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Robert M Boddey - One of the best experts on this subject based on the ideXlab platform.

  • Use of the 15N natural abundance technique to quantify Biological Nitrogen Fixation by woody perennials
    Nutrient Cycling in Agroecosystems, 2000
    Co-Authors: Robert M Boddey, Mark B. Peoples, Brian Palmer, Peter J. Dart
    Abstract:

    Biological Nitrogen Fixation (BNF) associated with trees and shrubs plays a major role in the functioning of many ecosystems, from natural woodlands to plantations and agroforestry systems, but it is surprisingly difficult to quantify the amounts of N_2 fixed. Some of the problems involved in measuring N_2 Fixation by woody perennials include: (a) diversity in occurrence, and large plant-to-plant variation in growth and nodulation status of N_2-fixing species, especially in natural ecosystems; (b) long-term, perennial nature of growth and the seasonal or year-to-year changes in patterns of N assimilation; and (c) logistical limitations of working with mature trees which are generally impossible to harvest in their entirety. The methodology which holds most promise to quantify the contributions of N_2 Fixation to trees is the so-called `^15N natural abundance' technique which exploits naturally occurring differences in ^15N composition between plant-available N sources in the soil and that of atmospheric N_2. In this review we discuss probable explanations for the origin of the small differences in ^15N abundance found in different N pools in both natural and man-made ecosystems and utilise previously published information and unpublished data to examine the potential advantages and limitations inherent in the application of the technique to study N_2 Fixation by woody perennials. Calculation of the proportion of the plant N derived from atmospheric N_2 (%Ndfa) using the natural abundance procedure requires that both the ^15N natural abundance of the N derived from BNF and that derived from the soil by the target N_2-fixing species be determined. It is then assumed that the ^15N abundance of the N_2-fixing species reflects the relative contributions of the N derived from these two sources. The ^15N abundance of the N derived from BNF ( B ) can vary with micro-symbiont, plant species/provenance and growth stage, all of which create considerable difficulties for its precise evaluation. If the%Ndfa is large and the ^15N abundance of the N acquired from other sources is not several δ^15N units higher or lower than B , then this can be a major source of error. Further difficulties can arise in determining the ^15N abundance of the N derived from soil (and plant litter, etc.) by the target plant as it is usually impossible to predict which, if any, non-N_2-fixing reference species will obtain N from the same N sources in the same proportions with the same temporal and spatial patterns as the N_2-fixing perennial. The compromise solution is to evaluate the ^15N abundance of a diverse range of neighbouring non-N_2-fixing plants and to compare these values with that of the N_2-fixing species and the estimate of B . Only then can it be determined whether the contribution of BNF to the target species can be quantified with any degree of confidence. This review of the literature suggests that while the natural abundance technique appears to provide quantitative measures of BNF in tree plantation and agroforestry systems, particular difficulties may arise which can often limit its application in natural ecosystems.

  • the contribution of Biological Nitrogen Fixation for sustainable agricultural systems in the tropics
    Soil Biology & Biochemistry, 1997
    Co-Authors: Robert M Boddey, Joao Carlos De Moraes Sa, B J R Alves, Segundo Urquiaga
    Abstract:

