Abstract
Understanding the interactions between agricultural management and seasonal climate variability is essential for maintaining soil biological sustainability and resilience. This study evaluated the effects of irrigation regime (irrigated vs. rainfed) and seasonality (autumn vs. spring) on rhizosphere microbiome diversity and composition using 16S and ITS amplicon metabarcoding during 2024–2026. Rainfed vineyards showed substantially higher bacterial richness (median Chao1: ≈1,220 vs. 710) and greater fungal diversity and richness than irrigated vineyards (Shannon H′: 4.71 vs. 3.86; Chao1: ≈595 vs. 335, re-spectively). PERMANOVA based on Bray–Curtis dissimilarity confirmed irrigation re-gime as the main structuring factor for bacterial (R² = 0.264, p = 0.042) and fungal communities (R² = 0.272, p = 0.005), whereas seasonality had no significant effect (p > 0.30). Taxonomic analysis revealed a marked dominance of Ascomycota under irrigation (80–98% relative abundance), accompanied by reduced fungal evenness. The bacte-ria-to-fungi ratio indicated a higher bacterial proportion under rainfed conditions and in autumn. These results suggest a plant-mediated buffering effect in the rhizosphere and indicate that continuous irrigation may promote microbial homogenization, potentially reducing soil biodiversity. Controlled deficit irrigation strategies may therefore help preserve microbial diversity and support soil functionality and resilience in Mediterra-nean vineyards.