Harvesting reshapes greenhouse gas exchange in reservoir drawdown soils via soil state control and context-dependent microbial functions.

Reservoir drawdown zones, the seasonally exposed and re-flooded margins of reservoirs, are extensive pulsed wetlands that can act as hotspots of greenhouse gas (GHG) exchange. Vegetation harvesting is common in these zones, yet its net climate effect across CO2, CH4, and N2O, and the controls behind it, remain unclear. We compared harvested and unharvested plots across longitudinal river reaches and elevation bands in the drawdown zone of the Three Gorges Reservoir (China). We measured soil-atmosphere fluxes of CO2, CH4, and N2O, together with soil physicochemical properties and metagenome-derived functional markers. Harvesting increased CO2 flux and decreased CH4 flux, while N2O showed no detectable net treatment effect. Across analyses, soil hydrothermal and nutrient conditions were the dominant predictors of flux variation; microbial functional signals added information mainly through soil-dependent interactions. In CO2-equivalent terms, lower CH4 emissions only partly compensated for higher CO2, leaving a net positive effect under both 20- and 100-year horizons. These results underscore that harvest impacts in drawdown soils should be assessed as multi-gas trade-offs and interpreted through soil moisture-redox dynamics.