    Abstract The pressing need to increase food production in the tropics to feed the burgeoning population of the Third World requires that crop yields ha−1 must be increased without prejudicing the resource base for future generations. Biological Nitrogen Fixation (BNF), especially that associated with legumes, has great potential to contribute to productive and sustainable agricultural systems for the tropics, but more research is required to investigate how Biologically fixed N, and the increased BNF contributions resulting from research innovations, can be incorporated into viable agricultural systems to increase crop or pasture yields and to substitute N fertiliser inputs. A majority of the soils of the humid and semi-humid tropics have mineral fractions composed of 1:1 lattice clays or sesquioxides of relatively low capacity to retain nutrients (CEC) and water (WHC). It is the soil organic matter (SOM) which has high CEC (after liming) and WHC, and soils under undisturbed climax vegetation are usually high in organic matter which is responsible for their fertility. The key to the long term fertility of such soils is to maintain their soil organic matter by the preservation of crop residues and the selection of suitable crop rotations or fallows. In this review we examine several types of agricultural systems utilised in the tropics ranging from pastures, ley cropping, zero-till rotations as well as green manuring and discuss the management options that can be adopted to preserve their agricultural productivity through the strategic use of legumes in these systems, and their effects on pasture and crop yields. The introduction of forage legumes into tropical pastures can increase and sustain their productivity, with only modest inputs of lime and P and K fertilisers. Similarly, crop and pasture rotations (ley cropping) maintain SOM and soil fertility and crop yields can benefit greatly from the introduction of pasture legumes into the ley. Continuous cropping under minimum or zero tillage can maintain soil cover, and stimulate the retention of SOM, such that nutrient losses are often minimal, and legume derived N can be efficiently transferred to subsequent crops. The options for the resource-poor small-holder to efficiently utilise Biologically fixed N as a N supply for cereal grains are more limited and need more attention from researchers as well as less neglect from government organisations. The addition of lime and P fertiliser in modest quantities in many under-developed regions could make large contributions to increased crop yields. If such modest fertiliser inputs were to be combined with suitable crop rotations including green manure or grain legume crops, larger increases in crops yields could be achieved on a sustainable basis, but in many regions agricultural extension services are non-existent and poor farmers have little access to even these basic chemical inputs.

  • Biological Nitrogen Fixation in azospirillum strain maize genotype associations as evaluated by the 15n isotope dilution technique
    Biology and Fertility of Soils, 1996
    Co-Authors: Garcia I De Salamone, Segundo Urquiaga, J Dobereiner, Robert M Boddey
    Abstract:

    Few studies of the inoculation of cereal crops with N2-fixing bacteria have included more than one or two plant genotypes. In a recent study performed in Argentina using 12 different maize genotypes, it was found in 2 consecutive field experiments that several of them responded consistently, either negatively or positively, to inoculation with a mixture of strains of Azospirillum spp. The present study in post was performed to investigate the effect of inoculation of individual strains (and a mixture) of Azospirillum spp., and their nitrate reductase negative (NR-) mutants, on the growth of four of these maize genotypes. Two of these genotypes were grown in 15N-labelled soil with the aim of quantifying any contributions of Biological N2 Fixation. Two genotypes (Morgan 318 and Dekalb 4D-70) produced similar increases in grain yield when they were inoculated with a mixture of Azospirillum spp. strains or fertilized with the equivalent of 100 kg N ha-1. The other genotypes (Dekalb 2F-11 and CMS 22) showed little response to inoculation or N fertilization. The Morgan 318 and Dekalb 4D-70 genotypes showed a large increase in total N accumulation, suggesting that the response was due to increased N acquisition, but not due to bacterial nitrate reductase as the NR- mutants generally caused plant responses similar to those of the parent strains. Despite problems with the stabilization of the 15N enrichment in the soil, the 15N isotope dilution results indicated that there were very significant Biological Nitrogen Fixation (BNF) contributions to the Dekalb 4D-70 and CMS 22 maize genotypes.

  • Biological Nitrogen Fixation associated with sugar cane and rice contributions and prospects for improvement
    Plant and Soil, 1995
    Co-Authors: Robert M Boddey, Segundo Urquiaga, Vera Lucia Divan Baldani, O C De Oliveira, Veronica Massena Reis, F L De Olivares, J Dobereiner
    Abstract:

