Search Results (84)

Global food security is challenged by population growth and the environmental toll of conventional fertilizers. Enhancing biological nitrogen fixation (BNF) in legumes like soybean (Glycine max) is a sustainable fertilization alternative. This study investigates a graphitic carbon nitride/iron oxide (Fe₂O₃/g–C₃N₄ or FC) nanocomposite as a dual–functional fertilizer to improve iron (Fe) nutrition and BNF in soybeans. A pot experiment was conducted using different FC concentrations (10, 100, and 200 mg kg⁻¹), alongside controls. Results showed that the 100 mg kg⁻¹ FC treatment (FC2) was most effective, significantly increasing soybean biomass, nodule number, and nodule fresh weight. The FC2 treatment also enhanced photosynthetic rates and chlorophyll content (SPAD values) while reducing stomatal conductance and transpiration, indicating improved water–use efficiency. Furthermore, FC application bolstered the plant’s antioxidant system by increasing the activity of superoxide dismutase (SOD) and peroxidase (POD). Elemental analysis confirmed that FC treatments significantly increased the uptake and translocation of Fe and nitrogen (N) in plant tissues. These findings demonstrate that the FC nanocomposite acts as a highly effective nanofertilizer, simultaneously addressing iron deficiency and boosting nitrogen fixation to promote soybean growth. This work highlights its potential as a sustainable solution to enhance crop productivity and nutrient use efficiency in modern agriculture. Full article

Achieving food security for a growing population under a changing climate is a key concern in Senegal, where agriculture employs 77% of the workforce with a majority of small farmers who rely on the production of crops for their subsistence and for income generation. Moreover, due to the underproductive soils and variable rainfall, Senegal depends on imports to fulfil 70% of its food requirements. In this research, we considered four crops that are crucial for Senegalese agriculture: millet, sorghum, peanuts and rice. We used crop simulation models to explore existing yield gaps and optimal agronomic practices. Improving the N fertilizer management in sorghum and millet resulted in 40–100% increases in grain yields. Improved N symbiotic fixation in peanuts resulted in yield increases of 20–100% with highest impact in wetter locations. Optimizing irrigation management and N fertilizer use resulted in 20–40% gains. The best N fertilizer strategy for sorghum and millet included applying low rates at sowing and in early development stages and adjusting a third application, considering the expected rainfall. Peanut yields of the variety 73-33 were higher than Fleur-11 in all locations, and irrigation showed no clear economic advantage. The best N fertilizer management for rainfed rice included applying 30 kg N/ha at sowing, 25 days after sowing (DAS) and 45 DAS. The best combination of sowing dates for a possible double rice crop depended on irrigation costs, with a first crop planted in January or March and a second crop planted in July. Our work confirmed results obtained in field research experiments and identified management practices for increasing productivity and reducing yield variability. Those crop management practices can be implemented in pilot experiments to further validate the results and to disseminate best management practices for farmers in Senegal. Full article

Cereal/legume intercropping enhances legume nodulation and improves nitrogen use efficiency (NUE) in cereal crops. This facilitation of symbiotic nitrogen fixation (SNF) in intercropped legumes involves a complex eco-physiological mechanism driven by multiple factors. Among them, interspecific root interactions (IRIs) are a key factor influencing SNF in intercropped legumes. Currently, it remains unclear whether and how IRIs modulate SNF to affect NUE and yield formation in legume species. In this study, maize/pea intercropping with different types of root separation [no barrier (NB) and plastic barrier (PB)] and pea monocropping (IP) were simulated in a nitrogen (N)-free nutrient matrix in pots, and the SNF, N metabolism, and N partitioning were investigated. We demonstrated that IRIs optimize SNF performance. N assimilation is positively regulated following increases in enzyme activity and gene expression in intercropped roots and nodules. Furthermore, IRIs facilitate amino acid (AA) export from nodules to roots and shoots, which is followed by an increase in AA levels in leaves (source) and leaf exudates (sink). Overall, intensive SNF drives N metabolism and alters source-to-sink N partitioning, thereby increasing NUE (by 23%) and yield (by 15%) in intercropped pea. This study reveals the positive roles of IRIs to the NUE and yield and provides useful reference material for increasing N contents derived from SNF to maximize NUE and crop yields in intercropped legumes. Full article

