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Showing papers on "Nitrogen fixation published in 1988"


Journal ArticleDOI
TL;DR: Inhibition of legume nodule formation and N2 fixation by nitrate is inhibited and legume growth is inhibited by nitrates, respectively.
Abstract: (1988). Inhibition of legume nodule formation and N2 fixation by nitrate. Critical Reviews in Plant Sciences: Vol. 7, No. 1, pp. 1-23.

681 citations


Journal ArticleDOI
TL;DR: Nitrogen fixation appears important in making up deficits in nitrogen availability relative to phosphorus availability in many lakes, contributing to the phosphorus-limited status of these systems.
Abstract: Nitrogen fixation is mediated by a variety of autotrophic and heterotrophic bacteria. Cyanobacteria appear responsible for most planktonic fixation in aquatic ecosystems, and rates of fixation are high only when thcsc organisms make up a major percentage of the planktonic biomass, Planktonic nitrogen fixation tends to be low in oligotrophic and mesotrophic lakes (generally 20% of the nitrogen input to the Asko region of the Baltic Sea and 17% of the nitrogen input to the PeelHarvey estuary in Australia. Fixation in sediments of estuaries and eutrophic and mesotrophic lakes usually constitutes a small percentage of the nitrogen inputs to these systems. However, benthic fixation appears to be a major source of nitrogen for many oligotrophic tropical lagoons and for some oligotrophic lakes, even though fixation rates are moderate because other nitrogen inputs tend to be low. Nitrogen fixation probably is a fairly minor input of nitrogen to marine wetlands, which are generally open to other inputs, but contributes roughly half the total nitrogen input to some freshwater wetlands (bogs, cypress domes), where other inputs are more limited. Nitrogen fixation appears important in making up deficits in nitrogen availability relative to phosphorus availability in many lakes, contributing to the phosphorus-limited status of these systems. That many estuaries and coastal seas are nitrogen limited is due in part to the generally low rates of nitrogen fixation found in these systems.

540 citations


Journal ArticleDOI
TL;DR: The tendency toward less nitrogen fixation by plankton in estuaries and coastal marine ecosystems than in lakes subject to similar loadings of nitrogen and phosphorus may be due to a lower availability in oxic seawater of one or more trace elements required for nitrogen fixation, such as molybdenum and iron.
Abstract: Planktonic nitrogen fixation in lakes is strongly related to lake trophic status, with moderate and high rates usually occurring only in eutrophic lakes. Among eutrophic lakes, nitrogen fixation is related to the ratio of nitrogen loading to phosphorus loading to the lake; significant nitrogen fixation by planktonic organisms generally occurs only when the N: P ratio of the nutrient loading is near or below the Redfield ratio of 16: 1. In contrast, nitrogen fixation by planktonic organisms is generally low in estuaries even when the N: P ratio of nutrients inputs is low. The tendency toward less nitrogen fixation by plankton in estuaries and coastal marine ecosystems than in lakes subject to similar loadings of nitrogen and phosphorus may be due to a lower availability in oxic seawater of one or more trace elements required for nitrogen fixation, such as molybdenum and iron. Iron concentrations are generally lower in estuarine waters and seawater than in most lakes. And although molybdenum concentrations in seawater are actually higher than in lakes, molybdenum availability is probably lower, since sulfate inhibits molybdate assimilation by microbes. Molybdate is the primary form of molybdenum in oxic seawater, and the ratio of sulfate: molybdate is greater than in lakes. However, even in lakes sulfate is several orders of magnitude more abundant than molybdenum, and the ratio of dissolved sulfate to dissolved molybdenum typically is much greater than the ratio of sulfur to molybdenum apparently required by nitrogen-fixing cyanobacteria. Consequently, assimilation of molybdate by cyanobacteria is probably an energetically expensive process in all natural waters, but more so in seawater than in freshwaters. High concentrations of dissolved organic matter are known to favor blooms of cyanobacteria, perhaps by increasing iron and/or molybdenum availability through chelation. The primary controls on nitrogen fixation in sediments, wetlands, macrophyte beds, and cyanobacterial mats may be different from those for fixation by planktonic organisms. Both molybdenum and iron are probably more available in these systems than in oxic waters, since reducing conditions and high DOC concentrations will increase iron solubility and favor the stability of reduced forms of molybdenum; sulfate should not inhibit the assimilation of these reduced molybdenum compounds. Consequently, nitrogenase synthesis (and, therefore, nitrogen fixation) in wetlands and in sediments may be less energetically expensive than in oxic water columns. A major control on nitrogen fixation in sediments may be repression of nitrogenase synthesis by high concentrations of ammonium, a factor less important to planktonic fixation because of the much lower concentrations of ammonium generally found in water columns than in sediments.

