Global Asymmetric Temperature Responses of Soil Respiration During Warming and Cooling Phases

Abstract

Soil respiration is highly sensitive to temperature, and its responses to warming and cooling are commonly assumed to be symmetric in Earth system models. However, this symmetry has rarely been explicitly tested, particularly across different temporal scales. Using two global data sets spanning multiple ecosystems and temporal scales, we show that soil respiration exhibits scale-dependent asymmetry in apparent temperature sensitivity (Q₁₀) between warming and cooling phases. Q₁₀ was markedly higher during cooling at the daily scale, with the asymmetry weakened under the monthly scale. At the hourly scale, asymmetry was also detectable but varied in direction across ecosystem types. Machine-learning analyses revealed strong scale dependence in the drivers of Q₁₀, with short-term variability dominated by diurnal temperature cycles and soil moisture dynamics, and longer-term patterns shaped by climatic and vegetation properties. Nonlinear responses to soil temperature and moisture suggest that temperature sensitivity may be associated with microbial metabolic demand, substrate accessibility and their interactions. Despite phase-specific Q₁₀, fitting phase-specific model did not find significant difference in controls between warming and cooling phases. Consistently, incorporating soil temperature-moisture interactions significantly improves model performance, particularly at fine temporal scales. These results highlight the importance of testing Earth system models for their ability to capture phase- and timescale-dependent apparent temperature sensitivity, and provide opportunities to reduce uncertainties in the prediction of soil carbon–climate feedback.