The impact of agricultural land use on the linkages between soil microbial communities and agroecosystem functioning is depth-dependent

Soil carbon (C) and nitrogen (N) mineralization rates are critical indicators of ecosystem functioning in agricultural land. However, the effects of agricultural land use on the interactions between soil C and N mineralization at different soil depths, especially in tropical regions, are poorly understood. Here, a longan orchard (LO) was converted to a conventional tea plantation (CTP) and an organic tea plantation (OTP) in the tropical region of China, and the responses of fungal and bacterial communities to these changes were assessed. The characteristics of the microbial communities, enzyme activities, and N and C mineralization rates were evaluated in response to the changes in land use. It was found that LO and OTP had faster N and C mineralization rates than CTP in surface soil. However, in subsurface soil, LO and OTP showed a faster C mineralization rate and a slower N mineralization rate than CTP. Structural equation modeling revealed that pH and C/N were the most crucial factors affecting N and C mineralization rates in surface soil. In contrast,soil bacterial and fungal community structures were the principal drivers of both the C and N mineralization in subsurface soil. Although soil C and net N mineralization were positively correlated in surface soil, this was not seen in subsurface soil. Collectively, this study demonstrated that differential drivers and their effects on the interactions between soil C and N mineralization at different soil depths should be considered for more accurate prediction of soil C and N dynamics under land-use changes. [Display omitted] •Soil C and N mineralization were positively correlated in surface soil, but not in subsurface soil.•Bacterial and fungal communities’ response to agriculture LUC depended on soil depth.•Abiotic soil factors primarily controlled C and N mineralization rates in surface soil.•Soil microbial community predominantly regulated C and N mineralization in subsurface soil.•The decoupling of Cmin and Nmin is attributed to the lower level of C/N in subsurface soil.