e., decreased N fixed per unit of plant biomass) and an indirect effect (i.e., through plant biomass). In most experiments with plants grown in soils, SNF was proportional to plant biomass and was consequently only indirectly limited by P. Some cases using unfertilized and weathered soils (ultisols or oxisols), where plants were particularly P stressed, were an exception with both direct and indirect P limitations. Our global analysis of the P-SNF relationship indicated that P bioavailability commonly limited SNF flux. We conclude that the main driver of in situ P limitation is indirect via limitation of plant growth, except in certain cases where both indirect and direct constraints may play a role. These cases of severe P deficiency may be mainly found in weathered tropical soils of Africa and South America, probably in unfertilized croplands which are depleted in P due to repeated biomass harvests.

Tendon transfer fixation: comparing a tendon to tendon technique vs. bioabsorbable interference-fit screw fixation.

PubMed

Sabonghy, Eric Peter; Wood, Robert Michael; Ambrose, Catherine Glauber; McGarvey, William Christopher; Clanton, Thomas Oscar

2003-03-01

Tendon transfer techniques in the foot and ankle are used for tendon ruptures, deformities, and instabilities. This fresh cadaver study compares the tendon fixation strength in 10 paired specimens by performing a tendon to tendon fixation technique or using 7 x 20-25 mm bioabsorbable interference-fit screw tendon fixation technique. Load at failure of the tendon to tendon fixation method averaged 279N (Standard Deviation 81N) and the bioabsorbable screw 148N (Standard Deviation 72N) [p = 0.0008]. Bioabsorbable interference-fit screws in these specimens show decreased fixation strength relative to the traditional fixation technique. However, the mean bioabsorbable screw fixation strength of 148N provides physiologic strength at the tendon-bone interface.

Solar Water Splitting and Nitrogen Fixation with Layered Bismuth Oxyhalides.

PubMed

Li, Jie; Li, Hao; Zhan, Guangming; Zhang, Lizhi

2017-01-17

Hydrogen and ammonia are the chemical molecules that are vital to Earth's energy, environmental, and biological processes. Hydrogen with renewable, carbon-free, and high combustion-enthalpy hallmarks lays the foundation of next-generation energy source, while ammonia furnishes the building blocks of fertilizers and proteins to sustain the lives of plants and organisms. Such merits fascinate worldwide scientists in developing viable strategies to produce hydrogen and ammonia. Currently, at the forefronts of hydrogen and ammonia syntheses are solar water splitting and nitrogen fixation, because they go beyond the high temperature and pressure requirements of methane stream reforming and Haber-Bosch reaction, respectively, as the commercialized hydrogen and ammonia production routes, and inherit the natural photosynthesis virtues that are green and sustainable and operate at room temperature and atmospheric pressure. The key to propelling such photochemical reactions lies in searching photocatalysts that enable water splitting into hydrogen and nitrogen fixation to make ammonia efficiently. Although the past 40 years have witnessed significant breakthroughs using the most widely studied TiO 2 , SrTiO 3 , (Ga 1-x Zn x )(N 1-x O x ), CdS, and g-C 3 N 4 for solar chemical synthesis, two crucial yet still unsolved issues challenge their further progress toward robust solar water splitting and nitrogen fixation, including the inefficient steering of electron transportation from the bulk to the surface and the difficulty of activating the N≡N triple bond of N 2 . This Account details our endeavors that leverage layered bismuth oxyhalides as photocatalysts for efficient solar water splitting and nitrogen fixation, with a focus on addressing the above two problems. We first demonstrate that the layered structures of bismuth oxyhalides can stimulate an internal electric field (IEF) that is capable of efficiently separating electrons and holes after their formation and of

The Effect of Land-use Change and Management on Free-living N2 fixation in the Brazilian Atlantic Forest

NASA Astrophysics Data System (ADS)

De Oliveira Bomfim, B.; Silva, L. C. R.; Horwath, W. R.; Hello, J.; Doane, T. A.

2016-12-01

Globally, primary tropical forests are increasingly disturbed by deforestation, urbanization, agriculture, and cattle ranching. It has been recognized that the resulting (secondary) forests now play a key role in global biogeochemical cycles; however, little is known about alterations in forest function caused by the combination of disturbance and land use change. Fire, deforestation, and forest-to-monocrop conversion are all likely to affect biotic N inputs, yet our understanding of how free-living N2 fixation influences ecosystem response after disturbance remains poorly understood. Our research is assessing the role of asymbiotic (free-living) biological nitrogen fixation (BNF), a microbially-mediated process responsible for providing N inputs across terrestrial ecosystems and modulating the effect of fire and land cover in secondary forest succession. Free-living BNF is being quantified through incubations using stable isotope (15N2 labeling experiment) in different substrates (soil and leaf litter) under contrasting land use and management in the Brazilian Atlantic Forest, the most deforested Biome in Brazil with only 7% of its original cover. Soil and litter samples were collected in primary forests, 12-year secondary forests, Eucalyptus spp. plantations and 10-year Brachiaria brizantha pastures. Preliminary results indicate that free-living BNF rates did not vary significantly between either secondary land use (0.02 to 0.46 µg N2 fixed gDW-1 h-1), but rates were significantly higher in the litter layer (0.32 to 3.8 µg N2 fixed gDW-1 h-1) than in the surface soil (0 - 10 cm and 10 - 30 cm). Free-living BNF in this stretch of the Brazilian Atlantic Forest seems not to be significantly affected by contrasting land use and management.

PHYSIOLOGY OF NITROGEN FIXATION BY BACILLUS POLYMYXA

PubMed Central

Grau, F. H.; Wilson, P. W.

1962-01-01

Grau, F. H. (University of Wisconsin, Madison) and P. W. Wilson. Physiology of nitrogen fixation by Bacillus polymyxa. J. Bacteriol. 83:490–496. 1962.—Of 17 strains of Bacillus polymyxa tested for fixation of molecular nitrogen, 15 fixed considerable quantities (30 to 150 μg N/ml). Two strains of the closely related B. macerans did not use N2, but possibly other members of this species may do so. Confirmation of fixation was obtained by showing incorporation of N15 into cell material. Both iron and molybdenum are specifically required for fixation; without the addition of these metals to the nitrogen-free medium, the growth rate and the total nitrogen fixed were reduced about 30 to 50%. No requirement for added molybdenum could be shown when ammonia was the nitrogen source, and the absence of iron caused only a slight decrease in growth. Washed-cell suspensions of B. polymyxa containing an active hydrogenase readily incorporated N15 into cell materials when provided with mannitol, glucose, or pyruvate but not when formate was the substrate. Hydrogen is a specific inhibitor of fixation, reducing both the rate and final amount of nitrogen fixed; it did not reduce growth on ammonia. Fixation was strictly anaerobic, 1% oxygen in the gas phase being sufficient to stop fixation. Arsenate is a powerful inhibitor of fixation of N2 by washed-cell suspensions of B. polymyxa, indicating that high-energy phosphate may be significant for this process. PMID:13901244

N2 Fixation, Carbon Metabolism, and Oxidative Damage in Nodules of Dark-Stressed Common Bean Plants.

PubMed Central

Gogorcena, Y.; Gordon, A. J.; Escuredo, P. R.; Minchin, F. R.; Witty, J. F.; Moran, J. F.; Becana, M.

1997-01-01

Common beans (Phaseolus vulgaris L.) were exposed to continuous darkness to induce nodule senescence, and several nodule parameters were investigated to identify factors that may be involved in the initial loss of N2 fixation. After only 1 d of darkness, total root respiration decreased by 76% and in vivo nitrogenase (N2ase) activity decreased by 95%. This decline coincided with the almost complete depletion (97%) of sucrose and fructose in nodules. At this stage, the O2 concentration in the infected zone increased to 1%, which may be sufficient to inactivate N2ase; however, key enzymes of carbon and nitrogen metabolism were still active. After 2 d of dark stress there was a significant decrease in the level of N2ase proteins and in the activities of enzymes involved in carbon and nitrogen assimilation. However, the general collapse of nodule metabolism occurred only after 4 d of stress, with a large decline in leghemoglobin and antioxidants. At this final senescent stage, there was an accumulation of oxidatively modified proteins. This oxidative stress may have originated from the decrease in antioxidant defenses and from the Fe-catalyzed generation of activated oxygen due to the increased availability of catalytic Fe and O2 in the infected region. PMID:12223669

Legume-rhizobium symbiotic promiscuity and effectiveness do not affect plant invasiveness.

PubMed

Keet, Jan-Hendrik; Ellis, Allan G; Hui, Cang; Le Roux, Johannes J

2017-06-01

The ability to fix atmospheric nitrogen is thought to play an important role in the invasion success of legumes. Interactions between legumes and nitrogen-fixing bacteria (rhizobia) span a continuum of specialization, and promiscuous legumes are thought to have higher chances of forming effective symbioses in novel ranges. Using Australian Acacia species in South Africa, it was hypothesized that widespread and highly invasive species will be more generalist in their rhizobial symbiotic requirements and more effective in fixing atmospheric nitrogen compared with localized and less invasive species. To test these hypotheses, eight localized and 11 widespread acacias were examined using next-generation sequencing data for the nodulation gene, nodC , to compare the identity, species richness, diversity and compositional similarity of rhizobia associated with these acacias. Stable isotope analysis was also used to determine levels of nitrogen obtained from the atmosphere via symbiotic nitrogen fixation. No differences were found in richness, diversity and community composition between localized and widespread acacias. Similarly, widespread and localized acacias did not differ in their ability to fix atmospheric nitrogen. However, for some species by site comparisons, significant differences in δ15N isotopic signatures were found, indicating differential symbiotic effectiveness between these species at specific localities. Overall, the results support recent findings that root nodule rhizobial diversity and community composition do not differ between acacias that vary in their invasiveness. Differential invasiveness of acacias in South Africa is probably linked to attributes such as differences in propagule pressure, reasons for (e.g. forestry vs. ornamental) and extent of, plantings in the country. © The Author 2017. Published by Oxford University Press on behalf of the Annals of Botany Company. All rights reserved. For Permissions, please email: journals.permissions@oup.com

Optimized breeding strategies for multiple trait integration: II. Process efficiency in event pyramiding and trait fixation.

PubMed

Peng, Ting; Sun, Xiaochun; Mumm, Rita H

2014-01-01

Multiple trait integration (MTI) is a multi-step process of converting an elite variety/hybrid for value-added traits (e.g. transgenic events) through backcross breeding. From a breeding standpoint, MTI involves four steps: single event introgression, event pyramiding, trait fixation, and version testing. This study explores the feasibility of marker-aided backcross conversion of a target maize hybrid for 15 transgenic events in the light of the overall goal of MTI of recovering equivalent performance in the finished hybrid conversion along with reliable expression of the value-added traits. Using the results to optimize single event introgression (Peng et al. Optimized breeding strategies for multiple trait integration: I. Minimizing linkage drag in single event introgression. Mol Breed, 2013) which produced single event conversions of recurrent parents (RPs) with ≤8 cM of residual non-recurrent parent (NRP) germplasm with ~1 cM of NRP germplasm in the 20 cM regions flanking the event, this study focused on optimizing process efficiency in the second and third steps in MTI: event pyramiding and trait fixation. Using computer simulation and probability theory, we aimed to (1) fit an optimal breeding strategy for pyramiding of eight events into the female RP and seven in the male RP, and (2) identify optimal breeding strategies for trait fixation to create a 'finished' conversion of each RP homozygous for all events. In addition, next-generation seed needs were taken into account for a practical approach to process efficiency. Building on work by Ishii and Yonezawa (Optimization of the marker-based procedures for pyramiding genes from multiple donor lines: I. Schedule of crossing between the donor lines. Crop Sci 47:537-546, 2007a), a symmetric crossing schedule for event pyramiding was devised for stacking eight (seven) events in a given RP. Options for trait fixation breeding strategies considered selfing and doubled haploid approaches to achieve homozygosity

Safe intramedullary fixation of displaced midshaft clavicle fractures with 2.5mm Kirschner wires - technique description and a two-part versus multifragmentary fracture fixation outcome comparison.

PubMed

Bakota, Bore; Chan, Gareth; Staresinic, Mario; Rajput, Vishal; Phadnis, Joideep; Korac, Zelimir

2017-11-01

The aim of this study was to present a modified Murray and Schwarz 2.5-mm Kirschner wire (K-wire) intramedullary (IM) technique for fixation of displaced midshaft clavicle fractures (DMCF), and to compare the differences in treatment outcome of two-part (Robinson 2B.1) and multifragmentary (Robinson 2B.2) DMCF. A retrospective analysis of 91 patients who underwent IM fixation with a 2.5-mm K-wire for DMCF and had a 1-year post-operative follow-up between 2000 and 2012 was performed. The patients were allocated into two groups: Robinson 2B.1 (n = 64) and Robinson 2B.2 (n = 27). Assessed outcomes were non-union, reoperation rate, wire migration and infection. There was no statistically significant difference in the rate of non-union (2B.1,2B.2; 3.13%, 7.41%; p = 0.365), reoperation (2B.1, 2B.2; 3.13%, 7.41%; p = 0.365), K-wire migration (2B.1, 2B.2; 0.00%, 0.00%; p = 1.00) and clavicle shortening at 12-months (2B.1, 2B.2; 3.13%, 7.41%; p = 0.365). Intramedullary clavicle fixation with a 2.5-mm K-wire is a safe surgical technique. 2B.1 injuries treated with 2.5-mm IM K-wire fixation have relatively improved outcome compared with displaced 2B.2 fractures for both non-union and reoperation rates. There were no occurrences of implant migration with either 2B.1 or 2B.2 injuries, and a non-significant difference in implant irritation was documented with IM K-fixation. The non-union rate with K-wire IM fixation of 2B.1 injuries concords with the published results of other IM devices and thus this technique should be added to the surgeon's armamentarium when considering surgical treatment of such injuries. © 2017 Elsevier Ltd. All rights reserved.

Promoting helix pitch and trichome length to improve biomass harvesting efficiency and carbon dioxide fixation rate by Spirulina sp. in 660 m2 raceway ponds under purified carbon dioxide from a coal chemical flue gas.

PubMed

Cheng, Jun; Guo, Wangbiao; Ameer Ali, Kubar; Ye, Qing; Jin, Guiyong; Qiao, Zhanshan

2018-08-01

The helix pitch and trichome length of Spirulina sp. were promoted to improve the biomass harvesting efficiency and CO 2 fixation rate in 660 m 2 raceway ponds aerated with food-grade CO 2 purified from a coal chemical flue gas. The CO 2 fixation rate was improved with increased trichome length of the Spirulina sp. in a raceway pond with double paddlewheels, baffles, and CO 2 aerators (DBA raceway pond). The trichome length has increased by 33.3 μm, and CO 2 fixation rate has increased by 42.3% and peaked to 51.3 g/m 2 /d in a DBA raceway pond. Biomass harvesting efficiency was increased with increased helix pitch. When the day-average greenhouse temperature was 33 °C and day-average sunlight intensity was 72,100 lu×, the helix pitch of Spirulina sp. was increased to 56.2 μm. Hence the biomass harvesting efficiency was maximized to 75.6% and biomass actual yield was increased to 35.9 kg in a DBA raceway pond. Copyright © 2018 Elsevier Ltd. All rights reserved.

Disturbance and topography shape nitrogen availability and δ15 N over long-term forest succession

USGS Publications Warehouse

Perakis, Steven; Tepley, Alan J.; Compton, Jana

2015-01-01

Forest disturbance and long-term succession towards old-growth are thought to increase nitrogen (N) availability and N loss, which should increase soil δ15N values. We examined soil and foliar patterns in N and δ15N, and soil N mineralization, across 800 years of forest succession in a topographically complex montane landscape influenced by human logging and wildfire. In contrast to expectations, we found that disturbance caused declines in surface mineral soil δ15N values, both in logged forests measured 40–50 years after disturbance, and in unlogged forests disturbed by severe wildfire within the last 200 years. Both symbiotic N fixation and N transfers from disturbed vegetation and detritus could lower soil δ15N values after disturbance. A more important role for symbiotic N fixation is suggested by lower soil δ15N values in slow-successional sites with slow canopy closure, which favors early-successional N fixers. Soil δ15N values increased only marginally throughout 800 years of succession, reflecting soil N uptake by vegetation and strong overall N retention. Although post-disturbance N inputs lowered surface soil δ15N values, steady-state mass balance calculations suggest that wildfire combustion of vegetation and detritus can dominate long-term N loss and increase whole-ecosystem δ15N. On steeper topography, declining soil δ15N values highlight erosion and accelerated soil turnover as an additional abiotic control on N balances. We conclude for N-limited montane forests that soil δ15N and N availability are less influenced by nitrate leaching and denitrification loss than by interactions between disturbance, N fixation, and erosion.

Ecological consequences of the expansion of N2-fixing plants in cold biomes

USGS Publications Warehouse

Hiltbrunner, Erika; Aerts, Rien; Bühlmann, Tobias; Huss-Danell, Kerstin; Magnusson, Borgthor; Myrold, David D.; Reed, Sasha C.; Sigurdsson, Bjarni D.; Körner, Christian

2014-01-01

Research in warm-climate biomes has shown that invasion by symbiotic dinitrogen (N2)-fixing plants can transform ecosystems in ways analogous to the transformations observed as a consequence of anthropogenic, atmospheric nitrogen (N) deposition: declines in biodiversity, soil acidification, and alterations to carbon and nutrient cycling, including increased N losses through nitrate leaching and emissions of the powerful greenhouse gas nitrous oxide (N2O). Here, we used literature review and case study approaches to assess the evidence for similar transformations in cold-climate ecosystems of the boreal, subarctic and upper montane-temperate life zones. Our assessment focuses on the plant genera Lupinus and Alnus, which have become invasive largely as a consequence of deliberate introductions and/or reduced land management. These cold biomes are commonly located in remote areas with low anthropogenic N inputs, and the environmental impacts of N2-fixer invasion appear to be as severe as those from anthropogenic N deposition in highly N polluted areas. Hence, inputs of N from N2 fixation can affect ecosystems as dramatically or even more strongly than N inputs from atmospheric deposition, and biomes in cold climates represent no exception with regard to the risk of being invaded by N2-fixing species. In particular, the cold biomes studied here show both a strong potential to be transformed by N2-fixing plants and a rapid subsequent saturation in the ecosystem’s capacity to retain N. Therefore, analogous to increases in N deposition, N2-fixing plant invasions must be deemed significant threats to biodiversity and to environmental quality.

Nutrient Limitation of Native and Invasive N2-Fixing Plants in Northwest Prairies

PubMed Central

Thorpe, Andrea S.; Perakis, Steven; Catricala, Christina; Kaye, Thomas N.

2013-01-01

Nutrient rich conditions often promote plant invasions, yet additions of non-nitrogen (N) nutrients may provide a novel approach for conserving native symbiotic N-fixing plants in otherwise N-limited ecosystems. Lupinus oreganus is a threatened N-fixing plant endemic to prairies in western Oregon and southwest Washington (USA). We tested the effect of non-N fertilizers on the growth, reproduction, tissue N content, and stable isotope δ15N composition of Lupinus at three sites that differed in soil phosphorus (P) and N availability. We also examined changes in other Fabaceae (primarily Vicia sativa and V. hirsuta) and cover of all plant species. Variation in background soil P and N availability shaped patterns of nutrient limitation across sites. Where soil P and N were low, P additions increased Lupinus tissue N and altered foliar δ15N, suggesting P limitation of N fixation. Where soil P was low but N was high, P addition stimulated growth and reproduction in Lupinus. At a third site, with higher soil P, only micro- and macronutrient fertilization without N and P increased Lupinus growth and tissue N. Lupinus foliar δ15N averaged −0.010‰ across all treatments and varied little with tissue N, suggesting consistent use of fixed N. In contrast, foliar δ15N of Vicia spp. shifted towards 0‰ as tissue N increased, suggesting that conditions fostering N fixation may benefit these exotic species. Fertilization increased cover, N fixation, and tissue N of non-target, exotic Fabaceae, but overall plant community structure shifted at only one site, and only after the dominant Lupinus was excluded from analyses. Our finding that non-N fertilization increased the performance of Lupinus with few community effects suggests a potential strategy to aid populations of threatened legume species. The increase in exotic Fabaceae species that occurred with fertilization further suggests that monitoring and adaptive management should accompany any large scale applications. PMID

Nutrient limitation of native and invasive N2-fixing plants in northwest prairies

USGS Publications Warehouse

Thorpe, Andrea S.; Perakis, Steven S.; Catricala, Christina; Kaye, Thomas N.