Despite chemical exchange often serving as the first step in plant–microbe interactions, the specialized chemical metabolites produced by grass–Epichloë endophyte symbiosis as mediators of host growth, nutrient acquisition, and modulators of the rhizosphere community under low-nitrogen conditions are areas lacking in knowledge. In this study, we investigated the plant growth-promoting effects of the Epichloë endophyte strain and identified the growth of the Epichloë strain under different types of nitrogen source treatments. In addition to the in vitro test, we evaluated growth performance for Epichloë endophyte–infected plants (E+) and Epichloë endophyte–free plants (E−) in a pot trial under 0.01 mol/L urea treatment. Seedlings from E+ and E− groups were collected to analyze the plant bacterial microbiome and root metabolites. The E. gansuensis endophyte strain was found not to produce indoleacetic acid (IAA), pectinase, or contain ferritin. The nitrogenase gene, essential for nitrogen fixation, was also absent. These results suggest that E. gansuensis endophyte strains themselves do not contain attributes to promote plant growth. Concerning N fertilization, it was observed an increase in the colony diameter of E. gansuensis strain was observed only in the NO₃⁻-N (NN) treatment, while inhibition was observed in the urea-N (UN) treatment. E. gansuensis endophyte symbiosis significantly increased tiller number and plant dry weight. Overall, our results suggest that the E+ plants had more root forks and greater average root diameter compared to E− plants under the UN treatment. In a pot experiment using UN, data from 16S rRNA amplicon sequencing revealed that E. gansuensis endophyte infection significantly altered the bacterial community composition in shoot and root, and significantly increased Shannon (p < 0.001) and Chao 1 (p < 0.01) indexes. The relative abundance of Acidobacteriota, Actinomycetota, Cyanobacteriota, Fibrobacterota, Myxococcota, and Patescibacteria in the shoot, and Cyanobacteriota, Pseudomonadota, and Verrucomicrobiota in the root were significantly increased by E. gansuensis endophyte infection. Similarly, E. gansuensis endophyte symbiosis shifted the metabolite composition of the host plants, with the E+ plants showing a higher number of metabolites than the E− plants. In addition, co-metabolism network analysis revealed that the positive relevance between exudates and microorganisms in the root of the E+ plants is higher than that of the E− plants. These findings provide valuable insights into the knowledge of the effects of the symbiotic relationship between host plants and Epichloë endophyte on interspecific interactions of plant microbiome, beneficial for harnessing endophytic symbiosis, promoting plant growth. Full article

Microbial functional genes serve as the core genetic foundation driving microbial ecological functions; however, its microbial functional gene composition across varied habitats and its ecological adaptation interplay with plants remain understudied. In this study, we investigated the P. tabuliformis rhizosphere microbial functional genes which are related to N and P cycles across ridge and slope habitats between different elevational gradients, analyzed their composition and abundance, and analyzed their responses to environmental factors. Results showed that slope habitats had a significantly greater abundance of N and P cycling functional genes compared to those of ridge counterparts (p < 0.05). Specifically, slope environments showed an enhanced gene abundance associated with denitrification, nitrogen fixation, nitrification, assimilatory/dissimilatory nitrate reduction, and nitrogen transport processes, along with the superior expression of genes related to inorganic/organic phosphorus metabolism, phosphorus transport, and regulatory gene expression. These nutrient cycling gene levels were positively correlated with soil nutrient availability. Our findings revealed distinct ecological strategies: Ridge communities employ resource-conservative tactics, minimizing microbial investments to endure nutrient scarcity, whereas slope populations adopt competitive strategies through enriched high-efficiency metabolic genes and symbiotic microbial recruitment to withstand resource competition. Full article

