Changing precipitation exerts greater influence on soil heterotrophic than autotrophic respiration in a semiarid steppe

Abstract Future precipitationchange is anticipated to have a profound influence on ecosystem carbon (C) cycling, especially soil respiration, the largest C flux from the terrestrial ecosystemto the atmosphere. Due to different substrate sources and biological processes, the heterotrophic(SR h ) and autotrophic (SR a ) components of soil respiration(SR tot ) may respond to changing precipitationin different ways. Determining the differential responses of SR h and SR a to precipitationwill facilitate our evaluation of soil C storage and stability under future precipitationchange. Here, a 3-year precipitationmanipulation experiment with 5 levels of precipitation(±60%, ±30% and ambient growing season precipitation) was conducted in a semiarid steppe to determine the influence of precipitationon soil respiration. Results showed that SR tot increased nonlinearly with increasing water supply, in which, SR h increased much more than SR a . Consequently, the ratio of SR h to SR tot was enhanced significantly with increasing precipitation, i.e., from 41% to 62% as precipitationincreased from 122 mm to 408 mm. Structural equation modeling analysis indicated that changes in SR h and SR a were predominated by the soil water content (SWC) and plant growth, respectively. The stronger effects exerted by changes in precipitationon SWC compared with plant growth contributed to the greater change in SR h than in SR a . Additionally, SR a exhibited a higher temperature sensitivity than SR h . Thus, the increased soil temperature in the drought treatments had greater influence on SR a than SR h , and greatly offset the influence of drought stress on SR a , leading to the smaller change in SR a compared with SR h . Our study highlights the different responses of the two soil respirationcomponents to changing precipitation. These results indicate that future increases in precipitationin semiarid regions will increase soil heterotrophicrespiration which may accelerate the turnover of soil C, and further affect the stability of soil C stock.