Variation In Nitrogen Fixation Research Articles

THE EVALUATION OF STABLE ISOTOPIC RATIOS 13C AND 15N IN HUMIC ACIDS ALONG A FEN PEAT PROFILE

Mires are known as consistent environmental archives, but humic acids are the fraction of peat that is most recalcitrant and refractory to organic matter degradation, thus data on environmental changes during mire development can be recorded into them. This work was focused on the studies of stable isotopic ratios delta carbon-13 and delta nitrogen-15, and their distribution in humic acids within fen peat layers of different depths and peat composition. The variations in delta carbon-13 reflect isotopic variations in peat-forming plants over time and can be considered as a function of photosynthetic pathway that is being used to fix carbon dioxide. At the same time, variations in delta nitrogen-15 show nitrogen fixation in peat-forming plants and can be traced along with peat decomposition degree and depth. Properties of humic acids were studied in 2018 at 3 fens located in Latvia and Southern Finland, and comparatively they show properties. The method used for the determination of stable isotopes was the isotope-ratio mass spectrometry that was performed in the Faculty of Chemistry, University of Latvia. Results on delta carbon-13 indicate signal of C3 peat-forming plants, while signal of C4 peat-forming plants is not evident, which can be explained by non-efficient carbon dioxide fixation in fen vegetation. Results on delta nitrogen-15 show variations in nitrogen fixation in fen vegetation. Data show nitrogen fixation in terrestrial plants, however significant shifts in absolute isotope values indicate dependence on variations in peat decomposition degree and botanical composition. Data suggest that differences in peat botanical composition, decomposition degree and site dependent characteristics reflect in differences in delta carbon-13 and delta nitrogen-15 variations

Spatial and temporal variation in nitrogen fixation and its importance to phytoplankton in phosphorus‐rich lakes

Abstract Limnological theory posits that phosphorus (P) limits primary production in freshwater lakes, in part because fixation of atmospheric nitrogen (N2) can compensate for limitations in nitrogen (N) supply to phytoplankton. However, quantitative estimates of the degree to which N2 fixation satisfies planktonic N demand are rare. Here we used biweekly sampling during summer in seven lakes over 2 decades to estimate both planktonic N2 fixation and phytoplankton N demand. We further assessed the ability of biologically fixed N to satisfy N needs of primary producers in productive hardwater lakes. Phytoplankton N requirements, derived from estimates of phytoplankton productivity and N content, were moderately synchronous (S = 0.41) among lakes (ca. 0.1–9.2 mg N m–3 hr–1). In contrast, rates of N2 fixation determined using isotopic natural abundance method (NAM; 0.002–3.2 mg N m–3 hr–1), or heterocyte‐based calculations (0.10–1.78 mg N m–3 hr–1), varied asynchronously (SNAM = –0.03 and SHeterocyte = –0.11) among basins, accounted for a median of 3.5% (mean 11.3% ± 21.6) of phytoplankton demand, and were correlated to the abundance of Nostocales cyanobacteria when analysed using generalised additive models. Overall, the total mass of fixed N accounted for a median of only 3.0% of the spring standing stock of total dissolved N in study lakes (mean 7.5 ± 12.1%), with higher relative importance of fixed N in highly productive downstream lakes. Thus, while fixed N helps sustain primary productivity, particularly in years with high rates of N2‐fixation, it does not appear to eliminate N limitation of phytoplankton growth in these P‐rich hardwater lakes.

Nitrogen fixation and the diazotroph community in the temperate coastal region of the northwestern North Pacific

