CONSERVATION AGRICULTURAL MANAGEMENT PRACTICES OFFSET THE LOSS OF 13C-LABELED GLUCOSE IN SOIL UNDER MOISTURE PULSE EVENTS

Understanding the mechanisms of carbon (C) sequestration in soil under drying-rewetting cycles is essential for predicting the terrestrial C pool facing climate change. A 24-day incubation in microcosms was conducted with an agricultural soil under 36 years of conservation management. We added ¹³C-labelled glucose and applied different frequencies of drying-rewetting cycles to the microcosms. The fate of the ¹³C-labelled substrate in active and passive C pools was traced. Structural equation modelling was conducted to determine the relative importance of physical, chemical, and biochemical controls of the labile C accumulation in soil. The structural equation model shows that H₂O₂-resistant C pool is the major control of the newly added labile C accumulation under drying-rewetting cycles. It indicates that chemical stabilization and biochemical alteration rather than physical protection are major controls of labile C sequestration in soil under drying-rewetting cycles. The model also demonstrates that although the long-term agricultural conservation management practices can completely counteract the loss of soil total C caused by moisture pulse events, they are only able to offset the loss of newly added labile C to a limited extent.