Nitrogen Fixation System Research Articles

Driving Role of Zinc Oxide Nanoparticles with Different Sizes and Hydrophobicity in Metabolic Response and Eco-Corona Formation in Sprouts (Vigna radiata).

Zinc oxide nanoparticles (ZnO NPs) cause biotoxicity and pose a potential ecological threat; however, their effects on plant metabolism and eco-corona evolution between NPs and organisms remain unclear. This study clarified the molecular mechanisms underlying physiological and metabolic responses induced by three different ZnO NPs with different sizes and hydrophobicity in sprouts (Vigna radiata) and explored the critical regulation of eco-corona formation in root-nano systems. Results indicated that smaller-sized ZnO inhibited root elongation by up to 37.14% and triggered oxidative burst and apoptosis. Metabolomics confirmed that physiological maintenance after n-ZnO exposure was mainly attributed to the effective stabilization of nitrogen fixation and defense systems by biotransformation of the flavonoid pathway. Larger-sized or hydrophobic group-modified ZnO exhibited low toxicity in sprouts, with 0.89-fold upregulation of citrate in central carbon metabolism. This contributed to providing energy for resistance to NP stress through amino acid and carbon/nitrogen metabolism, accompanied by changes in membrane properties. Notably, smaller-sized and hydrophobic NPs intensely stimulated the release of root metabolites, forming corona complexes with exudates. The hydrogen-bonded wrapping mechanism in protein secondary structure and hydrophobic interactions of heterogeneous functional groups drove eco-corona formation, along with the corona evolution intensity of n-ZnO > s-ZnO > b-ZnO based on higher (α-helix + 3-turn helix)/β-sheet ratios. This study provides crucial insight into metabolic and eco-corona evolution in bionano fates.

Soil aggregate stability helps construct a stable nitrogen fixation system in lignite-based amendment-driven saline-sodic soil remediation

Lignite−based amendments are promising soil conditioners for improving crop yield and nitrogen use efficiency, but there is limited knowledge regarding the potential effects of lignite−based amendment on nitrogen cycling−related microbial communities and their impacts on NH3 volatilization and crop nitrogen uptake in saline−sodic farmland. Here, we investigated the influences of lignite bioorganic fertilizer (LBF) on NH3 volatilization, nitrogen uptake, and microbial communities containing nifH, amoA, and nirS genes through a two−year field experiment. Three treatments were considered in the experiment, i.e., a control treatment with no organic fertilizer application (CK), a farmyard manure treatment (FYM) involving the application of sheep manure at a rate of 21 t ha−1, and a LBF treatment with optimal application rates of 3.0 and 4.5 t ha−1. Results showed that compared with the control treatment (CK), the LBF treatment reduced the total NH3 volatilization by 22.3% and 13.5% in 2019 and 2020, respectively. In addition, the LBF treatment significantly increased sunflower nitrogen uptake by 52.5% and 114.2% in 2019 and 2020, respectively, in comparison with the CK treatment. Moreover, the LBF treatment not only increased the absolute abundance of the nifH gene by 111.5% and altered the core microbes in the nifH−containing community, but it also enhanced the complexity, stability, and cooperation of co−occurrence network of the nifH−containing community, which were positively related to the sunflower nitrogen uptake. The LBF and FYM treatments reduced NH3 volatilization by improving the soil aggregate stability and saturate hydraulic conductivity. These results indicated that LBF may offer a feasible measure to improve the sunflower nitrogen uptake by constructing a complex, stable, and cooperative nitrogen fixation system, without the risk of NH3 volatilization in saline−sodic farmland.

Temporal dynamics of rhizosphere bacterial community in the Robinia pseudoacacia–Mesorhizobium loti symbiotic system for remediation of cadmium-contaminated soils

