秦岭山地松栎混交林土壤养分空间变异及其与地形因子的关系

在陕西省境内秦岭山脉中段油松-锐齿槲栎混交林集中分布的区域设置20 块调查样地,采取土壤样品测定了该区森林土壤0~20、20~40 和40~60 cm 3 个土层的全氮、全磷、全钾、速效氮、速效磷、速效钾、有机质7 项养分指标。通过计算不同土壤养分指标的变异系数并应用典范对应分析(CCA)技术,对秦岭山地松栎混交林土壤养分空间变异与海拔、坡位、坡向和坡度4 项地形因子的关系进行分析。结果表明:①单因素方差分析显示,随着土层深度增加,全氮、有机质、速效氮、速效磷和速效钾含量均呈极显著下降趋势,而全磷、全钾在不同土层中的含量无显著性差异;②变异系数计算结果表明,各土层的7 项养分指标均表现为中等程度变异性,变异系数最大者是0~20 cm土层速效氮,最小者为0~20 cm土层全钾;③从CCA排序结果看,地形因子对不同土层养分变异的影响程度及因子种类明显不同。0~20 cm表层土壤养分变异受地形因子制约作用较小,20~40 cm土层养分的主要影响因子为坡向和海拔,40~60 cm土层养分的主要影响因子为海拔和坡位,而坡度和海拔则是控制0~60 cm整体土壤层养分变异的主要因素。综上所述,地形高异质性的微生境造成了秦岭山地松栎混交林土壤养分空间分布格局的差异。

The Relationship between Terrain Factors and Spatial Variability of Soil Nutrients for Pine-Oak Mixed Forest in Qinling Mountains

In the middle part of Qinling Mountains where the mixed forest of Pinus tabuliformis and Quercus aliena var. accuteserrata distributed densely, we set 20 sampling plots and took soil specimens to assay the contents of total nitrogen, total phosphorus, total potassium, available nitrogen, available phosphorus, available potassium and organic matter in three different soil layers (0-20 cm, 20-40 cm and 40-60 cm). By calculating the variable coefficients of those seven soil nutrient indices and using CCA ordination (canonical correspondence analysis), we analyzed the relationships between spatial variability of soil nutrients and four terrain factors (elevation, slope-position, aspect and slope). Results indicated that: 1) The One-way ANOVA analysis showed that the contents of total nitrogen, organic matter, available nitrogen, available phosphorus and available potassium have significant decline tendency with the increased depth of soil layer, while the contents of total phosphorus and total potassium have no significant difference in three different soil layers. 2) The results of variation coefficients showed that all of the seven soil nutrient indices have moderate variability. The highest variation coefficient is that of available nitrogen in 0-20 cm, and the least is that of total potassium in 0-20 cm. 3) From CCA diagram we can see that the different types of terrain factors have obviously different influences to different degrees on soil nutrient spatial variability. The effect of terrain factors on 0-20 cm surface soil is very weak; the main influence factors on 20-40 cm soil layer are aspect and elevation; for 40-60 cm soil layer, they are elevation and slope position; and as for the 0-60 cm layer they are slope and elevation. Above all, the high heterogeneity of terrain caused the different spatial distribution patterns of soil nutrients in the pine oak mixed forest in Qinling Mountains.