环境因素对密云水库上游流域土壤有机碳和全氮含量影响的通径分析

土壤是全球重要的碳库和氮库，在全球碳氮循环中具有重要地位。密云水库是华北地区最大的水库和北京市最重要的地表水水源地，其上游流域山地广布，地形复杂，气候变化明显，土壤类型和植被类型多样，影响土壤碳氮库的环境因素具有较强的变异性。为揭示环境因素对密云水库上游流域土壤有机碳（soil organic carbon，SOC）和全氮（total nitrogen，TN）含量的作用效应，采用野外采样、实验室分析与逐步回归分析和通径分析相结合的方法，研究了气候（温度和降水）、地形（海拔和坡度）、土壤理化性质（土壤容重、含水量、pH值和粘粒含量）等环境因素对流域SOC和TN含量的影响。结果表明：温度、土壤容重、含水量、pH值和粘粒含量对SOC含量的影响显著（P＆lt;0.001），其中各因子的直接通径系数依次为：土壤含水量（0.439）＞土壤容重（-0.324）＞pH值（-0.238）＞温度（-0.209）＞土壤粘粒含量（0.092），间接通径系数依次为：土壤容重（-0.425）＞土壤粘粒含量（0.305）＞土壤含水量（0.287）＞pH值（-0.179）＞温度（-0.043），因此，土壤含水量、pH值和温度主要通过直接作用影响SOC含量，而土壤容重和粘粒含量则主要通过其它因子的作用间接影响SOC含量。海拔、土壤容重、含水量、pH 值和粘粒含量对 TN 含量的影响显著（P＆lt;0.001），其中各因子的直接通径系数依次为：土壤含水量（0.456）＞海拔（0.234）＞土壤容重（-0.228）＞pH 值（-0.190）＞土壤粘粒含量（0.094），间接通径系数依次为：土壤容重（-0.484）＞土壤粘粒含量（0.301）＞海拔（0.247）＞土壤含水量（0.257）＞pH 值（-0.202），因此，土壤含水量主要通过直接作用影响TN含量，而土壤容重和粘粒含量主要通过土壤含水量的作用间接影响TN含量，海拔和土壤pH值的直接作用与间接作用

Path Analysis on Environmental Factors Controlling Soil Organic Carbon and Total Nitrogen Contents in the Upstream Watershed of Miyun Reservoir,North China

Soil comprises a major pool and plays an important role in the global C and N cycles. Miyun Reservoir is the largest reservoir in North China and also the Chinese capital’s most important drinking water source. There is high variability in the environmental factors that influence the regional soil C and N pools in the Upstream Watershed of Miyun Reservoir with complex terrain, climate change, diverse soil types and vegetation types. Effects of climate （temperature and precipitation）, topography （elevation and slope） and soil properties （soil bulk density, pH, water and clay contents） on soil organic carbon （SOC） and total nitrogen （TN） contents were investigated in the study to identify dominant environmental factors controlling SOC and TN contents in the Upstream Watershed of Miyun Reservoir of North China by soil sampling, laboratory analysis, stepwise regression analysis and path analysis. And the results showed as follows. Temperature, soil bulk density, pH, water and clay contents were the significant factors controlling SOC content, and the direct path coefficient of each factor was ranked in order of soil water content （0.439）〉soil bulk density （-0.324）〉soil pH （-0.238）〉temperature （-0.209）〉soil clay content （0.092）, while the indirect path coefficient was ranked as soil bulk density （-0.425）〉soil clay content （0.305）〉soil water content （0.287）〉soil pH （-0.179）〉temperature （-0.043）. Therefore, temperature, soil water content and pH mainly had direct effects on SOC content, while soil bulk density and clay content mainly had indirect effects through their contributions to other factors. Elevation, soil bulk density, pH, water and clay contents were the significant factors influencing TN content, and the direct path coefficient of each factor was ranked in order of soil water content （0.456） 〉 elevation （0.234） 〉 soil bulk density （-0.228） 〉 soil pH （-0.190） 〉 soil clay content （0.094）,while the indirect