Vegetation type and topographic characteristics are important factors that affect the amount and spatial distribution of the forest floor and the soil carbon cycling. However, the relationships among vegetation type, topographic characteristics, forest floor properties, soil properties and soil labile organic carbon (LOC) fractions remain to be elucidated. Here, we conducted a field observational study to explore the relationships between the soil LOC fractions (microbial biomass carbon (MBC), extractable organic carbon (EOC) and permanganate oxidizable carbon (Pox-C)) and forest floor characteristics under various vegetation types (forest, forest-steppe and steppe) and topographic features (slope position and aspect). Our results showed that the vegetation type and topography are both important factors that significantly influence the forest floor properties (i.e., stock, thickness and coverage). The soil total nitrogen and phosphorus were significantly increased, and the soil pH and bulk density were decreased, with an increase in litter stock, coverage and thickness. Simultaneously, the SOC and soil LOC fractions were increased significantly with the increase in litter stock, coverage and thickness. Over 50% of the variation in the SOC and soil LOC fractions was jointly explained by environmental factors, litter properties and soil properties. Our results demonstrated that the SOC and soil LOC fractions are directly influenced by soil physical and chemical properties (e.g., pH, bulk density and soil total nitrogen) and indirectly affected by external environmental factors. Changes in vegetation and topography lead to increases in the litter stock, coverage, thickness and water content in the backslope position and northern slope, which could create favorable soil nutrient and environmental conditions (e.g., higher soil moisture and lower bulk density) to further enhance SOC and soil LOC fraction sequestration. The forest floor potentially links environmental factors and soil properties and serves as an important factor for soil C cycling.

植被类型和地形特征是影响林地数量和空间分布以及土壤碳循环的重要因素。但是，植被类型，地形特征，林地特性，土壤特性和土壤不稳定有机碳（LOC）组分之间的关​​系仍有待阐明。在这里，我们进行了实地观察研究，以探讨各种植被类型下土壤LOC组分（微生物生物量碳（MBC），可萃取有机碳（EOC）和高锰酸盐可氧化碳（Pox-C））与林地特征之间的关系（森林，森林草原和草原）和地形特征（坡度和坡度）。我们的研究结果表明，植被类型和地形都是显着影响林地特性（即种群，厚度和覆盖率）的重要因素。土壤总氮和磷显着增加，土壤pH和堆积密度降低，凋落物的数量，覆盖率和厚度增加。同时，随着凋落物种群，覆盖率和厚度的增加，SOC和土壤LOC分数也显着增加。SOC和土壤LOC分数变化的50％以上是由环境因素，垫料特性和土壤特性共同解释的。我们的结果表明，SOC和土壤LOC分数直接受到土壤理化性质（例如pH，容重和土壤总氮）间接受外部环境因素影响。植被和地形的变化导致后坡位置和北坡的凋落物种群，覆盖率，厚度和水含量增加，这可能会创造有利的土壤养分和环境条件（例如更高的土壤湿度和更低的容重），从而进一步提高SOC和土壤LOC分数固存。林地可能将环境因素与土壤特性联系起来，并成为土壤碳循环的重要因素。较高的土壤水分和较低的堆积密度），以进一步提高SOC和土壤LOC分数固存。林地可能将环境因素与土壤特性联系起来，并成为土壤碳循环的重要因素。较高的土壤水分和较低的堆积密度），以进一步提高SOC和土壤LOC分数固存。林地可能将环境因素与土壤特性联系起来，并成为土壤碳循环的重要因素。