Heterotrophic respiration and its proportion to total soil respiration decrease with warming but increase with clipping

Abstract

Revealing how heterotrophic respiration (Rh) and its contribution to soil respiration (Rs, Rh/Rs ratio) respond to climate warming and land-use change is crucial for advancing our understanding of the feedback between the terrestrial carbon (C) cycle and future climate changes. Here we conducted a 7-year manipulation experiment by warming and clipping to explore their impacts on Rh and Rh/Rs ratio in an alpine meadow on the Qinghai-Tibet Plateau. Infrared heaters were used to simulate climate warming and clipping was applied to mimic yearly hay or biofuel harvest. We found that, on average, warming significantly decreased Rh/Rs ratio by 5.5%, which was attributed to the little change in Rh and increased autotrophic respiration (Ra, 18.3%) under warming. In contrast, clipping significantly increased Rh/Rs ratio by 8.1%, which was mainly due to the clipping-induced increase in Rh (22.6%) and decrease in Ra (3.9%). Warming or clipping-induced changes in Rh and the Rh/Rs ratio were mainly controlled by the microbial metabolic quotient, microbial biomass C and nitrogen, soil moisture, and soil temperature. Moreover, warming and clipping both increased Rs by 13.2% and 15.5%, respectively, over the study period. Our study highlights the differential responses of the two soil respiration components to warming and clipping, and suggests that climate warming does not necessarily increase Rh but clipping largely stimulates Rh, which may accelerate the turnover and losses of soil C in this alpine meadow. Hence, quantifying how Rh and the Rh/Rs ratio respond to global changes has large implications for better predicting the future ecosystem C cycle and its feedback to climate system in ecosystem models.