Preliminary strain-specific and non-additive effects of single versus mixed DSE inoculation on rhizosphere microbiome and nutrient cycling relative to plant biomass in Chinese yam.

Abstract

Aims: To mitigate Chinese yam continuous cropping obstacles, this study assessed single and mixed dark septate endophyte (DSE) inoculation effects on yam growth, soil characteristics and rhizosphere microbial communities, offering references for optimizing rhizosphere microenvironment of continuously cropped medicinal plant soils.

Methods and results: 9 DSE strains were isolated from yam roots for single/mixed seedling pot inoculation; We found that growth-promoting effects differed by strain. Acrocalymma and Setophoma terrestris were the most commonly isolated DSE species, but strains with lower isolation rates Paraphoma ledniceana, Amesia atrobrunnea, and Zopfiella pilifera exhibited the most pronounced positive effects on yam root biomass. Increasing the number of co-inoculated strains did not proportionally enhance yam growth but progressively restructured soil microbial communities. However, mixed DSE inoculation as a whole showed no obvious growth promotion compared with the control. Fungal co-occurrence networks exhibited higher modularity and clustering, while bacterial communities had greater connectivity, especially under P. ledniceana and Fusarium sp. inoculation. Biosynthesis was the most abundant predicted function of rhizosphere microbes, with bacteria predicted to be enriched in detoxification and fungi in degradation-related pathways. Two strains of Chaetomiaceae and Periconia epilithographicola increased soil pH, organic carbon and available phosphorus, while available nitrogen decreased after DSE inoculation. Importantly, P. epilithographicola inoculation enhanced mycorrhizal fungi and mitigated microbial imbalance.

Conclusions: Single and mixed DSE inoculations regulate rhizosphere microbial assembly and nutrient cycling via species-specific effects. Screening beneficial DSE consortia and characterizing their influence on rhizosphere networks provides preliminary theoretical insights and and candidate strains that may relieve yam replant obstacles in future applications.