Objective Labile organic carbon (LOC) responds more sensitively to changes in soil carbon pools than total organic carbon. This study investigates the seasonal dynamics and driving factors of soil ROC in typical boreal forest types in the Greater Khingan Mountains during the growing season, aiming to provide a scientific basis for assessing regional soil carbon cycling and informing forest management strategies.

Method We selected four representative forest types in northern Greater Khingan, including Dahurian larch (Larix gmelinii) forest, Scots pine (Pinus sylvestris var. mongolica) forest, white birch (Betula platyphylla) forest, and aspen (Populus davidiana) forest as study sites. Soil samples were collected monthly from May to September 2023 at depths of 0–10 cm and 10–20 cm. We measured microbial biomass carbon (MBC), dissolved organic carbon (DOC), easily oxidizable organic carbon (EOC), and particulate organic carbon (POC) to analyze their seasonal dynamics and influencing factors.

Result From May to September, MBC, DOC, EOC, and POC concentrations ranged from 107.36 to 931.92 mg/kg, 74.31 to 442.8 mg/kg, 7.23 to 14.97 g/kg, and 2.07 to 27.17 g/kg, respectively, with mean values following the order POC > EOC > MBC > DOC. Concentrations in broadleaf forests were significantly higher than those in coniferous forests (P < 0.05). MBC, EOC, and POC exhibited a unimodal pattern, peaking in August, whereas DOC peaked in May and then declined gradually. (2) Forest type, soil depth, month, and their interactions significantly affected LOC content (P < 0.001), with the relative importance of individual factors ranked as soil depth > month > forest type. (3) Soil temperature, moisture, β-glucosidase activity, and nitrogen content showed significant positive correlations with LOC, while bulk density and pH exhibited significant negative correlations (P < 0.05). Precipitation and air relative humidity primarily influenced MBC and DOC.

Conclusion The seasonal dynamics of soil LOC in boreal forests are jointly regulated by soil depth, hydrothermal conditions, and enzyme activity. Broadleaf forests demonstrated greater LOC accumulation capacity due to higher-quality litter inputs. This study reveals the component-specific response mechanisms of LOC, offering a scientific foundation for predicting carbon sink functions of boreal forests under climate change scenarios.