    15N isotope and N balance studies performed over the last few years have shown that several Brazilian varieties of sugarcane are capable of obtaining over 60% of their Nitrogen (<150 kg N ha-1 year-1) from Biological Nitrogen Fixation (BNF). This may be due to the fact that this crop in Brazil has been systematically bred for high yields with low fertilizer N inputs. In the case of wetland rice, N balance experiments performed both in the field and in pots suggest that 30 to 60 N ha-1 crop-1 may be obtained from plant-associated BNF and that different varieties have different capacities to obtain N from this source. 15N2 incorporation studies have proved that wetland rice can obtain at least some N from BNF and acetylene reduction (AR) assays also indicate differences in N2-fixing ability between different rice varieties. However in situ AR field estimates suggest plant-associated BNF inputs to be less than 8 kg N ha-1 crop-1. The problems associated with the use of the 15N dilution technique for BNF quantification are discussed and illustrated with data from a recent study performed at EMBRAPA-CNPAB. Although many species of diazotrophs have been isolated from the rhizosphere of both sugarcane and wetland rice, the recent discovery of endophytic N2-fixing bacteria within roots, shoots and leaves of both crops suggests, at least in the case of sugarcane, that these bacteria may be the most important contributors to the observed BNF contributions. In sugarcane both Acetobacter diazotrophicus and Herbaspirillum spp. have been found within roots and aerial tissues and these microorganisms, unlike Azospirillum spp. and other rhizospheric diazotrophs, have been shown to survive poorly in soil. Herbaspirillum spp. are found in many graminaceous crops, including rice (in roots and aerial tissue), and are able to survive and pass from crop to crop in the seeds. The physiology, ecology and infection of plants by these endophytes are fully discussed in this paper. The sugarcane/endophytic diazotroph association is the first efficient N2-fixing system to be discovered associated with any member of the gramineae. As yet the individual roles of the different diazotrophs in this system have not been elucidated and far more work on the physiology and anatomy of this system is required. However, the understanding gained in these studies should serve as a foundation for the improvement/development of similar N2-fixing systems in wetland rice and other cereal crops.

  • Biological Nitrogen Fixation associated with sugar cane
    Plant and Soil, 1991
    Co-Authors: Robert M Boddey, Segundo Urquiaga, Veronica Massena Reis, J Dobereiner
    Abstract:

    A recent15N dilution/N balance study confirmed that certain sugar cane varieties are capable of obtaining large contributions of Nitrogen from plant-associated N2 Fixation. It was estimated that up to 60 to 80% of plant N could be derived from this source, and under good conditions of water and mineral nutrient supply, it may be possible to dispense with N fertilization of these varieties altogether. The recently discovered bacterium,Acetobacter diazotrophicus, apparently responsible for this N2 Fixation associated with the plants, has unique physiological properties for a diazotroph, such as tolerance to low pH, and high sugar and salt concentrations, lack of nitrate reductase, and Nitrogenase activity which tolerates short-term exposure to ammonium. Furthermore, it also behaves as an endophyte, in that it is unable to infect sugar cane plants unless through damaged tissue or by means of VA mycorrhizae and is propagated via the planting material (stem pieces).

Segundo Urquiaga - One of the best experts on this subject based on the ideXlab platform.

  • bradyrhizobium as the only rhizobial inhabitant of mung bean vigna radiata nodules in tropical soils a strategy based on microbiome for improving Biological Nitrogen Fixation using bio products
    Frontiers in Plant Science, 2021
    Co-Authors: Vinicio Oliosi Favero, Gustavo Ribeiro Xavier, Norma Gouvea Rumjanek, Rita Hilario De Carvalho, Victoria Monteiro Da Motta, Ana Beatriz Carneiro Leite, Marcia Reed Rodrigues Coelho, Segundo Urquiaga
    Abstract:

