Microbial Functional Redundancy and Resilience in Response to Drought

Drought can strongly affect soil microbes, which are essential for ecosystem functions. Functional redundancy (FR), in which different microbes can perform similar functions, might help communities withstand stress. How cover crop species alter FR and affect microbial stability under drought is not well characterized. In this study, we examined how drought and crop type shape bacterial and fungal communities. We examined rhizobiomes from three monocultures (field pea, forage radish, and cereal rye), a three-species mixture, and control soil microbiomes under ambient and drought conditions, using amplicon sequencing. Bacterial diversity and predicted functions were more negatively affected by drought than predicted fungal traits, which remained stable. We anticipated that higher plant diversity would enhance microbial resistance, but this was not observed. The three-species mixture did not maintain FR or network complexity as effectively as the monocultures. Under ambient conditions, the mixture supported greater microbial diversity, yet it experienced the most significant decline in redundancy under drought. Among the monocultures, rye harbored the most stable microbial community, retaining functional redundancy and sustaining complex microbial interaction networks. In contrast, radish and pea communities changed more under drought, showing reduced redundancy and simplified network structures. These findings indicate that the identity of the cover crop has a more substantial influence on microbial functional resistance than species richness alone. Selecting appropriate cover crop species, rather than simply increasing diversity, may be a more effective strategy for maintaining soil microbial functions and supporting plant performance under drought conditions.