Nitrogen Fixation Potential Research Articles

The role of proton excreted by Advenella kashmirensis DF12 during ammonium assimilation in phosphate solubilization.

Phosphate-solubilizing bacteria (PSB) can solubilize soil fixed phosphorus (P) to plant available forms. In previous studies, the mechanisms of inorganic phosphate solubilization by PSB mostly focused on the acidolysis of organic acids. Here we screened a highly efficient PSB, Advenella kashmirensis DF12, with the maximum P solubilization of 590 mg L- 1 at 6 days. In addition to its P solubilizing ability, DF12 also showed a tolerance to pH from 5 to 10 and a nitrogen fixation potential. The multiple functions of DF12 and its wide adaptability to various environmental conditions make it a promising biofertilizer candidate. The combined analysis of extracellular metabolites and intracellular metabolome data revealed that the production of organic acid (mainly gluconic acid) is not the only mechanism of P solubilized by DF12, the solubilized P content was not correlated with the gluconic acid concentration but was in a highly significant positive correlation with proton concentration, extrusion of proton during NH4+ assimilation plays a key role in phosphate solubilization. Moreover, the contribution of NH4+ assimilation to phosphorus solubilization is generally present in PSB. Therefore, we proposed that applying ammonium fertilizer in P-deficient soil is more appropriate, it can not only supplement nitrogen fertilizer, but also enhance P use efficiency, which contributes to worldwide fertilizer use reduction and efficiency improvement.

Assessment of legume species for biological nitrogen fixation potential in smallholder farming systems of Kiambu County, Kenya: A participatory approach

This study examined the Biological Nitrogen Fixation (BNF) potential of various legume species in Limuru, Kiambu County, Kenya, focusing on smallholder mixed crop-livestock farmers. Nitrogen is vital to plant growth, particularly for protein synthesis and photosynthesis. Biological nitrogen fixation (BNF), a process by which legumes transform atmospheric nitrogen into a usable form, increases soil fertility and decreases synthetic fertilisers need. The problem addressed was identifying the most effective legumes for improving soil fertility in this region. Using purposive sampling, community-based organisations (CBOs) participated in focus group discussions, where farmers planted experimental plots, collected soil samples, and counted nodules. Destructive sampling was employed during flowering to assess nodulation, with nodules classified based on their ability to fix nitrogen. Results showed Rose coco beans ranked highest due to their efficient nitrogen fixation and adaptability to varying soils and temperatures, followed by Albus lupin and Black and White faba beans. Desmodium also demonstrated persistent nodulation, while indigenous Kienyeji legumes, though less efficient, improved soil fertility. Garden peas, cowpeas, and green grams had lower nitrogen-fixing performance in Limuru's cool, humid climate. This study concludes that Rose coco beans and Albus lupins are highly suitable for improving soil fertility in the region. Participatory methods strengthened farmers' knowledge of sustainable agriculture, and qualitative data highlighted the practical value of BNF legumes. Future research should expand legume trials and explore the use of rhizobia inoculants to further enhance BNF efficiency, supporting long-term agricultural sustainability.

Assessing the combined impacts of microplastics and nickel oxide nanomaterials on soybean growth and nitrogen fixation potential

The excessive presence of polystyrene microplastic (PS-MPx) and nickel oxide nanomaterials (NiO-NPs) in agriculture ecosystem have gained serious attention about their effect on the legume root-nodule symbiosis and biological nitrogen fixation (BNF). However, the impact of these contaminants on the root-nodule symbiosis and biological N2-fixation have been largely overlooked. The current findings highlighted that NiO-NMs at 50 mg kg−1 improved nodule formation and N2-fixation potential, leading to enhanced N2 uptake by both roots and shoots, resulting in increased plant growth and development. While single exposure of PS-MPx (500 mg kg−1) significantly reduced the photosynthetic pigment (8–14 %), phytohormones (9–25 %), nodules biomass (24 %), N2-related enzymes (12–17 %) that ultimately affected the N2-fixation potential. Besides, co-exposure of MPx and NiO at 100 mg kg−1 altered the nodule morphology. Additionally, single and co-exposure of MPx and NiO-NMs at 100 mg kg−1 reduced the relative abundance of Proteobacteria, Gemmatimonadota, Actinobacteria, Firmicutes, and Bacteroidetes is associated with N2-cycling and N2-fixation potential. The findings of this study will contribute to understanding the potential risks posed by MPx and NiO-NMs to leguminous crops in the soil environment and provide scientific insights into the soybean N2-fixation potential.