414 citations


Journal ArticleDOI
TL;DR: In this article, the growth and N2-fixation of Trifolium repens were measured in pots, using 15N techniques, on either metal-contaminated or uncontaminated soils which came from field plots which last received sewage sludge (Contaminated) or farmyard manure (uncontaminate) more than 20 years ago.
Abstract: The growth and N2-fixation of Trifolium repens was measured in pots, using 15N techniques, on either metal-contaminated or uncontaminated soils which came from field plots which last received sewage sludge (contaminated) or farmyard manure (uncontaminated) more than 20 years ago. Plants grown on sludged soil had lower concentrations of N and smaller yields; the root nodules were small, white, numerous and ineffective in N2-fixation. By contrast, nodules on plants grown on farmyard manure-treated soil were pink (indicating the presence of leghaemoglobin), large and few in number, characteristic of effective nodules. The depressive effect on yield was overcome, at least in the short-term, by adding nitrogen fertilizer to the soil. Concentrations of metals in the leaf material were low and direct phytotoxic effects unlikely. The two soils were mixed in various proportions to test the effects of increasing concentrations of extractable metals in the soil on N2-fixation. A 50% reduction in fixation was observed in soil containing approximately the following concentrations (mg kg−1) of metals extracted by EDTA: 165Zn, 60 Cu, 7.3 Ni and 5.3 Cd. Corresponding “total” concentrations (mg kg−1) were 334 Zn, 99 Cu, 27 Ni and 10 Cd. These results are discussed in relation to the current guidelines designed to limit the accumulation of metals in agricultural soils receiving sewage sludge.

213 citations


Journal ArticleDOI
TL;DR: It is concluded that the whole legume-Rhizobium symbiosis should be considered when improving legume growth and yield under nutrient stress conditions.
Abstract: Mineral nturient defiencies are a major constraint limiting legume nitrogen fixation and yield. In this review general techniques for assessing nutrient involvement in symbiotic nitrogen fixation are described and specific methods are outlined for determining which developmental phase of the symbiosis is most sensitive to nutrient deficiency. The mineral nutrition of the Rhizobium component of the symbiosis is considered both as the free living organism in the soil and as bacteroids in root nodules. Rhizobial growth and survival in soils is not usually limited by nutrient availability. Multiplication of rhizobia in the legume rhizosphere is limited by low Ca availability. Nodule initiation is affected by severe Co deficiency through effects on rhizobia. Nodule development is limited by severe B deficiency via an effect on plant cell growth. Fe deficiency limits nodule development by affecting rhizobia and strains of rhizobia differ widely in their ability to acquire sufficient Fe for their symbiotic development. Nodule function requires more Mo than does the host plant, and in some symbioses nitrogen fixation may be specifically limited by low availability of Ca, Co, Cu and Fe. The importance of the peribacteriod membrane in determining nutrient availability to bacteroids is considered. It is concluded that the whole legume-Rhizobium symbiosis should be considered when improving legume growth and yield under nutrient stress conditions. Differences among rhizobial strains in their ability to obtain mineral nutrients from their environment may be agronomically important.

181 citations



Journal ArticleDOI
TL;DR: It is suggested that denitrification arose prior to aerobic respiration and that nitrification arose after the advent of an aerobic atmosphere, and for the first time that HNO, predicted to be the main product of atmospheric photochemical reactions involving NO on the primitive Earth by photochemical models, would eventually become NO2− and NO3− after reaching the Earth's surface.
Abstract: The energetics of nitrogen transformation reactions and the evolution of nitrogen cycling are examined. It is suggested that meteor impact-produced fixed nitrogen could have caused the entire reservoir of the earth's N2 to convert into fixed nitrogen at the end of accretion. The abiotic fixation rate on the early earth by lightning is estimated at about 1-3 X 10 to the 16th molecules of NO/J. It is found that biological nitrogen fixation may have evolved after the development of an aerobic atmosphere. It is shown that HNO could eventually become NO2(-) and NO3(-) after reaching the earth's surface. It is concluded that the evolutionary sequence for the biological transformation of nitrogen compounds is ammonification - denitrification - nitrification - nitrogen fixation.

157 citations


Book
01 Jan 1988
TL;DR: Part 1 Metabolism: the flexibility and variety of algal metabolism, G.P.Stewart light-induced proton efflux of the cyanobacterium "anabaena variabilis", S.C.Scherer et al dark respiration in cyanobacteria, H.J.Matthijs and H.E.Syrett.
Abstract: Part 1 Metabolism: the flexibility and variety of algal metabolism, G.E. Fogg nitrogen reserves and dynamic reservoirs in cyanobacteria, N.G.Carr uptake and utilization of nitrogen compounds, P.J.Syrett. Part 2 Biosynthesis: lipid metabolism, J.L.Harwood et al tetrapyrrole biosynthesis - the C5 pathway, A.J.Smith and L.J.Rogers. Part 3 Bio-energetics: molecular biology of photosynthetic reaction centres, A.C.Stewart light-induced proton efflux of the cyanobacterium "anabaena variabilis", S.Scherer et al dark respiration in cyanobacteria, H.C.P.Matthijs and H.J.Lubberding nitrogen fixation, J.R.Gallon and A.E.Chaplin. Part 4 Regulation: calcium-mediated regulation in the cyanobacteria?, R.J.Smith thioredoxin and enzyme regulation, P.Rowell et al the responses of cyanobacteria to salt stress, R.H.Reed and W.D.P.Stewart. Part 5 Interactions: nutrient interactions in the marine environment, Anthony G.Davies algal extracellular products - antimicrobial substances, A.K.Jones cyanobacterial toxins, G.A.Codd and G.K.Poon alga-invertebrate symbiosis, A.E.Douglas. Part 6 Biotechnology: the biotechnology of microalgae and cyanobacteria, N.W.Kerby and W.D.P.Stewart seaweed biotechnology - current status and future prospects, L.V.Evans and D.M.Butler making mutants and influencing genes - the genetic exploitation of algae and cyanobacteria, R.A.Lewin.