    The mung bean has a great potential under tropical conditions given its high content of grain protein. Additionally, its ability to benefit from Biological Nitrogen Fixation (BNF) through association with native rhizobia inhabiting nodule microbiome provides most of the Nitrogen independence on fertilizers. Soil microbial communities which are influenced by biogeographical factors and soil properties, represent a source of rhizobacteria capable of stimulating plant growth. The objective of this study is to support selection of beneficial bacteria that form positive interactions with mung bean plants cultivated in tropical soils, as part of a seed inoculation program for increasing grain yield based on the BNF and other mechanisms. Two mung bean genotypes (Camaleao and Esmeralda) were cultivated in 10 soil samples. Nodule microbiome was characterized by next-generation sequencing using Illumina MiSeq 16S rRNA. More than 99% of nodule sequences showed similarity with Bradyrhizobium genus, the only rhizobial present in nodules in our study. Higher bacterial diversity of soil samples collected in agribusiness areas (MW_MT-I, II or III) was associated with Esmeralda genotype, while an organic agroecosystem soil sample (SE_RJ-V) showed the highest bacterial diversity independent of genotype. Furthermore, OTUs close to Bradyrhizobium elkanii have dominated in all soil samples, except in the sample from the organic agroecosystem, where just B. japonicum was present. Bacterial community of mung bean nodules is mainly influenced by soil pH, K, Ca, and P. Besides a difference on nodule colonization by OTU sequences close to the Pseudomonas genus regarding the two genotypes was detected too. Although representing a small rate, around 0.1% of the total, Pseudomonas OTUs were only retrieved from nodules of Esmeralda genotype, suggesting a different trait regarding specificity between macro- and micro-symbionts. The microbiome analysis will guide the next steps in the development of an inoculant for mung bean aiming to promote plant growth and grain yield, composed either by an efficient Bradyrhizobium strain on its own or co-inoculated with a Pseudomonas strain. Considering the results achieved, the assessment of microbial ecology parameters is a potent coadjuvant capable to accelerate the inoculant development process and to improve the benefits to the crop by soil microorganisms.

  • the contribution of Biological Nitrogen Fixation for sustainable agricultural systems in the tropics
    Soil Biology & Biochemistry, 1997
    Co-Authors: Robert M Boddey, Joao Carlos De Moraes Sa, B J R Alves, Segundo Urquiaga
    Abstract:

    Abstract The pressing need to increase food production in the tropics to feed the burgeoning population of the Third World requires that crop yields ha−1 must be increased without prejudicing the resource base for future generations. Biological Nitrogen Fixation (BNF), especially that associated with legumes, has great potential to contribute to productive and sustainable agricultural systems for the tropics, but more research is required to investigate how Biologically fixed N, and the increased BNF contributions resulting from research innovations, can be incorporated into viable agricultural systems to increase crop or pasture yields and to substitute N fertiliser inputs. A majority of the soils of the humid and semi-humid tropics have mineral fractions composed of 1:1 lattice clays or sesquioxides of relatively low capacity to retain nutrients (CEC) and water (WHC). It is the soil organic matter (SOM) which has high CEC (after liming) and WHC, and soils under undisturbed climax vegetation are usually high in organic matter which is responsible for their fertility. The key to the long term fertility of such soils is to maintain their soil organic matter by the preservation of crop residues and the selection of suitable crop rotations or fallows. In this review we examine several types of agricultural systems utilised in the tropics ranging from pastures, ley cropping, zero-till rotations as well as green manuring and discuss the management options that can be adopted to preserve their agricultural productivity through the strategic use of legumes in these systems, and their effects on pasture and crop yields. The introduction of forage legumes into tropical pastures can increase and sustain their productivity, with only modest inputs of lime and P and K fertilisers. Similarly, crop and pasture rotations (ley cropping) maintain SOM and soil fertility and crop yields can benefit greatly from the introduction of pasture legumes into the ley. Continuous cropping under minimum or zero tillage can maintain soil cover, and stimulate the retention of SOM, such that nutrient losses are often minimal, and legume derived N can be efficiently transferred to subsequent crops. The options for the resource-poor small-holder to efficiently utilise Biologically fixed N as a N supply for cereal grains are more limited and need more attention from researchers as well as less neglect from government organisations. The addition of lime and P fertiliser in modest quantities in many under-developed regions could make large contributions to increased crop yields. If such modest fertiliser inputs were to be combined with suitable crop rotations including green manure or grain legume crops, larger increases in crops yields could be achieved on a sustainable basis, but in many regions agricultural extension services are non-existent and poor farmers have little access to even these basic chemical inputs.