2013-01-01

Nutrient rich conditions often promote plant invasions, yet additions of non-nitrogen (N) nutrients may provide a novel approach for conserving native symbiotic N-fixing plants in otherwise N-limited ecosystems. Lupinus oreganus is a threatened N-fixing plant endemic to prairies in western Oregon and southwest Washington (USA). We tested the effect of non-N fertilizers on the growth, reproduction, tissue N content, and stable isotope δ15N composition of Lupinus at three sites that differed in soil phosphorus (P) and N availability. We also examined changes in other Fabaceae (primarily Vicia sativa and V. hirsuta) and cover of all plant species. Variation in background soil P and N availability shaped patterns of nutrient limitation across sites. Where soil P and N were low, P additions increased Lupinus tissue N and altered foliar δ15N, suggesting P limitation of N fixation. Where soil P was low but N was high, P addition stimulated growth and reproduction in Lupinus. At a third site, with higher soil P, only micro- and macronutrient fertilization without N and P increased Lupinus growth and tissue N. Lupinus foliar δ15N averaged −0.010‰ across all treatments and varied little with tissue N, suggesting consistent use of fixed N. In contrast, foliar δ15N of Vicia spp. shifted towards 0‰ as tissue N increased, suggesting that conditions fostering N fixation may benefit these exotic species. Fertilization increased cover, N fixation, and tissue N of non-target, exotic Fabaceae, but overall plant community structure shifted at only one site, and only after the dominant Lupinus was excluded from analyses. Our finding that non-N fertilization increased the performance of Lupinus with few community effects suggests a potential strategy to aid populations of threatened legume species. The increase in exotic Fabaceae species that occurred with fertilization further suggests that monitoring and adaptive management should accompany any large scale applications.

Nodule morphology, symbiotic specificity and association with unusual rhizobia are distinguishing features of the genus Listia within the southern African crotalarioid clade Lotononis s.l.

PubMed Central

Ardley, Julie K.; Reeve, Wayne G.; O'Hara, Graham W.; Yates, Ron J.; Dilworth, Michael J.; Howieson, John G.

2013-01-01

Background and Aims The legume clade Lotononis sensu lato (s.l.; tribe Crotalarieae) comprises three genera: Listia, Leobordea and Lotononis sensu stricto (s.s.). Listia species are symbiotically specific and form lupinoid nodules with rhizobial species of Methylobacterium and Microvirga. This work investigated whether these symbiotic traits were confined to Listia by determining the ability of rhizobial strains isolated from species of Lotononis s.l. to nodulate Listia, Leobordea and Lotononis s.s. hosts and by examining the morphology and structure of the resulting nodules. Methods Rhizobia were characterized by sequencing their 16S rRNA and nodA genes. Nodulation and N2 fixation on eight taxonomically diverse Lotononis s.l. species were determined in glasshouse trials. Nodules of all hosts, and the process of infection and nodule initiation in Listia angolensis and Listia bainesii, were examined by light microscopy. Key Results Rhizobia associated with Lotononis s.l. were phylogenetically diverse. Leobordea and Lotononis s.s. isolates were most closely related to Bradyrhizobium spp., Ensifer meliloti, Mesorhizobium tianshanense and Methylobacterium nodulans. Listia angolensis formed effective nodules only with species of Microvirga. Listia bainesii nodulated only with pigmented Methylobacterium. Five lineages of nodA were found. Listia angolensis and L. bainesii formed lupinoid nodules, whereas nodules of Leobordea and Lotononis s.s. species were indeterminate. All effective nodules contained uniformly infected central tissue. Listia angolensis and L. bainesii nodule initials occurred on the border of the hypocotyl and along the tap root, and nodule primordia developed in the outer cortical layer. Neither root hair curling nor infection threads were seen. Conclusions Two specificity groups occur within Lotononis s.l.: Listia species are symbiotically specific, while species of Leobordea and Lotononis s.s. are generally promiscuous and interact with rhizobia of

Evolutionary signals of symbiotic persistence in the legume–rhizobia mutualism

PubMed Central

Werner, Gijsbert D. A.; Cornwell, William K.; Cornelissen, Johannes H. C.; Kiers, E. Toby

2015-01-01

Understanding the origins and evolutionary trajectories of symbiotic partnerships remains a major challenge. Why are some symbioses lost over evolutionary time whereas others become crucial for survival? Here, we use a quantitative trait reconstruction method to characterize different evolutionary stages in the ancient symbiosis between legumes (Fabaceae) and nitrogen-fixing bacteria, asking how labile is symbiosis across different host clades. We find that more than half of the 1,195 extant nodulating legumes analyzed have a high likelihood (>95%) of being in a state of high symbiotic persistence, meaning that they show a continued capacity to form the symbiosis over evolutionary time, even though the partnership has remained facultative and is not obligate. To explore patterns associated with the likelihood of loss and retention of the N2-fixing symbiosis, we tested for correlations between symbiotic persistence and legume distribution, climate, soil and trait data. We found a strong latitudinal effect and demonstrated that low mean annual temperatures are associated with high symbiotic persistence in legumes. Although no significant correlations between soil variables and symbiotic persistence were found, nitrogen and phosphorus leaf contents were positively correlated with legumes in a state of high symbiotic persistence. This pattern suggests that highly demanding nutrient lifestyles are associated with more stable partnerships, potentially because they “lock” the hosts into symbiotic dependency. Quantitative reconstruction methods are emerging as a powerful comparative tool to study broad patterns of symbiont loss and retention across diverse partnerships. PMID:26041807

Evolutionary signals of symbiotic persistence in the legume-rhizobia mutualism.

PubMed

Werner, Gijsbert D A; Cornwell, William K; Cornelissen, Johannes H C; Kiers, E Toby

2015-08-18

Understanding the origins and evolutionary trajectories of symbiotic partnerships remains a major challenge. Why are some symbioses lost over evolutionary time whereas others become crucial for survival? Here, we use a quantitative trait reconstruction method to characterize different evolutionary stages in the ancient symbiosis between legumes (Fabaceae) and nitrogen-fixing bacteria, asking how labile is symbiosis across different host clades. We find that more than half of the 1,195 extant nodulating legumes analyzed have a high likelihood (>95%) of being in a state of high symbiotic persistence, meaning that they show a continued capacity to form the symbiosis over evolutionary time, even though the partnership has remained facultative and is not obligate. To explore patterns associated with the likelihood of loss and retention of the N2-fixing symbiosis, we tested for correlations between symbiotic persistence and legume distribution, climate, soil and trait data. We found a strong latitudinal effect and demonstrated that low mean annual temperatures are associated with high symbiotic persistence in legumes. Although no significant correlations between soil variables and symbiotic persistence were found, nitrogen and phosphorus leaf contents were positively correlated with legumes in a state of high symbiotic persistence. This pattern suggests that highly demanding nutrient lifestyles are associated with more stable partnerships, potentially because they "lock" the hosts into symbiotic dependency. Quantitative reconstruction methods are emerging as a powerful comparative tool to study broad patterns of symbiont loss and retention across diverse partnerships.

Impact of rhizobial inoculation and reduced N supply on biomass production and biological N2 fixation in common bean grown hydroponically.

PubMed

Kontopoulou, Charis-Konstantina; Liasis, Epifanios; Iannetta, Pietro Pm; Tampakaki, Anastasia; Savvas, Dimitrios

2017-10-01

Testing rhizobial inoculation of common bean (Phaseolus vulgaris L.) in hydroponics enables accurate quantification of biological N 2 fixation (BNF) and provides information about the potential of reducing inorganic N fertilizer use. In view of this background, common bean grown on pumice was inoculated with Rhizobium tropici CIAT899 (Rt) and supplied with either full-N (total nitrogen 11.2 mmol L -1 ), 1/3 of full-N or N-free nutrient solution (NS). BNF was quantified at the early pod-filling stage using the 15 N natural abundance method. Full-N supply to Rt-inoculated plants resulted in markedly smaller nodules than less- or zero-N supply, and no BNF. Rt inoculation of full-N-treated plants did not increase biomass and pod yield compared with non-inoculation. Restriction (1/3 of full-N) or omission of inorganic N resulted in successful nodulation and BNF (54.3 and 49.2 kg N ha -1 , corresponding to 58 and 100% of total plant N content respectively) but suppressed dry shoot biomass from 191.7 (full-N, +Rt) to 107.4 and 43.2 g per plant respectively. Nutrient cation uptake was reduced when inorganic N supply was less or omitted. Rt inoculation of hydroponic bean provides no advantage when full-N NS is supplied, while 1/3 of full-N or N-free NS suppresses plant biomass and yield, partly because the restricted NO 3 - supply impairs cation uptake. © 2017 Society of Chemical Industry. © 2017 Society of Chemical Industry.

SS 383: A NEW S-TYPE YELLOW SYMBIOTIC STAR?

DOE Office of Scientific and Technical Information (OSTI.GOV)

Baella, N. O.; Pereira, C. B.; Miranda, L. F.

Symbiotic stars are key objects in understanding the formation and evolution of interacting binary systems, and are probably the progenitors of Type Ia supernovae. However, the number of known symbiotic stars is much lower than predicted. We aim to search for new symbiotic stars, with particular emphasis on the S-type yellow symbiotic stars, in order to determine their total population, evolutionary timescales, and physical properties. The Two Micron All Sky Survey (2MASS) (J – H) versus (H – K {sub s}) color-color diagram has been previously used to identify new symbiotic star candidates and show that yellow symbiotics are locatedmore » in a particular region of that diagram. Candidate symbiotic stars are selected on the basis of their locus in the 2MASS (J – H) versus (H – K {sub s}) diagram and the presence of Hα line emission in the Stephenson and Sanduleak Hα survey. This diagram separates S-type yellow symbiotic stars from the rest of the S-type symbiotic stars, allowing us to select candidate yellow symbiotics. To establish the true nature of the candidates, intermediate-resolution spectroscopy is obtained. We have identified the Hα emission line source SS 383 as an S-type yellow symbiotic candidate by its position in the 2MASS color-color diagram. The optical spectrum of SS 383 shows Balmer, He I, He II, and [O III] emission lines, in combination with TiO absorption bands that confirm its symbiotic nature. The derived electron density (≅10{sup 8-9} cm{sup –3}), He I emission line intensity ratios, and position in the [O III] λ5007/Hβ versus [O III] λ4363/Hγ diagram indicate that SS 383 is an S-type symbiotic star, with a probable spectral type of K7-M0 deduced for its cool component based on TiO indices. The spectral type and the position of SS 383 (corrected for reddening) in the 2MASS color-color diagram strongly suggest that SS 383 is an S-type yellow symbiotic. Our result points out that the 2MASS color-color diagram is a powerful

NanoSIMS Analyses of Mo Indicate Nitrogenase Activity and Help Solve a N and C Fixation Puzzle in a Marine Cyanobacterium

NASA Astrophysics Data System (ADS)

Pett-Ridge, J.; Weber, P. K.; Finzi, J.; Hutcheon, I. D.; Capone, D. G.

2006-12-01

Diazotrophic cyanobacteria are capable of both CO2 and N2 fixation, yet must separate these two functions because the nitrogenase enzymes used in N2 fixation are strongly inhibited by O2 produced during photosynthesis. Some lineages, such as Anabaena, use specialized cells (heterocysts) to maintain functional segregation. However the mechanism of this segregation is poorly understood in Trichodesmium, a critical component of marine primary production in the tropical and subtropical North Atlantic. While some Trichodesmium studies suggest a temporal segregation of the nitrogen and carbon fixing processes, others indicate nitrogen fixation is spatially isolated in differentiated cells called diazocytes. In order to isolate the intracellular location of N fixation in both species, we used a combination of TEM, SEM and NanoSIMS analysis to map the distribution of C, N and Mo (a critical nitrogenase co-factor) isotopes in intact cells. NanoSIMS is a powerful surface analysis tool which combines nanometer-scale imaging resolution with the high sensitivity of mass spectrometry. Using cells grown in a 13CO^2 and 15N2 enriched atmosphere, our analyses indicate that in Anabaena, heterocysts are consistently enriched in Mo, and Mo accumulation suggests active N fixation (as opposed to N storage). In the non- heterocystous Trichodesmium, Mo is concentrated in sub-regions of individual cells, and is not associated with regions of N storage (cyanophycin granules). We suggest that NanoSIMS mapping of metal enzyme co- factors is a unique method of identifying physiological and morphological characteristics within individual bacterial cells. This combination of NanoSIMS analysis and high resolution microscopy allows isotopic analysis to be linked to morphological features and holds great promise for fine-scale studies of bacteria metabolism.

Microgravity Effects on the Early Events of Biological Nitrogen Fixation in Medicago Truncatula: Results from the SyNRGE Experiment

NASA Technical Reports Server (NTRS)

Stutte, Gary W.; Roberts, Michael

2012-01-01

SyNRGE (Symbiotic Nodulation in a Reduced Gravity Environment) was a sortie mission on STS-135 in the Biological Research in Canisters (BRIC) hardware to study the effect of microgravity on a plant-microbe symbiosis resulting in biological nitrogen fixation. Medicago truncatula, a model species for th legume family, was inoculated with its bacterial symbiont, Sinorhizobium meliloti, to observe early biomolecular events associated with infection and nodulation in Petri Dish Fixation Units (PDFU's).

Molybdenum and Phosphorus Interact to Constrain Asymbiotic Nitrogen Fixation in Tropical Forests

PubMed Central

Wurzburger, Nina; Bellenger, Jean Philippe; Kraepiel, Anne M. L.; Hedin, Lars O.

2012-01-01

Biological di-nitrogen fixation (N2) is the dominant natural source of new nitrogen to land ecosystems. Phosphorus (P) is thought to limit N2 fixation in many tropical soils, yet both molybdenum (Mo) and P are crucial for the nitrogenase reaction (which catalyzes N2 conversion to ammonia) and cell growth. We have limited understanding of how and when fixation is constrained by these nutrients in nature. Here we show in tropical forests of lowland Panama that the limiting element on asymbiotic N2 fixation shifts along a broad landscape gradient in soil P, where Mo limits fixation in P-rich soils while Mo and P co-limit in P-poor soils. In no circumstance did P alone limit fixation. We provide and experimentally test a mechanism that explains how Mo and P can interact to constrain asymbiotic N2 fixation. Fixation is uniformly favored in surface organic soil horizons - a niche characterized by exceedingly low levels of available Mo relative to P. We show that soil organic matter acts to reduce molybdate over phosphate bioavailability, which, in turn, promotes Mo limitation in sites where P is sufficient. Our findings show that asymbiotic N2 fixation is constrained by the relative availability and dynamics of Mo and P in soils. This conceptual framework can explain shifts in limitation status across broad landscape gradients in soil fertility and implies that fixation depends on Mo and P in ways that are more complex than previously thought. PMID:22470462

Multifrequency observations of symbiotic stars

NASA Technical Reports Server (NTRS)

Kenyon, Scott J.

1988-01-01

The discovery of symbiotic stars is described, and the results of multifrequency observations made during the past two decades are presented. Observational data identify symbiotic stars as long-period binary systems that can be divided into two basic physical classes: detached symbiotics containing a red giant (or a Mira variable), and semidetached symbiotics containing a lobe-filling red giant and a solar-type main sequence star. Three components are typically observed: (1) the cool giant component with an effective temperature of 2500-4000 K, which can be divided by the IR spectral classification into normal M giants (S-types) and heavily reddened Mira variables (D-types); (2) the hot companion displaying a bright blue continuum at UV wavelengths, which is sometimes also an X-ray source; and (3) a gaseous nebula enveloping the binary.

Novel, non-symbiotic isolates of Neorhizobium from a dryland agricultural soil.

PubMed

Soenens, Amalia; Imperial, Juan

2018-01-01

Semi-selective enrichment, followed by PCR screening, resulted in the successful direct isolation of fast-growing Rhizobia from a dryland agricultural soil. Over 50% of these isolates belong to the genus Neorhizobium , as concluded from partial rpoB and near-complete 16S rDNA sequence analysis. Further genotypic and genomic analysis of five representative isolates confirmed that they form a coherent group within Neorhizobium , closer to N. galegae than to the remaining Neorhizobium species, but clearly differentiated from the former, and constituting at least one new genomospecies within Neorhizobium. All the isolates lacked nod and nif symbiotic genes but contained a repABC replication/maintenance region, characteristic of rhizobial plasmids, within large contigs from their draft genome sequences. These repABC sequences were related, but not identical, to repABC sequences found in symbiotic plasmids from N. galegae , suggesting that the non-symbiotic isolates have the potential to harbor symbiotic plasmids. This is the first report of non-symbiotic members of Neorhizobium from soil.

On the Relationship Between Hydrogen Saturation in the Tropical Atlantic Ocean and Nitrogen Fixation by the Symbiotic Diazotroph UCYN-A

NASA Astrophysics Data System (ADS)

Moore, R. M.; Grefe, I.; Zorz, J.; Shan, S.; Thompson, K.; Ratten, J.; LaRoche, J.

2018-04-01

Dissolved hydrogen measurements were made at high resolution in surface waters along a tropical north Atlantic transect between Guadeloupe and Cape Verde in 2015 (Meteor 116). Parallel water samples acquired to assess the relative abundance of the nifH gene from several types of diazotrophs, indicated that Trichodesmium and UCYN-A were dominant in this region. We show that a high degree of correlation exists between the hydrogen saturations and UCYN-A nifH abundance, and a weak correlation with Trichodesmium. The findings suggest that nitrogen fixation by UCYN-A is a major contributor to hydrogen supersaturations in this region of the ocean. The ratio of hydrogen released to nitrogen fixed has not been determined for this symbiont, but the indications are that it may be high in comparison with the small number of diazotrophs for which the ratio has been measured in laboratory cultures. We speculate that this would be consistent with the diazotroph being an exosymbiont on its haptophyte host. Our high resolution measurements of hydrogen concentrations are capable of illustrating the time and space scales of inferred activity of diazotrophs in near real-time in a way that cannot be achieved by biological sampling and rate measurements requiring incubations with 15N2. Direct measurement of high resolution spatial variability would be relatively challenging through collection and analysis of biological samples by qPCR, and extremely challenging by 15N-uptake techniques, neither of which methods yields real-time data. Nonetheless, determination of fixation rates still firmly depends on the established procedure of incubations in the presence of 15N2.

Global terrestrial carbon and nitrogen cycling insensitive to estimates of biological N fixation

NASA Astrophysics Data System (ADS)

Steinkamp, J.; Weber, B.; Werner, C.; Hickler, T.

2015-12-01

Dinitrogen (N2) is the most abundant molecule in the atmosphere and incorporated in other molecules an essential nutrient for life on earth. However, only few natural processes can initiate a reaction of N2. These natural processes are fire, lightning and biological nitrogen fixation (BNF) with BNF being the largest source. In the course of the last century humans have outperformed the natural processes of nitrogen fixation by the production of fertilizer. Industrial and other human emission of reactive nitrogen, as well as fire and lightning lead to a deposition of 63 Tg (N) per year. This is twice the amount of BNF estimated by the default setup of the dynamic global vegetation model LPJ-GUESS (30 Tg), which is a conservative approach. We use different methods and parameterizations for BNF in LPJ-GUESS: 1.) varying total annual amount; 2.) annual evenly distributed and daily calculated fixation rates; 3.) an improved dataset of BNF by cryptogamic covers (free-living N-fixers). With this setup BNF is ranging from 30 Tg to 60 Tg. We assess the impact of BNF on carbon storage and grand primary production (GPP) of the natural vegetation. These results are compared to and evaluated against available independent datasets. We do not see major differences in the productivity and carbon stocks with these BNF estimates, suggesting that natural vegetation is insensitive to BNF on a global scale and the vegetation can compensate for the different nitrogen availabilities. Current deposition of nitrogen compounds and internal cycling through mineralization and uptake is sufficient for natural vegetation productivity. However, due to the coarse model grid and spatial heterogeneity in the real world this conclusion does not exclude the existence of habitats constrained by BNF.

δ15N constraints on long-term nitrogen balances in temperate forests

USGS Publications Warehouse

Perakis, S.S.; Sinkhorn, E.R.; Compton, J.E.

