Drying-rewetting legacy mitigates freezing-thawing effects on soil microbial communities and greenhouse gas emissions in plateau riparian wetlands

Climate change intensifies compound disturbances in soil ecosystems, yet how legacy effects from prior events shape microbial responses to subsequent stresses remains poorly understood. Here, we investigated the legacy effects of drying-rewetting (DW) and freeze-thaw (FT) on greenhouse gas (GHG) emissions and microbial community dynamics across riparian wetlands of the Tibetan Plateau with distinct land-use histories (urban, grazing, and natural). The results showed that urban soils consistently amplified CO₂ emissions compared to grazing and natural lands, whereas natural soils exhibited a pronounced decline in fungal ITS gene abundance, contrasting with the resilience observed in urban and grazing counterparts. Notably, sequential DW-FT perturbations triggered cross-stress mitigation, reducing CO₂ emissions and enriching Actinobacteria—a bacterial phylum negatively correlated with cumulative CO₂ release. Concurrently, DW legacies drove the taxonomic restructuring of fungal communities, favoring the dominance of Ascomycota in natural soils subjected to subsequent FT cycles. Prior DW exposure uniquely amplified the relative abundance of bacterial amplicon sequence variants (ASVs) under FT fluctuations, while standalone FT legacies lacked comparable regulatory capacity. Furthermore, in bacterial co-occurrence networks exposed to two DW cycles, an incomplete cluster emerged, indicating short-term adaptation via compartmentalization. Fungal clusters under FT cycles exhibited simplified co-response patterns but activated mutualism. Our study demonstrates that DW/FT legacy effects on GHG emissions and microbial communities are land-use dependent; DW legacies mitigate FT-induced microbiome disruptions in plateau riparian soils, with fungi showing heightened sensitivity to FT and bacteria displaying adaptability to DW, highlighting taxon-specific responses to compound disturbances.