Carbon quality mediates the temperature sensitivity of soil organic carbon decomposition in managed ecosystems

The carbon quality-temperature (CQT) hypothesis suggests that the temperature sensitivity (Q10) of soil organic carbon (SOC) decomposition is negatively related to soil C quality. This hypothesis was widely tested in various natural ecosystems, but the effect of soil C quality on the temperature response of SOC decomposition has not been well addressed in managed ecosystems. In this study, Q10 values of SOC decomposition were estimated in three adjacent managed ecosystems (planted forest (PF), paddy (PA), and upland (UL)) within the topsoil (0–5 cm) and subsoil (30–35 cm) layers of six sites across different climate zones in northeast China. The results suggested that the soil C quality differed significantly among the managed ecosystems (PF > PA > UL; P < 0.05) or soil types (P < 0.05), and decreased with soil depth (P < 0.001). Overall, Q10 values differed significantly across the ecosystems (PF < PA < UL) and soil types (P < 0.05), but were significantly greater in the subsoil than those in the topsoil (P < 0.001). The negative relationship between Q10 value and soil C quality suggested that the CQT hypothesis was applicable to ecosystem types, soil types, and soil profiles of the managed ecosystems. In addition, the Q10 value had a positive correlation with soil pH (P < 0.001). The results suggested that incorporating soil C quality and soil pH into models would help us to predict the feedbacks between soil C dynamics and global warming in managed ecosystems.