Rhizobia can be used to enhance the phytoremediation of cadmium-contaminated soils by legumes, and a symbiotic nitrogen-fixing system has been shown to reshape the structure of rhizosphere microbiota in a mining area. However, little is known about the temporal dynamics and possible roles of rhizosphere microbiota in rhizobia-enhanced phytoremediation. A rhizobox experiment was conducted using Robinia pseudoacacia alone or inoculated with Mesorhizobium loti HZ76 under greenhouse conditions. Rhizosphere bacterial communities were characterized over a 90-day period at three levels of cadmium (determined by the distance from the mining area; uncontaminated: 0.08 mg kg−1, contaminated: 0.39 and 1.72 mg kg−1). Rhizobial inoculation considerably improved the phytoremediation efficiency, such as increasing plant biomass and cadmium accumulation by approximately two times at 90 days after planting. The bacterial community structure shifted remarkably with increasing duration of remediation. Bacterial diversity exhibited a decreasing trend in the first 60 days and then recovered at 90 days. Despite having no discernible impact on the bacterial community structure in the rhizosphere, rhizobial inoculation enabled the enrichment of potentially beneficial taxa (e.g., Microvirga, Mesorhizobium, Diaphorobacter, Steroidobacter, Brevundimonas) with resistance to heavy metals and involvement in nutrient cycling. The bacterial co-occurrence networks of low and high cadmium-contaminated soils showed the highest average degree and clustering coefficient at 60 and 30 days, respectively. Some bacterial taxa involved in nitrogen fixation (e.g., Rhizobacter, Mesorhizobium), denitrification (e.g., Niastella, Nitrospira), and carbon turnover (e.g., Solirubrobacter, Brevundimonas) were found to be potential keystone taxa. The collective findings clarify possible mechanisms by which rhizosphere bacteria participate in phytoremediation of cadmium-contaminated mining soils using the R. pseudoacacia–M. loti symbiotic system.

Plasma nitrogen fixation system with dual-loop enhancement for improved energy efficiency and its efficacy for lettuce cultivation

Plasma nitrogen fixation (PNF) has been emerging as a promising technology for greenhouse gas-free and renewable energy-based agriculture. Yet, most PNF studies seldom address practical application-specific issues. In this work, we present the development of a compact and automatic PNF system for on-site agricultural applications. The system utilized a gliding-arc discharge as the plasma source and employed a dual-loop design to generate from air and water under atmospheric conditions. Experimental results showed that the system with a dual-loop design performs well in terms of energy costs and production rates. Optimal operational parameters for the system were determined through experimentation, resulting in an energy cost of 13.9 MJ mol−1 and an energy efficiency of 16 g kWh−1 for production, respectively. Moreover, the concentration of exhausted NO x was below the emission standards. Soilless lettuce cultivation experiments demonstrated that produced by the PNF system could serve as liquid nitrate nitrogen fertilizer. Overall, our work demonstrates the potential of the developed PNF system for on-site application in the production of green-leaf vegetables.

Proteome profiling of Paenibacillus sonchi genomovar Riograndensis SBR5T under conventional and alternative nitrogen fixation

Paenibacillus sonchi SBR5T is a Gram-positive, endospore-forming facultative aerobic diazotrophic bacterium that can fix nitrogen via an alternative Fe-only nitrogenase (AnfHDGK). In several bacteria, this alternative system is expressed under molybdenum (Mo)-limiting conditions when the conventional Mo-dependent nitrogenase (NifHDK) production is impaired. The regulatory mechanisms, metabolic processes, and cellular functions of N2 fixation by alternative and/or conventional systems are poorly understood in the Paenibacillus genus. We conducted a comparative proteomic profiling study of P. sonchi SBR5T grown under N2-fixing conditions with and without Mo supply through an LC-MS/MS and label-free quantification analysis to address this gap. Protein abundances revealed overrepresented processes related to anaerobiosis growth adaption, Fe-S cluster biosynthesis, ammonia assimilation, electron transfer, and sporulation under N2-fixing conditions compared to non-fixing control. Under Mo limitation, the Fe-only nitrogenase components were overrepresented together with the Mo-transporter system, while the dinitrogenase component (NifDK) of Mo‑nitrogenase was underrepresented. The dinitrogenase reductase component (NifH) and accessory proteins encoded by the nif operon had no significant differential expression, suggesting post-transcriptional regulation of nif gene products in this strain. Overall, this was the first comprehensive proteomic analysis of a diazotrophic strain from the Paenibacillaceae family, and it provided insights related to alternative N2-fixation by Fe-only nitrogenase. SignificanceIn this work, we try to understand how the alternative nitrogen fixation system, presented by some diazotrophic bacteria, works. For this, we used the SBR5 lineage of P. sonchi, which presents the alternative system in which the nitrogenase cofactor is composed only of iron. In addition, we tried to unravel the proteome of this strain in different situations of nitrogen fixation, since, for Gram-positive bacteria, these systems are little known. The results achieved, through LC-MS/MS and label-free quantitative analysis, showed an overrepresentation of proteins related to different processes involved with growth under stressful conditions in situations of nitrogen deficiency, in addition to suggesting that some encoded proteins by the nif operon may be regulated at post-transcriptional levels. Our findings represent important steps toward the elucidation of nitrogen fixation systems in Gram-positive diazotrophic bacteria.

