Labile carbon input suppresses Q10 of soil organic carbon decomposition by dynamically lowering microbial activation energy mediated by a shift in microbial metabolic strategy

Abstract

Understanding the temperature sensitivity (Q 10 ) of soil organic carbon (SOC) decomposition, as constrained by the activation energy (E a ) of microbial metabolism, is critical for predicting climate-carbon feedbacks. This study examined how exogenous glucose influences Q 10 in farmland soils across China’s major climatic zones under controlled temperatures (20, 30, 40 °C). β-glucosidase activity, microbial biomass carbon (MBC), and CO 2 flux were measured during a 59-day incubation experiment. Glucose addition significantly stimulated β-glucosidase activity, particularly at 40 °C, and increased CO 2 emissions by 2.21–6.50 times relative to controls. Despite enhanced microbial activity, glucose consistently reduced apparent Q 10 values (1.31–1.59 vs. 1.67–1.94 in the controls). This decrease was accompanied by lower apparent E a values (21.2–36.7 kJ mol −1 vs. 35.3–50.9 kJ mol −1 ), suggesting that labile C inputs may shift microbial metabolism toward energetically favourable and rapidly mineralizable substrates, potentially reducing the relative contribution of higher-E a decomposition processes associated with native SOC. MBC peaked between days 3 and 29 and declined by 8.31–19.35 % by day 59. Under glucose-free conditions, this decline coincided with increasing apparent E a . This pattern may suggest a greater reliance on enzyme-mediated decomposition of relatively recalcitrant C substrates under C-limited conditions. Mantel test analysis identified mean annual temperature, precipitation, clay content, available phosphorus, and available nitrogen as the main drivers of Q 10 variability, highlighting environmental regulation of the E a –Q 10 relationship. Overall, these results demonstrate that apparent E a is dynamically regulated by substrate availability, microbial strategies, and soil properties. Consequently, Q 10 reflects not only as a function of substrate chemistry, but also the thermodynamic state of microbial metabolism. By identifying apparent E a as a mechanistic link between microbial physiology, environmental conditions, and carbon-climate feedbacks, this study provides a stronger basis for improving SOC decomposition models.