The soybean is an important source of protein and is gaining popularity in Ghana due to a rising demand for its use in the poultry industry. However, the grain yield of soybeans is relatively low in the Upper West Region due to infertile soil and climate change. This study evaluated root nodulation and symbiotic effectiveness in 31 rhizobial isolates obtained from the nodules of soybeans planted at Da in the Upper West Region, Ghana, as well as measured photosynthetic activity of the soybean plants grown under glasshouse conditions. This study further assessed the tolerance of the rhizobial isolates to different levels of temperature, drought, salinity, and pH in the laboratory and also measured the ability of the isolates to produce indole-3-acetic acid. An infrared gas analyser and the ¹⁵N and ¹³C natural abundance techniques were used to assess the photosynthetic activity, N₂ fixation, and water-use efficiency, respectively. The results showed that the test isolates that induced greater photosynthetic rates from higher stomatal conductance also stimulated increased water loss via leaf transpiration in soybean plants. Isolates TUTGMGH9 and TUTGMGH19 elicited much higher shoot δ¹³C in the soybean host plant and induced higher shoot biomass, C accumulation, percent relative symbiotic effectiveness, and N₂ fixation relative to Bradyrhizobium strain WB74 and 5 mM of nitrate, which were used as positive controls. Although isolate TUTGMGH9 did not grow at 40 °C, it showed growth at 5% of PEG-6000, NaCl, and a low pH while also producing moderate IAA. However, for better utilisation of these rhizobial isolates as bioinoculants, their growth performance needs to be assessed under field conditions to ascertain their competitiveness and symbiotic efficacy. Full article

Root nodule bacterial isolates from field-grown chickpea were evaluated in glasshouse and field experiments based on infectivity, relative symbiotic effectiveness, nodule occupancy, plant yield and survivability in the soil rhizosphere for their use as inoculants to enhance chickpea production in Western Australia. Compared to the Australian commercial chickpea inoculant strain Mesorhizobium ciceri sv. ciceri CC1192, 10 new strains were ‘fast’ growers, averaging 72 h to grow in culture at 28 °C. The relative symbiotic effectiveness (RSE%) of the new strains in field experiments determined by shoot weight ranged from 77 to 111% in the Desi genotype (var. Kyabra) and 83 to 102% in Kabuli (var. Kimberley Large). Kyabra yielded greater output (2.4–3 t/ha) than Kimberley Large (1.2–1.8 t/ha), with mean 100 seed weights of 23 and 59 g, respectively. The rhizobial strains living in the rhizosphere presented a higher competitive ability for nodule occupancy than those in the bulk soil. Tukey’s multiple comparisons test showed no significant differences between the nodule occupancy ability of the introduced strains (i.e., 3/4, 6/7, N5, N300, K66, K188 and CC1192) in either Kyabra or Kimberley Large (p = 0.7321), but the strain competitiveness with each cultivar differed (p < 0.0001) for some of the test strains. Strains N5, N300, K72 and 6/7 were the top contenders that matched or beat CC1192 in nitrogen fixation traits. These findings show that new rhizobial strains derived from naturalized soil populations exhibited better adaptability to local soil conditions than CC1192. Full article