Abstract. Nitrogen fixation in temperate oceans is a potentially important, but poorly understood process that may influence the marine nitrogen budget. This study determined seasonal variations in nitrogen fixation and the diazotroph community within the euphotic zone in the temperate coastal region of the northwestern North Pacific. Nitrogen fixation as high as 13.6 nmol N L−1 d−1 was measured from early summer to fall when the surface temperature exceeded 14.2 °C (but was lower than 24.3 °C) and the surface nitrate concentration was low (≤ 0.30 μM), although we also detected nitrogen fixation in subsurface layers (42–62 m) where nitrate concentrations were high (> 1 μM). Clone library analysis results indicated that nifH gene sequences were omnipresent throughout the investigation period. During the period when nitrogen fixation was detected (early summer to fall), the genes affiliated with UCYN-A, Trichodesmium, and γ-proteobacterial phylotype γ-24774A11 were frequently recovered. In contrast, when nitrogen fixation was undetectable (winter to spring), many sequences affiliated with Cluster III diazotrophs (putative anaerobic bacteria) were recovered. Quantitative PCR analysis revealed that UCYN-A was relatively abundant from early to late summer compared with Trichodesmium and γ-24774A11, whereas Trichodesmium abundance was the highest among the three groups during fall.

Seasonal variation in nitrogen fixation and effects of climate change in a subarctic heath

Background and aims Nitrogen fixation associated with cryptogams is potentially very important in arctic and subarctic terrestrial ecosystems, as it is a source of new nitrogen (N) into these highly N limited systems. Moss-, lichen- and legume-associated N2 fixation was studied with high frequency (every second week) during spring, summer, autumn and early winter to uncover the seasonal variation in input of atmospheric N2 to a subarctic heath with an altered climate.

Variation in Nitrogen Fixation among Three Bush Bean Cultivars Grown in Kenya when Inoculated with Three Rhizobia Strains

Variation in Nitrogen Fixation among Three Bush Bean Cultivars Grown in Kenya when Inoculated with Three Rhizobia Strains

Latitudinal distribution of nitrogen isotopic composition in suspended particulate organic matter in tropical/subtropical seas

Natural nitrogen isotopic composition (δ15N) of suspended particulate organic matter (POM) and nitrogen fixation rates via 15N2 assay were measured in surface waters along 120° E from 30° N to 30° S in the Asian marginal seas (the East/South China Seas and the Sulu/Celebes/Java Seas) and the northeastern Indian Ocean in November–December 2005 and March 2006. The POM δ15N values ranged from−1.8 to 12.2‰ with an average of 3.6‰ and showed a decreasing trend towards the equator in both hemispheres. In parallel, the measured N2 fixation rates showed an increase from the subtropical to the tropical seas. This implies that a higher contribution of 15N-depleted POM was derived from enhanced N2 fixation. Water temperature and the stability of water column were partly responsible for the observed variations in nitrogen fixation. The large-scale spatial variations in suspended POM δ15N and N2 fixation rates suggest that the suspended POM δ15N may be a potential indicator of nitrogen fixation in surface waters in tropical/subtropical seas.

Nitrogen fixation by diazotrophic cyanobacteria in the Baltic Sea and transfer of the newly fixed nitrogen to picoplankton organisms

Nitrogen fixation ( 15N 2-tracer method) by filamentous cyanobacteria and the flux of the newly fixed nitrogen into picoplanktonic organisms were investigated during three cruises in the central Baltic Sea in July and August 1995 and July 1996. The diazotrophic cyanobacteria consisted mainly of Aphanizomenon and Nodularia and the picoplankton fraction mainly of Synechococcus, a coccoid nondiazotrophic cyanobacterium. The average N 2-fixation rate measured during the two July studies (3.9 nmol l −1 h −1 in 1995 and 2.4 nmol l −1 h −1 in 1996), was about 13 times higher than in August 1995 (0.3 nmol N 2 l −1 h −1). During the July studies, 5–10% of the total N 2-fixation was found in the picoplankton fraction, but none was found in August. The study shows that in the early stage of a cyanobacterial bloom new nitrogen is provided for the pelagic foodweb through release of recently fixed nitrogen by the diazotrophs, whereas in the late stage the input of new nitrogen occurs mainly through lysing of decaying filamentous cyanobacteria cells. Considerable temporal and local variations in nitrogen fixation found in this study indicate that broader studies in time and location are needed to assess the contribution of N 2-fixation to the nitrogen budget of the Baltic Sea.