152 citations


Journal ArticleDOI
TL;DR: This book contains 17 selections on Genetic regulation of nitrogen fixation; On the analysis of symbiotic genes of Rhizobium; Regulation of nitrogen assimilation by bacteria; Alternative and conventional nitrogenases; and The role of oxygen and hydrogen in nitrogen fixation.
Abstract: This book contains 17 selections. Some of the titles are: Genetic regulation of nitrogen fixation; On the analysis of symbiotic genes of Rhizobium; Regulation of nitrogen assimilation by bacteria; Alternative and conventional nitrogenases; and The role of oxygen and hydrogen in nitrogen fixation.

144 citations


Journal ArticleDOI
TL;DR: It is concluded that the failure of the infecting rhizobia to obtain adequate amounts of iron from the plant results in arrested nodule development and a failure of nitrogen fixation.
Abstract: Severely iron-deficient peanuts (Arachis hypogaaea L.) grown on calcareous soils in central Thailand failed to nodulate until given foliar iron applications. Glasshouse experiments were conducted on two cultivars (Tainan 9 and Robut 33-1) to identify which stage of the nodule symbiosis was most sensitive to iron-deficiency. Iron-deficiency did not limit growth of soil or rhizosphere populations of peanut liradyrhizobium. Similar numbers of root nodule initials formed in the roots of both control and iron-sprayed plants, showing that iron-deficiency did not directly affect root infection and nodule initiation. Plants sprayed with iron produced greater numbers of excisable nodules and carried a greater nodule mass than untreated plants. Five days after iron application, nodules on sprayed plants of CV. Tainan 9 contained 200-fold higher bacteroid numbers per unit weight and 14-fold higher concentrations of leghaemoglobain. The onset of nitrogenase activity was also delayed by iron deficiency in both cultivars. Tainan 9 appeared more sensitive to iron-deficiency than Robut 33-1 in terms of nodule mass produced, but both cultivars showed the same effect of iron-deficiency on nitrogenase activity per plant. It is concluded that the failure of the infecting rhizobia to obtain adequate amounts of iron from the plant results in arrested nodule development and a failure of nitrogen fixation.

128 citations


Book ChapterDOI
TL;DR: If establishment of the inoculated strain is demonstrated in plants grown in15N-labelled soil, the15N enrichment of the plants will reveal if any observed responses in N yield are due to N2-fixation or increased soil/fertilizer-N uptake.
Abstract: Diazotrophs have been isolated from the rhizosphere or roots of plants by many workers. To recognize a certain diazotroph as the most abundant bacterium at a certain site or as the principal agent responsible for N2-fixation is much more difficult. It is probable that many diazotrophs, including possibly the most efficient ones, have not been identified yet. The use of proper selective media which simulate the environment of the various diazotrophs in situ has led to the discovery of 10 new root-associated diazotrophs, three of them during 1986/1987 (Azospirillum halopraeferans, Herbaspirilium seropedicae and the recently proposed Acetobacter diazotrophicus). The importance of using a variety of carbon substrates in the growth media with pH indicators, and the use of N-free semi-solid media, is discussed. Recognition of plant-bacteria interactions requires, in addition to the identification of the bacteria, the demonstration of effects of the plant on the bacteria and of the bacteria on the plant. Confirmation of the identity of diazotrophs responsible for response of plants to inoculation must be made in experiments with strains labelled with antibiotic resistance or other markers. If establishment of the inoculated strain is demonstrated in plants grown in 15N-labelled soil, the 15N enrichment of the plants will reveal if any observed responses in N yield are due to N2-fixation or increased soil/fertilizer-N uptake.



Journal ArticleDOI
TL;DR: The freshwater cyanobacterium, Anabaena, was used as a laboratory model for the biochemical and physiological effects of iron, and Trichodesmium responded to iron additions indicating that it may be Fe limited in its natural environment.
Abstract: Iron availability may limit carbon and nitrogen fixation in the oceans. The freshwater cyanobacterium, Anabaena, was used as a laboratory model for the biochemical and physiological effects of iron. Increased iron nutrition, in the range of 10−8 M to 10−6 M resulted in increases of approximately four fold in carbon and nitrogen fixation rates. Chlorophyll concentration increased, and the relative amount of in vivo fluorescence was reduced with more iron. Natural samples of Trichodesmium, collected off Barbados and incubated with increased iron for two days, showed similar effects. Trichodesmium responded to iron additions indicating that it may be Fe limited in its natural environment. These responses to iron are consistent with the biochemical roles of iron in photosynthesis and nitrogen fixation. The results are discussed in the geochemical context of the sporadic total iron input to tropical oceans and possible implications to spatial and temporal patterns of productivity.