Distributed plasma-water-based nitrogen fixation system based on cascade discharge: Generation, regulation, and application

Plasma is a clean, environmentally friendly and low-energy-consumption technology that can be used to efficiently convert nitrogen gas (N2) into nitrogen compounds that can be absorbed by plants (such as NOx, NH3, etc.). However, most of the current research on plasma nitrogen fixation focuses on how to improve the yield and energy consumption of gaseous nitrogen fixation components. The research on gas treatment and absorption is still under development, which limits the development and application of distributed plasma nitrogen fixation devices. In this paper, we compared the combination methods of various discharge devices and found that the cascade discharge system of solar-driven dielectric barrier discharges (DBD) + 3-stage spark discharge can achieve high yield and low energy consumption of plasma-water-based nitrogen fixation. The measurement and simulation analysis of gaseous and aqueous plasma nitrogen fixation products shows that the oxidation of NO and NO2 (produced by spark discharge) by O3 (produced by DBD) is the working mechanism of the device to produce water-soluble N2O5. The aeroponics system developed based on this cascade discharge device has realized the aeroponics growth of lettuce, which has laid a certain theoretical and experimental foundation for the application development of distributed plasma nitrogen fixation.

Вплив засолення на бобові рослини та їхнє використання для відновлення родючості ґрунтів

Salinity is one of the biggest harmful stress factors that limit the stability of plants and their productivity, as well as reduce the fertility of soils. Therefore, the research on plant protection mechanisms against high salt concentration in the environment and the search for ways to increase their resistance to this stress factor are relevant today. The presented literature review describes the peculiarities of legume response to salt stress, in particular during the establishment of relationship with nodule bacteria. High concentrations of salt in soil lead to the interruption of some vital processes in legumes and thus cause a significant decrease in both crop quality and harvest size. So, the results of studies which indicate a negative effect of salt stress on growth and development, hormonal status, photosynthesis and carbon assimilation, osmotic processes, maintaining the ion homeostasis and the formation of reproductive organs are given. Special attention is paid to the question of the influence of salinity on the interaction between plants and rhizobia during nodule formation and their further functioning. It is noteworthy that the presence of certain adaptive mechanisms as well as the peculiarities of growth and development of legumes, in particular their capability to form symbiotic nitrogen fixation systems with nodule bacteria, suggest a possibility of using certain species of this family for the remediation of saline soils. The importance of the selection of salt-resistant rhizobia strains and the effectiveness of rhizobia in combination with other beneficial microorganisms for agriculture are noted.

Characterization and Optimization of Plasma Electrolytic Process for Conversion of Molecular Nitrogen to Ammonia in Aqueous Water at Atmospheric Pressure

Ammonia (NH3) is widely used in the chemical and agricultural industries and is of growing interest as a potential energy carrier. Most of the current global NH3 production utilizes the Haber-Bosch process which has a large environmental and physical footprint. For this reason, there have been substantial efforts to develop an alternative process that can be sustainable and distributed. Recently, plasma-based electrolysis reactors have shown promise to convert molecular nitrogen to various forms of fixed nitrogen such as ammonia, nitrate, and nitrite in water at atmospheric pressure. However, selectivity and control over the products has not been adequately demonstrated. In this work, we studied a plasma formed in pure nitrogen gas or mixtures containing nitrogen gas at the surface of liquid water. Various products were characterized in the liquid phase including ammonium ions, nitrate ions, nitrite ions, and hydrogen peroxide as a function of pH, discharge current, and time. In addition, continuous direct current (DC) was compared to pulsed DC voltage plasma operation. We find that the selectivity to different nitrogen products depends on the solution conditions. These results could be used to inform optimization and scale up of similar plasma-liquid systems for sustainable nitrogen fixation.

