Abstract: Current climate projections indicate warming trends with daily minimum temperature increasing more rapidly than daily maximum temperatures—termed diurnal asymmetric warming. While such warming profoundly affects terrestrial ecosystems, its implications for soil carbon cycling remain poorly understood. Here we quantify responses of soil organic carbon (SOC) and its fractions to diurnal asymmetric warming. After 1.1-Yr’s diurnal asymmetric warming, both particulate organic carbon (POC) and mineral-associated organic carbon (MAOC) decreased significantly. Specifically, nighttime warming alone induced a 1.9 times greater SOC loss than daytime warming. Mechanistically, continuous nighttime warming enhanced microbial carbon metabolism by shifting microbial life strategy (eg, toward r-strategists) and increasing carbon use efficiency. These findings deepen the mechanistic understanding of soil carbon cycling under climate warming and provide a critical scientific basis for refining predictive accuracy in carbon-climate feedback models.

Key words: diurnal asymmetric warming, soil organic carbon, carbon fractions, microbial carbon use efficiency, microbial K/r strategy ratio