Vertically distinct patterns of soil carbon and nitrogen stock depletion associated with Moso bamboo encroachment into subtropical forests

Abstract

Moso bamboo ( Phyllostachys edulis ) expansion is strongly associated with soil degradation in subtropical forests, but the underlying abiotic and biotic factors regulating soil organic carbon (SOC) and total nitrogen (TN) stocks across different stands remain unclear. Here, we investigated depth-dependent (0–40 cm) changes in SOC and TN stocks, alongside the abundances of autotrophic ( cbbL ) and denitrifying ( nosZ ) functional genes, associated with bamboo encroachment into broad-leaved (BLF) and coniferous forests (CF). While bamboo invasion consistently depleted SOC and TN pools across the entire 0–40 cm soil profile in both stands, the most severe relative losses exhibited distinct depth-dependent patterns linked to divergent ecological pathways. In the BLF, the prominent stock depletions in the topsoil (0–10 cm) were jointly associated with a hypothesized litter-induced soil priming effect and the physical degradation of the surface microenvironment. Conversely, in the CF, the most severe stock reductions occurred in the sub-soil layer (20–40 cm), where shifts in soil bulk density and moisture likely weakened the physical protection of legacy organic matter and potentially exacerbated resource limitations for deep-soil microbes. Concurrently, the decline in cbbL and nosZ gene abundances served as sensitive potential microbial indicators reflecting these severe environmental stresses. These findings underscore the necessity of depth-explicit and stand-tailored strategies for mitigating soil degradation, and suggest that incorporating belowground functional genes could improve future plant invasion risk assessments in subtropical ecosystems.