Understory vegetation management regulates soil carbon and nitrogen storage in rubber plantations.

Effective management of understory vegetation is crucial for forest biodiversity conservation and ecosystem functions. However, the impact of various understory management practices on key ecosystem processes, such as soil nutrient cycling in tree crop plantations, remains poorly understood. This study quantified the 7-year cumulative effects on soil organic carbon (SOC) and total nitrogen (STN) stocks in rubber plantations under four understory management practices: (i) conventional management (RC) as the control, (ii) herbicide application (RH), (iii) natural regeneration (RN), and (iv) replacement with leguminous shrub (RA). Compared to RC, RN and RA increased the average number of native and invasive species and produced high above- and belowground biomass. Conversely, RH decreased the species number and belowground biomass. More SOC and STN were stored in 0.0–0.2 m topsoil in both RN (+ 9.6 Mg C ha^–1; + 0.7 Mg N ha^–1) and RA (+ 10.7 Mg C ha^–1; + 0.6 Mg N ha^–1) than RC, while they remained stable in RN but declined in RA from deeper layers of 0.2–1.0 m. Across the entire 1 m soil profile, the annual increment of SOC stocks in RN and RA reached 1.7 and 1.0 Mg C ha^–1 yr^–1, respectively, and of STN stocks reached 0.02 and − 0.14 Mg N ha^–1 yr^–1. However, RH decreased SOC and STN stocks and corresponding annual increments for the entire profile. The variations in SOC and STN stocks in the topsoil were attributed primarily to aboveground biomass and determined by belowground biomass in the deeper soil. Moreover, litter depth also effectively reflected SOC and STN dynamics. These results suggest that the implementation of natural regeneration and agroforestry system in the understory of rubber plantations offers significant potential for increasing soil C and N stocks. Our findings imply that sustainable understory management practices, especially natural regeneration and agroforestry system, will benefit for understory plants conservation and soil nutrient supply in tree crop plantations. [ABSTRACT FROM AUTHOR]