Biological Fixation Of Atmospheric Nitrogen Research Articles

Performance of Rhizobial Inoculants on Yield and Yield Components of Faba Bean in Southern Ethiopia

Biological fixation of atmospheric nitrogen by legumes is a known way to recycle nitrogen into a plant-available form. The efficiency of nitrogen fixation depends on the legume genotype and requires a host-specific rhizobia strain for nodule formation and yield enhancement. Therefore, the field experiment was conducted to evaluate the performance of rhizobial inoculants on yield and yield components of faba bean under rainy conditions during two consecutive main growing seasons.

Response of soybean crop with different combinations of seed treatment and application of nitrogen, cobalt, and molybdenum topdressing

Nitrogen is the element most demanded by the soybean crop, and the biological fixation of atmospheric nitrogen is the main means to supply it. In contrast, micronutrients and chemical treatments applied on seeds together with the inoculant can alter the phenomenon of biological fixation of atmospheric nitrogen. This work aimed to evaluate the effect of chemical products, micronutrients, and nitrogen fertilization on the nodulation, development, and yield of soybean. The experiment was developed in a field and a greenhouse in the municipality of Toledo, Brazil. A randomized block with four repetitions was used as an experimental design. This design had eight treatments, namely: T1 - Control (seeds treated with insecticide); T2 - Seeds treated with insecticides and inoculated with Bradyrhizobium; T3 - Untreated seeds inoculated with Bradyrhizobium; T4 Seeds treated with insecticides and cobalt-molybdenum (CoMo), inoculated with Bradyrhizobium; T5 - Seeds with CoMo inoculated with Bradyrhizobium; T6 - Seeds treated with insecticides, inoculated with Bradyrhizobium and with foliar application of CoMo; T7 - Seeds treated with insecticides, inoculated with Bradyrhizobium and with the application of nitrogen in cover; T8 - Seeds treated with nitrogen by broadcast. No significant differences were observed between treatments on the nodules numbers, stem diameter, plant height, root length, the mass of 1000 grains, and yield. The application of nitrogen at the R2 stage (a plant with an open flower in one of the two uppermost nodes of the main stem with a fully developed leaf) and in association with the inoculant + CoMo without seed treatment provided a greater number of nodes, pods, and grains per plant.

N2 fixation associated with the bryophyte layer is suppressed by low levels of nitrogen deposition in boreal forests

Biological fixation of atmospheric nitrogen (N2) by bryophyte-associated cyanobacteria is an important source of plant-available N in the boreal biome. Information on the factors that drive biological N2 fixation (BNF) rates is needed in order to understand the N dynamics of forests under a changing climate. We assessed the potential of several cryptogam species (the feather mosses Hylocomium splendens and Pleurozium schreberi, a group of Dicranum bryophytes, two liverworts, and Cladina lichens) to serve as associates of cyanobacteria or other N2-fixing bacteria (diazotrophs) using acetylene reduction assay (ARA). We tested the hypotheses that the legacy of chronic atmospheric N deposition reduces BNF in the three bryophyte species, sampled from 12 coniferous forests located at latitudes 60–68° N in Finland. In addition, we tested the effect of moisture and temperature on BNF. All species studied showed a BNF signal in the north, with the highest rates in feather mosses. In moss samples taken along the north–south gradient with an increasing N bulk deposition from 0.8 to 4.4 kg ha−1 year−1, we found a clear decrease in BNF in both feather mosses and Dicranum group. BNF turned off at N deposition of 3–4 kg ha−1 year−1. Inorganic N (NH4-N + NO3-N) best predicted the BNF rate among regression models with different forms of N deposition as explanatory variables. However, in southern spruce stands, tree canopies modified the N in throughfall so that dissolved organic N (DON) leached from canopies compensated for inorganic N retained therein. Here, both DON and inorganic N negatively affected BNF in H. splendens. In laboratory experiments, BNF increased with increasing temperature and moisture. Our results suggest that even relatively low N deposition suppresses BNF in bryophyte-associated diazotrophs. Further, BNF could increase in northern low-deposition areas, especially if climate warming leads to moister conditions, as predicted.