2011-01-01

Biogeochemical theory emphasizes nitrogen (N) limitation and the many factors that can restrict N accumulation in temperate forests, yet lacks a working model of conditions that can promote naturally high N accumulation. We used a dynamic simulation model of ecosystem N and δ15N to evaluate which combination of N input and loss pathways could produce a range of high ecosystem N contents characteristic of forests in the Oregon Coast Range. Total ecosystem N at nine study sites ranged from 8,788 to 22,667 kg ha−1 and carbon (C) ranged from 188 to 460 Mg ha−1, with highest values near the coast. Ecosystem δ15N displayed a curvilinear relationship with ecosystem N content, and largely reflected mineral soil, which accounted for 96–98% of total ecosystem N. Model simulations of ecosystem N balances parameterized with field rates of N leaching required long-term average N inputs that exceed atmospheric deposition and asymbiotic and epiphytic N2-fixation, and that were consistent with cycles of post-fire N2-fixation by early-successional red alder. Soil water δ15NO3 − patterns suggested a shift in relative N losses from denitrification to nitrate leaching as N accumulated, and simulations identified nitrate leaching as the primary N loss pathway that constrains maximum N accumulation. Whereas current theory emphasizes constraints on biological N2-fixation and disturbance-mediated N losses as factors that limit N accumulation in temperate forests, our results suggest that wildfire can foster substantial long-term N accumulation in ecosystems that are colonized by symbiotic N2-fixing vegetation.

[Cloning, mutagenesis and symbiotic phenotype of three lipid transfer protein encoding genes from Mesorhizobium huakuii 7653R].

PubMed

Li, Yanan; Zeng, Xiaobo; Zhou, Xuejuan; Li, Youguo

2016-12-04

Lipid transfer protein superfamily is involved in lipid transport and metabolism. This study aimed to construct mutants of three lipid transfer protein encoding genes in Mesorhizobium huakuii 7653R, and to study the phenotypes and function of mutations during symbiosis with Astragalus sinicus. We used bioinformatics to predict structure characteristics and biological functions of lipid transfer proteins, and conducted semi-quantitative and fluorescent quantitative real-time PCR to analyze the expression levels of target genes in free-living and symbiotic conditions. Using pK19mob insertion mutagenesis to construct mutants, we carried out pot plant experiments to observe symbiotic phenotypes. MCHK-5577, MCHK-2172 and MCHK-2779 genes encoding proteins belonged to START/RHO alpha_C/PITP/Bet_v1/CoxG/CalC (SRPBCC) superfamily, involved in lipid transport or metabolism, and were identical to M. loti at 95% level. Gene relative transcription level of the three genes all increased compared to free-living condition. We obtained three mutants. Compared with wild-type 7653R, above-ground biomass of plants and nodulenitrogenase activity induced by the three mutants significantly decreased. Results indicated that lipid transfer protein encoding genes of Mesorhizobium huakuii 7653R may play important roles in symbiotic nitrogen fixation, and the mutations significantly affected the symbiotic phenotypes. The present work provided a basis to study further symbiotic function mechanism associated with lipid transfer proteins from rhizobia.

Effect of light on N2 fixation and net nitrogen release of Trichodesmium in a field study

NASA Astrophysics Data System (ADS)

Lu, Yangyang; Wen, Zuozhu; Shi, Dalin; Chen, Mingming; Zhang, Yao; Bonnet, Sophie; Li, Yuhang; Tian, Jiwei; Kao, Shuh-Ji

2018-01-01

Dinitrogen fixation (NF) by marine cyanobacteria is an important pathway to replenish the oceanic bioavailable nitrogen inventory. Light is the key to modulating NF; however, field studies investigating the light response curve (NF-I curve) of NF rate and the effect of light on diazotroph-derived nitrogen (DDN) net release are relatively sparse in the literature, hampering prediction using models. A dissolution method was applied using uncontaminated 15N2 gas to examine how the light changes may influence the NF intensity and DDN net release in the oligotrophic ocean. Experiments were conducted at stations with diazotrophs dominated by filamentous cyanobacterium Trichodesmium spp. in the western Pacific and the South China Sea. The effect of light on carbon fixation (CF) was measured in parallel using the 13C tracer method specifically for a station characterized by Trichodesmium bloom. Both NF-I and CF-I curves showed a Ik (light saturation coefficient) range of 193 to 315 µE m-2 s-1, with light saturation at around 400 µE m-2 s-1. The proportion of DDN net release ranged from ˜ 6 to ˜ 50 %, suggesting an increasing trend as the light intensity decreased. At the Trichodesmium bloom station, we found that the CF / NF ratio was light-dependent and the ratio started to increase as light was lower than the carbon compensation point of 200 µE m-2 s-1. Under low-light stress, Trichodesmium physiologically preferred to allocate more energy for CF to alleviate the intensive carbon consumption by respiration; thus, there is a metabolism tradeoff between CF and NF pathways. Results showed that short-term ( < 24 h) light change modulates the physiological state, which subsequently determined the C / N metabolism and DDN net release by Trichodesmium. Reallocation of energy associated with the variation in light intensity would be helpful for prediction of the global biogeochemical cycle of N by models involving Trichodesmium blooms.

The impact of hydrophobic hernia mesh coating by omega fatty acid on atraumatic fibrin sealant fixation.

PubMed

Gruber-Blum, S; Brand, J; Keibl, C; Redl, H; Fortelny, R H; May, C; Petter-Puchner, A H

2015-08-01

Fibrin sealant (FS) is a safe and efficient fixation method in open intraperitoneal hernia repair. While favourable results have been achieved with hydrophilic meshes, hydrophobic (such as Omega fatty acid coated) meshes (OFM) have not been specifically assessed so far. Atrium C-qur lite(®) mesh was tested in rats in models of open onlay and intraperitoneal hernia repair. 44 meshes (2 × 2 cm) were implanted in 30 male Sprague-Dawley rats in open (n = 2 meshes per animal) and intraperitoneal technique (IPOM; n = 1 mesh per animal). Animals were randomised to four groups: onlay and IPOM sutured vs. sealed. Follow-up was 6 weeks, sutured groups serving as controls. Evaluation criteria were mesh dislocation, adhesions and foreign body reaction. FS provided a reliable fixation in onlay technique, whereas OFM meshes dislocated in the IPOM position when sealed only. FS mesh fixation was safe with OFM meshes in open onlay repair. Intraperitoneal placement of hydrophobic meshes requires additional fixation and cannot be achieved with FS alone.

The relationship between nitrogen fixation and the production of HD from D2 by cell-free extracts of soya-bean nodule bacteroids

PubMed Central

Turner, G. L.; Bergersen, F. J.

1969-01-01

1. Cell-free extracts prepared from soya-bean nodule bacteroids produced HD from D2 in the presence of dithionite, an ATP-generating system and nitrogen. 2. Crude extracts of bacteroids or of Azotobacter vinelandii showed some background D2 exchange when any one of these was omitted. 3. Partial purification of bacteroid extracts diminished this background activity and gave increased D2 exchange and nitrogen fixation. 4. Although increasing pN2 stimulated both reactions, the apparent Km (N2) for nitrogen fixation was much higher than the apparent Km (N2) for D2 exchange when partially purified bacteroid extracts were used. 5. Carbon monoxide was a competitive inhibitor of nitrogen fixation by partially purified bacteroid extracts, but D2 exchange was inhibited in a non-competitive fashion. 6. These results are discussed in relation to the possible existence of enzyme-bound intermediates of nitrogen fixation. PMID:5353527

Effect of systemic herbicides on N2-fixing and phosphate solubilizing microorganisms in relation to availability of nitrogen and phosphorus in paddy soils of West Bengal.

PubMed

Das, Amal Chandra; Debnath, Anjan

2006-11-01

A field experiment has been conducted with four systemic herbicides viz., butachlor [N-(butoxymethyl)-2-chloro-2',6'-diethyl-acetanilide], fluchloralin [N-(2-chloroethyl)-(2,6-dinitro-N-propyl-4-trifluoromethyl) aniline], oxadiazon [5-terbutyl-3-(2,4-dichloro-5-isopro poxyphenyl)-1,3,4-oxadiazol-2-one] and oxyfluorfen [2-chloro-1-(3-ethoxy-4-nitrophenyl)-4-(trifluoromethyl) benzene] at their recommended field rates (2.0, 1.5, 0.4 and 0.12kga.i.ha(-1), respectively) to investigate their effects on growth and activities of aerobic non-symbiotic N(2)-fixing bacteria and phosphate solubilizing microorganisms in relation to availability of nitrogen and phosphorus in the rhizosphere soils as well as yield of the rice crop (Oryza sativa L cv. IR-36). Application of herbicides, in general, highly stimulated the population and activities of the target microorganisms, which resulted in a greater amount of atmospheric nitrogen fixation and phosphate solubilization in the rhizosphere soils of the test crop. The greater microbial activities subsequently augmented the mineralization and availability of nitrogen and phosphorus in the soil solution, which in turn increased the yield of the crop. Among the herbicides, oxyfluorfen was most stimulative followed by fluchloralin and oxadiazon in augmenting the microbial activities in soil. Butachlor also accentuated the mineralization and availability of nitrogen due to higher incitement of non-symbiotic N(2)-fixing bacteria in paddy soil. The grain and straw yields of the crop were also significantly increased due to the application of oxyfluorfen (20.2% and 21%) followed by fluchloralin (13.1% and 15.4%) and butachlor (9.1% and 10.2%), respectively.

Metaproteomics of a gutless marine worm and its symbiotic microbial community reveal unusual pathways for carbon and energy use

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kleiner, Manuel; Wentrop, C.; Lott, C.

Low nutrient and energy availability has led to the evolution of numerous strategies for overcoming these limitations, of which symbiotic associations represent a key mechanism. Particularly striking are the associations between chemosynthetic bacteria and marine animals that thrive in nutrient-poor environments such as the deep-sea because the symbionts allow their hosts to grow on inorganic energy and carbon sources such as sulfide and CO2. Remarkably little is known about the physiological strategies that enable chemosynthetic symbioses to colonize oligotrophic environments. In this study, we used metaproteomics and metabolomics to investigate the intricate network of metabolic interactions in the chemosynthetic associationmore » between Olavius algarvensis, a gutless marine worm, and its bacterial symbionts. We propose novel pathways for coping with energy and nutrient limitation, some of which may be widespread in both free-living and symbiotic bacteria. These include (i) a pathway for symbiont assimilation of the host waste products acetate, propionate, succinate and malate, (ii) the potential use of carbon monoxide as an energy source, a substrate previously not known to play a role in marine invertebrate symbioses, (iii) the potential use of hydrogen as an energy source, (iv) the strong expression of high affinity uptake transporters, and (v) novel energy efficient steps in CO2 fixation and sulfate reduction. The high expression of proteins involved in pathways for energy and carbon uptake and conservation in the O. algarvensis symbiosis indicates that the oligotrophic nature of its environment exerted a strong selective pressure in shaping these associations.« less

Dinitrogen fixation associated with shoots of aquatic carnivorous plants: is it ecologically important?

PubMed Central

Sirová, Dagmara; Šantrůček, Jiří; Adamec, Lubomír; Bárta, Jiří; Borovec, Jakub; Pech, Jiří; Owens, Sarah M.; Šantrůčková, Hana; Schäufele, Rudi; Štorchová, Helena; Vrba, Jaroslav

2014-01-01

Background and Aims Rootless carnivorous plants of the genus Utricularia are important components of many standing waters worldwide, as well as suitable model organisms for studying plant–microbe interactions. In this study, an investigation was made of the importance of microbial dinitrogen (N2) fixation in the N acquisition of four aquatic Utricularia species and another aquatic carnivorous plant, Aldrovanda vesiculosa. Methods 16S rRNA amplicon sequencing was used to assess the presence of micro-organisms with known ability to fix N2. Next-generation sequencing provided information on the expression of N2 fixation-associated genes. N2 fixation rates were measured following 15N2-labelling and were used to calculate the plant assimilation rate of microbially fixed N2. Key Results Utricularia traps were confirmed as primary sites of N2 fixation, with up to 16 % of the plant-associated microbial community consisting of bacteria capable of fixing N2. Of these, rhizobia were the most abundant group. Nitrogen fixation rates increased with increasing shoot age, but never exceeded 1·3 μmol N g–1 d. mass d–1. Plant assimilation rates of fixed N2 were detectable and significant, but this fraction formed less than 1 % of daily plant N gain. Although trap fluid provides conditions favourable for microbial N2 fixation, levels of nif gene transcription comprised <0·01 % of the total prokaryotic transcripts. Conclusions It is hypothesized that the reason for limited N2 fixation in aquatic Utricularia, despite the large potential capacity, is the high concentration of NH4-N (2·0–4·3 mg L–1) in the trap fluid. Resulting from fast turnover of organic detritus, it probably inhibits N2 fixation in most of the microorganisms present. Nitrogen fixation is not expected to contribute significantly to N nutrition of aquatic carnivorous plants under their typical growth conditions; however, on an annual basis the plant–microbe system can supply nitrogen in the order of

Improvement in nitrogen fixation capacity could be part of the domestication process in soybean

PubMed Central

Muñoz, N; Qi, X; Li, M-W; Xie, M; Gao, Y; Cheung, M-Y; Wong, F-L; Lam, H-M

2016-01-01

Biological nitrogen fixation (BNF) in soybeans is a complex process involving the interplay between the plant host and the symbiotic rhizobia. As nitrogen supply has a crucial role in growth and development, higher nitrogen fixation capacity would be important to achieve bigger plants and larger seeds, which were important selection criteria during plant domestication by humans. To test this hypothesis, we monitored the nitrogen fixation-related performance in 31 cultivated and 17 wild soybeans after inoculation with the slow-growing Bradyrhizobium diazoefficiens sp. nov. USDA110 and the fast-growing Sinorhizobium (Ensifer) fredii CCBAU45436. Our results showed that, in general, cultivated soybeans gave better performance in BNF. Electron microscopic studies indicated that there was an exceptionally high accumulation of poly-β-hydroxybutyrate bodies in bacteroids in the nodules of all wild soybeans tested, suggesting that the C/N balance in wild soybeans may not be optimized for nitrogen fixation. Furthermore, we identified new quantitative trait loci (QTLs) for total ureides and total nodule fresh weight by employing a recombinant inbred population composed of descendants from a cross between a cultivated and a wild parent. Using nucleotide diversity (θπ), divergence index (Fst) and distribution of fixed single-nucleotide polymorphisms as parameters, we found that some regions in the total ureides QTL on chromosome 17 and the total nodule fresh weight QTL on chromosome 12 exhibited very low diversity among cultivated soybeans, suggesting that these were traits specially selected during the domestication and breeding process. PMID:27118154

Rhizobium cellulase CelC2 is essential for primary symbiotic infection of legume host roots

PubMed Central

Robledo, M.; Jiménez-Zurdo, J. I.; Velázquez, E.; Trujillo, M. E.; Zurdo-Piñeiro, J. L.; Ramírez-Bahena, M. H.; Ramos, B.; Díaz-Mínguez, J. M.; Dazzo, F.; Martínez-Molina, E.; Mateos, P. F.

2008-01-01

The rhizobia–legume, root-nodule symbiosis provides the most efficient source of biologically fixed ammonia fertilizer for agricultural crops. Its development involves pathways of specificity, infectivity, and effectivity resulting from expressed traits of the bacterium and host plant. A key event of the infection process required for development of this root-nodule symbiosis is a highly localized, complete erosion of the plant cell wall through which the bacterial symbiont penetrates to establish a nitrogen-fixing, intracellular endosymbiotic state within the host. This process of wall degradation must be delicately balanced to avoid lysis and destruction of the host cell. Here, we describe the purification, biochemical characterization, molecular genetic analysis, biological activity, and symbiotic function of a cell-bound bacterial cellulase (CelC2) enzyme from Rhizobium leguminosarum bv. trifolii, the clover-nodulating endosymbiont. The purified enzyme can erode the noncrystalline tip of the white clover host root hair wall, making a localized hole of sufficient size to allow wild-type microsymbiont penetration. This CelC2 enzyme is not active on root hairs of the nonhost legume alfalfa. Microscopy analysis of the symbiotic phenotypes of the ANU843 wild type and CelC2 knockout mutant derivative revealed that this enzyme fulfils an essential role in the primary infection process required for development of the canonical nitrogen-fixing R. leguminosarum bv. trifolii-white clover symbiosis. PMID:18458328

Glacial-Interglacial and Holocene N2O Stable Isotope Changes Constrain Terrestrial N Cycling

NASA Astrophysics Data System (ADS)

Schmitt, J.; Spahni, R.; Bock, M.; Seth, B.; Stocker, B. D.; Ri, X.; Schilt, A.; Brook, E.; Otto-Bliesner, B. L.; Liu, Z.; Prentice, I. C.; Fischer, H.; Joos, F.

2015-12-01

The land biosphere contributes most to the natural source of the long-lived greenhouse gas nitrous oxide (N2O), with N2O emissions being dependent on the turnover rate of both the terrestrial nitrogen (N) and carbon (C) cycle. The C:N stoichiometry of vegetation and soil organic matter links the cycles intimately. Sustained plant productivity increase must be supported by biological N fixation. Intensified N cycling in turn enhances N loss and thereby N2O emissions. The temporal and spatial dynamics of terrestrial N and C cycles and related terrestrial N2O emissions are poorly constrained over the glacial-interglacial transition and the Holocene. Here we reconstruct increased terrestrial N2O emissions since the Last Glacial Maximum based on N2O concentration and isotope measurements on several ice cores and show that this N2O increase can be explained by N cycle modelling - provided N fixation is allowed to respond dynamically to increasing N demand and turnover. The Ice core reconstructions suggest a deglacial increase of 1.1 ± 0.4 Tg N/yr in terrestrial and 0.6 ± 0.4 Tg/yr in oceanic N2O emissions, but relatively constant terrestrial emissions over the Holocene. Transient simulations with a Dynamic Global Vegetation Model are shown to represent the climate and CO2 induced changes in terrestrial N2O emission, and suggest a deglacial increase in biological N fixation by 20%, independently of its absolute magnitude. Deciphering the response of biological N fixation during climatic changes is an important factor for our understanding of plant growth and the land carbon sink, alongside anthropogenic greenhouse gas emissions.

Two Major Clades of Bradyrhizobia Dominate Symbiotic Interactions with Pigeonpea in Fields of Côte d'Ivoire

PubMed Central

Fossou, Romain K.; Ziegler, Dominik; Zézé, Adolphe; Barja, François; Perret, Xavier

2016-01-01

In smallholder farms of Côte d'Ivoire, particularly in the northeast of the country, Cajanus cajan (pigeonpea) has become an important crop because of its multiple beneficial facets. Pigeonpea seeds provide food to make ends meet, are sold on local markets, and aerial parts serve as forage for animals. Since it fixes atmospheric nitrogen in symbiosis with soil bacteria collectively known as rhizobia, C. cajan also improves soil fertility and reduces fallow time. Yet, seed yields remain low mostly because farmers cannot afford chemical fertilizers. To identify local rhizobial strains susceptible to be used as bio-inoculants to foster pigeonpea growth, root nodules were collected in six fields of three geographically distant regions of Côte d'Ivoire. Nodule bacteria were isolated and characterized using various molecular techniques including matrix-assisted laser desorption/ionization time of flight (MALDI-TOF) mass spectrometry (MS) and DNA sequencing. These molecular analyses showed that 63 out of 85 nodule isolates belonged to two major clades of bradyrhizobia, one of which is known as the Bradyrhizobium elkanii super clade. Phylogenies of housekeeping (16S-ITS-23S, rpoB) and symbiotic (nifH) genes were not always congruent suggesting that lateral transfer of nitrogen fixation genes also contributed to define the genome of these bradyrhizobial isolates. Interestingly, no field-, plant-, or cultivar-specific effect was found to shape the profiles of symbiotic strains. In addition, nodule isolates CI-1B, CI-36E, and CI-41A that belong to distinct species, showed similar symbiotic efficiencies suggesting that any of these strains might serve as a proficient inoculant for C. cajan. PMID:27891120

CARBON DIOXIDE FIXATION.

DOE Office of Scientific and Technical Information (OSTI.GOV)

FUJITA,E.

2000-01-12

Solar carbon dioxide fixation offers the possibility of a renewable source of chemicals and fuels in the future. Its realization rests on future advances in the efficiency of solar energy collection and development of suitable catalysts for CO{sub 2} conversion. Recent achievements in the efficiency of solar energy conversion and in catalysis suggest that this approach holds a great deal of promise for contributing to future needs for fuels and chemicals.