Acclimation of Cyanobacterial Communities in Rice Fields and Response of Nitrogenase Activity to Light Regime

The short-term and long-term effects of light regime on nitrogenase activity (NA) and cyanobacterial communities in rice fields (Valencia, Spain) were examined. Daily variation in nitrogen fixation was measured during three periods of the crop cycle: tillering (formation of secondary stems in the rice plants), heading (formation of reproductive structures), and maturity. Two locations were examined over two consecutive years (1994 and 1995). Despite differences in the crop-cycle periods, location, and year, a consistent pattern of nitrogen fixation was observed, with a main activity peak in the morning and another in the late evening. Short-term experiments, performed on two cyanobacterial blooms (Nostoc sp. and Anabaena sp.) exposed to natural light under plant canopy (7% incidence irradiance), and to different light intensities under neutral density screens without plant cover (full sunlight, 43%, 26%, and 13% of incident irradiance), indicated that nitrogenase activity (NA) was dependent on both light intensity and quality. In long-term experiments, where natural communities of cyanobacteria were exposed to one month of different light intensities, changes in the species composition of the three main genera of heterocystous cyanobacteria (Nostoc, Anabaena, and Calothrix) were observed. The light intensity at which communities were exposed for one month became the optimum irradiance for NA for each cyanobacterial community. Assays performed at higher or lower irradiances showed lower NA. Nitrogen fixation followed a pattern of seasonal variation along the crop cycle. Values were low at the beginning of the crop (May), reached a maximum value at the end of the tillering stage (June), and declined thereafter until the end of the cultivation cycle (September).

Seasonal and site-specific variations in nitrogen fixation in a high arctic area, Ny-Ålesund, Spitsbergen

Nitrogen fixation was measured in different habitats in the area of Ny-Ålesund, Spitsbergen, using the acetylene reduction method on intact soil cores and Nostoc commune growing in macroscopic sheet communities. The samples were incubated both under constant conditions (19 °C and 200 μE∙m−2∙s−1) and under in situ conditions. Cyanobacteria were considered to be the major nitrogen-fixing organisms. The nitrogen fixation rates showed a seasonal variation during the growing season of 1994, with low activities just after the snow melt, increasing until the middle of August and showing a rapid decline after the snow fell on August 29. The soil temperature at the time of sampling showed a positive, linear correlation with the nitrogen fixation activities measured on intact soil cores, whereas the nitrogen fixation activities measured in situ of N. commune showed a positive, linear dependence on the moisture content in the sheets and the incubation temperatures inside the incubation vessels during the experiments. The optimal temperature of the nitrogen fixation activity was about 20 °C, both for N. commune and a Puccinellia salt marsh. The highest nitrogen fixation rate measured in situ was at a patterned ground, which had the highest pH, the highest concentrations of extractable calcium and magnesium, and the highest C:N ratio measured.Key words: nitrogen fixation, cyanobacteria, Nostoc commune, high arctic.

Seasonal variations in nitrogen-fixation (acetylene reduction) and sulphate-reduction rates in the rhizosphere of Zostera noltii: nitrogen fixation by sulphate-reducing bacteria

Nitrogen-fixation (acetylene reduction) rates were measured over an annual cycle in meadows of the seagrass Zostera noltii Hornem in the Bassin d'Arcachon, south-west France, between March 1994 and February 1995, using both slurry and whole-core techniques. Measured rates using the slurry technique consistently overestimated those determined on whole cores, probably due to the release of labile organic carbon sources as a result of root damage during preparation of the slurries. Thus, the whole-core technique may provide a more accurate estimate of in situ activity, since disturbance of physicochemical gradients of oxygen, sulphide, nutrients and the relationship between the plant roots and the rhizosphere microflora is minimised. Rates measured by the whole-core method were 1.8- to 4-fold greater (dependent upon season) in the light than those measured during dark incubations, indicating that organic carbon diffusing from the plant roots during photosynthesis was an important factor in regulating nitrogen fixation in the rhizosphere. Additions of sodium molybdate, a specific inhibitor of sulphate-reducing bacteria (SRB) inhibited acetylene-reduction activity by >80% as measured by both the slurry and whole-core techniques throughout the year, inferring that SRB were the dominant component of the nitrogen-fixing microflora. A mutualistic relationship between Z. noltii and nitrogen-fixing SRB in the rhizosphere, based on the exchange of organic carbon and fixed nitrogen is proposed. Acetylene- and sulphate-reduction rates showed distinct summer peaks which correlated with a reduced availability of ammonium in the sediment and the annual growth cycle of Z. noltii in the basin. Overall, these data indicate that acetylene reduction (nitrogen fixation) activity in the rhizosphere of Z. noltii was regulated both by the availability of organic carbon from the plant roots and maintenance of a low NH 4 + concentration in the vicinity of the plant roots due to efficient assimilation of NH 4 + by Z. noltii during the growth season. Nitrogenfixation rates determined from acetylene-reduction rates measured using the whole-core technique ranged from 0.1 to 7.3 mg N m-2d-1, depending on season, and were calculated to contribute between 0.4 and 1.1 g N m-2yr-1, or 6.3 to 12% of the annual fixed nitrogen requirement of Z. noltii.

