武夷山自然保护区不同海拔甜槠天然林土壤有机碳变化特征及影响因素

为揭示中亚热带常绿阔叶林建群种--甜槠天然林不同海拔土壤有机碳含量垂直分布差异及影响机制，以武夷山自然保护区甜槠天然林单一植被类型为研究对象，在其集中分布的5个海拔梯度（540、700、850、1022、1200 m）范围内设置固定样地，测定每个海拔梯度不同深度土层土壤因子（土壤全氮、全磷、土壤pH值、容重、土壤有机质、粉粒、砂粒、粘粒）、气候因子（土壤温度）、植被因子（细根生物量）及土壤有机碳含量等指标，分析了土壤有机碳沿海拔及垂直土层分布特征，并在主成分分析基础上构建了基于主控因子的线性回归模型。结果表明：（1）同一海拔高度，土壤有机碳含量在土壤垂直剖面分布具有明显的"表聚性"现象；同一土层深度，随着海拔升高，土壤有机碳含量逐渐增加，但增幅随土层深度增加而减小，高海拔地区有助于土壤有机碳的固存；（2）不同土层土壤有机碳含量与海拔、土壤全氮、土壤含水量、土壤粉粒呈极显著正相关（P<0.01），与土壤温度、土壤容重、土壤粘粒、砂粒呈极显著负相关（P<0.01）；土壤细根生物量、土壤有机质与土壤有机碳含量在土壤表层（0-10、10-20 cm）呈极显著（P<0.01）或显著正相关（P<0.05）；土壤pH值、土壤砂粒与土壤有机碳含量在20-30 cm土层呈显著负相关（P<0.05），但与其他土层关系不显著（P>0.05）；海拔因素是影响土壤有机碳含量分布的主要因素，其次为土壤因素，植被因素主要影响土壤表层有机碳含量分布。（3）海拔因素能通过影响与土壤有机碳形成和转化的因子及改变土壤有机碳的累积和分解速率，对土壤有机碳的分布产生影响。（4）多元线性回归模型拟合R²高于一元线性回归模型拟合R²，能解释土壤有机碳含量变异的82.1%-98.1%。由此可见，不同环境因子组合可以更好的解释不同土层土壤有机碳含量随海拔梯度的变异。

Change characteristics and influencing factors of soil organic carbon in Castanopsis eyrei natural forests at different altitudes in Wuyishan Nature Reserve

Castanopsis eyrei is one of the main dominant species in the mid-subtropical evergreen broad-leave forest, and plays an important role in the subtropical forest ecosystem in China. In order to reveal the differences in the vertical distribution of soil organic carbon content of Castanopsis eyrei natural forest at different altitudes and its influencing factors, this study took the single vegetation type of the natural forest of Castanopsis eyrei in Wuyishan Nature Reserve as the research object. Fixed sample plots were set up within the range of 5 altitude gradients (540 m, 700 m, 850 m, 1022 m, and 1200 m) distributed in a concentrated manner. By measuring soil factors (soil total nitrogen, total phosphorus, soil pH value, bulk density, soil organic matter, silt, sand and clay), climate factors (soil temperature), vegetation factors (fine root biomass) and soil organic carbon content at different depths of each elevation gradient, the distribution characteristics of soil organic carbon along the uplift and vertical soil layers were analyzed. A linear regression model based on principal component analysis was constructed. The results show that:(1) At the same altitude, the distribution of soil organic carbon content in the vertical profile of soil has obvious "surface aggregation" phenomenon; At the same soil depth, the content of soil organic carbon gradually increases with the increase of altitude, but the increase rate decreases with the increase of soil depth, and the high altitude area is conducive to the retention of soil organic carbon. (2) Soil organic carbon content in different soil layers is positively correlated with altitude, soil total nitrogen, soil water content and soil silt (P<0.01), and negatively correlated with soil temperature, soil bulk density, soil clay and sand (P<0.01);In the surface layer of soil (0-10 cm, 10-20 cm), the biomass of fine roots and soil organic carbon content, soil organic matter and soil organic carbon content are extremely significant (P<0.01) or significantly positively correlated (P<0.05). There is a significant negative correlation between soil pH and soil organic carbon content(P<0.05), and between soil sand and soil organic carbon content in 20-30 cm soil layer (P<0.05), but there is no significant correlation between these two factors and soil organic carbon content in other soil layers (P>0.05). Altitude is the main factor affecting the distribution of soil organic carbon content, followed by soil, and vegetation mainly affects the distribution of soil surface organic carbon content. (3) Altitude factors can affect the distribution of soil organic carbon by affecting the formation and transformation factors of soil organic carbon and changing the accumulation and decomposition rate of soil organic carbon. (4) The fitting R² of the multiple linear regression model is higher than that of the one-variable linear regression model, which can explain 82.1%-98.1% of the variation of soil organic carbon content. It can be seen that different combinations of environmental factors can better explain the variation of soil organic carbon content in different soil layers with altitude gradients.