Different responses of soil respiration to reduced throughfall in spring and winter under contrasting hydrological conditions in a temperate forest

Drought events are predicted to be more frequent and severe in the future and have significant impacts on terrestrial carbon (C) cycling. However, it is highly uncertain whether the soil CO₂ efflux response to drought is identical under different hydrological conditions. In a precipitation manipulation experiment in a temperate forest in Central China, we implemented a 30 % decrease in throughfall in spring and winter in plots under rainout shelters to simulate drought-occurrence timing during two contrasting hydrological years, i.e., 2019 (dry with a total throughfall 44.6 % below the long-term mean (1063 mm)) and 2020 (wet with a total throughfall 39.2 % above the long-term mean). Reduced throughfall in spring significantly decreased soil respiration by 22.9 % in the dry year but did not affect it in the wet year; whereas reduced throughfall in winter had neutral impacts on soil respiration in the dry year but increased it by 23.0 % in the wet year. These findings suggest dependence of reduced throughfall in spring and winter responses of soil respiration upon hydrological variations in the temperate forest. The negative effects of reduced throughfall in spring on soil respiration can be attributed to the decreases in microbial biomass C, and the stimulation of soil respiration under reduced throughfall in winter via promoting fine root biomass. Our findings indicate that hydrological condition may alter the driving factors, forming contrasting mechanisms to regulate soil respiration, and highlight the importance of precipitation variations in mediating the responses of soil respiration to drought timing in the temperate forest in Central China.