Journal ArticleDOI
TL;DR: Soybeans were grown in a glasshouse in sand-vermiculite medium supplied daily with a mineral nutrient solution essentially free of combined N or containing 5 mM nitrate of known 15N abundance to estimate utilisation of atmospheric N2 by nodulated plants.
Abstract: Soybeans were grown in a glasshouse in sand-vermiculite medium supplied daily with a mineral nutrient solution essentially free of combined N or containing 5 mM nitrate of known 15N abundance. The natural abundance of 15N in parts of plants and in nitrogen remaining in the medium was determined from 15 days after planting until fruiting. In nodulated plants completely dependent on N2 fixation for growth, the δ15N of plant nitrogen was uniformly negative at 56 days (overall mean: -0.90± 0.17) after adjustment for the effect of seed nitrogen. The δ15N of root nodules increased with time (max. 9.6‰), as that of shoots declined (min. - 1.3 ‰). The δ15N of every mainstem trifoliolate leaf and of the first (unifoliolate) leaf declined from initially positive values (0.5 to 2 ‰) to about - 2‰ with similar time courses, irrespective of the time of initiation. There were no significant losses of N from the plants during growth. There were differences between the δ15N of the total N of root-bleeding xylem sap and of sap extracted by vacuum treatment of stems. These were due to differences between the proportions of ureide-N and amino-N and between the δ15N values of these components. When nodulated plants were supplied daily with 5 mM nitrate (δ15N = 7.68‰) between 21 and 35 days, N2 fixation was reduced to 63% of N assimilated but growth and accumulation of nitrogen were affected little. Following removal of nitrate, there were changes in growth which led to enhanced nodulation and N2 fixation. The δ15N of the total N of trifoliolate leaves which were initiated or expanded before or during the period of nitrate treatment remained positive; those expanded or initiated after the treatment became negative in δ15N, as in the corresponding leaves of untreated nodulated plants. The δ15N of nodules was unaffected by the nitrate treatment. In plants (non-nod. Clark '63) supplied continuously with nitrate, the δ15N of the total N of entire plants rose quickly from values for seeds, but to values significantly higher than in the nitrate. These results are discussed in relation to the effects on the use of 15N natural abundance data for estimating utilisation of atmospheric N2 by nodulated plants.

Book ChapterDOI
TL;DR: This chapter focuses on nitrogen fixation in cyanobacterial mats, where the availability of combined nitrogen alone is too low to allow development of the mat, and it is assumed that in many mats nitrogen fixation is performed by nonheterocystous organisms.
Abstract: Publisher Summary This chapter focuses on nitrogen fixation in cyanobacterial mats. Intertidal sediments, hot springs, salt ponds, salt marshes, and mangrove forest sediments are often characterized by dense populations of cyanobacteria. Benthic filamentous cyanobacteria may form rigid structures, called cyanobacterial mats. Cyanobacterial mats usually contain a very high biomass, and in many environments, especially intertidal sediments, the availability of combined nitrogen alone is too low to allow development of the mat. Therefore, biological nitrogen fixation in many mats will be of paramount importance. Many cyanobacteria are known to fix nitrogen. Not only cyanobacteria that differentiate heterocysts, but also several unicellular and filamentous cyanobacteria without heterocysts have been shown to fix nitrogen. The majority of cyanobacterial mats are built by filamentous, nonheterocystous cyanobacteria. Therefore, it can be assumed that in many mats nitrogen fixation is performed by nonheterocystous organisms. In cyanobacterial mats, two different methods of nitrogenase measurement can be used. These are the bell-jar method for in situ measurements and the cork-borer sampling technique.

Journal ArticleDOI
19 Aug 1988-Science
TL;DR: The current results imply that the glutamine synthetase-catalyzed step in ammonia assimilation, a plant function, strongly influences overall dinitrogen fixation in legumes.
Abstract: An approximate doubling in plant growth, total plant nitrogen, nodulation, and overall dinitrogen fixation of alfalfa are the consequences of the action of a toxin delivered by a Pseudomonas infesting the alfalfa rhizosphere. The toxin, tabtoxinine-beta-lactam, inactivates selectively one form of glutamine synthetase in the nodules. Thus, normal glutamine synthetase-catalyzed ammonia assimilation is significantly impaired; yet these plants assimilated about twice the normal amount of nitrogen. How plants regulate dinitrogen fixing symbiotic associations is an important and unresolved question; the current results imply that the glutamine synthetase-catalyzed step in ammonia assimilation, a plant function, strongly influences overall dinitrogen fixation in legumes.

Journal ArticleDOI
TL;DR: It is submitted that this technique for determining the effectiveness of Rhizobia in soil, combined with a plant-infection method for counting rhizobia, can be a reliable guide to the need for inoculation in the field.
Abstract: A method for estimating the nitrogen-fixing capacity of a population of rhizobia resident in soil is presented. legume test plants, growing under microbiologically-controlled conditions in test tubes packed with a vermiculite substrate moistened with a nitrogen-free plant nutrient solution, are inoculated directly with a suspension of the soil under examination. Rhizobia in the soil nodulate the test plants, and the amount of foliage dry matter produced in the 28 days after inoculation is regarded as an index of their effectiveness. An inoculum of at least 30, and preferably 100, rhizobia is needed to ensure that nitrogen fixation is not masked by delayed nodulation. The new method is tentatively described as the ‘whole-soil inoculation’ technique. Appraisals were made withTrifolium subterraneum L. andRhizobium trifolii and withMedicago sativa L. andR. meliloti. Soil-borne pathogens did not interfere with plant growth. The whole-soil inoculation technique was less tedious and time-consuming than an alternative method which involved extracting representative isolates from the soil and testing their effectiveness individually, and appeared to give more realistic values for the nitrogen-fixing capacity of the soil as a whole. Used in association with a field experiment, the whole-soil inoculation technique confirmed microbiologically that there had been an agronomic response to surface application of inoculant to poorly-nodulatedT. subterraneum pasture. It is submitted that this technique for determining the effectiveness of rhizobia in soil, combined with a plant-infection method for counting rhizobia, can be a reliable guide to the need for inoculation in the field.

