The co-inoculation of Pseudomonas chlororaphis H1 and Bacillus altitudinis Y1 promoted soybean [Glycine max (L.) Merrill] growth and increased the relative abundance of beneficial microorganisms in rhizosphere and root

Fungal endophytes influence soil organic carbon and nitrogen fractions promoting carbon sequestration and improving grain yield in soybean

Fungal endophyte inoculants present a promising avenue for enhancing carbon sequestration in agricultural systems. These endophytes can significantly influence soil organic carbon (SOC) and nitrogen (N) fractions by modulating root exudation, soil aggregation, and organic matter decomposition. We investigated the effectiveness of commercial-stage fungal endophyte seed inoculants in an Australian soybean field trial to increase yield, total SOC, stable SOC fractions, and soil N. After one growing season, specific inoculants (Thozetella sp. and Leptodontidium sp.) and dosages increased soybean grain yield and stocks of soil organic matter (SOM) as aggregate occluded particulate organic matter (oPOM) C and N, and mineral-associated organic matter (MAOM) C and N in the topsoil layer (0-15 cm). Furthermore, positive correlations were established between grain yield and the stocks of oPOM (C and N) and MAOM (C and N) in the topsoil layer (0-15 cm). Importantly, increasing grain yield was significantly and positively associated with the proportion of oPOM-C and N stocks to total SOM stock, providing evidence of significant carbon sequestration in oPOM. However, the proportion of MAOM-C and N stock to total SOM stock decreased significantly with increasing grain yield, indicating higher proportion of MAOM is being turned over relative to other SOM fractions although the absolute amounts of MAOM-C and N remained stable. These findings suggest that fungal endophytes and dosages may have variable but potentially beneficial impacts on crop growth, yield and play a crucial role in altering SOM fractions. This alteration potentially leads to changed carbon sequestration strategies, emphasising the need for further research into fungal endophyte-mediated carbon sequestration mechanisms.

Serendipita indica-dominated synthetic microbial consortia enhanced tartary buckwheat growth and improved its tolerance to drought stress

The cultivation of tartary buckwheat serves dual roles, offering health benefits and nutritional advantages. Nonetheless, its cultivation is challenged by issues such as soil degradation and climatic drought. Plant growth-promoting (PGP) microorganisms hold promise for addressing these challenges. In this study, we investigated the effects of Serendipita indica inoculation on the root-associated microbial communities of tartary buckwheat. Additionally, we used S. indica to construct synthetic microbial consortia, and their role in promoting the growth and enhancing the drought resistance of tartary buckwheat was evaluated. This study found that the colonization of S. indica in tartary buckwheat promoted the enrichment of beneficial microorganisms such as Actinobacteriota, Sphingomonas, and Mortierella, while reducing the relative abundance of pathogenic genera including Cladosporium, Alternaria, and Acremonium. In addition, the inoculation of the microbial consortia significantly promoted the photosynthesis and biomass accumulation of tartary buckwheat, while also improving soil structure and fertility. Under drought conditions, introducing microbial groups markedly boosted root development, lowered the density of stomata and rate of transpiration in tartary buckwheat leaves, and decreased H2O2 and Malondialdehyde (MDA) levels, thus greatly enhancing tartary buckwheat's resistance to drought. In conclusion, our findings demonstrated that the microbial consortia constructed with S. indica can significantly promote the growth of tartary buckwheat and enhance its drought resistance. However, the specific molecular mechanisms underlying these effects require further investigation in future studies. These findings will provide important theoretical support for the development of novel microbial fertilizers.

Co-exposure impact of nickel oxide nanomaterials and Bacillus subtilis on soybean growth and nitrogen assimilation dynamics

Nickel oxide nanoparticles (NiO-NPs) pose potential threats to agricultural production. Bacillus subtilis has emerged as a stress-mitigating microbe that alleviates the phytotoxicity caused by NiO-NPs. However, the mechanisms underlying its effectiveness, particularly in root-nodule symbiosis and biological N2-fixation (BNF), remain unclear. Here, we tested the combined exposure of NiO-NPs (50 mg kg-1) and B. subtilis on soybean (Glycine max L.) growth and BNF. Combined exposure increased root length, shoot length, root biomass, and shoot biomass by 19% to 26%, while Ni (200 mg kg-1) reduced them by 38% to 53% compared to the control. NiO-NPs at 100 and 200 mg kg-1 significantly (P < 0.05) reduced nodule formation by 16% and 58% and Nitrogen assimilation enzyme activities levels (urease, nitrate reductase, glutamine synthetase, and glutamate synthetase) by 13% to 57%. However, co-exposure with B. subtilis improved nodule formation by 22% to 44%. Co-exposure of NiO-NPs (200 mg kg-1) with B. subtilis increased peroxidase, catalase, and glutathione peroxidase activity levels by 20%, 16%, and 14% while reducing malondialdehyde (14%) and hydrogen peroxide (12%) levels compared to NiO-NPs alone. Additionally, co-exposure of NiO-NPs (100 and 200 mg kg-1) with B. subtilis enhanced the relative abundance of Stenotrophomonas, Gemmatimonas, and B. subtilis, is associated with N2-cycling and N2-fixation potential. This study confirms that B. subtilis effectively mitigates NiO-NP toxicity in soybean, offering a sustainable method to enhance BNF and crop growth and contribute to addressing global food insecurity.