Genomic basis for the unique phenotype of the alkaliphilic purple nonsulfur bacterium Rhodobaca bogoriensis.

Although several species of purple sulfur bacteria inhabit soda lakes, Rhodobaca bogoriensis is the first purple nonsulfur bacterium cultured from such highly alkaline environments. Rhodobaca bogoriensis strain LBB1T was isolated from Lake Bogoria, a soda lake in the African Rift Valley. The phenotype of Rhodobaca bogoriensis is unique among purple bacteria; the organism is alkaliphilic but not halophilic, produces carotenoids absent from other purple nonsulfur bacteria, and is unable to grow autotrophically or fix molecular nitrogen. Here we analyze the draft genome sequence of Rhodobaca bogoriensis to gain further insight into the biology of this extremophilic purple bacterium. The strain LBB1T genome consists of 3.91 Mbp with no plasmids. The genome sequence supports the defining characteristics of strain LBB1T, including its (1) production of a light-harvesting 1-reaction center (LH1-RC) complex but lack of a peripheral (LH2) complex, (2) ability to synthesize unusual carotenoids, (3) capacity for both phototrophic (anoxic/light) and chemotrophic (oxic/dark) energy metabolisms, (4) utilization of a wide variety of organic compounds (including acetate in the absence of a glyoxylate cycle), (5) ability to oxidize both sulfide and thiosulfate despite lacking the capacity for autotrophic growth, and (6) absence of a functional nitrogen-fixation system for diazotrophic growth. The assortment of properties in Rhodobaca bogoriensis has no precedent among phototrophic purple bacteria, and the results are discussed in relation to the organism's soda lake habitat and evolutionary history.

Catalytic production of ammonia from dinitrogen employing molybdenum complexes bearing N-heterocyclic carbene-based PCP-type pincer ligands

Mechanistic insight into the catalytic production of ammonia from dinitrogen is needed to improve the synthesis of this vital molecule. Here we study the use of samarium diiodide (SmI2) and water in the presence of molybdenum complexes that bear PCP-type pincer ligands to synthesize ammonia. The proton-coupled electron transfer during the formation of a N–H bond on the molybdenum imide complex was found to be the rate-determining step at high catalyst concentrations. Additionally, the dimerization step of the catalyst became the rate-determining step at low catalyst concentrations. We designed PCP-type pincer ligands with various substituents at the 5- and 6-positions and observed that electron-withdrawing groups promoted the reaction rate, as predicted by density functional theory calculations. A molybdenum trichloride complex that bears a trifluoromethyl group functioned as the most effective catalyst and produced up to 60,000 equiv. ammonia based on the molybdenum atom of the catalyst, with a molybdenum turnover frequency of up to 800 equiv. min−1. The findings reported here can contribute to the development of an environmentally friendly next-generation nitrogen-fixation system.

Advances in Semiconductor-Based Nanocomposite Photo(electro)catalysts for Nitrogen Reduction to Ammonia.

Photo(electro)catalytic nitrogen fixation technology is a promising ammonia synthesis technology using clean solar and electric energy as the driving energy. Abundant nitrogen and water as raw materials uphold the principle of green and sustainable development. However, the generally low efficiency of the nitrogen reduction reaction has seriously restricted the application and development of this technology. The paper introduces the nitrogen reduction process and discusses the main challenges and differences in the current photo(electro)catalytic nitrogen fixation systems. It focuses on promoting the adsorption and activation of N2 and the resolution and diffusion of NH3 generated. In recent years, reviews of the modification strategies of semiconductor materials in light of the typical cases of nitrogen fixation have been reported in the literature. Finally, the future development trend of this field is analyzed and prospected.

Plasma-Activated Mist: Continuous-Flow, Scalable Nitrogen Fixation, and Aeroponics