Nitrogen cycling in microbial mats: rates and patterns of denitrification and nitrogen fixation

Spatial and temporal variations in nitrogen fixation and denitrification rates were examined between July 1991 and September 1992 in the intertidal regions of Tomales Bay (California, USA). Microbial mat communities inhabited exposed mudflat and vegetated marsh surface sediments. Mudflat and marsh sediments exhibited comparable rates of nitrogen fixation. Denitrification rates were higher in marsh sediments. Nitrogen fixation rates were lowest during January at both sites, whereas highest rates occurred during summer and fall. Denitrification rates were highest during fall and winter months in marsh sediments, while rates in mudflat sediments were highest during summer and fall. In mudflat sediments, nitrogen fixation and denitrification rates, integrated over 24 h, ranged from 6 to 79 mg N m-1 d-1 and 1 to 10 mg N m-2 d-1, respectively. Rates of denitrification represented between 6 and 20% of nitrogen fixation rates during the day, but exceeded or were equivalent to nitrogen fixation rates at night. The highest integrated rates of both nitrogen fixation and denitrification occurred during July, whereas, the highest percent loss occurred during spring when denitrification rates amounted to 20% of nitrogen fixation rates during the day. Over an annual cycle, inputs of fixed N to mudflat communities occurred exclusively during daylight. These results underscore the importance of determining integrated diel rates of both nitrogen fixation and denitrification when constructing N budgets. Using this approach, it was shown that microbial denitrification can represent a significant loss of combined nitrogen from mats on daily as well as monthly time scales.

Ontogenic variation in nitrogen fixation and accumulation of nitrogen in mungbean, blackgram, cowpea, and groundnut

Ontogenic variations in N2 fixation and accumulation of N by the mungbean (Vigna radiata L. Wilczek), blackgram (Vigna mungo L. Hepper), cowpea (Vigna unguiculata L. Walp.), and groundnut (Arachis hypogaea L.) were studied by a 15N-dilution technique. Pots filled with 7 kg of red yellow podzolic soil were used. Samples were taken 20, 40, 60, and 80 days after emergence which approximately corresponded to preflowering, flowering, early/mid-pod filling and late pod filling stages, respectively. During early growth (up to 40 days after emergence), the carryover of seed N accounted for a considerable fraction of the total plant N in the legumes, the highest being in the groundnut. With a correction for carryover, the groundnut derived over 45% of its N content from the atmosphere 20 days after emergence whereas the corresponding figures were 33% for the blackgram and about 28% for the cowpea and mungbean. Between flowering and early pod fill, there was a rapid increase in N2 fixation in all legumes except in groundnut which showed highest fixation from 60 to 80 days after emergence. In the mungbean, N2 fixation and uptake of soil N were insignificant 60 days after emergence while in other legumes these processes continued beyond this time. All legumes derived about 90% of their N from atmosphere by 80 days after emergence. However, due to considerable interspecific differences in total N yield the final amount of N2 fixed showed an appreciable variation among legumes. It was highest in the groundnut (443 mg N plant-1) followed by the cowpea (385), blackgram (273), and mungbean (145), respectively. The groundnut maintained nodules until the late pod filling stage while in other legumes, nodules senesced progressively following the mid-pod filling stage. During pod filling there was a net mobilization of N from vegetative tissues to developing pods in the mungbean, which amounted to about 20% of N in seeds. This mobilization was not evident in other legumes.