Potential Nitrogen Fixing Rhizobia Isolated from Some Wild Legumes of Nagaland Based on RAPD with Nif-directed Primer and Their Biochemical Activities

Wild legumes are widely dispersed and can survive in challenging environments as bacteria dwell in their nodules and help each other. Although Nagaland is home to many wild legume varieties, research on the microbial diversity that goes along with them is still in its infancy. This work aimed to characterize several wild legume root nodules and distinguish possible rhizobial isolates using RAPD and nif-directed RPO1 primer. Nodule bacteria were isolated in Yeast extract culture media. Based on their colony morphology, 150 isolates were selected for performing RAPD with nif-directed RPO1 primer. Eighty-four isolates were bonded with RPO1 primer, and a few biochemical tests were conducted on RPO1-positive isolates. Activities that promoted plant development were also investigated for these isolates. Of all the isolates, 18 exhibited phosphate solubilization capacity, while 38 isolates were found to produce IAA. This study entails a large variety of rhizobia in the nodules, which were able to promote growth. Hence, these isolates promise to be bio-fertilizers that could improve agricultural operations.

Linking main ecological clusters of soil bacterial–fungal networks and nitrogen cycling genes to crop yields under diverse cropping systems in the North China Plain

BackgroundCrop rotation changes crop species and the associated management strategies, significantly influencing soil fertility and soil microbial communities. Interactions among the species in microbial communities are important for soil nutrient cycling. Yet, the contribution of soil microbial interactions to crop yield and soil nitrogen-cycle function under wheat–maize and wheat–soybean rotation conversion remains unclear. An 8-year field experiment was conducted to investigate the impact of simple [8-year wheat–maize rotation (8WM) and 8-year wheat–soybean rotation (8WS)] and diverse cropping systems [4-year wheat–soybean followed by 4-year wheat–maize rotation (4WS4WM) and 4-year wheat–maize followed by 4-year wheat–soybean rotation (4WM4WS)] on crop yield, soil properties, bacterial–fungal co-occurrence networks and nitrogen functional potentials. The abundances of genes with nitrogen fixation (nifH), nitrification (AOB and nxrA) and denitrification (narG, nirK, norB and nosZ) potentials were quantified and bacterial and fungal communities were characterized.Results4WS4WM led to higher succeeding maize yields and lower bacterial–fungal network complexity, nitrogen fixation potentials and denitrifying potentials than 8WM. Meanwhile, 4WM4WS exhibited higher succeeding wheat and soybean yields, network complexity and lower nitrifying potentials than 8WS. The ecological cluster with the most nitrifying and denitrifying bacterial species (Module#5) and that with the least species (Module#3) dominated the potentials of nitrogen fixation, nitrification and denitrification and succeeding maize yields in 4WS4WM and 8WM. Module#4 with the highest abundances of nitrifying bacteria (Nitrosomonadaceae) and Module#2 with the most species dominated the nitrifying potentials and succeeding wheat and soybean yields in 4WM4WS and 8WS. Soil water content, organic carbon, dissolved organic carbon, NO3− and pH were key drivers influencing Module#3 and Module#5, while only NH4+ significantly affected Module#2 and Module#4.ConclusionsThese findings demonstrate the importance of ecological clusters within soil microbial network in regulating crop yield and soil nitrogen cycling, and identify specific ecological clusters dominating nitrogen functional potentials in wheat–maize and wheat–soybean rotations, offering science-based recommendations for sustainable crop rotation practices.Graphical

Rhizobium Inoculant and Seed-Applied Fungicide Effects Improve the Drought Tolerance of Soybean Plants as an Effective Agroecological Solution under Climate Change Conditions.

