Divergent control and variation in bacterial and fungal necromass carbon respond to the abandonment of rice terraces.

The abandonment of rice terraces in hilly agroecosystems in recent decades has caused substantial changes in microbial characteristics and their impact on microbial necromass carbon (MNC) and soil organic carbon (SOC). Nevertheless, the regulatory mechanisms and impact pathways of MNC remain unclear. Here, soil samples were collected from 0 to 120 cm soil profiles in rice terraces, dry land (DL), and forest land (FL) for analysis. After converting rice terraces to DL and FL, MNC decreased significantly by 31.12% and 38.33%, while SOC decreased significantly by 51.26% and 29.87% respectively. These reductions are due to the loss of terrace management practices and associated functions. There were no significant changes in bacterial necromass carbon (BNC), whereas fungal necromass carbon (FNC) experienced a significant decrease. As a result, the decline in SOC may be primarily attributed to the reduction in FNC. BNC and FNC were regulated by bacterial life history strategies and fungal biomass, respectively. However, bacterial copiotrophs experienced a significant reduction after rice terrace abandonment. The regulation of BNC may be influenced by other factors, potentially offsetting the negative impact of abandonment. Dissolved organic carbon and bulk density were the primary control factors for bacterial community composition and fungal biomass, respectively. Additionally, the impact of soil layers on the alterations in MNC and SOC was more significant compared to the abandonment of rice terraces. These findings indicate that short-term abandonment of rice terraces results in a decrease in SOC, potentially compromising the ecological service function of the hilly agroecosystems. In the face of rapid population growth and global warming, it is crucial to minimize terrace abandonment and enhance utilization rates. This approach will effectively support sustainable terrace management and ecological services.