Stable oxic-anoxic transitional interface is beneficial to retard soil carbon loss in drained peatland

Peatlands are vital carbon sink globally and have been drained severely. An oxic-anoxic transitional (OAO) interface was created in drained peatlands profile during long-term water table fluctuation. Here, we aimed to investigate how the CO2 release at the OAO interface respond to climate warming and exogenous carbons addition. We found that the carbon at OAO interface was complex, with higher proportion of aromatics, aliphatics and Fe-bound organic carbons. The microbial activity and diversity at OAO interlayer were lowest. Through a lab incubation, we found that the cumulative CO2 emission at OAO interface was 12.36 ± 1.57 mg CO2 g−1C, 117.6% and 36.6% lower than the upper oxic soil (26.89 ± 1.05 μg CO2 g−1C) and deep anoxic (16.88 ± 1.56 μg CO2 g−1C) layer, respectively. Moreover, the CO2 emission at the OAO interface was least warming-responsive under anoxic dominated conditions. These results reveal that the OAO interface could work as a buffer to retard drained peatland carbon lose under warming climate. However, the CO2 emission at the OAO interface was extremely sensitive to exogenous carbons, which increased by 53.9%–72.1% after exogenous carbon addition, implying that the buffer capacity of OAO interface will collapse if being exposed to available carbons from plant or soil macromolecular carbons. Our results demonstrated that maintain a stable OAO interface was beneficial to reduce drained peatlands carbon loss, and the priority is to ease the priming effect caused by exogenous carbons.