Rhizobial inoculation in combination with fungicidal seed treatment is an effective solution for improving soybean resistance to modern climate changes due to the maximum implementation of the plant's stress-protective antioxidant properties and their nitrogen-fixing potential, which will contribute to the preservation of the environment. Model ecosystems at different stages of legume-rhizobial symbiosis formation, created by treatment before sowing soybean seeds with a fungicide (fludioxonil, 25 g/L) and inoculation with an active strain of Bradyrhizobium japonicum (titer 109 cells per mL), were subjected to microbiological, biochemical, and physiological testing methods in controlled and field conditions. Seed treatment with fungicide and rhizobia showed different patterns in the dynamics of key antioxidant enzymes in soybean nodules under drought conditions. Superoxide dismutase activity increased by 32.7% under moderate stress, while catalase increased by 90.6% under long-term stress. An increase in the antioxidant enzyme activity induced the regulation of lipoperoxidation processes during drought and after the restoration of irrigation. Regeneration after stress was evident in soybean plants with a combination of fungicide seed treatment and rhizobial inoculant, where enzyme levels and lipoperoxidation processes returned to control plant levels. Applying seed treatment with fungicide and Rhizobium led to the preservation of the symbiotic apparatus functioning in drought conditions. As proof of this, molecular nitrogen fixation by nodules has a higher efficiency of 25.6% compared to soybeans without fungicide treatment. In the field, fungicidal treatment of seeds in a complex with rhizobia inoculant induced prolongation of the symbiotic apparatus functioning in the reproductive period of soybean ontogenesis. This positively affected the nitrogen-fixing activity of soybeans during the pod formation stage by more than 71.7%, as well as increasing soybean yield by 12.7% in the field. The application of Rhizobium inoculant and fungicide to seeds contributed to the development of antioxidant protection of soybean plants during droughts due to the activation of key enzymatic complexes and regulation of lipoperoxidation processes, which have a positive effect on nitrogen fixation and productivity of soybeans. This is a necessary element in soybean agrotechnologies to improve plant adaptation and resilience in the context of modern climate change.

Biocontrol potentiality of <i>Burkholderia vietnamiensis</i> nrv12 against the rice blast fungus <i>magnaporthe oryzae</i>

Rice blast disease, caused by the pathogenic fungus Magnaporthe oryzae, is a widespread infection leading to serious crop loss worldwide. In order to achieve sustainable agriculture, root-associated bacteria have been applied to manage fungal diseases and promote growth. The present study aimed to evaluate in vitro the growth-promoting ability and in vivo biocontrol activity against M. oryzae of rice rhizosphere bacterium. Out of sixty-eight isolates recovered from the rhizosphere of blast-infected rice plants, isolate NRV12 exhibited the highest antifungal activity against M. oryzae SH, with an inhibition percentage of 72.7±3.44%. By analysis of 16S rRNA sequence associated with morphology, physiological and biochemical tests, the strain was identified as Burkholderia vietnamiensis. In addition, NRV12 produced hydrolytic enzymes (amylase, cellulase, protease), indole acetic acid (IAA), exhibited nitrogen-fixing potential and the ability to solubilize phosphate and zinc. Innoculation with NRV12 significantly promoted in vivo rice seedling growth to 23.3% as compared to the non-bacteria-treated seedlings. Importantly, infected rice seedlings treated with NRV12 led to a 40% disease reduction in rice blast. These findings suggest that NRV12 is a valuable and promising isolate with biocontrol potential against rice blast caused by M. oryzae.

Impact of biological fungicides on the formation and functioning of symbiotic system soybean–Bradyrhizobium japonicum

