Geographic Variations and Multiple Drivers of Soil Organic Carbon Stability in Larch Plantations

ABSTRACT Clarifying the distribution patterns and drivers of soil organic carbon (SOC) and its labile fractions is essential for evaluating forest carbon sinks. Larch, which is widely distributed across northern China and has strong environmental stress tolerance, exhibits an unclear SOC spatial variation pattern in its plantations. We hypothesized that soil properties act as direct drivers, whereas geographic and climatic factors exert indirect effects via hydrothermal conditions. Based on 0–30 cm soil samples from 41 sites, we examined the spatial variations and multiple drivers of SOC, particulate organic carbon (POC), easily oxidizable organic carbon (EOC), and dissolved organic carbon (DOC). Combined with random forest and structural equation modeling, we disentangled the multi‐scale driving factors and regulatory pathways of these carbon fractions. Results showed that SOC and labile fractions decreased with soil depth and exhibited clear latitudinal and longitudinal gradients, with SOC and EOC increasing along both latitude and longitude. EOC (7.55 ± 0.45 g kg −1 ) and POC (5.24 ± 0.52 g kg −1 ) were the dominant fractions, whereas DOC (0.132 ± 0.008 g kg −1 ) accounted for the smallest proportion. Soil nitrogen and phosphorus were key direct drivers of SOC, POC, and EOC variations. Geographic factors, particularly latitude, strongly influenced POC and DOC through effects on hydrothermal conditions such as the mean annual temperature and precipitation. Overall, soil properties served as direct intrinsic drivers, whereas geographic and climatic factors and stand characteristics operated mainly through indirect pathways by regulating carbon input and decomposition. These findings provide a scientific basis for enhancing soil carbon sequestration in larch plantations.