English

It is unanimously admitted that the chemical fertilizers and pesticides used in modern agriculture create a real environmental and public health problems. One of the promising solutions to substitute these agrochemicals products is the use of bio-resources, including plant growth promoting rhizobacteria (PGPR). The PGPR focused more and more scientific attention in recent decades. These rhizospheric bacteria colonize actively the root system of plants and improve their growth and yield. The PGPR use different mechanisms of action to promote plant growth. These mechanisms were grouped into three clusters according to the PGPR effects on plant physiology. These groups are as follow: (i) biofertilization including biological fixation of atmospheric nitrogen, phosphate solubilization, siderophores production and exopolysaccharides production; (ii) phytostimulation including production of indole acetic acid, gibberellins, cytokinins and ethylene; and (ii) biocontrol including induction of systemic resistance, competition for iron, nutrient and space, production of antibiotics, lytic enzymes, hydrogen cyanide and volatile compounds. In view of the latest advances in PGPR biotechnology, this paper proposes to do the review on PGPR in rhizosphere and describes the different mechanisms used by PGPR to promote the plants growth and health. In prospect to a healthy and sustainable agriculture, respectful of environment, the PGPR approach revealed as one of the best alternatives. Keywords: Rhizosphere, plant growth promoting rhizobacteria (PGPR), root colonization, biofertilization, biocontrol, biostimulation, interaction plant-microorganisms, sustainable agriculture

Carbon and nitrogen stable isotope ratios of pelagic zooplankton elucidate ecohydrographic features in the oligotrophic Red Sea

Although zooplankton occupy key roles in aquatic biogeochemical cycles, little is known about the pelagic food web and trophodynamics of zooplankton in the Red Sea. Natural abundance stable isotope analysis (SIA) of carbon (δ13C) and N (δ15N) is one approach to elucidating pelagic food web structures and diet assimilation. Integrating the combined effects of ecological processes and hydrography, ecohydrographic features often translate into geographic patterns in δ13C and δ15N values at the base of food webs. This is due, for example, to divergent 15N abundances in source end-members (deep water sources: high δ15N, diazotrophs: low δ15N). Such patterns in the spatial distributions of stable isotope values were coined isoscapes. Empirical data of atmospheric, oceanographic, and biological processes, which drive the ecohydrographic gradients of the oligotrophic Red Sea, are under-explored and some rather anticipated than proven. Specifically, five processes underpin Red Sea gradients: (a) monsoon-related intrusions of nutrient-rich Indian Ocean water; (b) basin scale thermohaline circulation; (c) mesoscale eddy activity that causes up-welling of deep water nutrients into the upper layer; (d) the biological fixation of atmospheric nitrogen (N2) by diazotrophs; and (e) the deposition of dust and aerosol-derived N. This study assessed relationships between environmental samples (nutrients, chlorophyll a), oceanographic data (temperature, salinity, current velocity [ADCP]), particulate organic matter (POM), and net-phytoplankton, with the δ13C and δ15N values of zooplankton collected in spring 2012 from 16°28′ to 26°57′N along the central axis of the Red Sea. The δ15N of bulk POM and most zooplankton taxa increased from North (Duba) to South (Farasan). The potential contribution of deep water nutrient-fueled phytoplankton, POM, and diazotrophs varied among sites. Estimates suggested higher diazotroph contributions in the North, a greater contribution of POM in the South, and of small phytoplankton in the central Red Sea. Consistent variation across taxonomic and trophic groups at latitudinal scale, corresponding with patterns of nutrient stoichiometry and phytoplankton composition, indicates that the zooplankton ecology in the Red Sea is largely influenced by hydrographic features. It suggests that the primary ecohydrography of the Red Sea is driven not only by the thermohaline circulation, but also by mesoscale activities that transports nutrients to the upper water layers and interact with the general circulation pattern. Ecohydrographic features of the Red Sea, therefore, aid in explaining the observed configuration of its isoscape at the macroecological scale.