Uncoupling between dinitrogen fixation and primary productivity in the eastern Mediterranean Sea

NASA Astrophysics Data System (ADS)

Rahav, Eyal; Herut, Barak; Stambler, Noga; Bar-Zeev, Edo; Mulholland, Margaret R.; Berman-Frank, Ilana

2013-03-01

In the nitrogen (N)-impoverished photic zones of many oceanic regions, prokaryotic organisms fixing atmospheric dinitrogen (N2; diazotrophs) supply an essential source of new nitrogen and fuel primary production. We measured dinitrogen fixation and primary productivity (PP) during the thermally stratified summer period in different water regimes of the oligotrophic eastern Mediterranean Sea, including the Cyprus Eddy and the Rhodes Gyre. Low N2 fixation rates were measured (0.8-3.2 µmol N m-2 d-1) excluding 10-fold higher rates in the Rhodes Gyre and Cyprus Eddy ( 20 µmol N m-2 d-1). The corresponding PP increased from east to west (200-2500 µmol C m-2 d-1), with relatively higher productivity recorded in the Rhodes Gyre and Cyprus Eddy (2150 and 2300 µmol C m-2 d-1, respectively). These measurements demonstrate that N2 fixation in the photic zone of the eastern Mediterranean Sea contributes only negligibly by direct inputs to PP (i.e., cyanobacterial diazotrophs) and is in fact uncoupled from PP. By contrast, N2 fixation is significantly coupled to bacterial productivity and to net heterotrophic areas, suggesting that heterotrophic N2 fixation may in fact be significant in this ultraoligotrophic system. This is further substantiated by the high N2 fixation rates we measured from aphotic depths and by the results of phylogenetic analysis in other studies showing an abundance of heterotrophic diazotrophs.

High-nitrogen fixation rates in the particulate and dissolved pools in the Western Tropical Pacific (Solomon and Bismarck Seas)

NASA Astrophysics Data System (ADS)

Berthelot, H.; Benavides, M.; Moisander, P. H.; Grosso, O.; Bonnet, S.

2017-08-01

Dinitrogen (N2) fixation rates were investigated in the euphotic layer of the Bismarck and Solomon Seas using 15N2 incubation assays taking into account both the particulate and the dissolved pools. Average depth-integrated particulate N2 fixation rates were 203 (range 43-399) and 1396 (range 176-3132) μmol N m-2 d-1 in the Bismarck and Solomon Seas, respectively. In both seas, N2 fixation measured in the dissolved pool was similar to particulate N2 fixation, highlighting the potentially substantial underestimation of N2 fixation in oceanic budgets when only particulate N2 fixation is considered. Among the diazotroph phylotypes targeted using quantitative polymerase chain reaction amplification of nifH genes, Trichodesmium was the most abundant. Regression analyses suggest that it accounted for the major proportion of N2 fixation. However, unicellular cyanobacterial and non-cyanobacterial diazotrophs were also occasionally abundant. This study reports high pelagic N2 fixation rates and confirms that the Western Tropical South Pacific is a hot spot for marine N2 fixation.

Comprehensive EST analysis of the symbiotic sea anemone, Anemonia viridis

PubMed Central

Sabourault, Cécile; Ganot, Philippe; Deleury, Emeline; Allemand, Denis; Furla, Paola

2009-01-01

Background Coral reef ecosystems are renowned for their diversity and beauty. Their immense ecological success is due to a symbiotic association between cnidarian hosts and unicellular dinoflagellate algae, known as zooxanthellae. These algae are photosynthetic and the cnidarian-zooxanthellae association is based on nutritional exchanges. Maintenance of such an intimate cellular partnership involves many crosstalks between the partners. To better characterize symbiotic relationships between a cnidarian host and its dinoflagellate symbionts, we conducted a large-scale EST study on a symbiotic sea anemone, Anemonia viridis, in which the two tissue layers (epiderm and gastroderm) can be easily separated. Results A single cDNA library was constructed from symbiotic tissue of sea anemones A. viridis in various environmental conditions (both normal and stressed). We generated 39,939 high quality ESTs, which were assembled into 14,504 unique sequences (UniSeqs). Sequences were analysed and sorted according to their putative origin (animal, algal or bacterial). We identified many new repeated elements in the 3'UTR of most animal genes, suggesting that these elements potentially have a biological role, especially with respect to gene expression regulation. We identified genes of animal origin that have no homolog in the non-symbiotic starlet sea anemone Nematostella vectensis genome, but in other symbiotic cnidarians, and may therefore be involved in the symbiosis relationship in A. viridis. Comparison of protein domain occurrence in A. viridis with that in N. vectensis demonstrated an increase in abundance of some molecular functions, such as protein binding or antioxidant activity, suggesting that these functions are essential for the symbiotic state and may be specific adaptations. Conclusion This large dataset of sequences provides a valuable resource for future studies on symbiotic interactions in Cnidaria. The comparison with the closest available genome, the sea

Development of a new biofertilizer with a high capacity for N2 fixation, phosphate and potassium solubilization and auxin production.

PubMed

Leaungvutiviroj, Chaveevan; Ruangphisarn, Pimtida; Hansanimitkul, Pikul; Shinkawa, Hidenori; Sasaki, Ken

2010-01-01

Biofertilizers that possess a high capacity for N(2) fixation (Azotobacter tropicalis), and consist of phosphate solubilizing bacteria (Burkhoderia unamae), and potassium solubilizing bacteria (Bacillus subtilis) and produce auxin (KJB9/2 strain), have a high potential for growth and yield enhancement of corn and vegetables (Chinese kale). For vegetables, the addition of biofertilizer alone enhanced growth 4 times. Moreover, an enhancement of growth by 7 times was observed due to the addition of rock phosphate and K-feldspar, natural mineral fertilizers, in combination with the biofertilizer.

Symbiotic ciliates receive protection against UV damage from their algae: a test with Paramecium bursaria and Chlorella.

PubMed

Summerer, Monika; Sonntag, Bettina; Hörtnagl, Paul; Sommaruga, Ruben

2009-05-01

We assessed the photoprotective role of symbiotic Chlorella in the ciliate Paramecium bursaria by comparing their sensitivity to UV radiation (UVR) with Chlorella-reduced and Chlorella-free (aposymbiotic) cell lines of the same species. Aposymbiotic P. bursaria had significantly higher mortality than the symbiotic cell lines when exposed to UVR. To elucidate the protection mechanism, we assessed the algal distribution within the ciliate using thin-sections and transmission electron microscopy and estimated the screening factor by Chlorella based on an optical model. These analyses evidenced a substantial screening factor ranging, from 59.2% to 93.2% (320nm) for regular algal distribution. This screening efficiency reached up to approximately 100% when Chlorella algae were dislocated to the posterior region of the ciliate. The dislocation was observed in symbiotic ciliates only under exposure to UV plus photosynthetically active radiation (PAR) or to high PAR levels. Moreover, under exposure to UVB radiation and high PAR, symbiotic P. bursaria aggregated into dense spots. This behavior could represent an efficient avoidance strategy not yet described for ciliates. Analyses of the intact symbiosis and their algal symbionts for UV-screening compounds (mycosporine-like amino acids and sporopollenin) proved negative. Overall, our results show that photoprotection in this ciliate symbiosis represents an additional advantage to the hitherto postulated nutritional benefits.

Dynamics of N2 fixation and fate of diazotroph-derived nitrogen in a low-nutrient, low-chlorophyll ecosystem: results from the VAHINE mesocosm experiment (New Caledonia)

NASA Astrophysics Data System (ADS)

Bonnet, Sophie; Berthelot, Hugo; Turk-Kubo, Kendra; Fawcett, Sarah; Rahav, Eyal; L'Helguen, Stéphane; Berman-Frank, Ilana

2016-05-01

N2 fixation rates were measured daily in large (˜ 50 m3) mesocosms deployed in the tropical southwest Pacific coastal ocean (New Caledonia) to investigate the temporal variability in N2 fixation rates in relation with environmental parameters and study the fate of diazotroph-derived nitrogen (DDN) in a low-nutrient, low-chlorophyll ecosystem. The mesocosms were fertilized with ˜ 0.8 µM dissolved inorganic phosphorus (DIP) to stimulate diazotrophy. Bulk N2 fixation rates were replicable between the three mesocosms, averaged 18.5 ± 1.1 nmol N L-1 d-1 over the 23 days, and increased by a factor of 2 during the second half of the experiment (days 15 to 23) to reach 27.3 ± 1.0 nmol N L-1 d-1. These later rates measured after the DIP fertilization are higher than the upper range reported for the global ocean. During the 23 days of the experiment, N2 fixation rates were positively correlated with seawater temperature, primary production, bacterial production, standing stocks of particulate organic carbon (POC), nitrogen (PON) and phosphorus (POP), and alkaline phosphatase activity, and negatively correlated with DIP concentrations, DIP turnover time, nitrate, and dissolved organic nitrogen and phosphorus concentrations. The fate of DDN was investigated during a bloom of the unicellular diazotroph UCYN-C that occurred during the second half of the experiment. Quantification of diazotrophs in the sediment traps indicates that ˜ 10 % of UCYN-C from the water column was exported daily to the traps, representing as much as 22.4 ± 5.5 % of the total POC exported at the height of the UCYN-C bloom. This export was mainly due to the aggregation of small (5.7 ± 0.8 µm) UCYN-C cells into large (100-500 µm) aggregates. During the same time period, a DDN transfer experiment based on high-resolution nanometer-scale secondary ion mass spectrometry (nanoSIMS) coupled with 15N2 isotopic labeling revealed that 16 ± 6 % of the DDN was released to the dissolved pool and 21 ± 4

Mini-Fragment Fixation Is Equivalent to Bicortical Screw Fixation for Horizontal Medial Malleolus Fractures.

PubMed

Wegner, Adam M; Wolinsky, Philip R; Robbins, Michael A; Garcia, Tanya C; Amanatullah, Derek F

2018-05-01

Horizontal fractures of the medial malleolus occur through application of valgus or abduction force through the ankle that creates a tension failure of the medial malleolus. The authors hypothesize that mini-fragment T-plates may offer improved fixation, but the optimal fixation construct for these fractures remains unclear. Forty synthetic distal tibiae with identical osteotomies were randomized into 4 fixation constructs: (1) two parallel unicortical cancellous screws; (2) two parallel bicortical cortical screws; (3) a contoured mini-fragment T-plate with 2 unicortical screws in the fragment and 2 bicortical screws in the shaft; and (4) a contoured mini-fragment T-plate with 2 bicortical screws in the fragment and 2 unicortical screws in the shaft. Specimens were subjected to offset axial tension loading on a servohydraulic testing system and tracked using high-resolution video. Failure was defined as 2 mm of articular displacement. Analysis of variance followed by a Tukey-Kramer post hoc test was used to assess for differences between groups, with significance defined as P<.05. The mean stiffness (±SD) values of both mini-fragment T-plate constructs (239±83 N/mm and 190±37 N/mm) and the bicortical screw construct (240±17 N/mm) were not statistically different. The mean stiffness values of both mini-fragment T-plate constructs and the bicortical screw construct were higher than that of a parallel unicortical screw construct (102±20 N/mm). Contoured T-plate constructs provide stiffer initial fixation than a unicortical cancellous screw construct. The T-plate is biomechanically equivalent to a bicortical screw construct, but may be superior in capturing small fragments of bone. [Orthopedics. 2018; 41(3):e395-e399.]. Copyright 2018, SLACK Incorporated.

Models of symbiotic stars

NASA Technical Reports Server (NTRS)

Friedjung, Michael

1993-01-01

One of the most important features of symbiotic stars is the coexistence of a cool spectral component that is apparently very similar to the spectrum of a cool giant, with at least one hot continuum, and emission lines from very different stages of ionization. The cool component dominates the infrared spectrum of S-type symbiotics; it tends to be veiled in this wavelength range by what appears to be excess emission in D-type symbiotics, this excess usually being attributed to circumstellar dust. The hot continuum (or continua) dominates the ultraviolet. X-rays have sometimes also been observed. Another important feature of symbiotic stars that needs to be explained is the variability. Different forms occur, some variability being periodic. This type of variability can, in a few cases, strongly suggest the presence of eclipses of a binary system. One of the most characteristic forms of variability is that characterizing the active phases. This basic form of variation is traditionally associated in the optical with the veiling of the cool spectrum and the disappearance of high-ionization emission lines, the latter progressively appearing (in classical cases, reappearing) later. Such spectral changes recall those of novae, but spectroscopic signatures of the high-ejection velocities observed for novae are not usually detected in symbiotic stars. However, the light curves of the 'symbiotic nova' subclass recall those of novae. We may also mention in this connection that radio observations (or, in a few cases, optical observations) of nebulae indicate ejection from symbiotic stars, with deviations from spherical symmetry. We shall give a historical overview of the proposed models for symbiotic stars and make a critical analysis in the light of the observations of symbiotic stars. We describe the empirical approach to models and use the observational data to diagnose the physical conditions in the symbiotics stars. Finally, we compare the results of this empirical

Nitrogen Fixation (Acetylene Reduction) Associated with Duckweed (Lemnaceae) Mats

PubMed Central

Zuberer, D. A.

1982-01-01

Duckweed (Lemnaceae) mats in Texas and Florida were investigated, using the acetylene reduction assay, to determine whether nitrogen fixation occurred in these floating aquatic macrophyte communities. N2-fixing microorganisms were enumerated by plating or most-probable-number techniques, using appropriate N-free media. Results of the investigations indicated that substantial N2-fixation (C2H2) was associated with duckweed mats in Texas and Florida. Acetylene reduction values ranged from 1 to 18 μmol of C2H4 g (dry weight)−1 day−1 for samples incubated aerobically in light. Dark N2 fixation was always two- to fivefold lower. 3-(3,4-Dichlorophenyl)-1,1-dimethylurea (7 to 10 μM) reduced acetylene reduction to levels intermediate between light and dark incubation. Acetylene reduction was generally greatest for samples incubated anaerobically in the light. It was estimated that 15 to 20% of the N requirement of the duckweed could be supplied through biological nitrogen fixation. N2-fixing heterotrophic bacteria (105 cells g [wet weight]−1 and cyanobacteria (105 propagules g [wet weight]−1 were associated with the duckweed mats. Azotobacter sp. was not detected in these investigations. One diazotrophic isolate was classified as Klebsiella. PMID:16345992

Tolerance or avoidance: drought frequency determines the response of an N2 -fixing tree.

PubMed

Minucci, Jeffrey M; Miniat, Chelcy Ford; Teskey, Robert O; Wurzburger, Nina

2017-07-01

Climate change is increasing drought frequency, which may affect symbiotic N 2 fixation (SNF), a process that facilitates ecosystem recovery from disturbance. Here, we assessed the effect of drought frequency on the ecophysiology and SNF rate of a common N 2 -fixing tree in eastern US forests. We grew Robinia pseudoacacia seedlings under the same mean soil moisture, but with different drought frequency caused by wet-dry cycles of varying periodicity. We found no effect of drought frequency on final biomass or mean SNF rate. However, seedlings responded differently to wet and dry phases depending on drought frequency. Under low-frequency droughts, plants fixed carbon (C) and nitrogen (N) at similar rates during wet and dry phases. Conversely, under high-frequency droughts, plants fixed C and N at low rates during dry phases and at high rates during wet phases. Our findings suggest that R. pseudoacacia growth is resistant to increased drought frequency because it employs two strategies - drought tolerance or drought avoidance, followed by compensation. SNF may play a role in both by supplying N to leaf tissues for acclimation and by facilitating compensatory growth following drought. Our findings point to SNF as a mechanism for plants and ecosystems to cope with drought. © 2017 The Authors. New Phytologist © 2017 New Phytologist Trust.

Dynamics of N2 fixation and fate of diazotroph-derived nitrogen in a low nutrient low chlorophyll ecosystem: results from the VAHINE mesocosm experiment (New Caledonia)

NASA Astrophysics Data System (ADS)

Bonnet, S.; Berthelot, H.; Turk-Kubo, K.; Fawcett, S.; Rahav, E.; l'Helguen, S.; Berman-Frank, I.

2015-12-01

N2 fixation rates were measured daily in large (~ 50 m3) mesocosms deployed in the tropical South West Pacific coastal ocean (New Caledonia) to investigate the spatial and temporal dynamics of diazotrophy and the fate of diazotroph-derived nitrogen (DDN) in a low nutrient, low chlorophyll ecosystem. The mesocosms were intentionally fertilized with ~ 0.8 μM dissolved inorganic phosphorus (DIP) to stimulate diazotrophy. Bulk N2 fixation rates were replicable between the three mesocosms, averaged 18.5 ± 1.1 nmol N L-1 d-1 over the 23 days, and increased by a factor of two during the second half of the experiment (days 15 to 23) to reach 27.3 ± 1.0 nmol N L-1 d-1. These rates are higher than the upper range reported for the global ocean, indicating that the waters surrounding New Caledonia are particularly favourable for N2 fixation. During the 23 days of the experiment, N2 fixation rates were positively correlated with seawater temperature, primary production, bacterial production, standing stocks of particulate organic carbon, nitrogen and phosphorus, and alkaline phosphatase activity, and negatively correlated with DIP concentrations, DIP turnover time, nitrate, and dissolved organic nitrogen and phosphorus concentrations. The fate of DDN was investigated during the bloom of the unicellular diazotroph, UCYN-C, that occurred during the second half of the experiment. Quantification of diazotrophs in the sediment traps indicates that ~ 10 % of UCYN-C from the water column were exported daily to the traps, representing as much as 22.4 ± 5.5 % of the total POC exported at the height of the UCYN-C bloom. This export was mainly due to the aggregation of small (5.7 ± 0.8 μm) UCYN-C cells into large (100-500 μm) aggregates. During the same time period, a DDN transfer experiment based on high-resolution nanometer scale secondary ion mass spectrometry (nanoSIMS) coupled with 15N2 isotopic labelling revealed that 16 ± 6 % of the DDN was released to the dissolved pool

Deepwater Nitrogen Fixation: Who's Doing it, Where, and Why?

NASA Astrophysics Data System (ADS)

Montoya, J. P.; Weber, S.; Vogts, A.; Voss, M.; Saxton, M.; Joye, S. B.

2016-02-01

Nitrogen availability frequently limits marine primary production and N2-fixation plays an important role in supporting biological production in surface waters of many oligotrophic regions. Although subsurface waters typically contain high concentrations of nitrate and other nutrients, measurements from a variety of oceanic settings show measurable, and at times high rates of N2-fixation in deep, dark waters below the mixed layer. We have explored the distribution of N2-fixation throughout the water column of the Gulf of Mexico (GoM) during a series of cruises beginning shortly after the Deepwater Horizon (DWH) spill in 2010 and continuing at roughly annual intervals. These cruises allowed us to sample oligotrophic waters across a range of depths, and to explore the connections between the C and N cycles mediated by release of oil and gas (petrocarbon) from natural seeps as well as anthropogenic sources (e.g., the DWH). We used stable isotope abundances (15N and 13C) in particles and zooplankton in combination with experimental measurements of N2-fixation and CH4 assimilation to assess the contribution of oil- and gas-derived C to the pelagic food web, and the impact of CH4 releases on the pelagic C and N cycles. Our isotopic measurements document the movement of petrocarbon into the pelagic food web, and our experiments revealed that high rates of N2-fixation were widespread in deep water immediately after the DWH incident, and restricted to the vicinity of natural seeps in subsequent years. Unfortunately, these approaches provided no insight into the organisms actually responsible for N2-fixation and CH4-assimilation. We used nano-scale Secondary Ion Mass Spectrometry (nanoSIMS) to image the organisms responsible for these processes, and molecular approaches to explore the diversity of methanotrophs and diazotrophs present in the system. The ability to resolve isotopic distributions on the scale of individual cells is a critical part of bridging the gap between

The (C III lambda 1909/Si III lambda 1892) ratio as a diagnostic for planetary nebulae and symbiotic stars

NASA Technical Reports Server (NTRS)

Feibelman, Walter A.; Aller, Lawrence H.

1987-01-01

Suitable IUE archival material on planetary nebulae has been examined to determine the log R /F(lambda 1909 C III)/F(lambda 1892 Si III)/ as a discriminant for distinguishing planetary nebulae from symbiotic stars and related objects. The mean value of log R for 73 galactic planetaries is 1.4, while that of extragalactic planetaries appears to be slightly lower, and that for symbiotics is 0.3. The lower value of log R for symbiotics is easily understood as a consequence of their higher densities. A plot of log R versus N-epsilon indicates that 80 percent of the planetaries fall into the range of log R between 1.2 and 1.8, but some of the 'peculiar' and bipolar nebulae fall below log R = 1.2. The corresponding N(C++)/N(Si++) ionic ratio varies over a large range.

