Afforestation resists the drought disturbance on soil carbon sink in subtropical agricultural ecosystems

Abstract

Southwest China (SWC), which belongs to the subtropical climatic zone and has been the largest terrestrial carbon sink in China over the past 30 years, has been frequently disturbed by flash drought events since the 21st century. Due to its intensive land use changes during past decades, SWC has also become a global critical area of vegetation restoration. Drought disturbances and land use changes potentially affect local soil organic carbon (SOC), but how SOC responds to land-use and cover-change (LUCC) under drought disturbance in SWC is still unknown. Here, we explored the responses of SOC to vegetation cover changes when drought occurred with different frequencies in SWC. Based on multisource data synthesis, the drought conditions of SWC from 2001 to 2018 are appraised by referring to multiple drought indices, and the SOC content of the 0–10 cm soil layer in SWC is also estimated. Certain areas were disturbed by droughts more than 6 times during the last two decades, while there was an average 20.02% increase in SOC in the SWC subtropical region. Among the different subtropical ecosystems, the average SOC content increased from 25.81 g kg -1 to 33.35 g kg -1 in agricultural land, 30.4 g kg -1 to 34.97 g kg -1 in forest, and 26.97 g kg -1 to 32.89 g kg -1 in grassland. The results also indicated that drought has a significant impact on subtropical forests and agricultural land compared to grasslands. Additionally, mainly due to the self-adjustment abilities of forest ecosystems and human interference on agricultural lands, the SOC stock in subtropical forest responses is more susceptible to drought disturbance, but its capability to resist drought is stronger than that in agricultural land. Superimposing the influence of LUCC, afforestation in abandoned farmland has a positive influence on soil carbon accumulation and can greatly mitigate the adverse effects of extreme climate events on SOC accumulation under special drought patterns and conditions in the SWC subtropical zone. Moreover, the droughts that occur in SWC are considered to be a short-term moderate temperature rise that has a promoting effect on SOC sinks in afforestation areas. Our findings contribute to understanding the implications of extreme climate events and anthropogenic activities on the terrestrial carbon cycle in subtropical agricultural ecosystems.