Biological nitrogen fixation (acetylene reduction) associated with blue-green algal (cyanobacterial) communities in the Beachwood Mangrove Nature Reserve II. Seasonal variation in acetylene reduction activity

Seasonal variation in nitrogen fixation of blue-green algae associated with Avicennia marina (Forssk.) Vierh. pneumatophores and wet and dry surface sediments were investigated in the Beachwood Mangrove Nature Reserve by means of the acetylene reduction technique. The blue-green algae identified were all non-heterocystous and have been reported to fix nitrogen. The dominant blue-green algae were Lyngbya confervoides C.Ag. ex Gomont, Oscillatoria limosa Ag. ex Gomont and Microcoleus chthonoplastes Thuret ex Gomont in the pneumatophore, wet and dry surface habitats, respectively. A marked seasonal variation in ARA (acetylene reduction activity) was apparent, with summer maxima being recorded. This coincided with maximum nitrogen-fixing blue-green algal numbers, temperature, light intensity and day length. Seasonal variations in organic carbon, inorganic nitrogen, salinity, percentage moisture and bacterial numbers are discussed. It was estimated that nitrogen fixation by blue-green algal communities supplies 24.3% of the annual nitrogen requirements of the mangrove swamp. Seisoenvariasie in stikstofbinding van blougroen alge geassosieer met pneumatofore van Avicennia marina (Forssk.) Vierh. en nat en droë oppervlaksedimente is in die Beachwood Mangliet-natuurreservaat deur middel van die asetileenreduksietegniek ondersoek. Die blougroen alge wat geïdentifiseer is, was almal nie-heterosisties en is aangeteken as stikstofbindend. Die dominante blougroen alge was Lyngbya confervoides C.Ag. ex Gomont, Oscillatoria limosa Ag. ex Gomont en Microcoleus chthonoplasteslhuret ex Gomont in die pneumatofore, nat en droë oppervlakhabitats, onderskeidelik. ‘n Merkbare seisoenvariasie in ARA (asetileen-reduksieaktiwiteit) was duidelik, met maksimums in die somer aangeteken. Dit het ooreengekom met ‘n maksimum aantal stikstofbindende blou-groen alge, asook maksimum temperatuur, ligintensiteit en daglengte. Seisoensvariasies in organiese koolstof, anorganiese stikstof, soutgehalte, persentasie vog en aantal bakterieë word bespreek. Na raming voorsien stikstofbinding deur blougroenalg-gemeenskappein 24.3% van die jaarlikse stikstofbehoeftes van die manglietmoeras.

The physiology and biochemistry of cultivar-strain interactions in the white clover-Rhizobium symbiosis

Two white clover cultivars were inoculated with two Rhizobium leguminosarum bv. trifolii strains in a factorial series of experiments. Plants were grown in axenic conditions in nitrogen free nutrient solution in a controlled environment room. Variations in nitrogen fixation were dependent partly upon general strain effects, partly upon general cultivar effects but there were also substantial differences attributable to precise interactions between specific combinations. The physiological and biochemical basis of these differences was examined. There were variations in the onset of nodulation and nitrogenase (acetylene reduction) activity. The rate at which nitrogenase activity developed also differed between associations as did the average size and number of nodules but none of these effects correlated well with differences in plant dry matter accumulation. Studies on nodule biochemistry revealed that the major nitrogen fixation enzymes were present in all four associations. Nodule protein content and enzyme activity (on a g nodule fresh weight basis) were substantially greater in associations formed by the more effective strain but cannot explain the interactive effect on dry matter accumulation. The relevance of these data to our understanding of factors regulating variations in nitrogen fixation is discussed.