Carbon dioxide (CO₂) is the most abundant greenhouse gas (GHG) in the atmosphere and the substrate for the photosynthetic fixation of carbohydrates in plants. Increasing GHGs from anthropogenic emissions is warming the Earth’s atmospheric system at an alarming rate and changing its climate, which can affect photosynthesis and other biochemical reactions in crop plants favorably or unfavorably, depending on plant species. For the substrate role in plant carbon reduction reactions, CO₂ concentration ([CO₂]) in air potentially enhances photosynthesis. However, N uptake and availability for protein synthesis can be a potential limiting factor in enhanced biomass synthesis under enriched [CO₂] conditions across species. Legumes are C₃ plants and symbiotic N fixers and are expected to benefit from enhanced [CO₂] in the air. However, the concurrent increase in air temperatures with enhanced [CO₂] demands more detailed investigations on the effects of [CO₂] enhancement on grain legume growth and yield. In this article, we critically reviewed and presented the online literature on growth, phenology, photosynthetic rate, stomatal conductance, productivity, soil health, and insect behavior under elevated [CO₂] and temperature conditions. The review revealed that specific leaf weight, pod weight, and nodule number and weight increased significantly under elevated [CO₂] of up to 750 ppm. Under elevated [CO₂], two mechanisms that were affected were the photosynthesis rate (increased) and stomatal conductivity (decreased), which helped enhance water use efficiency in the C₃ legume plants to achieve higher yields. Exposure of legumes to elevated levels of [CO₂] when water stressed resulted in an increase of 58% in [CO₂] uptake, 73% in transpiration efficiency, and 41% in rubisco carboxylation and decreased stomatal conductance by 15–30%. The elevated [CO₂] enhanced the yields of soybean by 10–101%, peanut by 28–39%, mung bean by 20–28%, chickpea by 26–31%, and pigeon pea by 31–38% over ambient [CO₂]. However, seed nutritional qualities like protein, Zn, and Ca were significantly decreased. Increased soil temperatures stimulate microbial activity, spiking organic matter decomposition rates and nutrient release into the soil system. Elevated temperatures impact insect behavior through higher plant feeding rates, posing an enhanced risk of invasive pest attacks in legumes. However, further investigations on the potential interaction effects of elevated [CO₂] and temperatures and extreme climate events on growth, seed yields and nutritional qualities, soil health, and insect behavior are required to develop climate-resilient management practices through the development of novel genotypes, irrigation technologies, and fertilizer management for sustainable legume production systems. Full article

Nitrogen (N), while the most abundant element in the atmosphere, is an essential soil nutrient that limits plant growth. Leguminous plants naturally possess the ability to fix atmospheric nitrogen through symbiotic relationships with rhizobia in their root nodules. However, the widespread use of synthetic N fertilizers in modern agriculture has led to N enrichment in soils, causing complex and profound effects on legumes. Amid ongoing debates about how leguminous plants respond to N enrichment, the present study compiles 2174 data points from 162 peer-reviewed articles to analyze the impacts and underlying mechanisms of N enrichment on legumes. The findings reveal that N enrichment significantly increases total legume biomass by 30.9% and N content in plant tissues by 13.2% globally. However, N enrichment also leads to notable reductions, including a 5.8% decrease in root-to-shoot ratio, a 21.2% decline in nodule number, a 29.3% reduction in nodule weight, and a 27.1% decrease in the percentage of plant N derived from N₂ fixation (%Ndfa). Legume growth traits and N₂-fixing capability in response to N enrichment are primarily regulated by climatic factors, such as mean annual temperature (MAT) and mean annual precipitation (MAP), as well as the aridity index (AI) and N fertilizer application rates. Correlation analyses show that plant biomass is positively correlated with MAT, and tissue N content also exhibits a positive correlation with MAT. In contrast, nodule numbers and tissue N content are negatively correlated with N fertilizer application rates, whereas %Ndfa shows a positive correlation with AI and MAP. Under low N addition, the increase in total biomass in response to N enrichment is twice as large as that observed under high N addition. Furthermore, regions at lower elevations with abundant hydrothermal resources are especially favorable for total biomass accumulation, indicating that the responses of legumes to N enrichment are habitat-specific. These results provide scientific evidence for the mechanisms underlying legume responses to N enrichment and offer valuable insights and theoretical references for the conservation and management of legumes in the context of global climate change. Full article

