Rainwater-borne H₂O₂ differentially alters microbial structure and functions in acidic and alkaline flooded paddy soils

Rainwater-borne hydrogen peroxide (H₂O₂) is ubiquitous, yet the effects of its deposition on soil microbiomes and biogeochemical cycling remain poorly understood. Microcosm incubations of acidic and alkaline soils demonstrated that H₂O₂ reshapes soil microbial communities and metabolic functions via pH-dependent oxidative pathways. H₂O₂ input increased reactive oxygen species (ROS) in both soil types, but hydroxyl radical (^•OH) production was much stronger in acidic soils compared to the alkaline soils. This perturbation increased microbial richness, shifted bacterial and eukaryotic diversity in contrasting directions, and caused greater bacterial than eukaryotic restructuring. Co-occurrence networks became more complex in acidic soils but simplified in alkaline soils. Functionally, H₂O₂ reorganized taxon-associated genes for C, N, P, S and Fe cycling, with acidic soils showing suppressed denitrification, methane oxidation and dissimilatory sulfate reduction, but enhancing many iron oxidation, while alkaline soils showed the opposite tendency. pH and ROS (H₂O₂ and ^•OH) accounted for microbial functional composition, with Fe cycling being closely linked to these drivers. Field observations also support these findings, highlighting the role of soil pH in modulating microbial responses to oxidative deposition and establishing rainwater-derived ROS as an overlooked driver of soil microbial functioning and redox-coupled biogeochemical cycling under future climate scenarios.