Dataset for: Throughfall promotes surface soil organic carbon accumulation but impairs deep-soil stabilization in a subtropical evergreen broadleaf forest

Rainfall redistribution by forest canopies alters both the pathways of water and solute inputs, yet its role in soil carbon (C) stabilization remains poorly understood. We conducted a field soil column experiment in a subtropical evergreen broadleaf forest to compare the effects of throughfall and bulk precipitation on soil organic carbon (SOC) and its functional fractions―particulate organic carbon (POC) and mineral-associated organic carbon (MAOC). Compared with bulk precipitation, throughfall enhanced surface SOC across seasons, associated with a clear shift toward strengthened nutrient–SOC coupling and fueled by high-quality dissolved organic matter (DOM). POC dynamics were also transformed: under bulk precipitation, they were balanced by rainfall inputs and microbial processing, whereas under throughfall, they became dominated by the internal processing of high-quality leachates. In deeper soils, this efficient surface processing likely induced substrate starvation, which, potentially compounded by altered infiltration, led to a significant net loss of stable, deep-soil MAOC, especially during the dry season. Despite these distinct stabilization pathways between treatments, the POC: MAOC ratio, as well as the proportional contributions of POC and MAOC to SOC, remained stable. However, this apparent stability appears to be a statistically insensitive metric that masks these profound, depth-specific C fraction responses. Together, these findings reveal a rainfall-pathway trade-off: throughfall promotes efficient, nutrient-coupled surface C accumulation but at the cost of destabilizing the deep-soil C pool, leading to a net loss of MAOC. This highlights the need to integrate pathway-specific and depth-specific processes when projecting the long-term stability of forest soil C under changing precipitation regimes.