Background. In order to reduce the negative impact of mineral fertilizers and pesticides on agroecosystems, environmentally friendly plant protection systems are increasingly being utilized in soybean cultivation technologies. These systems aim to provide essential nutrients to plants while minimizing ecological harm. Materials and Methods. In vegetative studies, the processes of formation and functioning of symbiotic systems in soybeans with active strains of nodulating bacteria Bradyrhizobium japonicum (РC07, PC09, B78, B144) were investigated under the influence of pre-sowing seed treatment with the biofungicides Mycosan-N and Phytocide-r. Microbiological, physiological, statistical methods, and gas chromatography were employed in the research. Results. The impact of biological fungicides on the nodulation activity of nodule bacteria has been identified. It was determined that with comprehensive treatment of soybean seeds with B. japonicum РC07 and Mycosan-N, the mass of nodules formed on the roots exceeded that of the control plants by 7‒22 %, and under the influence of Phytocide-r, the mass was lower by 6‒20 % throughout the vegetation period. With the combined application of B. japonicum PC09 and Mycosan-N, a decrease in the number of root nodules by 8‒25 % and a reduction in their mass by 18‒35 % was observed throughout the vegetation period. Under the influence of Phytocide-r, with the inoculation of rhizobia strain PC09, the number of nodules was lower compared to the control plants only in the full flowering stage. At the same time, the reduction in their mass was 6‒20 % throughout the entire observation period. A stimulating effect of both biofungicides on the formation of the symbiotic apparatus involving strains B. japonicum B78 and B144 has been identified. With the combined application of B. japonicum РC07 and Phytocide-r, nitrogenase activity of symbiotic systems decreased by 7 % only in the stage of three true leaves compared to plants whose seeds were treated only with rhizobia. The nitrogenase activity of symbiotic systems formed with the participation of B. japonicum B78 and under the influence of Mycosan-N increased by 28 %, 15 %, and 12 % in the stages of three true leaves, budding, and full flowering, respectively. The action of Phytocide-r, with the inoculation by the nodule bacteria B78, resulted in an increase in nitrogenase activity by 14 % only in the budding stage. Under the comprehensive treatment of soybean seeds with involved biofungicides and B. japonicum B144, an increase in the intensity of N2 assimilation was noted by 29‒34 % in the stage of three true leaves and by 10‒16 % in the budding stage. Conclusions. The application of a scientifically justified selection of rhizobial strains and biological plant protection agents for pre-sowing treatment of soybean seeds will enable a more complete realization of their nitrogen-fixing potential and phytoprotective effects.

Adaptations to nitrogen availability drive ecological divergence of chemosynthetic symbionts.

Bacterial symbionts, with their shorter generation times and capacity for horizontal gene transfer (HGT), play a critical role in allowing marine organisms to cope with environmental change. The closure of the Isthmus of Panama created distinct environmental conditions in the Tropical Eastern Pacific (TEP) and Caribbean, offering a "natural experiment" for studying how closely related animals evolve and adapt under environmental change. However, the role of bacterial symbionts in this process is often overlooked. We sequenced the genomes of endosymbiotic bacteria in two sets of sister species of chemosymbiotic bivalves from the genera Codakia and Ctena (family Lucinidae) collected on either side of the Isthmus, to investigate how differing environmental conditions have influenced the selection of symbionts and their metabolic capabilities. The lucinid sister species hosted different Candidatus Thiodiazotropha symbionts and only those from the Caribbean had the genetic potential for nitrogen fixation, while those from the TEP did not. Interestingly, this nitrogen-fixing ability did not correspond to symbiont phylogeny, suggesting convergent evolution of nitrogen fixation potential under nutrient-poor conditions. Reconstructing the evolutionary history of the nifHDKT operon by including other lucinid symbiont genomes from around the world further revealed that the last common ancestor (LCA) of Ca. Thiodiazotropha lacked nif genes, and populations in oligotrophic habitats later re-acquired the nif operon through HGT from the Sedimenticola symbiont lineage. Our study suggests that HGT of the nif operon has facilitated niche diversification of the globally distributed Ca. Thiodiazotropha endolucinida species clade. It highlights the importance of nitrogen availability in driving the ecological diversification of chemosynthetic symbiont species and the role that bacterial symbionts may play in the adaptation of marine organisms to changing environmental conditions.

Ecological plasticity, stability, and nitrogen-fixing capacity of edible bean cultivars in the Forest-Steppe of Ukraine