  • Biological Nitrogen Fixation in azospirillum strain maize genotype associations as evaluated by the 15n isotope dilution technique
    Biology and Fertility of Soils, 1996
    Co-Authors: Garcia I De Salamone, Segundo Urquiaga, J Dobereiner, Robert M Boddey
    Abstract:

    Few studies of the inoculation of cereal crops with N2-fixing bacteria have included more than one or two plant genotypes. In a recent study performed in Argentina using 12 different maize genotypes, it was found in 2 consecutive field experiments that several of them responded consistently, either negatively or positively, to inoculation with a mixture of strains of Azospirillum spp. The present study in post was performed to investigate the effect of inoculation of individual strains (and a mixture) of Azospirillum spp., and their nitrate reductase negative (NR-) mutants, on the growth of four of these maize genotypes. Two of these genotypes were grown in 15N-labelled soil with the aim of quantifying any contributions of Biological N2 Fixation. Two genotypes (Morgan 318 and Dekalb 4D-70) produced similar increases in grain yield when they were inoculated with a mixture of Azospirillum spp. strains or fertilized with the equivalent of 100 kg N ha-1. The other genotypes (Dekalb 2F-11 and CMS 22) showed little response to inoculation or N fertilization. The Morgan 318 and Dekalb 4D-70 genotypes showed a large increase in total N accumulation, suggesting that the response was due to increased N acquisition, but not due to bacterial nitrate reductase as the NR- mutants generally caused plant responses similar to those of the parent strains. Despite problems with the stabilization of the 15N enrichment in the soil, the 15N isotope dilution results indicated that there were very significant Biological Nitrogen Fixation (BNF) contributions to the Dekalb 4D-70 and CMS 22 maize genotypes.

  • Biological Nitrogen Fixation associated with sugar cane and rice contributions and prospects for improvement
    Plant and Soil, 1995
    Co-Authors: Robert M Boddey, Segundo Urquiaga, Vera Lucia Divan Baldani, O C De Oliveira, Veronica Massena Reis, F L De Olivares, J Dobereiner
    Abstract:

    15N isotope and N balance studies performed over the last few years have shown that several Brazilian varieties of sugarcane are capable of obtaining over 60% of their Nitrogen (<150 kg N ha-1 year-1) from Biological Nitrogen Fixation (BNF). This may be due to the fact that this crop in Brazil has been systematically bred for high yields with low fertilizer N inputs. In the case of wetland rice, N balance experiments performed both in the field and in pots suggest that 30 to 60 N ha-1 crop-1 may be obtained from plant-associated BNF and that different varieties have different capacities to obtain N from this source. 15N2 incorporation studies have proved that wetland rice can obtain at least some N from BNF and acetylene reduction (AR) assays also indicate differences in N2-fixing ability between different rice varieties. However in situ AR field estimates suggest plant-associated BNF inputs to be less than 8 kg N ha-1 crop-1. The problems associated with the use of the 15N dilution technique for BNF quantification are discussed and illustrated with data from a recent study performed at EMBRAPA-CNPAB. Although many species of diazotrophs have been isolated from the rhizosphere of both sugarcane and wetland rice, the recent discovery of endophytic N2-fixing bacteria within roots, shoots and leaves of both crops suggests, at least in the case of sugarcane, that these bacteria may be the most important contributors to the observed BNF contributions. In sugarcane both Acetobacter diazotrophicus and Herbaspirillum spp. have been found within roots and aerial tissues and these microorganisms, unlike Azospirillum spp. and other rhizospheric diazotrophs, have been shown to survive poorly in soil. Herbaspirillum spp. are found in many graminaceous crops, including rice (in roots and aerial tissue), and are able to survive and pass from crop to crop in the seeds. The physiology, ecology and infection of plants by these endophytes are fully discussed in this paper. The sugarcane/endophytic diazotroph association is the first efficient N2-fixing system to be discovered associated with any member of the gramineae. As yet the individual roles of the different diazotrophs in this system have not been elucidated and far more work on the physiology and anatomy of this system is required. However, the understanding gained in these studies should serve as a foundation for the improvement/development of similar N2-fixing systems in wetland rice and other cereal crops.