Journal ArticleDOI
01 Jan 1988-Nature
TL;DR: This work identifies some environmental factors that may control the development and growth of marine N2 fixers and experimentally manipulating them in nitrogen-depleted North Carolina coastal Atlantic Ocean water has addressed the paradox of ecologically insignificant rates of N2 fixation in such waters.
Abstract: Chronic deficiencies in biologically utilizable nitrogen control primary production in vast segments of the world's oceans1–3. A priori, it would appear that these conditions offer selective advantages to N2-fixing microorganisms (eubacteria and cyanobacteria). Most studies, however, concur that ecologically insignificant rates of N2 fixation are found in such waters4–6. We have addressed this paradox by identifying some environmental factors that may control the development and growth of marine N2 fixers and experimentally manipulating them in nitrogen-depleted North Carolina coastal Atlantic Ocean water. The availability of phosphorus, iron and molybdenum, required for both synthesis and function of the N2-fixing enzyme complex nitrogenase7, was sufficient to support the growth of N2-fixers. However, colonizable inorganic and organic surfaces were important for the development and proliferation of N2-fixing microbial consortia (mixtures of eubacteria, and cyanobacteria plus eubacteria). Surface-associated N2 fixation potentials were much more dependent on organic than on inorganic nutrient enrichment, and were affected by the incidence and magnitude of localized O2 depletion in the surface-associated micro-zones. As molecular O2 is a potent inhibitor of N2 fixation in many marine microorganisms, the extent to which biological nitrogen demands can be met by N2 fixation depends on the presence and maintenance of O2 depleted microzones.

Journal ArticleDOI
TL;DR: In a study of the plant communities of two Australian rainforests, it was found that pioner species had high levels of nitrate reductase and were predominantly leaf nitrate assimilators, and low levels of chloroplastic glutamine synthetase imply that, in some of these woody plants, photorespiratory ammonia is re-assimilated via cytosolic glutamine Synthetase.
Abstract: In a study of the plant communities of two Australian rainforests, it was found that pioner species had high levels of nitrate reductase (EC 1.6.6.1) and were predominantly leaf nitrate assimilators. Under- and over-storey species had low levels of shoot and root nitrate reductase activity, and many of them showed little capacity for nitrate reduction even when nitrate ions were freely available. Although closed-forest species have lower levels of nitrate reductase than those of gaps and forest margins, their total nitrogen contents were similar, suggesting the former utilize nitrogen sources other than nitrate ions. Glutamine synthetase (EC 6.3.1.2) was present in the leaves of all species examined. In the leaves of pioneer species the chloroplastic isoform of glutamine synthetase predominted, while in most of the species typical of closed-forest the cytosolic isoform accounted for at least 40% of total leaf activity. Low levels of chloroplastic glutamine synthetase were correlated with a low capacity for leaf nitrate reduction, and both are characteristic of many species that regenerate and grow for some time in shade. Low levels of chloroplastic glutamine synthetase imply that, in some of these woody plants, photorespiratory ammonia is re-assimilated via cytosolic glutamine synthetase.

Journal ArticleDOI
TL;DR: The effect of salinity and inoculation on growth, ion uptake and nitrogen fixation by Vigna radiata was drastically affected at high salt concentration and most of the studied strains of Rhizobium were salt tolerant.
Abstract: This study reports the effect of salinity and inoculation on growth, ion uptake and nitrogen fixation byVigna radiata. A soil ECe level of 7.5 dS m−1 was quite detrimental causing about 60% decline in dry matter and grain yield of mungbean plants whereas a soil ECe level of 10.0 dS m−1 was almost toxic. In contrast most of the studied strains of Rhizobium were salt tolerant. Nevertheless, nodulation, nitrogen fixation and total nitrogen concentration in the plant was drastically affected at high salt concentration. A noticeable decline in acetylene reduction activity occurred when salinity level increased to 7.5 dS m−1.