The purpose of this study was to investigate the influence of climatic conditions of the research years on changes in productivity and environmental plasticity and stability of edible bean cultivars. Furthermore, the study investigated the nitrogen-fixing potential of edible bean cultivars for the biologisation of agriculture. The study was conducted in the conditions of the educational and production department of the Uman National University of Horticulture during 2020-2022, using nine cultivars of edible beans. Standard methods of statistical analysis were used to study the parameters of adaptive variability. As a result of the comparative study, the characteristics of various parameters of the adaptive potential of edible bean cultivars were established by the following traits: the onset of the technical ripeness phase: Bianco and Extra Grano Violetto – 78 days. The cultivars Windsor Broad (16.42 t/ha), Bianco (13.73 t/ha), and Svitiaz (11.51 t/ha) stood out in terms of yield and adaptability in the technical ripeness phase, the cultivars Bacchus (1.92 t/ha) and Svitiaz (1.90 t/ha) – in terms of yield and adaptability in the biological ripeness phase; cultivars with high protein content in immature grain: Karmazin (12.77 g/100 g), Windsor Broad (13.51 g/100 g), Bianco (14.30 g/100 g), and Green lowland (14.43 g/100 g); cultivars with high nitrogen-fixing capacity: Ukrainian Sloboda (67.7 kg/ha), Windsor Broad (71.0 kg/ha), and Extra Grano Violetto (75.7 kg/ha). The results of the statistical analysis showed a significant influence of environmental conditions on the formation of productivity indicators of edible bean cultivars and a greater dependence on environmental conditions (CVA = 10.40-82.7%) than on the genetic component (CVG = 5.76-39.7%). The data suggest a tendency for yields to be inversely related to yield stability, with low-yielding cultivars showing stability and high-yielding cultivars showing instability. The presented findings suggest an idea of the change in the productivity parameters of edible beans under contrasting weather conditions, which makes it possible to identify cultivars with high productivity for food purposes and with a higher proportion of high-protein and energy-rich consumer products. Cultivars with increased nitrogen-fixing capacity were identified, which will help reduce the use of synthetic fertilisers

DIAZOTROPHIC ENDOPHYTE Klebsiella sp. N5 FROM SORGHUM SHOWS CROSS-COLONIZATION AND PLANT GROWTH PROMOTION IN RICE

Rice necessitates the highest levels of N fertilizers during its cultivation increasing demand for nitrogen fertilizers as well as negatively affecting the environment. Endophytic diazotrophic bacteria were isolated from sorghum, out of 35 isolates Klebsiella sp. N5 showed maximum potential for biological nitrogen fixation. Primary screening of strain N5 was done with acetylene reduction assay indicating dry root activity of 638.55 nmol C2H4 h-1 g-1. That was further confirmed by nifH gene amplification. The strain was identified morphologically, biochemically and 16S rDNA sequencing analysis and identified as Klebsiella sp. strain N5. This strain exhibited other plant growth-promoting (PGP) traits, such as phosphate solubilization, production of indole acetic acid, siderophore activity, ACC deaminase activity, and anti-fungal activity. PGP endophyte N5 was inoculated into rice seedlings to investigate its interaction under axenic conditions and to characterize its ability to colonize non-native host plant rice. Extensive colonization of rice roots was corroborated by Scanning electron microscopy. In-planta experiments with rice seeds inoculated with Klebsiella sp. N5 showed significant improvements in various agronomic traits such as increase in shoot length, root length, fresh and dry weight of root and shoot, chlorophyll content, and nitrogen content of the plant and soil compared to the untreated plants. Klebsiella sp. N5, a cross colonizer from sorghum (C4 plant) to rice (C3 plant) plays a crucial role in facilitating the acquisition of essential resources such as nitrogen, phosphorus, and iron through direct mechanisms. This study expands the horizon for its potential as a valuable bioinoculant for sustainable agricultural practices, particularly in non-native host rice, paving the way for future field trials.

The cumulative impact of temperature and nitrogen availability on the potential nitrogen fixation and extracellular polymeric substances secretion by Dolichospermum