Inoculation with Bradyrhizobium japonicum enhances the organic and fatty acids content of soybean (Glycine max (L.) Merrill) seeds

Soybean (Glycine max (L.) Merrill) is one of the most important food crops for human and animal consumption, providing oil and protein at relatively low cost. The least expensive source of nitrogen for soybean is the biological fixation of atmospheric nitrogen by the symbiotic association with soil bacteria, belonging mainly to the genus Bradyrhizobium. This study was conducted to assess the effect of the inoculation of G. max with Bradyrhizobium japonicum on the metabolite profile and antioxidant potential of its seeds. Phenolic compounds, sterols, triterpenes, organic acids, fatty acids and volatiles profiles were characterised by different chromatographic techniques. The antioxidant activity was evaluated against DPPH, superoxide and nitric oxide radicals. Inoculation with B. japonicum induced changes in the profiles of primary and secondary metabolites of G. max seeds, without affecting their antioxidant capacity. The increase of organic and fatty acids and volatiles suggest a positive effect of the inoculation process. These findings indicate that the inoculation with nodulating B. japonicum is a beneficial agricultural practice, increasing the content of bioactive metabolites in G. max seeds owing to the establishment of symbiosis between plant and microorganism, with direct effects on seed quality.

Moss-cyanobacteria associations as biogenic sources of nitrogen in boreal forest ecosystems.

The biological fixation of atmospheric nitrogen (N) is a major pathway for available N entering ecosystems. In N-limited boreal forests, a significant amount of N2 is fixed by cyanobacteria living in association with mosses, contributing up to 50% to the total N input. In this review, we synthesize reports on the drivers of N2 fixation in feather moss-cyanobacteria associations to gain a deeper understanding of their role for ecosystem-N-cycling. Nitrogen fixation in moss-cyanobacteria associations is inhibited by N inputs and therefore, significant fixation occurs only in low N-deposition areas. While it has been shown that artificial N additions in the laboratory as well as in the field inhibit N2 fixation in moss-cyanobacteria associations, the type, as well as the amounts of N that enters the system, affect N2 fixation differently. Another major driver of N2 fixation is the moisture status of the cyanobacteria-hosting moss, wherein moist conditions promote N2 fixation. Mosses experience large fluctuations in their hydrological status, undergoing significant natural drying and rewetting cycles over the course of only a few hours, especially in summer, which likely compromises the N input to the system via N2 fixation. Perhaps the most central question, however, that remains unanswered is the fate of the fixed N2 in mosses. The cyanobacteria are likely to leak N, but whether this N is transferred to the soil and if so, at which rates and timescales, is unknown. Despite our increasing understanding of the drivers of N2 fixation, the role moss-cyanobacteria associations play in ecosystem-N-cycling remains unresolved. Further, the relationship mosses and cyanobacteria share is unknown to date and warrants further investigation.

Biblioteca subtrativa de raízes de soja em resposta à inoculação com Bradyrhizobium japonicum

Soybean [ Glycine max (L.) Merr.] is the most important legume cropped worldwide, with an economic value attributed mainly to the high protein content of the grain, which, in turn, demands a heavy supply of nitrogen. An environmentally friendly source of nitrogen at low cost to farmers is represented by the biological fixation of atmospheric nitrogen that takes place is association with symbiotic bacteria. For the soybean, the association occurs mainly with bacteria belonging to the species Bradyrhizobium japonicum and Bradyrhizobium elkanii , but our knowledge about gene expression associated with the symbiosis is still poor. This work—part of an effort by the Soybean Genome Consortium (Genosoja)—was conducted with the aim of achieving better understanding about the functionality of the genes expressed in soybean roots in the early stages of the interaction with B. japonicum . The study was performed with soybean plants growing under greenhouse conditions, inoculated (or not) with strain CPAC 15 (=SEMIA 5079) of B. japonicum , which is broadly used in Brazilian commercial inoculants. Total RNA was extracted, the mRNA was isolated and a subtractive library was constructed. Sequencing analysis generated 4,621,072 reads, which were assembled in 3,776 sequences, defined as the differentially expressed sequences of the inoculated versus non-inoculated treatments. The sequences were categorized according to their molecular function and grouped with representatives of antioxidant activities, molecular transduction, transporters and enzyme regulation activities, but with an emphasis on catalytic and molecular binding/signaling

