Assisted natural regeneration promotes soil carbon stabilization through fungal residue pathways in subtropical forests

Forest restoration is widely recognized as a nature-based solution for climate change mitigation, yet the effects of different restoration pathways on the formation of persistent soil organic carbon (SOC) remain insufficiently resolved. We compared SOC and microbial residue carbon (MRC), a persistent SOC fraction derived from microbial necromass, in 10-year-old assisted natural regeneration (ANR) and tree plantations relative to mature natural forests. After a decade, the reduction in SOC in plantations (6.20 ± 0.25 g kg⁻¹) was 27% lower than in natural forests, whereas ANR showed only a 15% reduction (3.44 ± 0.30 g kg⁻¹), corresponding to a 44% mitigation of SOC loss relative to plantations. ANR maintained fungal residue carbon at levels comparable to the natural forest, whereas plantations exhibited approximately 20% reductions. Partial least squares path modeling revealed that semi-decomposed litter and fine root inputs, rather than microbial enzyme activity, were the predominant direct drivers of MRC accumulation. Together, these findings demonstrate that restoration pathways influence not only the magnitude but also the mechanisms of soil carbon sequestration, underscoring the central role of plant–fungal linkages for stabilizing SOC under ongoing global change.