Citrus Genotype Modulates Rhizosphere Microbiome Structure and Function Under Drought Stress

Drought stress substantially impairs citrus growth and alters the rhizosphere microbial composition; however, the role of these microbial communities in plant drought tolerance remains poorly understood. This study investigated the rhizosphere microbial structure, soil enzymatic activities, and physicochemical properties of drought-tolerant (DR) and drought-sensitive (DS) citrus varieties under drought stress conditions. High-throughput sequencing revealed that drought significantly altered microbial community composition, reducing the bacterial Shannon diversity by about 15% and enriching Gram-negative, stress-tolerant, and potentially pathogenic bacteria, as well as plant pathogenic fungi (upregulated 25.4% in DS), while reducing undefined saprotrophs (downregulated from 76.2 to 54.0% in DS). Notably, the DR variety exhibited a more stable and complex bacterial network, with 23.5% more edges and a higher proportion of positive correlations (54.3%), higher enrichment of beneficial fungi like Penicillium and Trichoderma, and unique recruitment of mycorrhizal fungi (up to 10.2%), which were nearly absent in DS. Furthermore, soil catalase and urease activities decreased under drought stress conditions. In contrast, acid phosphatase activity increased by up to 40% in DR. Correlation analyses indicated that these microbial shifts were closely associated with changes in soil nutrient availability. Our findings demonstrated that the drought-tolerant citrus variety modulates its rhizosphere microbiome towards a more cooperative and resilient state, highlighting the critical role of host-specific microbial recruitment in enhancing plant adaptation to drought stress for sustainable agriculture.