Effects of Soil Steam Sterilization on Red Clover, Its Associated Soil Microorganisms, and Mutualistic Symbionts Under Recurrent Drought

The rhizosphere is a biodiversity hotspot, shaped by intricate interactions between plants and soil microorganisms. Drought events increasingly threaten agroecosystems by negatively impacting both plant productivity and associated microbial communities. Mutualistic interactions with arbuscular mycorrhizal fungi (AMF), rhizobia, and plant growth‐promoting microorganisms enhance plant tolerance to abiotic stressors while supporting water and nutrient uptake. One approach to disentangling the role of soil microbes in plant biomass production is to compare sterilized and untreated soils. In this study, we used steam sterilization to reduce microbial load while preserving soil structure, thereby allowing us to isolate microbial contributions to plant performance under recurrent drought. We investigated the diversity and dynamics of AMF, Rhizobium root nodule bacteria, and soil microbial communities (fungi and bacteria) in the rhizosphere of Trifolium pratense (red clover) exposed to two consecutive drought events in both steam‐sterilized and untreated soil. Steam sterilization significantly increased plant biomass under both wet and dry conditions. Contemporarily, we observed reduced pathogen pressure (e.g., Fusarium and Ilyonectria ) and not severely affected abundances of AMF and rhizobia. Drought consistently induced higher AMF abundance and compositional changes, notably stimulating Funneliformis mosseae , regardless of soil treatment. Fungal communities responded more strongly to drought than bacterial communities, particularly in sterilized soils. Our findings demonstrate that steam sterilization is a valuable tool for promoting plant productivity and resilience. This has practical implications for sustainable agriculture in drought‐prone environments.