Journal ArticleDOI
TL;DR: Soil nitrate repressed nodulation, and repression of nodulation at the normal rate of inoculation by intermediate concentrations of nitrate resulted in reduced N yields because of insufficient N supply to the crop during the final stages of growth.
Abstract: Effects of soil nitrate and numbers of Bradyrhizobium japonicum on the development and functioning of a soybean symbiosis and on crop production were studied in a field experiment at Breeza, New South Wales, Bragg soybean was grown with irrigation on soil, initially free of B. japonicum , with four rates of fertilizer-N (0, 100, 200, 300 kg N ha −1 as ammonium nitrate applied 6 weeks before sowing to provide four concentrations of soil nitrate) and four rates of inoculation [nil, normal (n). 100n, 1000n]. The inoculant strain was B. japonicum CB1809. Observations were made on nodulation, the relative abundance of ureidcs in xylem exudates as an index of N 2 fixation, dry matter and seed yield, and total nitrogen in shoots and seed. Results showed clearly that soil nitrate repressed nodulation, that the effect was magnified as soil nitrate concentrations increased, but that inhibition was substantially ameliorated by increased numbers of rhizobia. The relative abundance of ureides in xylem exudates responded similiarly. The highest yields of dry matter and of N in shoots and in seed occurred at the highest rates of inoculation (100n, 1000n) at intermediate and high soil nitrate (N100, N200, N300); at low soil nitrate (N0), yields were increased by inoculation per se but not by the rate used. Uninoculated plants did not nodulate and yields in these plots reflected concentrations of soil nitrate. Data suggested that soil nitrate and N 2 fixation were not always complementary in meeting the N requirements of the growing crop. Absence of rhizobia. except at the highest rate of nitrate, and repression of nodulation at the normal rate of inoculation by intermediate concentrations of nitrate resulted in reduced N yields because of insufficient N supply to the crop during the final stages of growth.

Book ChapterDOI
TL;DR: The nitrogenase activity of Azospirillum spp.
Abstract: The nitrogenase activity ofAzospirillum spp. is efficiently regulated by environmental factors. InA. brasilense andA. lipoferum a rapid ‘switch off’ of nitrogenase activity occurs after the addition of ammonium chloride. As in photosynthetic bacteria, a covalent modification of nitrogenase reductase (Fe-protein) is involved. InA. amazonense, a non-covalent mechanism causes only a partial inhibition of nitrogenase activity after ammonium chloride is added. In anaerobic conditions, nitrogenase reductase is also ‘switched off’ by a covalent modification inA. brasilense andA. lipoferum. Short-time exposure ofAzospirillum to increased oxygen levels causes a partially reversible inhibition of nitrogenase activity, but no covalent modification is involved.Azospirillum spp. show variations in their oxygen tolerance. High levels of carotenoids confer a slightly improved oxygen tolerance. Certain amino acids (e. g. glutamate, aspartate, histidine and serine) affect growth and nitrogen fixation differently inAzospirillum spp. Amino acids may influence growth and nitrogen fixation ofAzospirillum in the association with plants.Azospirillum brasilense andA. halopraeferens are the more osmotolerant species. They utilize most amino acids poorly and accumulate glycine betaine, which also occurs in osmotically stressed grasses as a compatible solute to counteract osmotic stress. Nitrogen fixation is stimulated by glycine betaine and choline. Efficient iron acquisition is a prerequisite for competitive and aerotoleran growth and for high nitrogenase activity.Azospirillum halopraeferens andA. amazonense assimilate iron reasonably well, whereas growth of someA. brasilense andA. lipoferum strains is severely inhibited by iron limitation and by competition with foreign microbial iron chelators. However, growth of certain iron-limitedA. brasilense strains is stimulated by the phytosiderophore mugineic acid. Thus, various plant-derived substances may stimulate growth and nitrogen fixation ofAzospirillum.


Journal ArticleDOI
TL;DR: Five soybean varieties belonging to four maturity groups and their respective nonnodulating isolines were planted at three sites along an elevational transect in Hawaii to study the effect of elevation-associated changes in temperature on yield, soil N uptake, and N= fixation.
Abstract: The exploitation of the soybe an [Glycine max (L.) Merr.] -Bradyrhizobium japonicum symbiosis in varied environments requires an understanding of factors that may affect fixed and soil N assimilation. Temperature affects both soybean maturity and N requirement, and soil N availability. Five soybean varieties belonging to four maturity groups (00, IV, VI, and VIII) and their respective nonnodulating isolines were planted at three sites along an elevational transect in Hawaii to study the effect of elevation-associated changes in temperature on yield, soil N uptake, and N= fixation. The mean soil/air temperatures during the experiment were 24/23, 23/21, and 20/IS°C, with 7, 8, and 9°C differentials between mean maximum and mean minimum air temperatures at elevations of 320, 660, and 1050 m , respectively. The soils of the two lower sites were Humoxic Tropohumults and that of the highest site was Entic Dystrandept. The seeds were inoculated at planting with B. japonicum. Plants were harvested at physiological maturity. Average dry matter yield and N accumulation at the highest site was only 48 and 41%, respectively, of that at the lowest site. Early maturing varieties were relatively more affected by high elevation than were later varieties. Within each site, late -maturing varieties produced greater yield and accumulated more N than did the early varieties. Nitrogen fixation contributed 80, 66, and 97% to total plant N at the lowest, intermediate, and highest sites, respectively. Differences between sites in the proportion of N from fixation we re due to differences in the availability and uptake of soil N. Although total N assimilation between varieties differed in some cases by more than 400%, the proportions of N derived from fixation were similar within a site. On a per-day basis, N accumulation was similar among varieties at a site. Since the different maturity groups had similar average N assimilation rates per day within a site, and since soil N mineralization rate per day at a site can be assumed to be constant, the proportion of total N derived from N2 fixation is necessarily constant. Since the proportion of N derived from fixation is yield independent at a site, it may be possible to predict the relative contributions of soil N and symbiotic N2 fixation to soybean through characterization of the processes that affect N availability at a site. Data from in vitro soil N mineralization and a greenhouse pot test indicated that low temperature may have decreased root growth and uptake of soil N, or soil N availability more than it reduced N2 fixation. Additional Index Words: Glycine max, Temperature, Non-nodulating isoline, Symbiotic nitrogen fixation, Bradyrhizobium japonicum.