Weed Control for Winter Faba Bean Cover Crop in South Florida

Faba bean is an important leguminous winter crop in warm temperate and subtropical areas that has been cultivated for more than 10,000 years as a source of protein in human and livestock diets. It is also grown to enhance yields of other crops. Faba bean provides nitrogen in agricultural systems through the unique process of biological fixation of atmospheric nitrogen by symbiosis with Rhizobium bacteria. This substantially reduces the need for nitrogen fertilizers, which contribute to both carbon dioxide and nitrous oxide emissions. This 2-page fact sheet written by D.C. Odero provides weed control recommendations. Published by the UF Department of Agronomy, April 2011. SS-AGR-345/AG355: Weed Control for Winter Faba Bean Cover Crop in South Florida (ufl.edu)

Hydrogen production by Trichodesmium erythraeum Cyanothece sp. and Crocosphaera watsonii

Diazotrophic cyanobacteria are important components of marine ecosystems, where they contribute to primary production and provide a source of fixed nitrogen (N). During biological fixation of atmospheric nitrogen (N2), hydrogen is produced as an obligate by-product. The present study investigated the potential contribution of 4 marine diazotrophs to the pool of dissolved H2 in the oceans. N2 fixation, as measured by acetylene reduction, and H2 production rates were monitored throughout the diel period in cultures of the filamentous Trichodesmium erythraeum strain IMS101, and the unicellular organisms Cyanothece sp. strain ATCC 51142 and Crocosphaera watsonii strains WH8501 and WH0002. H2 production coincided with diel variations in N2 fixation for each strain regardless of whether N2 fixation peaked during the day or night. Chlorophyll-normalized rates of H2 production ranged 100-fold from a maximum of 3 nmol µg chl a -1 h -1 in T. erythraeum IMS101 cul- tures to 0.03 nmol µg chl a -1 h -1 in Crocosphaera watsonii WH0002. Overall, the ratio of net H2 pro- duced to N2 fixed varied from 0.05 to 0.003 in the unicellular cyanobacteria, compared to 0.3 in the filamentous T. erythraeum IMS101, indicating that unicellular cyanobacteria produce less, or alterna- tively, re-assimilate more of the H2 produced during N2 fixation. Crocosphaera watsonii has recently been identified as a significant source of fixed N in the marine environment, and an efficient recy- cling of H2 would provide a valuable source of energy to their respiratory electron transport chain. Furthermore, the magnitude of H2 produced by T. erythraeum IMS101 strongly implicates this organism in the production of H2 in the upper ocean.

A natural 15N approach to determine the biological fixation of atmospheric nitrogen by biological soil crusts of the Negev Desert

Biological soil crusts are important cryptogamic communities covering the sand dunes of the north-western Negev. The biological crusts contain cyanobacteria and other free-living N(2)-fixing bacteria and are hence able to fix atmospheric nitrogen (N). This is why they are considered to be one of the main N input pathways into the desert ecosystem. However, up to now, in situ determinations of the N(2) fixation in the field are not known to have been carried out. We examined the natural (15)N method to determine the biological N(2) fixation by these soil crusts under field conditions. This novel natural (15)N method uses the lichen Squamarina with symbiotic green algae--which are unable to fix N(2)--as a reference in order to determine N(2) fixation. Depending on the sampling location and year, the relative biological fixation of atmospheric nitrogen was estimated at 84-91% of the total N content of the biological soil crust. The cyanobacteria-containing soil lichen Collema had a fixation rate of about 88%. These fixation rates were used to derive an absolute atmospheric N input of 10-41 kg N ha(-1) year(-1). These values are reasonable results for the fixation of atmospheric N(2) by the biological crusts and cyanolichens and are in agreement with other comparable lab investigations. As far as we are aware, the results presented are the first to have been obtained from in situ field measurements, albeit only one location of the Negev with a small number of samples was investigated.