Nitrogen fixation underpins diverse biological and industrial processes and is currently one of the leading producers of carbon emissions at a global scale. Radical solutions to decarbonize nitrogen fixation include plasma-electrified ammonia (NH3) synthesis using water and atmospheric nitrogen. Here, we resolve the intrinsic limitations of the state-of-the-art solutions in (i) energy efficiency; (ii) scalability; (iii) direct use of clean renewable energy; and (iv) direct sustainable application of water-based nitrogen fixation by the novel, scalable plasma-enabled process and system for the continuous-flow, scalable nitrogen fixation, and aeroponics using plasma-activated mist (PAM). The new approach is based on the continuous, scalable, in-flow generation of PAM containing NH4+, NO3–, NO2–, and other nitrogen-fixation species through the reaction of large-area uniform air plasma and high-flux water mist containing large area-to-volume ratio micron-sized droplets. Through the solar-energy-driven plasma-assisted oxidation confined within the droplet micro-reactors, a liquid-phase nitrogen fixation product dominated by NO3– is produced. This PAM nitrogen fixation system is applied for the continuous delivery of nitrogen-based nutrients directly to the roots of living plants using a custom-designed aeroponic system which increases the leaf emergence rate and leaf area of bean sprouts by more than 30%. The unique energy concentration in droplet microreactors leads to the much increased (from 2 to 39 times) energy efficiency at a larger scale compared to the key types of common lab-scale plasma reactors. Compatibility with direct solar power, flow-reactor chemistry, and electrified processes at industry-relevant scales make this low-cost, low-carbon-footprint, renewable-energy-driven process and system promising for the widespread sustainable and distributed production and applications of plasma-enabled nitrogen fixation.

Paraburkholderia bengalensis sp. nov. isolated from roots of Oryza sativa, IR64.

Paraburkholderia bengalensis sp. nov. strain IR64_4_BI was isolated from rice roots cultivated in Madhyamgram field station of Bose Institute, West Bengal, India. IR64_4_BI is a Gram-negative, motile, nitrate-reducing, nitrogen-fixing bacterium. Whole-cell fatty acid analyses of IR64_4_BI show C16:0, summed feature 8 (comprising C18:1ω7c and/or C18:1 ω 6c) and summed feature 3(C16:1 w7c/C16:1 w6c or C16:1 ω 7c/C16:1 ω 6c) were the predominant fatty acids. 16S rRNA phylogeny showed that it was most similar to P. phymatum STM815T (98.5% identity), P. terrae KMY02T (98.44% identity) and P. hospita LMG 20598T (98.32% identity). The Average Nucleotide Identity-BLAST (ANIb) of P. bengalensis IR64_4_BI with P. hospita DSM 17164T, P. terrae DSM 17804T, P. phymatum STM815T and P. hospita LMG 20598T was 83.11, 83.52, 84.5 and 83.12% respectively. Comparison of genome sequence of IR64_4_BI with other species of Paraburkholderia using the Multi-locus species tree software show that P. bengalensis IR64_4_BI is a novel species. The ability of P. bengalensis IR64_4_BI to survive on nitrogen-free medium under microaerophilic conditions and the abundance of nitrogen metabolism-related genes makes this strain a potential candidate for developing a nitrogen-fixing system in rice. Based on genotypic, phenotypic and chemotaxonomic studies, we propose that IR64_4_BI (= MTCC 13051 = JCM 34777) is a new species of Paraburkholderia which has been assigned as Paraburkholderia bengalensis sp.nov.

K+-Intercalated carbon nitride with electron storage property for high-efficiency visible light driven nitrogen fixation

Photocatalytic nitrogen fixation is one of the most promising sustainable energy conversion technologies and might serve as a cheaper and more energy-efficient alternative to the capital- and energy-intensive Haber-Bosch process. However, the solution to solve the nitrogen fixation kinetic problem induced by high reduction potential of intermediates remains a grand challenge. In this work, the kinetic problem of nitrogen fixation is addressed under ambient conditions using K+-intercalated crystalline carbon nitride (KCCN) with an electron storage property. Combined with vigorous N2 chemisorption and activation properties of nitrogen vacancies (NVs), a photocatalytic nitrogen fixation system is constructed, where the NVs on KCCN chemisorb and activate N2 molecule, and subsequently reduce it to NH3 by multielectron reactions facilitated by the stored electrons of KCCN. The unique structure of KCCN-NVs demonstrates a high NH3 production rate of 3.51 mmol h−1 g−1 under visible light irradiation and an apparent quantum yield of 2.05% at λ = 430 nm. This work offers an intriguing solution toward the development of nitrogen-fixing photocatalysts.

New framework of integrated electrocatalysis systems for nitrogen fixation

The novel hybridized and integrated nitrogen fixation system has been demonstrated based on the self-power triboelectric nanogenerators as the power generator, which supplies the new framework for future energy harvesting and conversion.