Journal ArticleDOI
TL;DR: It was concluded that growth on histidine as the sole source of nitrogen, carbon, and energy may be used for the taxonomic characterization of Azospirillum spp.
Abstract: The utilization of amino acids for growth and their effects on nitrogen fixation differ greatly among the several strains of each species of Azospirillum spp. that were examined. A. brasiliense grew poorly or not at all on glutamate, aspartate, serine, or histidine as the sole nitrogen and carbon sources. Nitrogen fixation by most A. brasiliense strains was inhibited only slightly even by 10 mM concentrations of these amino acids. In contrast, A. lipoferum and A. amazonense grew very well on glutamate, aspartate, serine, or histidine as the sole nitrogen and carbon sources; nitrogen fixation, which was measured in the presence of malate or sucrose, was severely inhibited by these amino acids. It was concluded that growth on histidine as the sole source of nitrogen, carbon, and energy may be used for the taxonomic characterization of Azospirillum spp. and for the selective isolation of A. lipoferum. The different utilization of various amino acids by Azospirillum spp. may be important for their establishment in the rhizosphere and for their associative nitrogen fixation with plants. The physiological basis for the different utilization of glutamate by Azospirillum spp. was investigated further. A. brasiliense and A. lipoferum exhibited a high affinity for glutamate uptake (Km values for uptake were 8 and 40 microM, respectively); the Vmax was 6 times higher in A. lipoferum than in A. brasiliense. At high substrate concentrations (10 mM), the nonsaturable component of glutamate uptake was most active in A. lipoferum and A. amazonense.(ABSTRACT TRUNCATED AT 250 WORDS)

Journal ArticleDOI
TL;DR: Improved management compared with traditional practices common in northern Syria for growing field bean, chickpea, lentil, peas, peas and vetch was shown to increase significantly the crop nitrogen uptake and subsequent protein yields in either hay, grain or straw.
Abstract: Improved management compared with traditional practices common in northern Syria for growing field bean (Vicia faba L.), chickpea (Cicer arietinum), lentil (Lens culinaris), peas (Pisum sativum) and vetch (Vicia sativa) was shown to increase significantly (P < 0·001) the crop nitrogen (N) uptake and subsequent protein yields in either hay, grain or straw. This intervention more than doubled N uptake in 1982–3 when averaged over crops and locations increasing from 31·8 kg N/ha under traditional management to 68·7 kg N/ha under improved management. Improved management also increased the proportion of nitrogen uptake that was derived from symbiotic nitrogen fixation by the crop from 55 to 69%. The treatments which gave improved crop N uptake were application of phosphate fertilizer, reduced row spacing and control of weeds. Seed inoculation with rhizobia had little or no effect on N uptake or on the proportion of N that was fixed biologically by the crop. Environmental effects on productivity, as expressed by seasonal and locational differences, were as, or more, important than management-imposed effects.Differences in N uptake by barley, following either a legume crop or barley, indicated that the residual effects of the legume crop amounted to approximately 10 kg N/ha. This represents a substantial contribution to the N nutrition of a barley crop in the dry areas of northern Syria.

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TL;DR: The technique used to measure dinitrogen fixation proved to be useful and reliable enough to discriminate between various genotypes, grown over a period of two years in two different soils.
Abstract: Before starting a breeding program aimed at improving the nitrogen nutrition ofVicia faba, the authors tried an alternative technique to the acetylene reduction assay, to measure some genetic variability in the plant material. The quantity of dinitrogen fixed by several cultivars ofVicia faba was estimated using a low enrichment15N tracer method and high precision15N mass spectrometry. The fababeans were cultivated for two years in two different soils.