Nitrogen-fixing cyanobacteria not only cause severe blooms but also play an important role in the nitrogen input processes of lakes. The production of extracellular polymeric substances (EPS) and the ability to fix nitrogen from the atmosphere provide nitrogen-fixing cyanobacteria with a competitive advantage over other organisms. Temperature and nitrogen availability are key environmental factors in regulating the growth of cyanobacteria. In this study, Dolichospermum (formerly known as Anabaena) was cultivated at three different temperatures (10 °C, 20 °C, and 30 °C) to examine the impact of temperature and nitrogen availability on nitrogen fixation capacity and the release of EPS. Initially, confocal laser scanning microscopy (CLSM) and the quantification of heterocysts at different temperatures revealed that lower temperatures (10 °C) hindered the differentiation of heterocysts under nitrogen-deprived conditions. Additionally, while heterocysts inhibited the photosynthetic activity of Dolichospermum, the secretion of EPS was notably affected by nitrogen limitation, particularly at 30 °C. Finally, real-time quantitative polymerase chain reaction (qPCR) was used to measure the expression of nitrogen-utilizing genes (ntcA and nifH) and EPS synthesis-related genes (wzb and wzc). The results indicated that under nitrogen-deprived conditions, the expression of each gene was upregulated, and there was a significant correlation between the upregulation of nitrogen-utilizing and EPS synthesis genes (P < 0.05). Our findings suggested that Dolichospermum responded to temperature variation by affecting the formation of heterocysts, impacting its potential nitrogen fixation capacity. Furthermore, the quantity of EPS released was more influenced by nitrogen availability than temperature. This research enhances our comprehension of interconnections between nitrogen deprivation and EPS production under the different temperatures.

Rhizobium leguminosarum bv.viciae Potential Assessment using Dosha faba Bean Isolates from Central and North Gondar, Ethiopia

Purpose: The objective this study was to evaluate nitrogen fixation effectiveness, survival and compatibility of the isolates of on two different soils that came from Dabat and Shentia sites at Gondar, Ethiopia. The author recommends that the isolates test their nitrogen fixing potential under field conditions in slightly acidic and neutral soil before being used as commercial biofertilzer inoculants. The present study provides potential nitrogen fixer input for agricultural research centers. Methodology: Soil physicochemical analysis and most probable number were done according to their standard procedure. Three top strains were selected as inoculants for faba beans grown on the slightly acidic Shentia soil and the slightly neutral Dabat soil with their control. The symbiotic effectiveness of the strains was evaluated based on plant agronomy and total nitrogen of the plant. The results of the strains analyzed by SPSS version 26. Findings: The highest rhizobium population size was 5.8 x102 cells g-1 soil, while the lowest was 1.7 x102 cell g-1 soil observed at the Dabat and Shentia sites, respectively. There is limited nitrogen and phosphorus content other were enough. It was significant difference inter-strain difference in the all agronomic parameter of all treatments in soil compared to each based on agronomic parameter, but across soils there was no significant different except shoot fresh weight. The result of these studies showed that two Rhizobium leguminosarum bv.viciae isolates and other combinations of them had considerable effect on agronomic properties. Unique Contribution to Theory, Practice and Policy: The application of biological nitrogen fixation through Rhizobium inoculums is promoted as a solution to the problem of poor soil fertility in areas where legumes are cultivated. In most of the developing countries, including Ethiopia, biological nitrogen fixation technology has not fully flourished, so this study was initiated to evaluate fixation potential of isolates.

Effect of Plant Growth-Promoting Bacteria (PGPB) on the Development of Pea crop (Pisum sativum L.)

Microorganisms are of great importance in agriculture in terms of plant nutrients by reducing the need for chemical fertilization. In recent years, plant growth-promoting bacteria (PGPB) have been widely used as biological fertilizers (BF) in agriculture. This study was conducted to determine the effect of plant growth-promoting bacteria on the development of pea plants. Firstly the phosphate solubilization and nitrogen fixation potentials of the bacteria used in this study were determined. In the study, the effects of 4 different combinations, F1 [(Rhizobium sp. (FR-13) and Pseudomonas alcaligenes (FDG121)], F2 [(Pseudomonas fluorescens biotype F (FDG-7), Rhizobium sp. (FR-18) and Bacillus-megaterium-GC subgroup B(FDG-134)], F3 [Arthrobacter oxydans (FDG-72), Bacillus-megaterium-GC subgroup B (FDG-146), Rhizobium sp. (FR-11)] and F4 [Acinetobacter genospecies 9 (FDG-116), Brevibacillus agri (FDG-118), Methylobacterium zatmanii (FDG-123) and Bacillus-megaterium-GC subgroup A (FDG-153)] were investigated. Formulations made with bacteria that were found to be the best in terms of the properties specified among these strains were tested against pea plants under greenhouse conditions and their effects on the plant's total fresh and dry weight were investigated. The study was set up to have 3 replications. As a result of the statistical analysis made with the data obtained, the formulations used compared to the control; F2, F3 and F1 applications were important in total fresh weight, respectively, and F2 and F3 applications were important in total dry weight. As a result, these 3 formulations are especially effective on the yield of pea plants and can be used as potential biofertilizers.