Petroleum-contaminated soil extent recorded by δ<sup>15</sup>N and δ<sup>13</sup>C of plants and soils

Petroleum contamination in terrestrial environments caused by industrial activities is a significant problem that has received considerable attention. Carbon and nitrogen isotopic compositions (δ<sup>13</sup>C and δ<sup>15</sup>N) effectively describe the behavior of plants and soils under petroleum contamination stress. To better understand plant and soil responses to petroleum-contaminated soil, δ<sup>13</sup>C and δ<sup>15</sup>N values of the plants (<i>Trifolium repens</i>, Leguminosae with C<sub>3</sub> photosynthesis pathway, and <i>Agropyron cristatum</i> with C<sub>4</sub> photosynthesis pathway) and the soil samples under one-month exposure to different extents of petroleum contamination were measured. The results showed that petroleum contamination in the soil induced the soil δ<sup>15</sup>N values to increase and δ<sup>13</sup>C values to decrease; from 1.9‰ to 3.2‰ and from −23.6‰ to −26.8‰, respectively. However, the δ<sup>13</sup>C values of <i>Agropyron cristatum</i> decreased from −29.8‰ to −31.6‰, and the δ<sup>13</sup>C values of<i> Trifolium repens</i> remained relatively stable from −12.6‰ to −13.1‰, indicating that they have different coping strategies under petroleum-contaminated soil conditions. Moreover, the δ<sup>15</sup>N values of <i>Trifolium repens</i> decreased from 5.6‰ to 0.8‰ near the air δ<sup>15</sup>N values under petroleum-contaminated soil, which implies that their nitrogen fixation system works to reduce soil petroleum stress. The δ<sup>13</sup>C and δ<sup>15</sup>N values of <i>Agropyron cristatum</i> and <i>Trifolium repens</i> reflect changes in the metabolic system when they confront stressful environments. Therefore, stable isotopic compositions are useful proxies for monitoring petroleum-contaminated soil and evaluating the response of plants to petroleum contamination stress.

The flavin transferase ApbE flavinylates the ferredoxin:NAD+-oxidoreductase Rnf required for N2 fixation in Azotobacter vinelandii.

Azotobacter vinelandii, the model microbe in nitrogen fixation studies, uses the ferredoxin:NAD+-oxidoreductase Rnf to regenerate ferredoxin (flavodoxin), acting as an electron donor for nitrogenase. However, the relative contribution of Rnf to nitrogenase functioning is unknown because this bacterium contains another ferredoxin reductase, FixABCX. Furthermore, Rnf is flavinylated in the cell, but the importance and pathway of this modification reaction also remain largely unknown. We constructed A. vinelandii cells with impaired activities of FixABCX and/or putative flavin transferase ApbE. The ApbE-deficient mutant could not produce covalently flavinylated membrane proteins and demonstrated markedly decreased flavodoxin:NAD+ oxidoreductase activity and significant growth defects under diazotrophic conditions. The double ΔFix/ΔApbE mutation abolished the flavodoxin:NAD+ oxidoreductase activity and the ability of A. vinelandii to grow in the absence of a fixed nitrogen source. ApbE flavinylated a truncated RnfG subunit of Rnf1 by forming a phosphoester bond between flavin mononucleotide and a threonine residue. These findings indicate that Rnf (presumably its Rnf1 form) is the major ferredoxin-reducing enzyme in the nitrogen fixation system and that the activity of Rnf depends on its covalent flavinylation by the flavin transferase ApbE.

Soybean Productivity Depending On The Elements Of Organic Cultivation Technology In The Short-Term Crop Rotation Of Ukrainian Polissia