The continuous release of glucosinolates into the soil by Brassicaceae root exudation is a prerequisite to maintaining toxic levels of breakdown products such as isothiocyanates (ITCs). ITCs influence plant and microbial diversity in ecosystems, while fungi and Rhizobiaceae are particularly injured. Studies explaining the molecular mechanisms of the negative effects are presently limited. Therefore, we investigated the early effects of cyclic ITC goitrin on proteomes of the host and symbiotic Mesorhizobium loti in the nodules of Lotus japonicus and of free-living bacteria. In the nodules, many host proteins had a higher abundance, among them, peroxidases and pathogenesis-related PR-10 proteins functioning in the abscisic-acid-activated signaling pathway. In the microsymbiont, transporter proteins as a prominent group are enhanced; some proteins involved in N-fixation decreased. The proteomes give a report about the loss of immunity suppression resulting in the termination of symbiosis, which initiates nodule senescence. Free-living M. loti are severely damaged, indicated, i.a., by a decrease in transporter proteins, the assumed candidates for goitrin protein complex formation, and high proteolysis. The production of chicoric acid by the accompanying bacteria is inhibitory for M. loti but connected to goitrin elimination, as confirmed by mass spectrometric (MS) analysis. In summary, the nodulation process is severely affected by goitrin, causing nodule dysfunction and failed nodule development. N deficiency conditions leads to yellowish leaves and leaf abscission. Full article

In rice, symbiotic N₂ fixation via nodule bacteroids does not take place naturally. Although N₂ fixation by endophytic and associative diazotrophs has been reported in rice, the main organs and seasonal regulation for the N₂ fixation have not been elucidated. In this study, seasonal changes in nitrogenase (acetylene reduction) activity and carbohydrate contents in elongated culm (EC), unelongated stem (US), and crown root (CR) were investigated in manure compost (MC)- and chemical fertilizer (CF)-applied rice. Nitrogenase activity increased after rooting (June) and reached the highest activity in US of MC-applied rice at panicle initiation (August). The sucrose content in EC continued to increase after rooting regardless of the applied materials, whereas the glucose content in US increased after rooting only in CF-applied rice, suggesting higher consumption of glucose in US of MC-applied rice. There were significant differences among bacterial microbiota in EC, US, and CR at panicle initiation. In addition, Clostridia class anaerobes were more abundant in US of MC-applied rice than in EC and CR of MC-applied rice. Such difference was not observed in US of CF-applied rice. These results suggest the suitability of US of MC-applied rice at panicle initiation as a site of N₂ fixation under anaerobic conditions. Full article

Biological nitrogen fixation (BNF) by symbiotic bacteria plays a vital role in sustainable agriculture. However, current quantification methods are often expensive and impractical. This study explores the potential of Raman spectroscopy, a non-invasive technique, for rapid assessment of BNF activity in soybeans. Raman spectra were obtained from soybean plants grown with and without rhizobia bacteria to identify spectral signatures associated with BNF. δN¹⁵ isotope ratio mass spectrometry (IRMS) was used to determine actual BNF percentages. Partial least squares regression (PLSR) was employed to develop a model for BNF quantification based on Raman spectra. The model explained 80% of the variation in BNF activity. To enhance the model’s specificity for BNF detection regardless of nitrogen availability, a subsequent elastic net (Enet) regularisation strategy was implemented. This approach provided insights into key wavenumbers and biochemicals associated with BNF in soybeans. Full article