Deciphering Microbial Community and Nitrogen Fixation in the Legume Rhizosphere.

Nitrogen is the most limiting factor in crop production. Legumes establish a symbiotic relationship with rhizobia and enhance nitrogen fixation. We analyzed 1,624 rhizosphere 16S rRNA gene samples and 113 rhizosphere metagenomic samples from three typical legumes and three non-legumes. The rhizosphere microbial community of the legumes had low diversity and was enriched with nitrogen-cycling bacteria (Sphingomonadaceae, Xanthobacteraceae, Rhizobiaceae, and Bacillaceae). Furthermore, the rhizosphere microbiota of legumes exhibited a high abundance of nitrogen-fixing genes, reflecting a stronger nitrogen-fixing potential, and Streptomycetaceae and Nocardioidaceae were the predominant nitrogen-fixing bacteria. We also identified helper bacteria and confirmed through metadata analysis and a pot experiment that the synthesis of riboflavin by helper bacteria is the key factor in promoting nitrogen fixation. Our study emphasizes that the construction of synthetic communities of nitrogen-fixing bacteria and helper bacteria is crucial for the development of efficient nitrogen-fixing microbial fertilizers.

Biological activity of sod-podzolic soils at different levels of radioactive contamination

The biological (enzymatic) activity of sod-podzolic soils has been investigated in the zone of mandatory resettlement and in the alienation zone of the Chornobyl Nuclear Power Plant (CNPP) under the influence of ionizing radiation. Gas chromatographic methods were used to determine potential nitrogenfixing (nitrogenase) activity, biochemical methods were applied to study the activity of hydrolytic enzymes (cellulase and protease) responsible for the decomposition of plant residues in the soil, as well as enzymes involved in oxidative-reductive reactions of organic matter transformation (catalase and polyphenoloxidases). Statistical analysis was also employed. The results of the conducted research indicate that a relatively low increase in the total dose rate in the radioactive contamination area (from 0.2 to 1.6 µGy/h) at Polygon No. 1 (the zone of mandatory resettlement near the village of Khrystynivka, Narodychi district, Zhytomyr region) stimulated potential nitrogenase activity of soil diazotrophs and the activity of both hydrolytic enzymes and oxidoreductases. High dose rates (up to 22.2, 61.6, and especially up to 84.0 mGy/h) at Polygon No. 2, located in the alienation zone of the CNPP directly in the area of the former Red Forest, led to a decrease in soil enzymatic activity. Thus, the obtained results unequivocally demonstrate the different nature of the impact of ionizing radiation levels on the biological activity of sod-podzolic soils. The more radioactive soil in the zone of mandatory resettlement stimulates the enzymatic activity of soil microbiota. This could be attributed to adaptive changes in the development and activity of microorganisms or changes in the composition of their communities, with a prevalence of radio-tolerant microbiota representatives. It is also possible that the manifestation of a radiobiological effect, such as radiation stimulation (radiation hormesis), accelerating the growth and development of microorganisms, may occur. In the alienation zone of the CNPP, with high radioactive contamination, the negative influence of ionizing radiation on the metabolism of soil microorganisms is preserved. The obtained results are highly correlated with the indicators of the abundance of nitrogen-fixing microorganisms in the investigated soils, as well as microorganisms representing the saccharolytic (fungi and cellulolytic bacteria) and peptolytic (ammonifiers) pathways of plant residue degradation, as previously demonstrated by us.

Rice straw increases microbial nitrogen fixation, bacterial and nifH genes abundance with the change of land use types.

