Rehydration under extreme drought conditions affected rhizosphere microorganisms more than bulk soil in broomcorn millet farmland

Rehydration is a primary adaptation strategy for alleviating the detrimental effects of drought on crop growth. However, the effects of rehydration on microbial communities in various compartments under drought conditions remain poorly understood. Herein, we explored the response patterns of bacterial and fungal community composition, diversity, ecological network, and assembly process in the bulk soil and rhizosphere of broomcorn millet farmland at 5, 10, 20, and 30 days after rehydration during drought conditions. Compared to drought, rehydration significantly decreased the organic matter (OM), total nitrogen (TN), available potassium (AK), available phosphorus (AP), nitrate nitrogen (NO3--N), and ammonium nitrogen (NH4+-N) contents in rhizosphere, but had no obvious influences on the OM and TN contents in bulk soil on the four sampling days. In the rhizosphere of broomcorn millet field, Firmicutes and Actinobacteria were enriched in drought condition, but Proteobacteria and Bacteroidetes were enriched in rehydration regime. Compared to drought, the relative abundances of Eurotiomycetes, Dothideomycetes, Mortierellomycetes, and Leotiomycetes were enhanced, but Sordariomycetes was reduced on the 5th and 10th days after rehydration. Rehydration increased the bacterial and fungal observed ASVs and Shannon index in the rhizosphere to varying degrees, but had little effect on the bulk soil. Null-model analysis indicated that rehydration deceased the stochastic process of fungal communities in the bulk soil, whereas had no influence on deterministic process of bacterial community in the bulk soil and rhizosphere. More importantly, rhizosphere properties had a greater impact on the bacterial and fungal community composition, diversity, and assembly process than bulk soil. Network analysis revealed that rehydration improved the interconnected taxa in the rhizosphere bacterial network, but reduced microbial interactions in the rhizosphere fungal network compared to drought. This work provides a theoretical foundation for elucidating the role of rehydration regime in governing the ecological services of microbiome of broomcorn millet farmland under drought conditions.