Outbursts in Symbiotic Binaries: Z and Continued Observation

NASA Technical Reports Server (NTRS)

Sonneborn, George (Technical Monitor); Keyes, Charles

2005-01-01

A major question for symbiotic stars concerns the nature and cause of their outbursts. A small subset of symbiotics, the "slow novae" are fairly well established as thermonuclear events that last on the order of decades. The several symbiotic "recurrent novae", which are much shorter and last on the order of months, are also thought to be thermonuclear runaways. Yet the majority of symbiotics are neither slow novae nor recurrent novae. These are the so-called "classical symbiotics," many of which show outbursts whose cause is not well understood. In some cases, jets are produced in association with an outburst, therefore an investigation into the causes of outbursts will yield important insights into the production of collimated outflows. To investigate the cause and nature of classical symbiotic outbursts, we initiated a program of multi- wavelength observations of these events. First of all in FUSE Cycle 2, we obtained six observational epochs of the 2000-2002 classic symbiotic outburst in the first target of our campaign - class prototype, Z Andromedae. That program was part of a coordinated multi-wavelength Target-of-Opportunity (TOO) campaign with FUSE, XMM, Chandra, MERLIN, the VLA, and ground-based spectroscopic and high time-resolution photometric observations. Our campaign proved the concept, utility, and need for coordinated multi-wavelength observations in order to make progress in understanding the nature of the outburst mechanisms in symbiotic stars. Indeed, the FUSE data were the cornerstone of this project. The present program is a continuation of that cycle 2 effort. Indeed, the observations acquired in this program are vital to the proper interpretation of the material acquired in cycle 2 as the new data cover the critical time period when the star continues to decline from outburst and actually returns to quiescence. The utilization of these data have allowed us to refine and complete description of our new model for classical symbiotic system

Symbiotic stars

NASA Technical Reports Server (NTRS)

Kafatos, M.; Michalitsianos, A. G.

1984-01-01

The physical characteristics of symbiotic star systems are discussed, based on a review of recent observational data. A model of a symbiotic star system is presented which illustrates how a cool red-giant star is embedded in a nebula whose atoms are ionized by the energetic radiation from its hot compact companion. UV outbursts from symbiotic systems are explained by two principal models: an accretion-disk-outburst model which describes how material expelled from the tenuous envelope of the red giant forms an inwardly-spiralling disk around the hot companion, and a thermonuclear-outburst model in which the companion is specifically a white dwarf which superheats the material expelled from the red giant to the point where thermonuclear reactions occur and radiation is emitted. It is suspected that the evolutionary course of binary systems is predetermined by the initial mass and angular momentum of the gas cloud within which binary stars are born. Since red giants and Mira variables are thought to be stars with a mass of one or two solar mass, it is believed that the original cloud from which a symbiotic system is formed can consist of no more than a few solar masses of gas.

Non-symbiotic Bradyrhizobium ecotypes dominate North American forest soils.

PubMed

VanInsberghe, David; Maas, Kendra R; Cardenas, Erick; Strachan, Cameron R; Hallam, Steven J; Mohn, William W

2015-11-01

The genus Bradyrhizobium has served as a model system for studying host-microbe symbiotic interactions and nitrogen fixation due to its importance in agricultural productivity and global nitrogen cycling. In this study, we identify a bacterial group affiliated with this genus that dominates the microbial communities of coniferous forest soils from six distinct ecozones across North America. Representative isolates from this group were obtained and characterized. Using quantitative population genomics, we show that forest soil populations of Bradyrhizobium represent ecotypes incapable of nodulating legume root hairs or fixing atmospheric nitrogen. Instead, these populations appear to be free living and have a greater potential for metabolizing aromatic carbon sources than their close symbiotic relatives. In addition, we identify fine-scaled differentiation between populations inhabiting neighboring soil layers that illustrate how diversity within Bradyrhizobium is structured by habitat similarity. These findings reconcile incongruent observations about this widely studied and important group of bacteria and highlight the value of ecological context to interpretations of microbial diversity and taxonomy. These results further suggest that the influence of this genus likely extends well beyond facilitating agriculture, especially as forest ecosystems are large and integral components of the biosphere. In addition, this study demonstrates how focusing research on economically important microorganisms can bias our understanding of the natural world.

Non-symbiotic Bradyrhizobium ecotypes dominate North American forest soils

PubMed Central

VanInsberghe, David; Maas, Kendra R; Cardenas, Erick; Strachan, Cameron R; Hallam, Steven J; Mohn, William W

2015-01-01

The genus Bradyrhizobium has served as a model system for studying host–microbe symbiotic interactions and nitrogen fixation due to its importance in agricultural productivity and global nitrogen cycling. In this study, we identify a bacterial group affiliated with this genus that dominates the microbial communities of coniferous forest soils from six distinct ecozones across North America. Representative isolates from this group were obtained and characterized. Using quantitative population genomics, we show that forest soil populations of Bradyrhizobium represent ecotypes incapable of nodulating legume root hairs or fixing atmospheric nitrogen. Instead, these populations appear to be free living and have a greater potential for metabolizing aromatic carbon sources than their close symbiotic relatives. In addition, we identify fine-scaled differentiation between populations inhabiting neighboring soil layers that illustrate how diversity within Bradyrhizobium is structured by habitat similarity. These findings reconcile incongruent observations about this widely studied and important group of bacteria and highlight the value of ecological context to interpretations of microbial diversity and taxonomy. These results further suggest that the influence of this genus likely extends well beyond facilitating agriculture, especially as forest ecosystems are large and integral components of the biosphere. In addition, this study demonstrates how focusing research on economically important microorganisms can bias our understanding of the natural world. PMID:25909973

Symbiotic Stars in X-rays

NASA Technical Reports Server (NTRS)

Luna, G. J. M.; Sokoloski, J. L.; Mukai, K.; Nelson, T.

2014-01-01

Until recently, symbiotic binary systems in which a white dwarf accretes from a red giant were thought to be mainly a soft X-ray population. Here we describe the detection with the X-ray Telescope (XRT) on the Swift satellite of 9 white dwarf symbiotics that were not previously known to be X-ray sources and one that was previously detected as a supersoft X-ray source. The 9 new X-ray detections were the result of a survey of 41 symbiotic stars, and they increase the number of symbiotic stars known to be X-ray sources by approximately 30%. Swift/XRT detected all of the new X-ray sources at energies greater than 2 keV. Their X-ray spectra are consistent with thermal emission and fall naturally into three distinct groups. The first group contains those sources with a single, highly absorbed hard component, which we identify as probably coming from an accretion-disk boundary layer. The second group is composed of those sources with a single, soft X-ray spectral component, which likely arises in a region where low-velocity shocks produce X-ray emission, i.e. a colliding-wind region. The third group consists of those sources with both hard and soft X-ray spectral components. We also find that unlike in the optical, where rapid, stochastic brightness variations from the accretion disk typically are not seen, detectable UV flickering is a common property of symbiotic stars. Supporting our physical interpretation of the two X-ray spectral components, simultaneous Swift UV photometry shows that symbiotic stars with harder X-ray emission tend to have stronger UV flickering, which is usually associated with accretion through a disk. To place these new observations in the context of previous work on X-ray emission from symbiotic stars, we modified and extended the alpha/beta/gamma classification scheme for symbiotic-star X-ray spectra that was introduced by Muerset et al. based upon observations with the ROSAT satellite, to include a new sigma classification for sources with

Diversity, Roles, and Biotechnological Applications of Symbiotic Microorganisms in the Gut of Termite.

PubMed

Zhou, Jing; Duan, Jiwei; Gao, Mingkun; Wang, Ying; Wang, Xiaohua; Zhao, Kai

2018-05-12

Termites are global pests and can cause serious damage to buildings, crops, and plantation forests. The symbiotic intestinal flora plays an important role in the digestion of cellulose and nitrogen in the life of termites. Termites and their symbiotic microbes in the gut form a synergistic system. These organism work together to digest lignocellulose to make the termites grow on nitrogen deficient food. In this paper, the diversity of symbiotic microorganisms in the gut of termites, including protozoan, spirochetes, actinomycetes, fungus and bacteria, and their role in the digestion of lignocellulose and also the biotechnological applications of these symbiotic microorganisms are discussed. The high efficiency lignocellulose degradation systems of symbiotic microbes in termite gut not only provided a new way of biological energy development, but also has immense prospect in the application of cellulase enzymes. In addition, the study on the symbiotic microorganisms in the gut of termites will also provide a new method for the biological control of termites by the endophytic bacteria in the gut of termites.

Morula-like cells in photo-symbiotic clams harboring zooxanthellae.

PubMed

Nakayama, K; Nishijima, M; Maruyama, T

1998-06-01

Symbiosis is observed between zooxanthellae, symbiotic dinoflagellates, and giant clams and related clams which belong to the families Tridacnidae and Cardiidae. We have previously shown that a photo-symbiotic clam Tridacna crocea has three types of hemocytes, the eosinophilic granular hemocyte with phagocytic activity, the agranular cell with electron lucent granules, and the morula-like cell with large (ca. 2 mum in diameter) colorless granules. The function of the morula-like cell is not clear, but it has not been reported in any other bivalves except photo-symbiotic clams T. crocea and Tridacna maxima. In order to clarify whether it is specific to photo-symbiotic clams or not, we studied hemocytes in the photo-symbiotic clams Tridacna derasa (Tridacnidae), Hippopus hippopus (Tridacnidae) and Corculum cardissa (Cardiidae), and a closely related non-symbiotic clam Fulvia mutica (Cardiidae). The eosinophilic granular hemocytes and the agranular cells were found in all of the clams examined. However, the morula-like cells which were packed with many large electron dense granules (ca. 2 mum in diameter), were observed only in the photo-symbiotic clams. In F. mutica, a closely related non-symbiotic clam, this type of hemocyte was not found. Instead a hemocyte with vacuoles and a few large granules containing peroxidase activity was observed. The large granules of F. mutica varied in size from ca. 1-9 mum in diameter. Present data suggests that the presence of morula-like cells is restricted to photo-symbiotic clams and that the hemocytes associated with the morula-like cells may have some functional relationship to symbiosis with zooxanthellae.

Seasonal patterns of periphyton nitrogen fixation in calcareous wetlands

NASA Astrophysics Data System (ADS)

Liao, X.; Inglett, P.

2011-12-01

Periphyton mats are an ecologically important component of the Everglades ecosystem and plays various vital ecological functions. However, nitrogen fixation of periphyton, has received little attention throughout much of the Everglades system. The objective of this study was to characterize the seasonal pattern of periphyton N2 fixation in the Hole-in-the-Donut (HID) of Florida Everglades, where farmed marl prairie wetlands have been restored through complete soil removal (CSR) to reduce nutrient levels. Two restored areas (i.e., cleared in 2000 and 2003) and a reference (natural and unfarmed) marl prairie wetland sites were selected in the HID. Seven times of sampling were performed across the wet and dry season during the 2010 and 2011. The annual fixed nitrogen was approximately 0.4gN m-2 yr-1 in the restored sites which was higher in the reference site (~0.2gN m-2 yr-1). All the three sites showed similar seasonal patterns of N2 fixation that is higher values were observed in the wet season; but the peak value was one month later in reference sits (i.e., September) comparing to the restored areas (i.e., July). The peak of periphyton AR rates in the 2000- and 2003-restored areas appeared in July (i.e., wet season) within the range of 20-79 nmols g-1dw h-1 and 31-53nmols g-1dw h-1, respectively. In contrast, the peak of reference site was observed in September with the range of 2-5 nmols g-1dw h-1. Stable N isotopic ratios (i.e., δ15N) also varied with time but didn't show consistent seasonal pattern as nitrogen fixation. N2 fixation positively correlated with periphyton total phosphorus (TP) and negatively correlated with total nitrogen and phosphorus molar ratios (TN:TP), indicating that N2 fixation would be a indicator of nutrient limitation. In general, δ15N was negatively correlated with nitrogenase activity but the correlation became weakened in the wet season, especially in the flooded July and September, which would be explained by other environmental

Termites create spatial structure and govern ecosystem function by affecting N2 fixation in an East African savanna.

PubMed

Fox-Dobbs, Kena; Doak, Daniel F; Brody, Alison K; Palmer, Todd M

2010-05-01

The mechanisms by which even the clearest of keystone or dominant species exert community-wide effects are only partially understood in most ecosystems. This is especially true when a species or guild influences community-wide interactions via changes in the abiotic landscape. Using stable isotope analyses, we show that subterranean termites in an East African savanna strongly influence a key ecosystem process: atmospheric nitrogen fixation by a monodominant tree species and its bacterial symbionts. Specifically, we applied the 15N natural abundance method in combination with other biogeochemical analyses to assess levels of nitrogen fixation by Acacia drepanolobium and its effects on co-occurring grasses and forbs in areas near and far from mounds and where ungulates were or were not excluded. We find that termites exert far stronger effects than do herbivores on nitrogen fixation. The percentage of nitrogen derived from fixation in Acacia drepanolobium trees is higher (55-80%) away from mounds vs. near mounds (40-50%). Mound soils have higher levels of plant available nitrogen, and Acacia drepanolobium may preferentially utilize soil-based nitrogen sources in lieu of fixed nitrogen when these sources are readily available near termite mounds. At the scale of the landscape, our models predict that termite/soil derived nitrogen sources influence >50% of the Acacia drepanolobium trees in our system. Further, the spatial extent of these effects combine with the spacing of termite mounds to create highly regular patterning in nitrogen fixation rates, resulting in marked habitat heterogeneity in an otherwise uniform landscape. In summary, we show that termite-associated effects on nitrogen processes are not only stronger than those of more apparent large herbivores in the same system, but also occur in a highly regular spatial pattern, potentially adding to their importance as drivers of community and ecosystem structure.

High spatial variation in population size and symbiotic performance of Rhizobium leguminosarum bv. trifolii with white clover in New Zealand pasture soils.

PubMed

Wakelin, Steven; Tillard, Guyléne; van Ham, Robert; Ballard, Ross; Farquharson, Elizabeth; Gerard, Emily; Geurts, Rene; Brown, Matthew; Ridgway, Hayley; O'Callaghan, Maureen

2018-01-01

Biological nitrogen fixation through the legume-rhizobia symbiosis is important for sustainable pastoral production. In New Zealand, the most widespread and valuable symbiosis occurs between white clover (Trifolium repens L.) and Rhizobium leguminosarum bv. trifolii (Rlt). As variation in the population size (determined by most probable number assays; MPN) and effectiveness of N-fixation (symbiotic potential; SP) of Rlt in soils may affect white clover performance, the extent in variation in these properties was examined at three different spatial scales: (1) From 26 sites across New Zealand, (2) at farm-wide scale, and (3) within single fields. Overall, Rlt populations ranged from 95 to >1 x 108 per g soil, with variation similar at the three spatial scales assessed. For almost all samples, there was no relationship between rhizobia population size and ability of the population to fix N during legume symbiosis (SP). When compared with the commercial inoculant strain, the SP of soils ranged between 14 to 143% efficacy. The N-fixing ability of rhizobia populations varied more between samples collected from within a single hill country field (0.8 ha) than between 26 samples collected from diverse locations across New Zealand. Correlations between SP and calcium and aluminium content were found in all sites, except within a dairy farm field. Given the general lack of association between SP and MPN, and high spatial variability of SP at single field scale, provision of advice for treating legume seed with rhizobia based on field-average MPN counts needs to be carefully considered.

High spatial variation in population size and symbiotic performance of Rhizobium leguminosarum bv. trifolii with white clover in New Zealand pasture soils

PubMed Central

Tillard, Guyléne; van Ham, Robert; Ballard, Ross; Farquharson, Elizabeth; Gerard, Emily; Geurts, Rene; Brown, Matthew; Ridgway, Hayley; O’Callaghan, Maureen

2018-01-01

Biological nitrogen fixation through the legume-rhizobia symbiosis is important for sustainable pastoral production. In New Zealand, the most widespread and valuable symbiosis occurs between white clover (Trifolium repens L.) and Rhizobium leguminosarum bv. trifolii (Rlt). As variation in the population size (determined by most probable number assays; MPN) and effectiveness of N-fixation (symbiotic potential; SP) of Rlt in soils may affect white clover performance, the extent in variation in these properties was examined at three different spatial scales: (1) From 26 sites across New Zealand, (2) at farm-wide scale, and (3) within single fields. Overall, Rlt populations ranged from 95 to >1 x 108 per g soil, with variation similar at the three spatial scales assessed. For almost all samples, there was no relationship between rhizobia population size and ability of the population to fix N during legume symbiosis (SP). When compared with the commercial inoculant strain, the SP of soils ranged between 14 to 143% efficacy. The N-fixing ability of rhizobia populations varied more between samples collected from within a single hill country field (0.8 ha) than between 26 samples collected from diverse locations across New Zealand. Correlations between SP and calcium and aluminium content were found in all sites, except within a dairy farm field. Given the general lack of association between SP and MPN, and high spatial variability of SP at single field scale, provision of advice for treating legume seed with rhizobia based on field-average MPN counts needs to be carefully considered. PMID:29489845

Appraisal of the nitrogen-15 natural-abundance method for quantifying dinitrogen fixation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bremer, E.; van Kessel, C.

Several investigators have questioned the use of the {sup 15}N natural-abundance method of estimating N{sub 2} fixation because of variability in soil {delta}{sup 15}N and small differences between the {delta}{sup 15}N of soil N and atmospheric N. Investigations were conducted to compare the {sup 15}N natural-abundance and {sup 15}N-isotope-dilution methods for estimating N{sub 2} fixation of field-grown pea (Pisum sativum L.) and lentil (Lens culinaris Medik.). Spatial variability was assessed at three sites by determining the {delta}{sup 15}N of non-N{sub 2}-fixing plants. Seasonal variation in {delta}{sup 15}N for spring and winter wheat (Triticum aestivum L.), flax (Linum usitatissimum L.), barleymore » (Hordeum vulgare L.), rape (Brassica napus L.) and lentil was determined at one site. Comparisons between {delta}{sup 15}N and {sup 15}N-enriched isotope-dilution methods for estimating N{sub 2} fixation by lentil were conducted at several sites over a 3-yr period. Variability in {delta}{sup 15}N of the reference plant was site dependent: the {delta}{sup 15}N ranged from 2.8 to 9.3 at the first site, 3.4 to 8.8 at the second site, and 3.5 to 6.2 at the third site. The average {delta}{sup 15}N of four of the five non-N{sub 2}-fixing plants increased from 5.4 at 42 d after planting to 6.9 at the final harvest. The fifth non-N{sub 2}-fixing plant, rape, accumulated most of its N during the first 42 d after planting, and its {delta}{sup 15}N value declined from 8.1 at 42 d after planting to 7.3 at the final harvest. Estimates of N{sub 2} fixation were not significantly different in 18 out of 21 comparisons; in two comparisons in the {delta}{sup 15}N method and in one comparison the {sup 15}N-enriched method provided higher estimates of N{sub 2} fixation. Overall, both methods appeared to provide equally reliable estimates of N{sub 2} fixation for lentil.« less

Rates of Dinitrogen Fixation and the Abundance of Diazotrophs in North American Coastal Waters Between Cape Hatteras and Georges Bank

NASA Technical Reports Server (NTRS)

Mulholland, M.R.; Bernhardt, P. W.; Blanco-Garcia, J. L.; Mannino, A.; Hyde, K.; Mondragon, E.; Turk, K.; Moisander, P. H.; Zehr, J. P.

2012-01-01

We coupled dinitrogen (N2) fixation rate estimates with molecular biological methods to determine the activity and abundance of diazotrophs in coastal waters along the temperate North American Mid-Atlantic continental shelf during multiple seasons and cruises. Volumetric rates of N2 fixation were as high as 49.8 nmol N L(sup -1) d(sup -1) and areal rates as high as 837.9 micromol N m(sup -2) d(sup -1) in our study area. Our results suggest that N2 fixation occurs at high rates in coastal shelf waters that were previously thought to be unimportant sites of N2 fixation and so were excluded from calculations of pelagic marine N2 fixation. Unicellular N2-fixing group A cyanobacteria were the most abundant diazotrophs in the Atlantic coastal waters and their abundance was comparable to, or higher than, that measured in oceanic regimes where they were discovered. High rates of N2 fixation and the high abundance of diazotrophs along the North American Mid-Atlantic continental shelf highlight the need to revise marine N budgets to include coastal N2 fixation. Integrating areal rates of N2 fixation over the continental shelf area between Cape Hatteras and Nova Scotia, the estimated N2 fixation in this temperate shelf system is about 0.02 Tmol N yr(sup -1), the amount previously calculated for the entire North Atlantic continental shelf. Additional studies should provide spatially, temporally, and seasonally resolved rate estimates from coastal systems to better constrain N inputs via N2 fixation from the neritic zone.