Soil microorganisms play an important role in soil ecosystems as the main decomposers of carbon and nitrogen. They have an indispensable impact on soil health, and any alterations in the levels of organic carbon and inorganic nitrogen can significantly affect soil chemical properties and microbial community composition. Previous studies have focused on the effects of carbon and nitrogen addition on a single type of soil, but the response of soil microorganisms to varying carbon and nitrogen inputs under different land soil use types have been relatively understudied, leaving a gap in our understanding of the key influencing factors. To address this gap, we conducted a study in the tropical regions of Hainan province, focusing on four distinct land use types: natural forest soil (NS), healthy banana soil (HS), diseased banana garden soil (DS), and paddy soil (PS). Within each of these environments, we implemented five treatments: CK, RS (rice straw), RSN (rice straw and NH4NO3), RR (rice root), and RRN (rice root and NH4NO3). Our aim was to investigate how soil bacteria response to changes in carbon and nitrogen inputs, and to assess their potential for biological nitrogen fixation. The results showed that the addition of rice straw increased the absorption and utilization of nitrate nitrogen by microorganisms. The addition of rice roots (RR) did not increase the absorption capacity of inorganic nitrogen by microorganisms, but increased the content of poorly soluble organic carbon. Most importantly, the addition of rice straw increased microbial respiration and the utilization efficiency of N2 by microorganisms, and the further addition of ammonium nitrate increased microbial respiration intensity. With the change of soil type, the rice straw increases microbial nitrogen fixation, bacterial and nifH genes abundance. Meanwhile, microbial respiration intensity is an important factor influencing the differences in the structure of bacterial communities. The addition of inorganic nitrogen resulted in ammonium nitrogen accumulation, reduced microbial richness and diversity, consequently diminishing the soil microorganisms to resist the environment. Therefore, we believe that with the change of soil types, corresponding soil nutrient retention strategies should be devised and incorporated while reducing the application of ammonium nitrogen, thus ensuring healthy soil development.

Insights into Genetic and Physiological Characteristics of Clover Rhizobia in Afghanistan Soils

Livestock production in Afghanistan highly relies on grazing and clover feed, which is a key component of pastures and forage crops. This study elucidated the genetic diversity of clover-nodulating rhizobia in different ecological regions and their effects on clover growth. A total of 57 rhizobia were isolated and their genetic diversities were studied through 16S rRNA and nifD genes. The isolates were inoculated to clover (Afghan local variety), to investigate the potential of nitrogen fixation and influences of clover growth. The 16S rRNA gene analysis showed two distinct groups of Rhizobium (94.7%) and Ensifer (5.3%) species. The nifD phylogenetic relationship revealed a high similarity to Rhizobium and a novel lineage group close to Rhizobium leguminosarum species. In the plant test, different genotypes significantly (p &lt; 0.01) exhibited an increase in plant biomass production, compared to the un-inoculated plants. Among genotypes, the highest plant biomass was recorded in PC8 (1769.0 mg/plant) and PC9 (1409.2 mg/plant) isolates as compared to un-inoculated plants (144.0 mg/plant). Moreover, these isolates showed maximum nitrogen fixation rates of 8.2 and 6.5 µM/plant, respectively. These isolates were identified as the most promising rhizobial strains for developing biofertilizers in the context of Afghanistan.

Importance of geometric effects in scaling up energy-efficient plasma-based nitrogen fixation

With the focus on feasibility evaluation of scaling-up plasma-based nitrogen fixation by combined experiments and thermodynamic modelling, we aim to tackle the challenge of design and development of an energy-efficient and scaled-up plasma reactor.

Kashi Tripti: A newly developed high-yielding mid-season edible-podded variety of vegetable pea

The COVID-19 epidemic has highlighted the crucial need to live a healthy lifestyle, particularly in metropolitan areas. As a result, there has been an increase in demand for functional foods that are high in important nutrients and support excellent health. Pea (Pisum sativum L.) is one of the oldest multipurpose legumes grown for human food, animal fodder, and ornamental and aids in ecosystem balance due to their innate nitrogen fixation potential (Devi et al., 2019; Devi et al., 2023). They are grown over an area of 7.04 and 2.59 million hectares for dry and green seeds, respectively (FAOSTAT, 2021). Peas have a beautiful balance of micro and macro nutrition profiles along with high dietary fiber, antioxidants and numerous important biomolecules, thus extremely useful in curing diabetes, cardio problems, certain cancers and many degenerative diseases (Kalloo et al., 2002; Kumari &amp; Deka, 2021; Sharma et al., 2023).