Asymmetric responses of soil heterotrophic respiration to rising and decreasing temperatures

Periodic changes in temperature commonly occur diurnally and seasonally. However, the response of soil heterotrophic respiration to rising and decreasing temperatures during these periods remains poorly understood; thus the feedback between climate change and carbon (C) cycling requires further investigation. In this study, soils from three grasslands in the Qinghai-Tibet Plateau were incubated separately at rising (from 5 degrees C to 31 degrees C) and decreasing (from 31 degrees C to 5 degrees C) temperatures modes over 161 days, to explore how soil heterotrophic respiration rates (R-S) respond to different temperature changes. The parameters of R-S and temperature sensitivity (Q(10)) were used for the analyses. In addition, microbial biomass C (MBC), microbial biomass nitrogen (N) (MBN), dissolved organic C (DOC), and other soil properties were measured. The results indicated a pronounced hysteresis of R-S for both rising and decreasing temperatures. Furthermore, the hysteresis loops differed in the different sites. R-S values were significantly higher for rising temperature (2.71 mu g C g(-1) d(-1)) versus decreasing temperature (1.75 mu g C g(-1) d(-1)) in all three alpine grasslands. The Q(10) values were significantly higher for decreasing temperature (2.42) versus increasing temperature (1.55), with these differences being observed over the 161-d incubation period. Furthermore, soil microbes (specifically, MBC and MBC/MBN) explained 46 -77% of the total variation in Q(10), followed by substrate and other properties. Our results provide experimental evidence for the asymmetric responses of soil heterotrophic respiration to rising and decreasing temperatures. In addition, the microbial effect was primarily associated with soil heterotrophic respiration, suggesting strong asymmetric responses to rising and decreasing temperatures that require investigation in future studies. (C) 2016 Elsevier Ltd. All rights reserved