Using the natural 15N abundance to assess the main nitrogen inputs into the sand dune area of the North-Western Negev desert (ISRAEL)

The variation of the natural 15N abundance is often used to evaluate the origin of nitrogen or the pathways of N input into ecosystems. We tried to use this approach to assess the main input pathways of nitrogen into the sand dune area of the north-western Negev Desert (Israel). The following two pathways are the main sources for nitrogen input into the system: i. Biological fixation of atmospheric nitrogen by cyanobacteria present in biological crusts and by N2-fixing vascular plants (e.g. the shrub Retama raetam); ii. Atmospheric input of nitrogen by wet deposition with rainfall, dry deposition of dust containing N compounds, and gaseous deposition. Samples were taken from selected environmental compartments such as biological crusts, sand underneath these crusts (down to a depth of 90 cm), N2-fixing and non-N2-fixing plants, atmospheric bulk deposition as well as soil from arable land north of the sandy area in three field campaigns in March 1998, 1999 and 2000. The δ15N values measured were in the following ranges: grass −2.5‰ to +1.5‰; R. reatam: +0.5‰ to +4.5‰; non-N2-fixing shrubs +1‰ to +7‰; sand beneath the biological crusts +4‰ to +20‰ (soil depth 2–90 cm); and arable land to the north up to 10‰. Thus, the natural 15N abundance of the different N pools varies significantly. Accordingly, it should be feasible to assess different input pathways from the various 15N abundances of nitrogen. For example, the biological N fixation rates of the Fabaceae shrub R. reatam from the 15N abundances measured were calculated to be 46–86% of biomass N derived from the atmosphere. The biological crusts themselves generally show slight negative 15N values (−3‰ to −0.5‰), which can be explained by biological N fixation. However, areas with a high share of lichens, which are unable to fix atmospheric nitrogen, show very negative values down to −10‰. The atmospheric N bulk deposition, which amounts to 1.9–3.8 kg N/ha yr, has a 15N abundance between 4.4‰ and 11.6‰ and is likely to be caused by dust from the arable land to the north. Thus, it cannot be responsible for the very negative values of lichens measured either. There must be an additional N input from the atmosphere with negative δ15N values, e.g. gaseous N forms (NO x , NH3). To explain these conflicting findings, detailed information is still needed on the wet, particulate and gaseous atmospheric deposition of nitrogen.

Nutrients in the Mediterranean Sea, mass balance and statistical analysis of concentrations with respect to environmental change

Experimental data obtained from the Algero–Provencal basin (Western Mediterranean) in 1994 illustrates the homogeneity of phosphate, nitrate and silicate concentrations in deep-water throughout this basin, comparable to temperature and salinity homogeneity. Nutrient mass balances across the straits of Gibraltar and Sicily enable us to estimate new production (NP) and f ratio (new vs. total production) in the inner basins. Rather low values of NP and f have been obtained. The f ratio ranges between 0.05 and 0.15. These values demonstrate the existence of spatial variability for Mediterranean oligotrophy. A statistical analysis of historical data together with new data acquired in 1994 demonstrate an increasing trend for phosphate and nitrate concentrations in deep water. In contrast, no change with time was detected for silicate concentrations. The trends for nutrient concentrations in deep water constitute new constraints for the study of atmospheric and terrestrial inputs of phosphate and nitrate. Nutrient concentration increases are much more dependent on these inputs than on the Atlantic influx across the strait of Gibraltar. The trends also provide information about the functioning of the Mediterranean ecosystem and could help to monitor the environmental change. The working out of marine budgets highlights an inadequate knowledge of external sources of nutrients and call into question the problems linked to external inputs: i) riverine particulate phosphorus transformation into phosphate at the land–sea interface and ii) the biological fixation of atmospheric nitrogen.