Genome-wide transcriptome profiling of nitrogen fixation in Paenibacillus sp. WLY78.

PubMed

Shi, Hao-wen; Wang, Li-ying; Li, Xin-xin; Liu, Xiao-meng; Hao, Tian-yi; He, Xiao-juan; Chen, San-feng

2016-03-01

Diazotrophic (nitrogen-fixing) Gram-positive and endospore-formed Paenibacillus spp. have potential uses as a bacterial fertilizer in agriculture. The transcriptional analysis of nitrogen fixation in Paenibacillus is lacking, although regulation mechanisms of nitrogen fixation have been well studied in Gram-negative diazotrophs. Here we report a global transcriptional profiling analysis of nitrogen fixation in Paenibacillus sp. WLY78 cultured under N2-fixing condition (without O2 and NH4(+)) and non-N2-fixing condition (air and 100 mM NH4(+)). The nif (nitrogen fixation) gene operon composed of 9 genes (nifBHDKENXhesAnifV) in this bacterium was significantly up-regulated in N2-fixing condition compared to non-N2-fixing condition, indicating that nif gene transcription is strictly controlled by NH4(+) and O2. qRT-PCR confirmed that these nif genes were differently expressed. Non-nif genes specifically required in nitrogen fixation, such as mod, feoAB and cys encoding transporters of Mo, Fe and S atoms, were coordinately transcribed with nif genes in N2-fixing condition. The transcript abundance of suf operon specific for synthesis of Fe-S cluster was up-regulated in N2-fixing condition, suggesting that Sul system, which takes place of nifS and nifU, plays important role in the synthesis of nitrogenase. We discover potential specific electron transporters which might provide electron from Fe protein to MoFe protein of nitrogenase. The glnR whose predicted protein might mediate nif transcription regulation by NH4(+) is significantly up-regulated in N2-fixing condition. The transcription levels of nitrogen metabolism and anaerobic respiration were also analyzed. The nif gene operon (nifBHDKENXhesAnifV) in Paenibacillus sp. WLY78 is significantly up-regulated in N2-fixing condition compared to non-N2-fixing condition. Non-nif genes specifically required in nitrogen fixation were also significantly up-regulated in N2-fixing condition. Fur and Fnr which are involved in

Nitrogen fixation dynamics of two diazotrophic communities in Mono Lake, California

USGS Publications Warehouse

Oremland, R.S.

1990-01-01

Two types of diazotrophic microbial communities were found in the littoral zone of alkaline hypersaline Mono Lake, California. One consisted of anaerobic bacteria inhabiting the flocculent surface layers of sediments. Nitrogen fixation (acetylene reduction) by flocculent surface layers occurred under anaerobic conditions, was not stimulated by light or by additions of organic substrates, and was inhibited by O2, nitrate, and ammonia. The second community consisted of a ball-shaped association of a filamentous chlorophyte (Ctenocladus circinnatus) with diazotrophic, nonheterocystous cyanobacteria, as well as anaerobic bacteria (Ctenocladus balls). Nitrogen fixation by Ctenocladus balls was usually, but not always, stimulated by light. Rates of anaerobic dark fixation equaled those in the light under air. Fixation in the light was stimulated by 3-(3,4-dichlorophenyl)-1,1-dimethylurea and by propanil [N-(3,4-dichlorophenyl)propanamide]. 3-(3,4-Dichlorophenyl)-1,1-dimethyl urea-elicited nitrogenase activity was inhibited by ammonia (96%) and nitrate (65%). Fixation was greatest when Ctenocladus balls were incubated anaerobically in the light with sulfide. Dark anaerobic fixation was not stimulated by organic substrates in short-term (4-h) incubations, but was in long-term (67-h) ones. Areal estimates of benthic N2 fixation were measured seasonally, using chambers. Highest rates (~29.3 ??mol of C2H4 m-2 h-1) occurred under normal diel regimens of light and dark. These estimates indicate that benthic N2 fixation has the potential to be a significant nitrogen source in Mono Lake.

Iron availability limits the ocean nitrogen inventory stabilizing feedbacks between marine denitrification and nitrogen fixation

NASA Astrophysics Data System (ADS)

Moore, J. Keith; Doney, Scott C.

2007-06-01

Recent upward revisions in key sink/source terms for fixed nitrogen (N) in the oceans imply a short residence time and strong negative feedbacks involving denitrification and N fixation to prevent large swings in the ocean N inventory over timescales of a few centuries. We tested the strength of these feedbacks in a global biogeochemical elemental cycling (BEC) ocean model that includes water column denitrification and an explicit N fixing phytoplankton group. In the northern Indian Ocean and over longer timescales in the tropical Atlantic, we find strong stabilizing feedbacks that minimize changes in marine N inventory over timescales of ˜30-200 years. In these regions high atmospheric dust/iron inputs lead to phosphorus limitation of diazotrophs, and thus a tight link between N fixation and surface water N/P ratios. Maintenance of the oxygen minimum zones in these basins depends on N fixation driven export. The stabilizing feedbacks in other regions are significant but weaker owing to iron limitation of the diazotrophs. Thus Fe limitation appears to restrict the ability of N fixation to compensate for changes in denitrification in the current climate, perhaps leading the oceans to lose fixed N. We suggest that iron is the ultimate limiting nutrient leading to nitrogen being the proximate limiting nutrient over wide regions today. Iron stress was at least partially alleviated during more dusty, glacial times, leading to a higher marine N inventory, increased export production, and perhaps widespread phosphorus limitation of the phytoplankton community. The increased efficiency of the biological pump would have contributed to the glacial drawdown in atmospheric CO2.

Biomechanical characterization of double-bundle femoral press-fit fixation techniques.

PubMed

Ettinger, M; Haasper, C; Hankemeier, S; Hurschler, C; Breitmeier, D; Krettek, C; Jagodzinski, M

2011-03-01

Press-fit fixation of patellar tendon bone anterior cruciate ligament autografts is an interesting technique because no hardware is necessary. To date, no biomechanical data exist describing an implant-free double-bundle press-fit procedure. The purpose of this study was to characterize the biomechanical properties of three double-bundle press-fit fixations. In a controlled laboratory study, the patellar-, quadriceps- and hamstring tendons of 10 human cadavers (age: 49.2 ± 18.5 years) were used. An inside out press-fit fixation with a knot in the semitendinosus and gracilis tendons (SG) combined with an additional bone block, with two quadriceps tendon bone block grafts (QU) was compared with press-fit fixation of two bone patellar tendon bone block (PT) grafts in 30 porcine femora. Constructs were cyclically stretched and then loaded until failure. Maximum load to failure, stiffness and elongation during failure testing and cyclical loading were investigated. The maximum load to failure was 703 ± 136 N for SG fixation, 632 ± 130 N for QU and 656 ± 127 N for PT fixation. Stiffness of the constructs averaged 138 ± 26 N/mm for SG, 159 ± 74 N/mm for QU, and 154 ± 50 N/mm for PT fixation. Elongation during initial cyclical loading was 1.2 ± 1.4 mm for SG, 2.0 ± 1.4 mm for QU, and 1.0 ± 0.6 mm for PT (significantly larger for PT and QU between the first 5 cycles compared with cycles 15-20th, P < 0.01). All investigated double-bundle fixation techniques were equal in terms of maximum load to failure, stiffness, and elongation. Unlike with single-bundle press-fit fixation techniques that have been published, no difference was observed between pure tendon combined with an additional bone block and tendon bone grafts. All techniques exhibited larger elongation during initial cyclical loading. All three press-fit fixation techniques that were investigated exhibit comparable biomechanical properties. Preconditioning of the constructs

Heterotrophic organisms dominate nitrogen fixation in the South Pacific Gyre

PubMed Central

Halm, Hannah; Lam, Phyllis; Ferdelman, Timothy G; Lavik, Gaute; Dittmar, Thorsten; LaRoche, Julie; D'Hondt, Steven; Kuypers, Marcel MM

2012-01-01

Oceanic subtropical gyres are considered biological deserts because of the extremely low availability of nutrients and thus minimum productivities. The major source of nutrient nitrogen in these ecosystems is N2-fixation. The South Pacific Gyre (SPG) is the largest ocean gyre in the world, but measurements of N2-fixation therein, or identification of microorganisms involved, are scarce. In the 2006/2007 austral summer, we investigated nitrogen and carbon assimilation at 11 stations throughout the SPG. In the ultra-oligotrophic waters of the SPG, the chlorophyll maxima reached as deep as 200 m. Surface primary production seemed limited by nitrogen, as dissolved inorganic carbon uptake was stimulated upon additions of 15N-labeled ammonium and leucine in our incubation experiments. N2-fixation was detectable throughout the upper 200 m at most stations, with rates ranging from 0.001 to 0.19 nM N h−1. N2-fixation in the SPG may account for the production of 8–20% of global oceanic new nitrogen. Interestingly, comparable 15N2-fixation rates were measured under light and dark conditions. Meanwhile, phylogenetic analyses for the functional gene biomarker nifH and its transcripts could not detect any common photoautotrophic diazotrophs, such as, Trichodesmium, but a prevalence of γ-proteobacteria and the unicellular photoheterotrophic Group A cyanobacteria. The dominance of these likely heterotrophic diazotrophs was further verified by quantitative PCR. Hence, our combined results show that the ultra-oligotrophic SPG harbors a hitherto unknown heterotrophic diazotrophic community, clearly distinct from other oceanic gyres previously visited. PMID:22170429

Microgravity Effects on the Early Events of Biological Nitrogen Fixation in Medicago Truncatula: Results from the SyNRGE Experiment

NASA Astrophysics Data System (ADS)

Stutte, Gary W.; Roberts, Michael S.

2013-02-01

SyNRGE (Symbiotic Nodulation in a Reduced Gravity Environment) was a sortie mission on STS-135 in the Biological Research in Canisters (BRIC) hardware to study the effect of μg on a plant-microbe symbiosis resulting in biological nitrogen fixation. Medicago truncatula, a model species for the legume family, was inoculated with its bacterial symbiont, Sinorhizobium meliloti, to observe early biomolecular events associated with infection and nodulation in Petri Dish Fixation Units (PDFU’s). Two sets of experiments were conducted in orbit and in 24-hour delayed ground controls. Experiments were designed to determine if S. meliloti would infect M. truncatula and initiate biomolecular changes associated with nodule formation and if the μg environment altered the host plant and/or bacteria to induce nodule formation upon return to 1g. Initial analysis results demonstrate that the legumes and bacteria cultivated in μg have potential to develop a symbiotic interaction, but suggest that μg alters their ability to form nodules upon return to 1g. (Research supported by NASA ESMD/ Advance Capabilities Division grant NNX10AR09A)

Estimation of biological nitrogen fixation by black locust in short-rotation forests using natural 15N abundance method

NASA Astrophysics Data System (ADS)

Veste, M.; Böhm, C.; Quinckenstein, A.; Freese, D.

2012-04-01

The importance of short rotation forests and agroforestry systems for woody biomass production for bioenergy will increase in Central Europe within the next decades. In this context, black locust (Robinia pseudoacacia) has a high growth potential especially at marginal, drought-susceptible sites such as occur in Brandenburg State (Eastern Germany). As a pioneer tree species black locust grows under a wide range of site conditions. The native range of black locust in Northern America is classified by a humid to sub-humid climate with a mean annual precipitation of 1020 to 1830 mm. In Central and Eastern Europe, this species is cultivated in a more continental climate with an annual precipitation often below 600 mm. Therefore, black locust is known to be relatively drought tolerant compared to other temperate, deciduous tree species. Because of its N2-fixation ability black locust plays generally an important role for the improvement of soil fertility. This effect is of particular interest at marginal sites in the post-mining landscapes. In order to estimate the N2-fixation potential of black locust at marginal sites leaf samples were taken from black locust trees in short rotation plantations planted between 1995 and 2007 in post-mining sites south of Cottbus (Brandenburg, NE Germany). The variation of the natural 15N abundance was measured to evaluate the biological nitrogen fixation. The nitrogen derived from the atmosphere can be calculated using a two-pool model from the quotient of the natural 15N abundances of the N2-fixing plant and the plant available soil N. Because representatively determining the plant available soil N is difficult, a non-N2-fixing reference plant growing at the same site with a similar root system and temporal N uptake pattern to the N2-fixing plant is often used. In our case we used red oak (Quercus rubra) as a reference. The average nitrogen content in the leaves of black locust ranged from 3.1% (C/N 14.8) in 15 years old trees to 3

Magnesium Fertilizer-Induced Increase of Symbiotic Microorganisms Improves Forage Growth and Quality.

PubMed

Chen, Jihui; Li, Yanpeng; Wen, Shilin; Rosanoff, Andrea; Yang, Gaowen; Sun, Xiao

2017-04-26

Magnesium (Mg) plays important roles in photosynthesis and protein synthesis; however, latent Mg deficiencies are common phenomena that can influence food quality. Nevertheless, the effects of Mg fertilizer additions on plant carbon (C):nitrogen (N):phosphorus (P) stoichiometry, an important index of food quality, are unclear and the underlying mechanisms unexplored. We conducted a greenhouse experiment using low-Mg in situ soil without and with a gradient of Mg additions to investigate the effect of Mg fertilizer on growth and stoichiometry of maize and soybean and also measure these plants' main symbiotic microorganisms: arbuscular mycorrhizal fungi (AMF) and rhizobium, respectively. Our results showed that Mg addition significantly improved both plant species' growth and also increased N and P concentrations in soybean and maize, respectively, resulting in low C:N ratio and high N:P ratio in soybean and low C:P and N:P ratios in maize. These results presumably stemmed from the increase of nutrients supplied by activation-enhanced plant symbiotic microorganisms, an explanation supported by statistically significant positive correlations between plant stoichiometry and plants' symbiotic microorganisms' increased growth with Mg addition. We conclude that Mg supply can improve plant growth and alter plant stoichiometry via enhanced activity of plant symbiotic microorganisms. Possible mechanisms underlying this positive plant-soil feedback include an enhanced photosynthetic product flow to roots caused by adequate Mg supply.

Nitrogen fixation apparatus

DOEpatents

Chen, Hao-Lin

1984-01-01

A method and apparatus for achieving nitrogen fixation includes a volumetric electric discharge chamber. The volumetric discharge chamber provides an even distribution of an electron beam, and enables the chamber to be maintained at a controlled energy to pressure (E/p) ratio. An E/p ratio of from 5 to 15 kV/atm of O.sub.2 /cm promotes the formation of vibrationally excited N.sub.2. Atomic oxygen interacts with vibrationally excited N.sub.2 at a much quicker rate than unexcited N.sub.2, greatly improving the rate at which NO is formed.

THE THERAPEUTIC USE OF SYMBIOTICS

PubMed Central

FLESCH, Aline Gamarra Taborda; POZIOMYCK, Aline Kirjner; DAMIN, Daniel De Carvalho

2014-01-01

Introduction Functional foods are health promoters and their use is associated with reduced risk of chronic degenerative and non-transmissible diseases. Examples are symbiotic. The association of one (or more) probiotic with a one (or more) prebiotic is called symbiotic, being the prebiotics complementary and probiotics synergistic, thus presenting a multiplicative factor on their individual actions. Objective To assess the evidences on the benefits of the use of symbiotics in the treatment of clinical and surgical situations. Methods The headings symbiotic, probiotic and prebiotic were searched in Pubmed/Medline in the last 15 years, and were selected 25 articles, used for database. Results The use of symbiotic may promote an increase in the number of bifidobacteria, glycemic control, reduction of blood cholesterol, balancing the intestinal flora which aids in reducing constipation and/or diarrhea, improves intestinal permeability and stimulation of the immune system. Clinical indications for these products has been expanded, in order to maximize the individual's physiological functions to provide greater. So, with the high interest in the clinical and nutritional control of disease, many studies have been conducted demonstrating the effectiveness of using symbiotic in improving and/or preventing various and/or symptoms of gastrointestinal diseases. Conclusion Symbiotic behave differently and positively in various pathological situations. PMID:25184774

Mesh fixation in laparoscopic incisional hernia repair: glue fixation provides attachment strength similar to absorbable tacks but differs substantially in different meshes.

PubMed

Rieder, Erwin; Stoiber, Martin; Scheikl, Verena; Poglitsch, Marcus; Dal Borgo, Andrea; Prager, Gerhard; Schima, Heinrich

2011-01-01

Laparoscopic ventral hernia repair has gained popularity among minimally invasive surgeons. However, mesh fixation remains a matter of discussion. This study was designed to compare noninvasive fibrin-glue attachment with tack fixation of meshes developed primarily for intra-abdominal use. It was hypothesized that particular mesh structures would substantially influence detachment force. For initial evaluation, specimens of laminated polypropylene/polydioxanone meshes were anchored to porcine abdominal walls by either helical titanium tacks or absorbable tacks in vitro. A universal tensile-testing machine was used to measure tangential detachment forces (TF). For subsequent experiments of glue fixation, polypropylene/polydioxanone mesh and 4 additional meshes with diverse particular mesh structure, ie, polyvinylidene fluoride/polypropylene mesh, a titanium-coated polypropylene mesh, a polyester mesh bonded with a resorbable collagen, and a macroporous condensed PTFE mesh were evaluated. TF tests revealed that fibrin-glue attachment was not substantially different from that achieved with absorbable tacks (median TF 7.8 Newton [N], range 1.3 to 15.8 N), but only when certain open porous meshes (polyvinylidene fluoride/polypropylene mesh: median 6.2 N, range 3.4 to 10.3 N; titanium-coated polypropylene mesh: median 5.2 N, range 2.1 to 11.7 N) were used. Meshes coated by an anti-adhesive barrier (polypropylene/polydioxanone mesh: median 3.1 N, range 1.7 to 5.8 N; polyester mesh bonded with a resorbable collagen: median 1.3 N, range 0.5 to 1.9 N), or the condensed PTFE mesh (median 3.1 N, range 2.1 to 7.0 N) provided a significantly lower TF (p < 0.01). Fibrin glue appears to be an appealing noninvasive option for mesh fixation in laparoscopic ventral hernia repair, but only if appropriate meshes are used. Glue can also serve as an adjunct to mechanical fixation to reduce the number of invasive tacks. Copyright © 2010 American College of Surgeons. Published by Elsevier

Seasonal patterns of climate controls over nitrogen fixation by Alnus viridis subsp

Treesearch

Jennifer S. Mitchell; Roger W. Ruess

2009-01-01

Patterns of and controls over N2 fixation by green alder were studied in post-fire, mid-succession, and white spruce upland forests in interior Alaska, focusing on the hypothesis that ecosystem-level nitrogen (N) inputs decrease with successional development. N2-fixation rates tracked plant phenology during the 1997 (...

Population control in symbiotic corals

DOE Office of Scientific and Technical Information (OSTI.GOV)

Falkowski, P.G.; Dubinsky, Z.; Muscatine, L.

1993-10-01

Stability in symbiotic association requires control of population growth between symbionts. The population density of zooxanthellae per unit surface area of most symbiotic corals is remarkably consistant. How is the population density of zooxanthellae maintained and what happens to the symbiotic association if the balance between algae and host is perturbed. The answers to these question, examined in this paper, provide a framework for understanding how the size of the component populations is controlled in symbiotic associations. The topic areas covered include the following: carbon economy in a symbiotic coral; effects of nutrient enrichment; the chemostat model of population control;more » the effects of exposure to ammonium levels. Ammonium ions and organic materials are the factors which maintain the density of zooxanthellae. 32 refs., 5 figs.« less

The Role of Nitrogen Fixation in Cyanobacterial Bloom Toxicity in a Temperate, Eutrophic Lake

PubMed Central

Beversdorf, Lucas J.; Miller, Todd R.; McMahon, Katherine D.

