南滚河国家级自然保护区典型植被类型土壤有机碳及全氮储量的空间分布特征

目的植被群落随山地海拔升高呈现有规律的垂直分布，能够引起样地微气候及土壤性质的改变，进而影响碳氮在土壤中的沉积。因此，不同典型植被类型土壤碳氮储量的空间分布特征是山地生态系统碳氮循环研究的重要内容。本文旨在探明南滚河自然保护区不同典型植被类型土壤有机碳及全氮储量沿海拔梯度的变化及其与环境因子的耦合关系。方法选取南滚河自然保护区沿海拔形成的3种典型植被类型（沟谷雨林、半常绿季雨林和中山湿性常绿阔叶林）为研究对象，研究不同植被类型之间土壤有机碳及全氮储量的变化规律，并运用线性回归和RDA冗余分析等方法研究环境因子沿海拔变化对土壤有机碳及全氮储量的影响。结果不同典型植被类型土壤有机碳与全氮储量随海拔升高呈现显著增加的变化趋势（P < 0.05），即沟谷雨林（89.10 t/hm2，11.94 t/hm2） < 半常绿季雨林（190.30 t/hm2，25.34 t/hm2） < 中山湿性常绿阔叶林（508.05 t/hm2，56.55 t/hm2），这种变化规律与凋落物厚度、年均降水量、土壤含水量、总有机碳及全氮沿海拔的变化相一致；不同植被类型土壤有机碳储量均随土层深度增加呈先增后降的垂直变化规律，而土壤全氮储量则随土层深度增加呈逐渐降低趋势；土壤有机碳及全氮储量与海拔、土壤含水量、总有机碳、全氮、凋落物厚度和年均降水量呈极显著正相关（P < 0.01），与土壤密度、pH、年均气温和土壤温度呈极显著负相关（P < 0.01），冗余分析表明凋落物厚度与土壤含水量是影响有机碳和全氮储量的主导因子。结论热带地区植被类型沿海拔梯度有规律的分布，能够通过改变样地微气候（如温度、水分）、凋落物输入（凋落物厚度）及土壤理化环境（如土壤密度、C与N含量等），进而显著影响土壤有机碳及全氮储量的空间分布。 

Spatial distribution characteristics of soil organic carbon and total nitrogen stocks across the different typical vegetation types in Nangunhe National Nature Reserve,southwestern China

ObjectiveThe change in vegetation types along the elevation gradient induces the alterations in site, microclimate and soil properties, thus in turn forms the variations of soil carbon and nitrogen stocks along the elevation gradient. We aimed to explore the variation characteristics of soil organic carbon and total nitrogen stocks along the elevation gradient in Nangunhe Nature Reserve, Yunnan Province of southwestern China and its coupling relationship with environmental factors.MethodThree typical vegetation types (i.e., ravine rainforest, semi-evergreen monsoon rainforest, mid-montane humid evergreen broadleaved forest) in Nangunhe Nature Reserve were applied to investigate the variation rules of soil organic carbon and total nitrogen stocks along the elevation gradient. The association of soil organic carbon and total nitrogen stocks to environmental factors was also analyzed through the general linear regression and RDA redundancy.ResultSoil organic carbon and total nitrogen stocks increased along the elevation gradient (P < 0.05). Soil organic carbon and total nitrogen stocks were ranked as ravine rainforest (89.10 t/ha, 11.94 t/ha) < semi-evergreen monsoon rainforest (190.30 t/ha, 25.34 t/ha) < mid-montane humid evergreen broadleaved forest (508.05 t/ha, 56.55 t/ha). The order was consistent with the variations in litter thickness, average annual precipitation, soil water content, total organic carbon and nitrogen. Soil organic carbon stocks of three vegetation types showed a vertical change of increasing first and then decreasing along the soil layers. However, total nitrogen stock decreased with increasing soil depth. Soil organic carbon and total nitrogen stocks were positively related with altitude, average annual precipitation, soil water content, litter thickness, total organic carbon and total nitrogen (P < 0.01), while average annual air temperature, soil temperature, soil pH and bulk density had negative correlation with soil organic carbon and total nitrogen stocks (P < 0.01). Redundancy analysis showed that litter thickness and soil water content were the dominant factors of soil organic carbon and total nitrogen stocks.ConclusionThe results indicated that change of vegetation types along the elevation gradient affected the variations in microclimate (i.e., temperature and water), litter input (litter thickness), and soil physicochemical properties (i.e., soil bulk density, and C and N concentration), which contributed to significant effects on the soil carbon and total nitrogen stocks in tropical area.