Les nouvelles technologies en agriculture : quelques leçons d'histoire

The tremendous innovations potential of the technologies being at present time settled by scientists provokes justified enthusiasms and fears. A brief flash-back upon events from the last forty years could make the debate more serene. Actually, some expectations not transferred into the production sector (twin calves, biological fixation of atmospheric nitrogen) recall us that research is a very uncertain activity. The evolution of programs generated by both crises in 1973 (fuels, soybean) emphasizes the impact of economic fluctuations on it. Finally, the economists will have to remain careful in order to make clear to the political and farm unions officials the nature and magnitude of unavoidable disruptions.

Nitrogen Fixation by Epiphylls in a Tropical Rainforest

Nitrogen Fixation by Epiphylls in a Tropical Rainforest

Biological fixation of atmospheric nitrogen in the Mediterranean Sea

Nutrient concentration in the Mediterranean Sea is controlled by water exchanges through the Strait of Gibraltar and by atmospheric and terrestrial inputs. Various peculiarities in the nitrogen and phosphorus geochemical cycles are pointed out, namely a low N: P atomic ratio (6.4) in terrestrial discharges, and a budget well balanced for phosphorus (where terrestrial discharges amount to about 80% of the outflow) but apparently very deficient in nitrogen, despite a high N: P atomic ratio (22), in Mediterranean deep waters. This suggests the possibility of a surprisingly high rate of direct atmospheric N uptake by the Mediterranean ecosystem (possibly seagrasses Posidonia oceanica and pelagic bacterioplankton species).

Bedeutung genetischer verfahren fýr die verbesserung der symbiontischen N2-Fixierung I. Genetische Grundlagen der N2-Fixierung

Summary The biological fixation of atmospheric nitrogen has become an important factor of plant pro duction in the world. In countries of temperate zones the symbiosis between legumes and rhizobia has a great importance. The level of N 2 -fixation is genetically controlled and depends on the interaction between the bacterial and plant genom. In this review the actual knowledge in basic research of genetics of rhizobia and host plants is analysed.

Novel aspects of nitrogen fixation

Only a fraction of the total agricultural need for nitrogen comes from natural or synthetic fertilizers. The remainder is satisfied largely through the biological fixation of atmospheric nitrogen. Whilst this is most efficiently effected by the Rhizobium-legume root nodule, free-living bacteria and blue-green algae are known to be capable of fixing appreciable amounts. Recently, attention has been focused on bacteria closely associated with roots of certain tropical grasses.

Plant Process: Biological Fixation of Atmospheric Nitrogen . E. N. Mishustin and V. K. Shil'nikova. Translated from the Russian edition (Moscow, 1968) by Alan Crozy. Pennsylvania State University Press, University Park, 1972. x, 420 pp., illus. $19.50.

Plant Process: <i>Biological Fixation of Atmospheric Nitrogen</i> . E. N. Mishustin and V. K. Shil'nikova. Translated from the Russian edition (Moscow, 1968) by Alan Crozy. Pennsylvania State University Press, University Park, 1972. x, 420 pp., illus. $19.50.

Nitrogen Fixation in a Subarctic Mire

An investigation of biological fixation of atmospheric nitrogen in situ, as part of the Swedish IBP Tundra Biome Project, was carried out during the summer of 1971. The main site was a subarctic continental, ombrotrophic mire with permafrost, situated near Abisko in Lappland (northern Sweden). Low nitrogen fixation, mainly by aerobic bacteria, occurred in elevated (ombrotrophic) areas of the mire. In large wet depressions and pools, on the other hand, fixation by blue-green algae was quite appreciable. The algae were found to be epiphytically or intracellularly associated with Sphagnum and Drepanocladus mosses. Lichens with blue-green algal phycobionts or cephalodia are rare at the investigated site, and the few plants tested showed comparatively small activity, probably due to poor nutritional status (ombrotrophic conditions). In other parts of the Tornetrdsk area they are however considered to be of great importance.