BioSolutions for Green Agriculture: Unveiling the Diverse Roles of Plant Growth-Promoting Rhizobacteria

The extensive use of chemical pesticides and fertilizers in conventional agriculture has raised significant environmental and health issues, including the emergence of resistant pests and pathogens. Plant growth-promoting rhizobacteria (PGPR) present a sustainable alternative, offering dual benefits as biofertilizers and biocontrol agents. This review delves into the mechanisms by which PGPR enhance plant growth, including nutrient solubilization, phytohormone production, and pathogen suppression. PGPR's commercial viability and application, particularly under abiotic stress conditions, are also examined. PGPR improves plant growth directly by enhancing nutrient uptake and producing growth-promoting substances and indirectly by inhibiting phytopathogens through mechanisms such as siderophore production and the secretion of lytic enzymes. Despite their potential, the commercialization of PGPR faces challenges, including strain specificity, formulation stability, and regulatory barriers. The review highlights the need for ongoing research to deepen our understanding of plant-microbe interactions and develop more robust PGPR formulations. Addressing these challenges will be crucial for integrating PGPR into mainstream agricultural practices and reducing reliance on synthetic agrochemicals. The successful adoption of PGPR could lead to more sustainable agricultural practices, promoting healthier crops and ecosystems.

Effects of a co-bacterial agent on the growth, disease control, and quality of ginseng based on rhizosphere microbial diversity

BACKGROUND

The ginseng endophyte Paenibacillus polymyxa Pp-7250 (Pp-7250) has multifaceted roles such as preventing ginseng diseases, promoting growth, increasing ginsenoside accumulation, and degrading pesticide residues, however, these effects still have room for improvements. Composite fungicides are an effective means to improve the biocontrol effect of fungicides, but the effect of Pp-7250 in combination with its symbiotic bacteria on ginseng needs to be further investigated, and its mechanism of action has not been elucidated. In this study, a series of experiments was conducted to elucidate the effect of Paenibacillus polymyxa and Bacillus cereus co-bacterial agent on the yield and quality of understory ginseng, and to investigate their mechanism of action.

RESULTS

The results indicated that P. polymyxa and B. cereus co-bacterial agent (PB) treatment improved ginseng yield, ginsenoside accumulation, disease prevention, and pesticide degradation. The mechanism is that PB treatment increased the abundance of beneficial microorganisms, including Rhodanobacter, Pseudolabrys, Gemmatimonas, Bacillus, Paenibacillus, Cortinarius, Russula, Paecilomyces, and Trechispora, and decreased the abundance of pathogenic microorganisms, including Ellin6067, Acidibacter, Fusarium, Tetracladium, Alternaria, and Ilyonectria in ginseng rhizosphere soil. PB co-bacterial agents enhanced the function of microbial metabolic pathways, biosynthesis of secondary metabolites, biosynthesis of antibiotics, biosynthesis of amino acids, carbon fixation pathways in prokaryotes, DNA replication, and terpenoid backbone biosynthesis, and decreased the function of microbial plant pathogens and animal pathogens.

CONCLUSION

The combination of P. polymyxa and B. cereus may be a potential biocontrol agent to promote the resistance of ginseng to disease and improve the yield, quality, and pesticide degradation.

Marvels of Bacilli in soil amendment for plant-growth promotion toward sustainable development having futuristic socio-economic implications

Microorganisms are integral components of ecosystems, exerting profound impacts on various facets of human life. The recent United Nations General Assembly (UNGA) Science Summit emphasized the critical importance of comprehending the microbial world to address global challenges, aligning with the United Nations Sustainable Development Goals (SDGs). In agriculture, microbes are pivotal contributors to food production, sustainable energy, and environmental bioremediation. However, decades of agricultural intensification have boosted crop yields at the expense of soil health and microbial diversity, jeopardizing global food security. To address this issue, a study in West Bengal, India, explored the potential of a novel multi-strain consortium of plant growth promoting (PGP) Bacillus spp. for soil bioaugmentation. These strains were sourced from the soil's native microbial flora, offering a sustainable approach. In this work, a composite inoculum of Bacillus zhangzhouensis MMAM, Bacillus cereus MMAM3), and Bacillus subtilis MMAM2 were introduced into an over-exploited agricultural soil and implications on the improvement of vegetative growth and yield related traits of Gylcine max (L) Meril. plants were evaluated, growing them as model plant, in pot trial condition. The study's findings demonstrated significant improvements in plant growth and soil microbial diversity when using the bacterial consortium in conjunction with vermicompost. Metagenomic analyses revealed increased abundance of many functional genera and metabolic pathways in consortium-inoculated soil, indicating enhanced soil biological health. This innovative bioaugmentation strategy to upgrade the over-used agricultural soil through introduction of residual PGP bacterial members as consortia, presents a promising path forward for sustainable agriculture. The rejuvenated patches of over-used land can be used by the small and marginal farmers for cultivation of resilient crops like soybean. Recognizing the significance of multi-strain PGP bacterial consortia as potential bioinoculants, such technology can bolster food security, enhance agricultural productivity, and mitigate the adverse effects of past agricultural activities.