Abstract: The characteristics of soil organic carbon (SOC) and its correlation with physicochemical indexes in different types of Larix gmelinii forest were studied based on field investigation and laboratory analysis. The results show that:(1) SOC contents were 13.42-142.18 g·kg^-1 with an average of 53.35 g·kg^-1 in 0-60 cm soil layer of Larix gmelinii forests, which presented an obvious surface aggregation and decreased as a power function pattern with soil depth. (2) SOC contents of different forest types ranked as:Ledum palustre-Larix gmelinii forest (64.14 g·kg^-1) > Rhododendron simsii-Larix gmelinii forest (63.48 g·kg^-1) > grass-Larix gmelinii forest (39.99 g·kg^-1). In the layer of 0-10 cm, SOC content in grass-Larix gmelinii forest was significantly lower than that of Ledum palustre-Larix gmelinii and Rhododendron simsii-Larix gmelinii forests; in which the differences were decreased with the increase of soil depth. (3) The highest contents of soil water and K₂O were found in soils from Ledum palustre-Larix gmelinii forest, the highest values of bulk density, available potassium, organic phosphorus and available phosphorus in soils were found in Rhododendron simsii-Larix gmelinii forest, and the highest values of pH, ammonium nitrogen, Na₂O, MgO, Al₂O₃, CaO and Fe₂O₃ in soils were found in grass-Larix gmelinii forest. The significant differences of the indexes were found between the grass-Larix gmelinii forest and Ledum palustre-Larix gmelinii, Rhododendron simsii-Larix gmelinii forests. (4) SOC content was positively correlated with soil water content, contents of ammonium nitrogen, available potassium and organic phosphorus, and negatively correlated with pH value. SOC content was negatively correlated with metal oxides contents, except for CaO content. According to multiple regression results, the undergrowth vegetation was an important origin of SOC in Larix gmelinii forest,[JP3]and the SOC contents in Ledum palustre-Larix gmelinii and Rhododendron simsii-Larix gmelinii forests were higher than that in grass-Larix gmelinii forest. In the process of forest management and vegetation restoration, the scientific and reasonable measures on restoration and management of undergrowth vegetation should be made to promote the coordinated growth of undergrowth vegetation and upper forest.

Key words: Larix gmelinii forest, forest soil, organic carbon content, forest type