  • Biological Nitrogen Fixation associated with sugar cane
    Plant and Soil, 1991
    Co-Authors: Robert M Boddey, Segundo Urquiaga, Veronica Massena Reis, J Dobereiner
    Abstract:

    A recent15N dilution/N balance study confirmed that certain sugar cane varieties are capable of obtaining large contributions of Nitrogen from plant-associated N2 Fixation. It was estimated that up to 60 to 80% of plant N could be derived from this source, and under good conditions of water and mineral nutrient supply, it may be possible to dispense with N fertilization of these varieties altogether. The recently discovered bacterium,Acetobacter diazotrophicus, apparently responsible for this N2 Fixation associated with the plants, has unique physiological properties for a diazotroph, such as tolerance to low pH, and high sugar and salt concentrations, lack of nitrate reductase, and Nitrogenase activity which tolerates short-term exposure to ammonium. Furthermore, it also behaves as an endophyte, in that it is unable to infect sugar cane plants unless through damaged tissue or by means of VA mycorrhizae and is propagated via the planting material (stem pieces).

Qicheng Bei - One of the best experts on this subject based on the ideXlab platform.

  • k strategic ammonia oxidizing bacteria capitalize on Biological Nitrogen Fixation in a flooded unfertilized rice soil
    Biology and Fertility of Soils, 2019
    Co-Authors: Qicheng Bei, Zubin Xie, Georg Cadisch, Frank Rasche
    Abstract:

    Less attention has been devoted to the understanding of the sequential effect of Biological Nitrogen Fixation (BNF) on microbial ammonia (NH3) oxidation in terrestrial soils. To shed light into this ecologically important relationship, a 15N2-DNA-stable isotope probing (SIP) technique was applied to explore the incorporation of 15N fixed by BNF into the genome of NH3 oxidizers in planted and non-planted flooded rice soils, using the α-subunit of NH3 monooxygenase (amoA gene) as a functional marker. The abundance and structural composition of archaeal and bacterial amoA genes in density-resolved fractions obtained from SIP were investigated by quantitative PCR, as well as terminal-restriction fragment length polymorphism and sequence analyses. Results revealed that bacterial rather than archaeal NH3 oxidizers assimilated 15N derived from BNF in both planted and non-planted flooded rice soils. The amoA genes in 15N-enriched “heavy” SIP gradient fractions were closely related to K-strategic Nitrosospira cluster 10, including Nitrosospira sp. AF-like bacteria, suggesting an ecological linkage of these two metabolically distinct processes. It remains unsolved from our study why exactly Nitrosospira cluster 10 was capitalizing on BNF. It could be suggested that K-strategy is the underlying ecological mechanism of sustainable, self-regulating terrestrial ecosystems such as traditional, unfertilized flooded rice soils. In this regard, it needs to be assayed if some rice-associated diazotrophs might also be classified as K-strategists, since BNF is an energy demanding metabolic process.

