Response of soil respiration to thinning is altered by thinning residue treatment in Cunninghamia lanceolata plantations

Forest thinning is a widely used practice in traditional and multiple function forest management. However, the effects of thinning residue treatment on soil respiration in forest are not fully understood. Here, a two-year field experiment quantified the effects of thinning intensity (medium and heavy thinning, 45% and 70% of volume removed, respectively) and the resulting residue treatment (retention and removal) on soil respiration in a subtropical Cunninghamia lanceolata plantation on a thin soil. Both thinning intensity and residue treatment significantly impacted on soil respiration. The control had a relative low mean soil respiration rate of 158 mg CO2 m−2 h−1 or 13.9 t ha−1 yr−1. Compared with the control, medium thinning with residue retained (MTR1) increased annual cumulative soil respiration by 13% only in the first year, while medium thinning with residue removal (MTR0) did not affect it in the two years. Heavy thinning with residue retention (HTR1) and removal (HTR0) elevated the mean annual cumulative respiration by 32% and 20%, respectively. Besides, there was no difference between MTR1 and HTR0. Soil respiration rate was correlated positively with soil temperature, moisture, and the concentrations of permanganate-oxidizable C and microbial biomass C, and inversely with the concentration of water-soluble organic C. Furthermore, heavy thinning with residue retention decreased the temperature sensitivity of soil respiration. Our findings highlight that the response of soil respiration to forest thinning was associated with thinning residue treatment.