The symbiotic nitrogen fixation between rhizobia and peanuts offers an advantage in reducing nitrogen fertilizer inputs, decreasing the incidence rate of peanuts, and enhancing soil fertility. Inoculating rhizobia agent is an effective pathway to improve both the quality and yield of peanuts, contributing to food security and promoting sustainable agricultural practices. This study conducted a one-year field experiment in a subtropical humid monsoon climate area in Southeast China to investigate the effects of rhizobia agents on the growth and crop yield of four peanut varieties (i.e., Taihua No.4, No.6, No.8, and No.10). Our research showed that inoculation with rhizobia agent can increase the plant height, lateral branch length, fresh root weight, and leaf area of the four peanut varieties. Meanwhile, inoculation with a rhizobia agent can significantly (p < 0.05) increase the ~50% number of root nodules. Especially for the early-maturing and drought-resistant variety, Taihua No.4 exhibited the highest number of nodules and peanut fruits per plant in the pod-setting stage after inoculation with rhizobia agent, i.e., 24.5 and 18.0, respectively. Under the conventional fertilization conditions (N-P₂O₅-K₂O 15-15-15, 450 kg/hm²), Taihua No.4 and No.6 inoculated with rhizobia agent achieved higher yield increase rates of 11.0% and 11.6% compared to other peanut varieties. This study indicated that the Taihua No.4 and No.6 are the most suitable peanut varieties for rhizobia inoculation and promotion, with enormous potential for yield increase. Meanwhile, optimizing rhizobia inoculation techniques and evaluating soil health status, economic benefits of peanuts, and applicable regions should be explored in the future. Full article

The soybean (Glycine max. L. Merr) can satisfy a large portion of its requirement for nitrogen (N) by living in symbiosis with symbiotic bacteria. However, this source of N may be inadequate in varieties with high yield potential. To fully exploit this potential, soybeans should additionally utilize mineral forms of nitrogen present in the soil. The aim of this study was to determine the effect of varied nitrogen fertilizer application rates on the dry weight of the separated parts of soybean plants and the whole plant, including the number and weight of root nodules, the potential to reduce atmospheric nitrogen (N₂), and the content and uptake of nitrogen. Four levels of pre-sowing nitrogen fertilizer supply were tested: 0, 60, 120, and 180 kg N·ha⁻¹. Measurements of the tested parameters were taken during the flowering stage and the fully ripe stage. During the flowering stage, a reduction in the number of root nodules was observed following the application of 120 and 180 kg N·ha⁻¹. In the fully ripe stage, each increase in nitrogen application caused a systematic decrease in the number of nodules on the roots. Increasing the level of nitrogen application therefore reduced the N₂ fixation potential of soybeans, regardless of the developmental stage. The use of high doses of nitrogen in soybean cultivation did not increase seed yield or the weight of the entire plant. With high doses of nitrogen, the content and accumulation of nitrogen in soybean seeds and total mass did not increase. Therefore, the content and yield of crude protein did not increase. The main organ of nitrogen accumulation in the soybean flowering stage was the leaves (58.6–64.8% of total N uptake), however, in the fully ripe stage, it was the seeds (66.8–74.2% of total N uptake). Full article

Non-symbiotic diazotrophic microbes are important contributors to global N budgets in cereal crops. Knowledge of the biogeography of the organisms in this functional guild increases our understanding of biological N fixation in diverse locations and climates. Here, we describe the diazotrophic community in the previously unstudied, extensive ricefields of southeast Missouri, using restriction fragment length polymorphism (RFLP) analysis and sequencing of nifH gene clones. While nine RFLP patterns were observed in random nifH clones, these groups were not all supported by gene sequencing, suggesting that the RFLP of nifH genes alone is not suitable for describing diazotrophic guilds. Dozens of nifH clones from Missouri ricefield soils were sequenced and analyzed phylogenetically. The nifH genes detected were predominantly from Geobacteraceae, most closely related to Geobacter and Geomonas species. There were substantial clusters of nifH clones most closely related to Desulfovibrionales and other Proteobacteria. Many of the clones did not closely cluster with nifH sequences from known isolates or clades. No cyanobacterial or archaeal sequences were detected in the Missouri ricefield soils. The microbial guild fixing N appeared to be rich in anaerobes and lithotrophs. Organisms in Geobacter and Geomonas seem to be cosmopolitan, but endemism was evident, since nifH clones were recovered that formed clusters not previously reported from ricefields in other locations. Full article