Asymmetric responses of soil heterotrophic respiration to rising and decreasing temperatures

- A pronounced hysteresis in soil heterotrophic respiration was observed during rising and decreasing temperatures.
- Q10 values were higher under decreasing temperatures than rising temperatures.
- Microbial community, and not substrate, control the response of soil heterotrophic respiration.

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 °C to 31 °C) and decreasing (from 31 °C to 5 °C) temperatures modes over 161 days, to explore how soil heterotrophic respiration rates (RS) respond to different temperature changes. The parameters of RS and temperature sensitivity (Q10) 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 RS for both rising and decreasing temperatures. Furthermore, the hysteresis loops differed in the different sites. RS values were significantly higher for rising temperature (2.71 μg C g−1 d−1) versus decreasing temperature (1.75 μg C g−1 d−1) in all three alpine grasslands. The Q10 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 Q10, 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.