Journal ArticleDOI
TL;DR: DeLaune et al. as mentioned in this paper used closed chamber techniques to measure denitrification fluxes from C. Crowley silt loam (Typic Albaqualfs) soil and found that 28% of the applied N-urea and 40% of N-KNO3 was trapped as N2 in the soil 33 d after N application.
Abstract: Denitrification has been proposed to be a major N loss mechanism from flooded systems, but direct measurement of the N, product has met with little success. A laboratory experiment was undertaken to determine if N-labeled dinitrogen gas was encapsulated in the saturated soil after applied N was denitrified in a Crowley silt loam (Typic Albaqualfs) soil. Under laboratory conditions, 28% of the applied \"N-urea and 40% of the N-KNO3 was trapped as N2 in the soil 33 d after N application. In addition, 77% of the applied \"NO;r and 44% of the \"N-urea was denitrified and recovered as N2. Additional Index Words: Stable N isotopes, N loss, Oryza saliva L., N transformations. F RICE (Oryza saliva L.) uses applied N inefficiently and recovery of fertilizer N rarely exceeds 40% (Craswell and Vlek, 1979; DeDatta, 1981). Ammonia (NH3) volatilization and/or denitrification can be major N loss mechanisms from the flooded soil-rice system (Patrick, 1982; Fillery et al., 1984). In the past, N losses due to NH3 volatilization and denitrification (N2O, N2) have been determined from the difference between fertilizer N additions, N uptake by crops, N leaching and residual soil N. Nitrogen balance studies were used as an indirect measure of N losses. Direct measurement of NH3 volatilization and denitrification have been restricted due to problems involved in making accurate field measurements and availability of high precision instrumentation (Freney et al., 1983; Ryden and Rolston, 1983; Parkin et al., 1984). Micrometeorological techniques are now being used to quantify NH3 volatilization from flooded rice systems. These techniques are preferred because they do not disturb soil or environmental processes which affect gas exchange (Denmead, 1983; Fillery et al., 1984; Fillery and S.K. DeDatta, 1986). Very few field experiments have quantified the rates and absolute amounts of denitrification. Direct measurement of N2 and N2O has been achieved in nonflooded systems using gas chromatographic techniques (N2O) and isotope ratio mass spectrometers to measure the N2, N2, and N2 intensities (R.olston et al., 1976; Mulvaney and Kurtz, 1982; Mosier et al., 1986; Mulvaney and Boast, 1986). Published results on direct measurement of measurable N2 denitrification fluxes from flooded field systems is severely lacking at this time. Lindau and Patrick (unpublished data, 1987) were unable to measure denitrification N2 fluxes from C.W. Lindau, W.H. Patrick, Jr., R.D. DeLaune, Lab. for Wetland Soils and Sediments (LWSS), Louisiana State Univ., Baton Rouge, LA 70803-7511; K.R. Reddy, Univ. of Florida, Gainesville, FL; and P.K. Bollich, Rice Res. Stn., Louisiana. Agric. Exp. Stn. Joint contribution from the Lab. for Wetland Soils and Sediments, Louisiana State Univ., and the Univ. of Florida. Received 14 August 1987. 'Corresponding author. Published in Soil Sci. Soc. Am. J. 52:538-540 (1988). flooded rice systems in field experiments conducted during the 1985, 1986, and 1987 growing seasons using N mass spectrometer techniques (Siegel et al., 1982). No detectable increases in the N2 and N2 concentrations above natural background levels were observed. Closed chamber techniques using highly labeled N-urea (30, 64, and 99 atom % N), collection times up to 24 h and headspace heights minimized to 2-3 cm were tried. The objective of this study was to assess the possibility some fraction of the N2 being produced during denitrification was being trapped beneath the floodwater in the saturated soil layers. Materials and Methods The soil used for the laboratory experiment was a Crowley silt loam (Typic Albaqualfs). It contained 7.0 g total C kg~' and 0.8 g total N kg '. Its cation exchange capacity was 9.4 cmolc kg\" of soil, and it had a pH of 5.8 (1:1, soil/water). The soil contained 10.8% clay, 70.7% silt, and 9.5% sand. Laboratory Procedures Large Pyrex® tubes (45.5-cm length by 5.0-cm i.d.) were fitted at the top with 34/45 ground glass joints and a stopcock and rubber septum for gas sampling (Fig. 1). Two hundred and fifty g of air-dried soil ground to pass through a 0.50-mm mesh sieve were placed in the tubes and lightly tapped until a 13-cm soil column formed. Distilled water was added to the soil from the bottom to prevent air entrapment, and a 2.0-cm floodwater layer established. The soil was incubated in the dark under atmospheric conditions for two months until a distinct aerobic-anaerobic interface developed (Reddy and Patrick, 1984). Labeled urea (64 atom % N) and KNO3 (71 atom % N) were dissolved and added to the column floodwater at a rate of 120 kg N ha~'. The column tops were sealed and the soil allowed to incubate for periods of 5, 10, 20, or 33 d at room temperature (2426 °C). A manometer was fitted to one column to monitor pressure changes within the sealed system over the incubation period. Only slight variations in pressure were observed and were attributed to minor changes in laboratory temperature. At the end of each incubation duplicate columns were removed for analysis. A gas-tight syringe was

Journal ArticleDOI
TL;DR: The fast growing strain, Azorhizobium caulinodans ORS571, isolated from stem nodules of the tropical legume Sesbania rostrata, can grow in the free-living state at the expense of molecular nitrogen.
Abstract: The fast growing strain, Azorhizobium caulinodans ORS571, isolated from stem nodules of the tropical legume Sesbania rostrata, can grow in the free-living state at the expense of molecular nitrogen. Five point mutants impaired in nitrogen fixation in the free-living state have been complemented by a plasmid containing the cloned fix-ABC region of strain ORS571. Genetic analysis of the mutants showed that one was impaired in fixC, one in fixA and the three others in a new gene, located upstream from fixA and designated nifO. Site-directed Tn5 mutagenesis was performed to obtain Tn5 insertions in fixB and fixC. The four genes are required for nitrogen fixation both in the free-living state and under symbiotic conditions. The nucleotide sequence of nifO was established. The gene is transcribed independently of fixA and does not correspond to fixX, recently identified in Rhizobium meliloti and R. leguminosarum. Biochemical analysis of the five point mutants showed that they synthesized normal amounts of nitrogenase components. It is unlikely that fixA, fixC and nifO are involved in electron transport to nitrogenase. FixC could be required for the formation of a functional nitrogenase component 2.