Variation in nitrogen fixation among populations ofFrankia sp. andCeanothus sp. in actinorhizal association

Wildland shrub improvement is needed for sound range and disturbed land revegetation practice. The possibility of selecting superior N2-fixingFrankia-Ceanothus spp. actinorhizal associations was examined. Greenhouse tests were used to expose various soil-borne microsymbiont andCeanothus sp. population accessions in reciprocal combination. The acetylene reduction rate was used as a measure of N2-fixation capacity. There was no significant interaction between host and microsymbiont regardless of source for all variables measured. The acetylene reduction rate, nodule number and mass, plant biomass, and root: shoot ratio were significantly different among soil sources. The acetylene reduction rate was not significantly different amongCeanothus sp. accessions. Neither was it strongly correlated with other variables. It was concluded that the N2-fixation rate is more a function ofFrankia sp. than the hostCeanothus sp. in actinorhizal associations. It appears possible to select soil sources with superior N2-fixing microsymbiont populations.

Nitrogen fixation by Nodularia spumigena Mertens (Cyanobacteriaceae). 1: Field studies and the contribution of blooms to the nitrogen budget of the Peel-Harvey Estuary, Western Australia

Variations in nitrogen fixation (acetylene reduction) by Nodularia spumigena blooms in the Peel-Harvey estuarine system were examined with respect to spatial (sampling station location, and depth) and temporal (seasonal and diurnal) distribution. The annual contributions of nitrogen fixation by the blooms to the nitrogen budget of the estuary were estimated to range from 309 to 713t. Contributions by nitrogen fixation were similar to the riverine inputs in the Harvey Estuary, but lower in the Peel Inlet.

Seasonal variation in nitrogen fixation, associated microbial populations, and carbohydrates in roots and rhizomes of Typha latifolia (Typhaceae)

Seasonal changes in nitrogen fixation, numbers of nitrogen-fixing bacteria associated with the roots, and rhizome–root carbohydrates were studied for the broad-leaved cattail, Typha latifolia L. Populations of anaerobic and aerobic diazotrophic bacteria were present on the root surface. Anaerobic bacteria predominated in the diazotrophic association, were more active in the acetylene reduction assay, and generally outnumbered aerobic bacteria by 2 to 1 during maximum rates of seasonal nitrogen fixation. The observed maximum nitrogen fixation rate coincided closely with reproductive development in Typha and peak microbial populations. Starch levels in rhizomes were nearly depleted during the middle of the growing season, whereas free sugar concentrations remained stable. Sugar concentrations in the roots increased rapidly during rhizome–root growth and decreased rapidly prior to peak nitrogenase activity.

Seasonal Variation in Nitrogen Fixation by Different Ages of Root Nodules of Alnus nepalensis Plantations, in the Eastern Himalayas

SUMMARY common in the Eastern Himalayas. (2) Five different ages of plantations from the Pankhasari range of the Kalimpong forest division in the Eastern Himalayas have been studied. Rates of nitrogen fixation (nitrogenase activity) by three different age-classes of root nodules was measured in July, October and December 1981 and April 1982. These months represent the rainy, transition, winter and early summer seasons. (3) Nitrogenase activity (acetylene reduction) was highest in July (high moisture and 25 'C average temperature) and lowest in December (dry and cold (9 0C), with litterfall). Activity was highest in younger nodules irrespective of tree age. (4) It is concluded that A. nepalensis plants in the Himalayas fix significant amounts of nitrogen.

Seasonal variation in nitrogen fixation by Nostoc commune Vaucher at the Vestfold Hills, Antarctica

Studies of in situ nitrogen fixation by the blue-green alga Nostoc, measured by acetylene reduction, were conducted over a 12 month period at the ice-free Vestfold Hills, Antarctica (68°34′S, 77°57...

Diel variation in nitrogen fixation by a marine blue-green alga, Trichodesmium thiebautii

Abstract A diel variation was demonstrated with respect to nitrogen fixing capacity of a marine blue-green alga, Trichodesmium thiebautii, collected from subtropical waters of the western North Pacific. A 200-fold difference was observed between day and night activities when measured at a light intensity of 12,000 lx. The pattern and extent of variation were different from diel variations reported for photosynthesis, nutrient uptake, and nitrogen fixation of natural populations of marine phytoplankton.