Community Assembly Mechanisms Underlying Divergent Responses of Indica and Japonica Rice Rhizosphere Microbiota to Drought Stress.

Drought stress markedly reduces rice yield, with notable genotypic variation in drought tolerance. While the rhizosphere microbiome is regarded as the second genome of plants, how the indica and japonica rice rhizosphere microbial communities respond to deficit irrigation and their relationship with yield remain to be elucidated. Here, we conducted field experiments using 12 indica and 12 japonica rice varieties under full and deficit irrigation regimes. Yield-related traits, including filled grain number, seed setting rate, two-plant yield, and thousand grain weight, were measured, and the rhizosphere microbial communities were characterized by 16S rRNA gene sequencing. In line with previous studies, japonica varieties showed superior drought resistance in terms of yield performance. Both rice genotype and irrigation regime significantly influenced the composition and functional potential of the rhizosphere microbiome. Compared to indica rice, the japonica rice rhizosphere was enriched with more beneficial microorganisms. Enrichment of nitrogen‑metabolism‑related groups, such as Microvirga and Nitrososphaeraceae, may contribute to rhizosphere nitrogen cycling and support nitrogen availability for the rice. Similarly, higher abundance of Streptomyces in japonica varieties under drought conditions may be associated with improved drought tolerance. These microbial genera were closely associated with rice yield. Moreover, the japonica rhizosphere microbiome was less disturbed by water limitation, showing higher stability. Overall, the rhizosphere microbiome of japonica rice exhibited functional optimization under drought stress by promoting the enrichment of beneficial and nitrogen-cycling microbes, thereby enhancing drought resistance and yield stability. This study demonstrated a significant correlation between rhizosphere microbial communities and rice yield, providing fundamental insights that may contribute to future strategies for optimizing crop productivity through microbiome management in sustainable agriculture.