2013-01-01

Toxic cyanobacterial blooms threaten freshwaters worldwide but have proven difficult to predict because the mechanisms of bloom formation and toxin production are unknown, especially on weekly time scales. Water quality management continues to focus on aggregated metrics, such as chlorophyll and total nutrients, which may not be sufficient to explain complex community changes and functions such as toxin production. For example, nitrogen (N) speciation and cycling play an important role, on daily time scales, in shaping cyanobacterial communities because declining N has been shown to select for N fixers. In addition, subsequent N pulses from N2 fixation may stimulate and sustain toxic cyanobacterial growth. Herein, we describe how rapid early summer declines in N followed by bursts of N fixation have shaped cyanobacterial communities in a eutrophic lake (Lake Mendota, Wisconsin, USA), possibly driving toxic Microcystis blooms throughout the growing season. On weekly time scales in 2010 and 2011, we monitored the cyanobacterial community in a eutrophic lake using the phycocyanin intergenic spacer (PC-IGS) region to determine population dynamics. In parallel, we measured microcystin concentrations, N2 fixation rates, and potential environmental drivers that contribute to structuring the community. In both years, cyanobacterial community change was strongly correlated with dissolved inorganic nitrogen (DIN) concentrations, and Aphanizomenon and Microcystis alternated dominance throughout the pre-toxic, toxic, and post-toxic phases of the lake. Microcystin concentrations increased a few days after the first significant N2 fixation rates were observed. Then, following large early summer N2 fixation events, Microcystis increased and became most abundant. Maximum microcystin concentrations coincided with Microcystis dominance. In both years, DIN concentrations dropped again in late summer, and N2 fixation rates and Aphanizomenon abundance increased before the lake mixed in

Mycorrhizal Symbiotic Efficiency on C3 and C4 Plants under Salinity Stress - A Meta-Analysis.

PubMed

Chandrasekaran, Murugesan; Kim, Kiyoon; Krishnamoorthy, Ramasamy; Walitang, Denver; Sundaram, Subbiah; Joe, Manoharan M; Selvakumar, Gopal; Hu, Shuijin; Oh, Sang-Hyon; Sa, Tongmin

2016-01-01

A wide range of C3 and C4 plant species could acclimatize and grow under the impact of salinity stress. Symbiotic relationship between plant roots and arbuscular mycorrhizal fungi (AMF) are widespread and are well known to ameliorate the influence of salinity stress on agro-ecosystem. In the present study, we sought to understand the phenomenon of variability on AMF symbiotic relationship on saline stress amelioration in C3 and C4 plants. Thus, the objective was to compare varied mycorrhizal symbiotic relationship between C3 and C4 plants in saline conditions. To accomplish the above mentioned objective, we conducted a random effects models meta-analysis across 60 published studies. An effect size was calculated as the difference in mycorrhizal responses between the AMF inoculated plants and its corresponding control under saline conditions. Responses were compared between (i) identity of AMF species and AMF inoculation, (ii) identity of host plants (C3 vs. C4) and plant functional groups, (iii) soil texture and level of salinity and (iv) experimental condition (greenhouse vs. field). Results indicate that both C3 and C4 plants under saline condition responded positively to AMF inoculation, thereby overcoming the predicted effects of symbiotic efficiency. Although C3 and C4 plants showed positive effects under low (EC < 4 ds/m) and high (>8 ds/m) saline conditions, C3 plants showed significant effects for mycorrhizal inoculation over C4 plants. Among the plant types, C4 annual and perennial plants, C4 herbs and C4 dicot had a significant effect over other counterparts. Between single and mixed AMF inoculants, single inoculants Rhizophagus irregularis had a positive effect on C3 plants whereas Funneliformis mosseae had a positive effect on C4 plants than other species. In all of the observed studies, mycorrhizal inoculation showed positive effects on shoot, root and total biomass, and in nitrogen, phosphorous and potassium (K) uptake. However, it showed negative

Distribution and rates of nitrogen fixation in the western tropical South Pacific Ocean constrained by nitrogen isotope budgets

NASA Astrophysics Data System (ADS)

Knapp, Angela N.; McCabe, Kelly M.; Grosso, Olivier; Leblond, Nathalie; Moutin, Thierry; Bonnet, Sophie

2018-05-01

Constraining the rates and spatial distribution of dinitrogen (N2) fixation fluxes to the ocean informs our understanding of the environmental sensitivities of N2 fixation as well as the timescale over which the fluxes of nitrogen (N) to and from the ocean may respond to each other. Here we quantify rates of N2 fixation as well as its contribution to export production along a zonal transect in the western tropical South Pacific (WTSP) Ocean using N isotope (δ15N) budgets. Comparing measurements of water column nitrate + nitrite δ15N with the δ15N of sinking particulate N at a western, central, and eastern station, these δ15N budgets indicate high, modest, and low rates of N2 fixation at the respective stations. The results also imply that N2 fixation supports exceptionally high, i.e. ≥ 50 %, of export production at the western and central stations, which are also proximal to the largest iron sources. These geochemically based rates of N2 fixation are equal to or greater than those previously reported in the tropical North Atlantic, indicating that the WTSP Ocean has the capacity to support globally significant rates of N2 fixation, which may compensate for N removal in the oxygen-deficient zones of the eastern tropical Pacific.

A Monte Carlo Study of Flux Ratios of Raman Scattered O VI Features at 6825 and 7082 Å in Symbiotic Stars

NASA Astrophysics Data System (ADS)

Lee, Young-Min; Lee, Dae-Sub; Chang, Seok-Jun; Heo, Jeong-Eun; Lee, Hee-Won; Hwang, Narae; Park, Byeong-Gon; Lee, Ho-Gyu

2016-12-01

Symbiotic stars are regarded as wide binary systems consisting of a hot white dwarf and a mass losing giant. They exhibit unique spectral features at 6825 and 7082 Å, which are formed via Raman scattering of O VI λλ 1032 and 1038 with atomic hydrogen. We adopt a Monte Carlo technique to generate the same number of O VI λ1032 and λ1038 line photons and compute the flux ratio F(6825)/F(7082) of these Raman scattered O VI features formed in neutral regions with a simple geometric shape as a function of H I column density N H I . In cylindrical and spherical neutral regions with the O VI source embedded inside, the flux ratio F(6825)/F(7082) shows an overall decrease from 3 to 1 as N H I increases in the range {10}22{--24} {{cm}}-2. In cases of slab geometry and other geometries with the O VI source outside the H I region, Rayleigh escape operates to lower the flux ratio considerably. For moderate values of {N}{{H}{{I}}}˜ {10}23 {{cm}}-2 the flux ratio behaves in a complicated way to exhibit a broad bump with a peak value of 3.5 in the case of a sphere geometry. We find that the ratio of Raman conversion efficiencies of O VI λλ 1032, 1038 ranges from 0.8 to 3.5. Our high resolution spectra of “D” type HM Sge and “S” type AG Dra obtained with the Canada-France-Hawaii Telescope show that the flux ratio F(6825)/F(7082) of AG Dra is significantly smaller than that of HM Sge, implying that “S” type symbiotics are characterized by higher N H I than “D” type symbiotics.

Themes from variation: probing the commonalities of symbiotic associations.

PubMed

Saffo, Mary Beth

2002-04-01

Research on symbiosis (including antagonistic and mutualistic associations) wrestles, directly or indirectly, with the paradox: why are symbiotic associations so prevalent in the biosphere in the face of ubiquitous immune or antibiotic defenses among organisms? The symposium "Living Together: the Dynamics of Symbiotic Interactions" considered several questions: 1. How do symbiotic species partners come together? Do symbioses share similar patterns of signal recognition and response? 2. What roles do nutrients and metabolites play in symbiotic interactions, and how are metabolic exchanges affected by environmental changes? 3. In what ways do the dynamics of multispecies symbioses differ from two-species associations? 4. How do antagonistic (parasitic, pathogenic) symbioses differ from mutualistic ones? In what ways do changes in the biotic and physical environment affect the evolutionary balance of symbiotic associations? 5. What are the coevolutionary patterns of symbiotic associations? 6. Which research techniques, and strategies of experimental design, might be useful across a broad range of symbiotic associations?Two themes emerged from the symposium. First, all the participants have incorporated multiple techniques and perspectives into their work, approaches which facilitate the understanding of symbiotic dynamics at several levels of biological organization. Secondly, many of the papers addressed genetic and environmental variation in symbiotic interactions. Such approaches are useful tools for analysis of the mechanics of interspecies interactions and for characterization of the most important factors which influence them. They provide us with the tools to evaluate symbioses in a world of complexity, variation and change.

Biomechanical comparison of blade plate and intramedullary nail fixation for tibiocalcaneal arthrodesis.

PubMed

Lee, Arthur T; Sundberg, Eric B; Lindsey, Derek P; Harris, Alex H S; Chou, Loretta B

2010-02-01

Tibiocalcaneal arthrodesis is an uncommon salvage procedure used for complex problems of the ankle and hindfoot. A biomechanical evaluation of the fixation constructs of this procedure has not been studied previously. The purpose of this study was to compare intramedullary nail to blade plate fixation in a deformity model in fatigue endurance testing and load to failure. Nine matched pairs of fresh frozen cadaveric legs underwent talectomy followed by fixation with a blade plate and 6.5-mm fully threaded cancellous screw or an ankle arthrodesis intramedullary nail. The specimens were loaded to 270 N at a rate of 3 Hz for a total of 250,000 cycles, followed by loading to failure. Intramedullary nail fixation demonstrated greater mean stiffness throughout the fatigue endurance testing, from cycles 10 through 250,000 (blade plate versus intramedullary nail; cycle 10, 93 +/- 34 N/mm versus 117 +/- 40 N/mm (t = 2.33, p = 0.04); cycle 100, 89 +/- 34 N/mm versus 118 +/- 42 N/mm (t = 3.16, p = 0.01); cycle 1000, 86 +/- 32 N/mm versus 120 +/- 45 N/mm (t = 3.52, p = 0.01); cycle 10,000, 83 +/- 36 N/mm versus 128 +/- 50 N/mm (t = 3.80, p = 0.01); cycle 100,000, 82 +/- 34 N/mm versus 126 +/- 52 N/mm (t = 3.70, p = 0.01); cycle 250,000, 80 +/- 31 N/mm versus 125 +/- 49 N/mm (t = 4.2, p = 0.003). There was no statistically significant difference between the intramedullary nail and blade plate fixation in cycle one or in load to failure; cycle 10, blade plate 70 +/- 38 N/mm and intramedullary nail 67 +/- 20 N/mm (t = 0.60, p = 0.56); load to failure, blade plate 808 +/- 193 N, IMN 1074 +/- 290 N) (p = 0.15). Intramedullary nail fixation was biomechanically superior to blade plate and screw fixation in a tibiocalcaneal arthrodesis construct. The ankle arthrodesis intramedullary nail provides greater stiffness for fixation in tibiocalcaneal arthrodesis, which may improve healing.

Dependence of wheat and rice respiration on tissue nitrogen and the corresponding net carbon fixation efficiency under different rates of nitrogen application

NASA Astrophysics Data System (ADS)

Sun, Wenjuan; Huang, Yao; Chen, Shutao; Zou, Jianwen; Zheng, Xunhua

2007-02-01

To quantitatively address the role of tissue N in crop respiration under various agricultural practices, and to consequently evaluate the impact of synthetic fertilizer N application on biomass production and respiration, and hence net carbon fixation efficiency ( E ncf), pot and field experiments were carried out for an annual rotation of a rice-wheat cropping system from 2001 to 2003. The treatments of the pot experiments included fertilizer N application, sowing date and planting density. Different rates of N application were tested in the field experiments. Static opaque chambers were used for sampling the gas. The respiration as CO2 emission was detected by a gas chromatograph. A successive biomass clipping method was employed to determine the crop autotrophic respiration coefficient ( R a). Results from the pot experiments revealed a linear relationship between R a and tissue N content as R a = 4.74N-1.45 ( R 2 = 0.85, P < 0.001). Measurements and calculations from the field experiments indicated that fertilizer N application promoted not only biomass production but also increased the respiration of crops. A further investigation showed that the increase of carbon loss in terms of respiration owing to fertilizer N application exceeded that of net carbon gain in terms of aboveground biomass when fertilizer N was applied over a certain rate. Consequently, the E ncf declined as the N application rate increased.

Postoperative symbiotic in patients with head and neck cancer: a double-blind randomised trial.

PubMed

Lages, Priscilla C; Generoso, Simone V; Correia, Maria Isabel T D

2018-01-01

Studies on the 'gut origin of sepsis' have suggested that stressful insults, such as surgery, can affect intestinal permeability, leading to bacterial translocation. Symbiotics have been reported to be able to improve gut permeability and modulate the immunologic system, thereby decreasing postoperative complications. Therefore we aimed to evaluate the postoperative use of symbiotics in head and neck cancer surgical patients for intestinal function and permeability, as well as the postoperative outcomes. Patients were double-blind randomised into the symbiotic (n 18) or the control group (n 18). Samples were administered twice a day by nasoenteric tube, starting on the 1st postoperative day until the 5th to 7th day, and comprised 109 colony-forming units/ml each of Lactobacillus paracasei, L. rhamnosus, L. acidophilus, and Bifidobacterium lactis plus 6 g of fructo-oligosaccharides, or a placebo (6 g of maltodextrin). Intestinal function (day of first evacuation, total stool episodes, stool consistency, gastrointestinal tract symptoms and gut permeability by diamine oxidase (DAO) enzyme) and postoperative complications (infectious and non-infectious) were assessed. Results of comparison of the pre- and postoperative periods showed that the groups were similar for all outcome variables. In all, twelve patients had complications in the symbiotic group v. nine in the control group (P>0·05), and the preoperative-postoperative DAO activity ranged from 28·5 (sd 15·4) to 32·7 (sd 11·0) ng/ml in the symbiotic group and 35·2 (sd 17·7) to 34·1 (sd 12·0) ng/ml in the control group (P>0·05). In conclusion, postoperative symbiotics did not impact on intestinal function and postoperative outcomes of head and neck surgical patients.

Carbon dioxide fixation in the metabolism of propylene and propylene oxide by Xanthobacter strain Py2.

PubMed Central

Small, F J; Ensign, S A

1995-01-01

Evidence for a requirement for CO2 in the productive metabolism of aliphatic alkenes and epoxides by the propylene-oxidizing bacterium Xanthobacter strain Py2 is presented. In the absence of CO2, whole-cell suspensions of propylene-grown cells catalyzed the isomerization of propylene oxide (epoxypropane) to acetone. In the presence of CO2, no acetone was produced. Acetone was not metabolized by suspensions of propylene-grown cells, in either the absence or presence of CO2. The degradation of propylene and propylene oxide by propylene-grown cells supported the fixation of 14CO2 into cell material, and the time course of 14C fixation correlated with the time course of propylene and propylene oxide degradation. The degradation of glucose and propionaldehyde by propylene-grown or glucose-grown cells did not support significant 14CO2 fixation. With propylene oxide as the substrate, the concentration dependence of 14CO2 fixation exhibited saturation kinetics, and at saturation, 0.9 mol of CO2 was fixed per mol of propylene oxide consumed. Cultures grown with propylene in a nitrogen-deficient medium supplemented with NaH13CO3 specifically incorporated 13C label into the C-1 (major labeled position) and C-3 (minor labeled position) carbon atoms of the endogenous storage compound poly-beta-hydroxybutyrate. No specific label incorporation was observed when cells were cultured with glucose or n-propanol as a carbon source. The depletion of CO2 from cultures grown with propylene, but not glucose or n-propanol, inhibited bacterial growth. We propose that propylene oxide metabolism in Xanthobacter strain Py2 proceeds by terminal carboxylation of an isomerization intermediate, which, in the absence of CO2, is released as acetone. PMID:7592382

The contribution of nitrogen fixation by cyanobacteria to particulate organic nitrogen in a constructed wetland

NASA Astrophysics Data System (ADS)

Zhang, X.; PAN, X.; MA, M.; Li, W.; Cui, L.

2016-12-01

N-fixing cyanobacteria can create extra nitrogen for aquatic ecosystems. Previous studies reported inconsistence patterns of the contribution of biological nitrogen fixation to the nitrogen pools in aquatic ecosystems. However, there were few studies concerning the effect of fixed nitrogen by cyanobacteria on the nitrogen removal efficiency in constructed wetlands. This study was performed at the Beijing Wildlife Rescue and Rehabilitation Centre, where a constructed lake for the habitation of waterfowls and a constructed wetland for purifying sewage from the lake are located. The composition of phytoplankton communities, the concentrations of particulate organic nitrogen (PON) and nitrogen fixation rates (Rn) in the constructed lake and the constructed wetland were compared throughout a growing season. We counted the densities of genus Anabaena and Microcystis cells, and explored their relationships with PON and Rn in water. The proportions of PON from various sources, including the ambient N2, waterfowl faeces, wetland sediments and the nitrates, were calculated by the natural abundance of 15N with the IsoSource software. The result revealed that the constructed lake was alternately dominated by Anabaena and Microcystis throughout the growing season, and the Rn was positively correlated with PON and the cell density of Anabaena (P < 0.05). This implied that the fixed nitrogen by N-fixing Anabaena might be utilized by non-N-fixing Microcystis, maintaining the fixed nitrogen with PON form. The ambient N2 composed 0.5 82% and 50.0 84.7% to the PON in the constructed lake and wetland respectively during the growing season. The proportions of PON from N2 increased to more than 80% when the Rn reached the highest in September. The result demonstrated that the nitrogen fixed by Anabaena might be utilized by non-N-fixing Microcystis which formed water blooms in summer. Therefore, the decline of the removal efficiency of PON in the constructed wetland in summer might

Ecosystem nitrogen fixation throughout the snow-free period in subarctic tundra: effects of willow and birch litter addition and warming.

PubMed

Rousk, Kathrin; Michelsen, Anders

2017-04-01

Nitrogen (N) fixation in moss-associated cyanobacteria is one of the main sources of available N for N-limited ecosystems such as subarctic tundra. Yet, N 2 fixation in mosses is strongly influenced by soil moisture and temperature. Thus, temporal scaling up of low-frequency in situ measurements to several weeks, months or even the entire growing season without taking into account changes in abiotic conditions cannot capture the variation in moss-associated N 2 fixation. We therefore aimed to estimate moss-associated N 2 fixation throughout the snow-free period in subarctic tundra in field experiments simulating climate change: willow (Salix myrsinifolia) and birch (Betula pubescens spp. tortuosa) litter addition, and warming. To achieve this, we established relationships between measured in situ N 2 fixation rates and soil moisture and soil temperature and used high-resolution measurements of soil moisture and soil temperature (hourly from May to October) to model N 2 fixation. The modelled N 2 fixation rates were highest in the warmed (2.8 ± 0.3 kg N ha -1 ) and birch litter addition plots (2.8 ± 0.2 kg N ha -1 ), and lowest in the plots receiving willow litter (1.6 ± 0.2 kg N ha -1 ). The control plots had intermediate rates (2.2 ± 0.2 kg N ha -1 ). Further, N 2 fixation was highest during the summer in the warmed plots, but was lowest in the litter addition plots during the same period. The temperature and moisture dependence of N 2 fixation was different between the climate change treatments, indicating a shift in the N 2 fixer community. Our findings, using a combined empirical and modelling approach, suggest that a longer snow-free period and increased temperatures in a future climate will likely lead to higher N 2 fixation rates in mosses. Yet, the consequences of increased litter fall on moss-associated N 2 fixation due to shrub expansion in the Arctic will depend on the shrub species' litter traits. © 2016 John Wiley & Sons Ltd.

Nitrogen fixation and hydrogen metabolism in cyanobacteria.

PubMed

Bothe, Hermann; Schmitz, Oliver; Yates, M Geoffrey; Newton, William E

2010-12-01

This review summarizes recent aspects of (di)nitrogen fixation and (di)hydrogen metabolism, with emphasis on cyanobacteria. These organisms possess several types of the enzyme complexes catalyzing N(2) fixation and/or H(2) formation or oxidation, namely, two Mo nitrogenases, a V nitrogenase, and two hydrogenases. The two cyanobacterial Ni hydrogenases are differentiated as either uptake or bidirectional hydrogenases. The different forms of both the nitrogenases and hydrogenases are encoded by different sets of genes, and their organization on the chromosome can vary from one cyanobacterium to another. Factors regulating the expression of these genes are emerging from recent studies. New ideas on the potential physiological and ecological roles of nitrogenases and hydrogenases are presented. There is a renewed interest in exploiting cyanobacteria in solar energy conversion programs to generate H(2) as a source of combustible energy. To enhance the rates of H(2) production, the emphasis perhaps needs not to be on more efficient hydrogenases and nitrogenases or on the transfer of foreign enzymes into cyanobacteria. A likely better strategy is to exploit the use of radiant solar energy by the photosynthetic electron transport system to enhance the rates of H(2) formation and so improve the chances of utilizing cyanobacteria as a source for the generation of clean energy.

Environmental forcing of nitrogen fixation in the eastern tropical and sub-tropical North Atlantic Ocean.