Over the past decades, intensive farming has operated under conditions of progressive degradation of the soil cover, maintaining production levels only at the expense of inadequate expenditure of non-renewable energy resources. The soils have acquired irreversible excessive compaction in the sub-arable part of the profile, and the dehumification has acquired a threatening status. The humus content in the soils of Ukraine decreased by almost 25%, and the average annual losses amount to 0.6-0.7 t/ha. Therefore, the search for ways to guarantee the reproduction of soil organic matter, reliable control and restoration of the optimal humus status is extremely relevant. The purpose of the study is to activate natural nitrogen-fixing systems using a mix of green manure and by-products of agricultural crops of short-term leguminous crop rotation. Field experiments were conducted on light grey soils during 2018-2020 in the experimental field of Polissia National University in a leguminous short-term rotation system. This study uses general scientific methods to establish the area of research, plan and lay experiments, conduct observations and analysis; visual – during the implementation of phenological observations; field – to study the relationship with abiotic factors; physiological – to determine the symbiotic effectiveness of preparations of biological origin. The technology of growing agricultural crops in leguminous crop rotation, which ensures the supply of raw materials of organic origin and the accumulation of air nitrogen by root nodule bacteria, has been theoretically substantiated and improved. It is established that one hectare of crop rotation area receives 6.8 tonnes of dry organic raw materials, which corresponds to 78.3 kg/ha of biological nitrogen. It is found out that inoculation of soybean seeds with a preparation of biological origin – Optimise 400, and treatment of soybean crops at BBCH microstages 60-63 with a complex microfertiliser on a chelated basis Nanovit Super+Magnesium Sulphate contributes to the active development of nodule bacteria, the number and weight of which is 81-89 pcs per plant and 510-572 kg/ha. Thus, the active symbiotic potential was 34.2-38.9 thousand kg/day. It is proved that during the growing season soybeans generate 357-400 kg/ha of biological nitrogen in the air, which provides a seed yield of 2.96-2.64 t/ha and leaves 117-160 kg/ha of nitrogen in the soil. The practical value of this study lies in the possibility of enriching the soil with organic matter and the biological form of nitrogen

DIAZOTROPH ACTIVITY REGULATING STRATEGY UNDER THEIR INTRODUCTION IN AGROCENOSES

Objective. Investigate approaches to managing the activity of soil diazotrophs and propose a strategy for its regulation. Methods. Theoretical, vegetation and field experiments, microbiological, gas chromatographic, mathematical and statistical. Results. The activity of beneficial soil microorganisms can change under the action of temperature, humidity, chemical compounds of various origin, and other microorganisms. It was established that, taking into account a significant variety of factors, it is necessary to develop a set of specific ways to increase the growth and functional activity of nitrogen-fixing bacteria, as well as their viability. It has been proved that the combination of diazotrophs forms an effective symbiotic leguminous-rhizobial system, which provides additional biological nitrogen in agrocenoses. At the same time, there was an increase in plant mass, chlorophyll content in the leaves, protein and oil content in the products. The combined use of diazotrophs increases the yield, in particular, soybeans by 9–16 % compared with inoculation by pure bacterial culture. Conclusion. Based on the analysis and generalization of the obtained research results, a strategy for regulating the activity of diazotrophs for their effective introduction into agrocenoses is proposed, which consists in combining bacteria of different species, selecting conditions for their co-cultivation and application upon stabilisation of the number of viable bacterial cells. The proposed strategy involves solving the problem by obtaining an inoculant, which is characterized by a high titre and a stable number of viable cells, which allows to obtain an effective nitrogen-fixing system. The strategy is tried-and-tested on the example of regulating the growth and functional activity of soybean nodule bacteria by combining diazotrophs of different species, substantiating the conditions of their co-cultivation and application to ensure positive interaction in the form of commensalism, as well as by regulating viability of diazotrophs by adding stabilisers to the medium.

An engineered, non-diazotrophic cyanobacterium and its application in bioelectrochemical nitrogen fixation

Summary The reduction of chemically inert nitrogen to ammonia is a critical step in the global nitrogen cycle. Microbial nitrogen fixation is a promising way to realize nitrogen reduction and ammonia production at mild conditions. Here, we report an engineered, non-diazotrophic Synechococcus elongatus PCC 7942 strain with nitrogen fixation activity that is constructed by integrating a modified nitrogenase gene cluster into the genome. The engineered S. elongatus PCC 7942 strain is employed in a bioelectrochemical nitrogen-fixation (e-BNF) system for ammonia production. Because the e-BNF system supplies adequate external electrons for the turnover of nitrogenase, the nitrogen fixation activity of the engineered S. elongatus PCC 7942 strain is significantly improved. After 48 h of reaction, the e-BNF system accumulates 173 μM of NH3, which is 21 times higher than that generated from solely photosynthesis-driven nitrogen fixation, with faradaic efficiency of 6.85%. This work may provide new insight into biological nitrogen-fixation systems and ammonium production.