  • soil aluminum oxides determine Biological Nitrogen Fixation and diazotrophic communities across major types of paddy soils in china
    Soil Biology & Biochemistry, 2019
    Co-Authors: Xiaojie Wang, Benjuan Liu, Yanhui Zhang, Heng Zhang, Yucheng Feng, Hongli Pan, Gang Liu, Xingwu Lin, Jianguo Zhu, Qicheng Bei
    Abstract:

    Abstract Biological Nitrogen Fixation (BNF) contributed greatly in maintaining the fertility of paddy soils without the application of chemical fertilizers for thousands of years. However, factors affecting the BNF and composition of diazotrophs in paddy soils across large geographic scales are still largely unknown. In this study, the field-based 15N2 labeling technique and nifH gene high-throughput sequencing were applied to four types of paddy soils collected from northeast to southwest China, representing major rice-growing areas. Results showed that the BNF amount had distinct geographical patterns and ranged from 2.2 ± 0.5 to 20.1 ± 3.7 kg N ha−1 during 42 days 15N2 labeling period, which was positively correlated with the abundance of Nostocales species. Among the soil properties analyzed, the contents of amorphous aluminum oxides may play a key role in determining the BNF amount and major N2-fixers across all paddy soils using a random forest model. Overall, our study demonstrates the potential biotoxic effects of aluminum oxides on the BNF in paddy soils in southern China and may has important implications for the enhancement of BNF in acidic Ultisols and Oxisols.

  • impacts of mo application on Biological Nitrogen Fixation and diazotrophic communities in a flooded rice soil system
    Science of The Total Environment, 2019
    Co-Authors: Qicheng Bei, Xiaojie Wang, Benjuan Liu, Yanhui Zhang, Gang Liu, Xingwu Lin, Qi Liu, Zhibin Lin, Ping Lan, Haiyang Jin
    Abstract:

    Molybdenum (Mo) deficiency in the farmland of China may limit Biological Nitrogen Fixation (BNF), however, the impact of Mo application on BNF capacities and diazotrophic communities in rice-soil systems is unclear. In this experiment, treatments in a 6.7 atom% 15N2-labelling field-based growth chamber for 74 days and treatments in a 99 atom% 15N2-labelling microcosm experiment for 40 days combined with 16S rRNA gene sequencing and DNA-stable isotope probing (SIP) were used to investigate the impacts of Mo application on BNF and diazotrophic communities. Our results showed that under the condition that no Nitrogen (N) fertilizer was applied, Mo application (500 g sodium molybdate ha-1) significantly increased N2 Fixation in a rice-Inceptisol system, from 22.3 to 53.1 kg N ha-1. Mo application significantly increased the number of nifH gene copies and the relative abundance of cyanobacteria in both growth chamber and microcosm experiments. Among cyanobacteria, the relative abundances of the most abundant genera Leptolyngbya and Microcoleus were significantly increased by Mo application. 15N2-DNA-SIP further demonstrated that Leptolyngbya and Microcoleus incorporated 15N2. Mo application greatly increased BNF in Mo-deficient paddy field (≤0.068 mg kg-1) and stimulated the growth of cyanobacteria. These results indicated that Mo application in Mo-deficient paddy field could be a useful measure to increase soil N input under no N fertilization.

Brett M Barney - One of the best experts on this subject based on the ideXlab platform.

  • key factors affecting ammonium production by an azotobacter vinelandii strain deregulated for Biological Nitrogen Fixation
    Microbial Cell Factories, 2020
    Co-Authors: Mary H Plunkett, Carolann M Knutson, Brett M Barney
    Abstract:

    The obligate aerobe Azotobacter vinelandii is a model organism for the study of Biological Nitrogen Fixation (BNF). This bacterium regulates the process of BNF through the two component NifL and NifA system, where NifA acts as an activator, while NifL acts as an anti-activator based on various metabolic signals within the cell. Disruption of the nifL component in the nifLA operon in a precise manner results in a deregulated phenotype that produces levels of ammonium that far surpass the requirements within the cell, and results in the release of up to 30 mM of ammonium into the growth medium. While many studies have probed the factors affecting growth of A. vinelandii, the features important to maximizing this high-ammonium-releasing phenotype have not been fully investigated. In this work, we report the effect of temperature, medium composition, and oxygen requirements on sustaining and maximizing elevated levels of ammonium production from a Nitrogenase deregulated strain. We further investigated several pathways, including ammonium uptake through the transporter AmtB, which could limit yields through energy loss or futile recycling steps. Following optimization, we compared sugar consumption and ammonium production, to attain correlations and energy requirements to drive this process in vivo. Ammonium yields indicate that between 5 and 8% of cellular protein is fully active Nitrogenase MoFe protein (NifDK) under these conditions. These findings provide important process optimization parameters, and illustrate that further improvements to this phenotype can be accomplished by eliminating futile cycles.