PubMed

Rijkenberg, Micha J A; Langlois, Rebecca J; Mills, Matthew M; Patey, Matthew D; Hill, Polly G; Nielsdóttir, Maria C; Compton, Tanya J; Laroche, Julie; Achterberg, Eric P

2011-01-01

During the winter of 2006 we measured nifH gene abundances, dinitrogen (N(2)) fixation rates and carbon fixation rates in the eastern tropical and sub-tropical North Atlantic Ocean. The dominant diazotrophic phylotypes were filamentous cyanobacteria, which may include Trichodesmium and Katagnymene, with up to 10(6) L(-1)nifH gene copies, unicellular group A cyanobacteria with up to 10(5) L(-1)nifH gene copies and gamma A proteobacteria with up to 10(4) L(-1)nifH gene copies. N(2) fixation rates were low and ranged between 0.032-1.28 nmol N L(-1) d(-1) with a mean of 0.30 ± 0.29 nmol N L(-1) d(-1) (1σ, n = 65). CO(2)-fixation rates, representing primary production, appeared to be nitrogen limited as suggested by low dissolved inorganic nitrogen to phosphate ratios (DIN:DIP) of about 2 ± 3.2 in surface waters. Nevertheless, N(2) fixation rates contributed only 0.55 ± 0.87% (range 0.03-5.24%) of the N required for primary production. Boosted regression trees analysis (BRT) showed that the distribution of the gamma A proteobacteria and filamentous cyanobacteria nifH genes was mainly predicted by the distribution of Prochlorococcus, Synechococcus, picoeukaryotes and heterotrophic bacteria. In addition, BRT indicated that multiple a-biotic environmental variables including nutrients DIN, dissolved organic nitrogen (DON) and DIP, trace metals like dissolved aluminum (DAl), as a proxy of dust inputs, dissolved iron (DFe) and Fe-binding ligands as well as oxygen and temperature influenced N(2) fixation rates and the distribution of the dominant diazotrophic phylotypes. Our results suggest that lower predicted oxygen concentrations and higher temperatures due to climate warming may increase N(2) fixation rates. However, the balance between a decreased supply of DIP and DFe from deep waters as a result of more pronounced stratification and an enhanced supply of these nutrients with a predicted increase in deposition of Saharan dust may ultimately determine the

Nitrogen Fixation by Gliding Arc Plasma: Better Insight by Chemical Kinetics Modelling.

PubMed

Wang, Weizong; Patil, Bhaskar; Heijkers, Stjin; Hessel, Volker; Bogaerts, Annemie

2017-05-22

The conversion of atmospheric nitrogen into valuable compounds, that is, so-called nitrogen fixation, is gaining increased interest, owing to the essential role in the nitrogen cycle of the biosphere. Plasma technology, and more specifically gliding arc plasma, has great potential in this area, but little is known about the underlying mechanisms. Therefore, we developed a detailed chemical kinetics model for a pulsed-power gliding-arc reactor operating at atmospheric pressure for nitrogen oxide synthesis. Experiments are performed to validate the model and reasonable agreement is reached between the calculated and measured NO and NO 2 yields and the corresponding energy efficiency for NO x formation for different N 2 /O 2 ratios, indicating that the model can provide a realistic picture of the plasma chemistry. Therefore, we can use the model to investigate the reaction pathways for the formation and loss of NO x . The results indicate that vibrational excitation of N 2 in the gliding arc contributes significantly to activating the N 2 molecules, and leads to an energy efficient way of NO x production, compared to the thermal process. Based on the underlying chemistry, the model allows us to propose solutions on how to further improve the NO x formation by gliding arc technology. Although the energy efficiency of the gliding-arc-based nitrogen fixation process at the present stage is not comparable to the world-scale Haber-Bosch process, we believe our study helps us to come up with more realistic scenarios of entering a cutting-edge innovation in new business cases for the decentralised production of fertilisers for agriculture, in which low-temperature plasma technology might play an important role. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Assessing nitrogen fixation in mixed- and single-species plantations of Eucalyptus globulus and Acacia mearnsii.

PubMed

Forrester, David I; Schortemeyer, Marcus; Stock, William D; Bauhus, Jürgen; Khanna, Partap K; Cowie, Annette L

2007-09-01

Mixtures of Eucalyptus globulus Labill. and Acacia mearnsii de Wildeman are twice as productive as E. globulus monocultures growing on the same site in East Gippsland, Victoria, Australia, possibly because of increased nitrogen (N) availability owing to N(2) fixation by A. mearnsii. To investigate whether N(2) fixation by A. mearnsii could account for the mixed-species growth responses, we assessed N(2) fixation by the accretion method and the (15)N natural abundance method. Nitrogen gained by E. globulus and A. mearnsii mixtures and monocultures was calculated by the accretion method with plant and soil samples collected 10 years after plantation establishment. Nitrogen in biomass and soil confirmed that A. mearnsii influenced N dynamics. Assuming that the differences in soil, forest floor litter and biomass N of plots containing A. mearnsii compared with E. globulus monocultures were due to N(2) fixation, the 10-year annual mean rates of N(2) fixation were 38 and 86 kg ha(-1) year(-1) in 1:1 mixtures and A. mearnsii monocultures, respectively. Nitrogen fixation by A. mearnsii could not be quantified on the basis of the natural abundance of (15)N because such factors as mycorrhization type and fractionation of N isotopes during N cycling within the plant confounded the effect of the N source on the N isotopic signature of plants. This study shows that A. mearnsii fixed significant quantities of N(2) when mixed with E. globulus. A decline in delta(15)N values of E. globulus and A. mearnsii with time, from 2 to 10 years, is further evidence that N(2) was fixed and cycled through the stands. The increased aboveground biomass production of E. globulus trees in mixtures when compared with monocultures can be attributed to increases in N availability.

Metabolic Adaptation, a Specialized Leaf Organ Structure and Vascular Responses to Diurnal N2 Fixation by Nostoc azollae Sustain the Astonishing Productivity of Azolla Ferns without Nitrogen Fertilizer.

PubMed

Brouwer, Paul; Bräutigam, Andrea; Buijs, Valerie A; Tazelaar, Anne O E; van der Werf, Adrie; Schlüter, Urte; Reichart, Gert-Jan; Bolger, Anthony; Usadel, Björn; Weber, Andreas P M; Schluepmann, Henriette

2017-01-01

Sustainable agriculture demands reduced input of man-made nitrogen (N) fertilizer, yet N 2 fixation limits the productivity of crops with heterotrophic diazotrophic bacterial symbionts. We investigated floating ferns from the genus Azolla that host phototrophic diazotrophic Nostoc azollae in leaf pockets and belong to the fastest growing plants. Experimental production reported here demonstrated N-fertilizer independent production of nitrogen-rich biomass with an annual yield potential per ha of 1200 kg -1 N fixed and 35 t dry biomass. 15 N 2 fixation peaked at noon, reaching 0.4 mg N g -1 dry weight h -1 . Azolla ferns therefore merit consideration as protein crops in spite of the fact that little is known about the fern's physiology to enable domestication. To gain an understanding of their nitrogen physiology, analyses of fern diel transcript profiles under differing nitrogen fertilizer regimes were combined with microscopic observations. Results established that the ferns adapted to the phototrophic N 2 -fixing symbionts N. azollae by (1) adjusting metabolically to nightly absence of N supply using responses ancestral to ferns and seed plants; (2) developing a specialized xylem-rich vasculature surrounding the leaf-pocket organ; (3) responding to N-supply by controlling transcripts of genes mediating nutrient transport, allocation and vasculature development. Unlike other non-seed plants, the Azolla fern clock is shown to contain both the morning and evening loops; the evening loop is known to control rhythmic gene expression in the vasculature of seed plants and therefore may have evolved along with the vasculature in the ancestor of ferns and seed plants.

Metabolic Adaptation, a Specialized Leaf Organ Structure and Vascular Responses to Diurnal N2 Fixation by Nostoc azollae Sustain the Astonishing Productivity of Azolla Ferns without Nitrogen Fertilizer

PubMed Central

Brouwer, Paul; Bräutigam, Andrea; Buijs, Valerie A.; Tazelaar, Anne O. E.; van der Werf, Adrie; Schlüter, Urte; Reichart, Gert-Jan; Bolger, Anthony; Usadel, Björn; Weber, Andreas P. M.; Schluepmann, Henriette

2017-01-01

Sustainable agriculture demands reduced input of man-made nitrogen (N) fertilizer, yet N2 fixation limits the productivity of crops with heterotrophic diazotrophic bacterial symbionts. We investigated floating ferns from the genus Azolla that host phototrophic diazotrophic Nostoc azollae in leaf pockets and belong to the fastest growing plants. Experimental production reported here demonstrated N-fertilizer independent production of nitrogen-rich biomass with an annual yield potential per ha of 1200 kg−1 N fixed and 35 t dry biomass. 15N2 fixation peaked at noon, reaching 0.4 mg N g−1 dry weight h−1. Azolla ferns therefore merit consideration as protein crops in spite of the fact that little is known about the fern’s physiology to enable domestication. To gain an understanding of their nitrogen physiology, analyses of fern diel transcript profiles under differing nitrogen fertilizer regimes were combined with microscopic observations. Results established that the ferns adapted to the phototrophic N2-fixing symbionts N. azollae by (1) adjusting metabolically to nightly absence of N supply using responses ancestral to ferns and seed plants; (2) developing a specialized xylem-rich vasculature surrounding the leaf-pocket organ; (3) responding to N-supply by controlling transcripts of genes mediating nutrient transport, allocation and vasculature development. Unlike other non-seed plants, the Azolla fern clock is shown to contain both the morning and evening loops; the evening loop is known to control rhythmic gene expression in the vasculature of seed plants and therefore may have evolved along with the vasculature in the ancestor of ferns and seed plants. PMID:28408911

Epidemic Spread of Symbiotic and Non-Symbiotic Bradyrhizobium Genotypes Across California.

PubMed

Hollowell, A C; Regus, J U; Gano, K A; Bantay, R; Centeno, D; Pham, J; Lyu, J Y; Moore, D; Bernardo, A; Lopez, G; Patil, A; Patel, S; Lii, Y; Sachs, J L

2016-04-01

The patterns and drivers of bacterial strain dominance remain poorly understood in natural populations. Here, we cultured 1292 Bradyrhizobium isolates from symbiotic root nodules and the soil root interface of the host plant Acmispon strigosus across a >840-km transect in California. To investigate epidemiology and the potential role of accessory loci as epidemic drivers, isolates were genotyped at two chromosomal loci and were assayed for presence or absence of accessory "symbiosis island" loci that encode capacity to form nodules on hosts. We found that Bradyrhizobium populations were very diverse but dominated by few haplotypes-with a single "epidemic" haplotype constituting nearly 30 % of collected isolates and spreading nearly statewide. In many Bradyrhizobium lineages, we inferred presence and absence of the symbiosis island suggesting recurrent evolutionary gain and or loss of symbiotic capacity. We did not find statistical phylogenetic evidence that the symbiosis island acquisition promotes strain dominance and both symbiotic and non-symbiotic strains exhibited population dominance and spatial spread. Our dataset reveals that a strikingly few Bradyrhizobium genotypes can rapidly spread to dominate a landscape and suggests that these epidemics are not driven by the acquisition of accessory loci as occurs in key human pathogens.

Symbiotic organism search algorithm for simulation of J- V characteristics and optimizing internal parameters of DSSC developed using electrospun TiO2 nanofibers

NASA Astrophysics Data System (ADS)

Vinoth, S.; Kanimozhi, G.; Kumar, Harish; Srinadhu, E. S.; Satyanarayana, N.

2017-12-01

In the present investigation, the recently developed, simple, robust, and powerful metaheuristic symbiotic organism search (SOS) algorithm was used for simulation of J- V characteristics and optimizing the internal parameters of the dye-sensitized solar cells (DSSCs) fabricated using electrospun 1-D mesoporous TiO2 nanofibers as photoanode. The efficiency ( η = 5.80 %) of the DSSC made up of TiO2 nanofibers as photoanode is found to be ˜ 21.59% higher compared to the efficiency ( η = 4.77 %) of the DSSC made up of TiO2 nanoparticles as photoanode. The observed high efficiency can be attributed to high dye loading as well as high electron transport in the mesoporous 1-D TiO2 nanofibers. Further, the validity and advantage of SOS algorithm are verified by simulating J- V characteristics of DSSC with Lambert-W function.

The interactive effects of temperature and light on biological nitrogen fixation in boreal forests.

PubMed

Gundale, Michael J; Nilsson, Madeleine; Bansal, Sheel; Jäderlund, Anders

2012-04-01

Plant productivity is predicted to increase in northern latitudes as a result of climate warming; however, this may depend on whether biological nitrogen (N)-fixation also increases. We evaluated how the variation in temperature and light affects N-fixation by two boreal feather mosses, Pleurozium schreberi and Hylocomium splendens, which are the primary source of N-fixation in most boreal environments. We measured N-fixation rates 2 and 4 wk after exposure to a factorial combination of environments of normal, intermediate and high temperature (16.3, 22.0 and 30.3°C) and light (148.0, 295.7 and 517.3 μmol m(-2) s(-1)). Our results showed that P. schreberi achieved higher N-fixation rates relative to H. splendens in response to warming treatments, but that the highest warming treatment eventually caused N-fixation to decline for both species. Light strongly interacted with warming treatments, having positive effects at low or intermediate temperatures and damaging effects at high temperatures. These results suggest that climate warming may increase N-fixation in boreal forests, but that increased shading by the forest canopy or the occurrence of extreme temperature events could limit increases. They also suggest that P. schreberi may become a larger source of N in boreal forests relative to H. splendens as climate warming progresses. © 2012 The Authors. New Phytologist © 2012 New Phytologist Trust.

Cyanobacterial Lactate Oxidases Serve as Essential Partners in N2 Fixation and Evolved into Photorespiratory Glycolate Oxidases in Plants[w

PubMed Central

Hackenberg, Claudia; Kern, Ramona; Hüge, Jan; Stal, Lucas J.; Tsuji, Yoshinori; Kopka, Joachim; Shiraiwa, Yoshihiro; Bauwe, Hermann; Hagemann, Martin

2011-01-01

Glycolate oxidase (GOX) is an essential enzyme involved in photorespiratory metabolism in plants. In cyanobacteria and green algae, the corresponding reaction is catalyzed by glycolate dehydrogenases (GlcD). The genomes of N2-fixing cyanobacteria, such as Nostoc PCC 7120 and green algae, appear to harbor genes for both GlcD and GOX proteins. The GOX-like proteins from Nostoc (No-LOX) and from Chlamydomonas reinhardtii showed high l-lactate oxidase (LOX) and low GOX activities, whereas glycolate was the preferred substrate of the phylogenetically related At-GOX2 from Arabidopsis thaliana. Changing the active site of No-LOX to that of At-GOX2 by site-specific mutagenesis reversed the LOX/GOX activity ratio of No-LOX. Despite its low GOX activity, No-LOX overexpression decreased the accumulation of toxic glycolate in a cyanobacterial photorespiratory mutant and restored its ability to grow in air. A LOX-deficient Nostoc mutant grew normally in nitrate-containing medium but died under N2-fixing conditions. Cultivation under low oxygen rescued this lethal phenotype, indicating that N2 fixation was more sensitive to O2 in the Δlox Nostoc mutant than in the wild type. We propose that LOX primarily serves as an O2-scavenging enzyme to protect nitrogenase in extant N2-fixing cyanobacteria, whereas in plants it has evolved into GOX, responsible for glycolate oxidation during photorespiration. PMID:21828292

Non-symbiotic haemoglobins-What's happening beyond nitric oxide scavenging?

PubMed

Hill, Robert D

2012-01-01

Non-symbiotic haemoglobins have been an active research topic for over 30 years, during which time a considerable portfolio of knowledge has accumulated relative to their chemical and molecular properties, and their presence and mode of induction in plants. While progress has been made towards understanding their physiological role, there remain a number of unanswered questions with respect to their biological function. This review attempts to update recent progress in this area and to introduce a hypothesis as to how non-symbiotic haemoglobins might participate in regulating hormone signal transduction. Advances have been made towards understanding the structural nuances that explain some of the differences in ligand association characteristics of class 1 and class 2 non-symbiotic haemoglobins. Non-symbiotic haemoglobins have been found to function in seed development and germination, flowering, root development and differentiation, abiotic stress responses, pathogen invasion and symbiotic bacterial associations. Microarray analyses under various stress conditions yield uneven results relative to non-symbiotic haemoglobin expression. Increasing evidence of the role of nitric oxide (NO) in hormone responses and the known involvement of non-symbiotic haemoglobins in scavenging NO provide opportunities for fruitful research, particularly at the cellular level. Circumstantial evidence suggests that non-symbiotic haemoglobins may have a critical function in the signal transduction pathways of auxin, ethylene, jasmonic acid, salicylic acid, cytokinin and abscisic acid. There is a strong need for research on haemoglobin gene expression at the cellular level relative to hormone signal transduction.

Significance of Herbaspirillum seropedicae inoculation and/or straw amendment on growth and dinitrogen fixation of wheat using 15N-dilution method.

PubMed

el-Komy, H M; Saad, O A; Hetta, A M

2003-01-01

The effect of Herbaspirillum seropedicae inoculation and/or maize straw (0, 5 and 10 Mg/hm2) amendment on the growth and N2 fixation of wheat was determined in pot experiments using 15N-dilution method. Inoculation resulted in accumulation of fixed nitrogen, and % N from atmosphere being 24.6 and 26.5% in wheat shoot and grain, respectively. Straw amendment reduced % Natm to 16.1 and 20.2% at high straw level (10 Mg/hm2). Rational nitrogen fertilization (180 kg N/hm2) completely inhibited N2 fixation by H. seropedicae inoculation. Bacterial inoculation increased dry shoot and grain yield up to 23 and 31%, respectively. The highest levels of shoot and grain dry mass (46.5 and 42.4%) were obtained by N-fertilization in both inoculated and uninoculated plants. Total shoot and grain N-yield increased irrespective of organic matter amendment by inoculation up to 9 and 25%, respectively. N-fertilized plants recorded a maximum increase in N-yield (57 and 51%). H. seropedicae was reisolated from inoculated wheat histosphere after harvesting (90 d from sowing). Neither organic matter nor mineral nitrogen applications had any marked effect on bacterial total counts colonizing wheat histosphere. Moreover, no symptoms of mottled stripe disease were observed on leaves and stems of inoculated plants.

Mycorrhizal Symbiotic Efficiency on C3 and C4 Plants under Salinity Stress – A Meta-Analysis

PubMed Central

Chandrasekaran, Murugesan; Kim, Kiyoon; Krishnamoorthy, Ramasamy; Walitang, Denver; Sundaram, Subbiah; Joe, Manoharan M.; Selvakumar, Gopal; Hu, Shuijin; Oh, Sang-Hyon; Sa, Tongmin

2016-01-01

A wide range of C3 and C4 plant species could acclimatize and grow under the impact of salinity stress. Symbiotic relationship between plant roots and arbuscular mycorrhizal fungi (AMF) are widespread and are well known to ameliorate the influence of salinity stress on agro-ecosystem. In the present study, we sought to understand the phenomenon of variability on AMF symbiotic relationship on saline stress amelioration in C3 and C4 plants. Thus, the objective was to compare varied mycorrhizal symbiotic relationship between C3 and C4 plants in saline conditions. To accomplish the above mentioned objective, we conducted a random effects models meta-analysis across 60 published studies. An effect size was calculated as the difference in mycorrhizal responses between the AMF inoculated plants and its corresponding control under saline conditions. Responses were compared between (i) identity of AMF species and AMF inoculation, (ii) identity of host plants (C3 vs. C4) and plant functional groups, (iii) soil texture and level of salinity and (iv) experimental condition (greenhouse vs. field). Results indicate that both C3 and C4 plants under saline condition responded positively to AMF inoculation, thereby overcoming the predicted effects of symbiotic efficiency. Although C3 and C4 plants showed positive effects under low (EC < 4 ds/m) and high (>8 ds/m) saline conditions, C3 plants showed significant effects for mycorrhizal inoculation over C4 plants. Among the plant types, C4 annual and perennial plants, C4 herbs and C4 dicot had a significant effect over other counterparts. Between single and mixed AMF inoculants, single inoculants Rhizophagus irregularis had a positive effect on C3 plants whereas Funneliformis mosseae had a positive effect on C4 plants than other species. In all of the observed studies, mycorrhizal inoculation showed positive effects on shoot, root and total biomass, and in nitrogen, phosphorous and potassium (K) uptake. However, it showed negative