  • efforts toward optimization of aerobic biohydrogen reveal details of secondary regulation of Biological Nitrogen Fixation by Nitrogenous compounds in azotobacter vinelandii
    Applied Microbiology and Biotechnology, 2018
    Co-Authors: Carolann M Knutson, Mary H Plunkett, Rachel A Liming, Brett M Barney
    Abstract:

    Biological Nitrogen Fixation (BNF) through the enzyme Nitrogenase is performed by a unique class of organisms known as diazotrophs. One interesting facet of BNF is that it produces molecular hydrogen (H2) as a requisite by-product. In the absence of N2 substrate, or under conditions that limit access of N2 to the enzyme through modifications of amino acids near the active site, Nitrogenase activity can be redirected toward a role as a dedicated hydrogenase. In free-living diazotrophs, Nitrogenases are tightly regulated to minimize BNF to meet only the growth requirements of the cell, and are often accompanied by uptake hydrogenases that oxidize the H2 by-product to recover the electrons from this product. The wild-type strain of Azotobacter vinelandii performs all of the tasks described above to minimize losses of H2 while also growing as an obligate aerobe. Individual alterations to A. vinelandii have been demonstrated that disrupt key aspects of the N2 reduction cycle, thereby diverting resources and energy toward the production of H2. In this work, we have combined three approaches to override the primary regulation of BNF and redirect metabolism to drive Biological H2 production by Nitrogenase in A. vinelandii. The resulting H2-producing strain was further utilized as a surrogate to study secondary, post-transcriptional regulation of BNF by several key Nitrogen-containing metabolites. The improvement in yields of H2 that were achieved through various combinations of these three approaches was compared and is presented along with the insights into inhibition of BNF by several Nitrogen compounds that are common in various waste streams. The findings indicate that both ammonium and nitrite hinder BNF through this secondary inhibition, but urea and nitrate do not. These results provide essential details to inform future biosynthetic approaches to yield Nitrogen products that do not inadvertently inhibit BNF.

John R Evans - One of the best experts on this subject based on the ideXlab platform.

  • phosphorus availability and elevated co2 affect Biological Nitrogen Fixation and nutrient fluxes in a clover dominated sward
    New Phytologist, 2006
    Co-Authors: Everard J Edwards, Stephanie Mccaffery, John R Evans
    Abstract:

    Summary • The response of Biological Nitrogen Fixation (BNF) to elevated CO2 was examined in white clover (Trifolium repens)-dominated swards under both high and low phosphorus availability. • Mixed swards of clover and buffalo grass (Stenotaphrum secundatum) were grown for 15 months in 0.2 m2 sand-filled mesocosms under two CO2 treatments (ambient and twice ambient) and three nutrient treatments [no N, and either low or high P (5 or 134 kg P ha−1); the third nutrient treatment was supplied with high P and N (240 kg N ha−1)]. • Under ambient CO2, high P increased BNF from 410 to 900 kg ha−1. Elevated CO2 further increased BNF to 1180 kg ha−1 with high P, but there was no effect of CO2 on BNF with low P. Allocation of N belowground increased by approx. 50% under elevated CO2 irrespective of supplied P. • The results suggest that where soil P availability is low, elevated CO2 will not increase BNF, and pasture quality could decrease because of a reduction in aboveground N.