黄土丘陵区表层土壤有机碳沿降水梯度的分布

沿368～591 mm降水量梯度选取7个调查地点、共63个调查样点，在每个样点选择恢复年限相近的林地、草地和农地，调查表层（0～30 cm）土壤有机碳的分布特征，分析气候、土层深度和土地利用类型等因素对土壤有机碳分布的影响.结果表明： 在黄土丘陵区368～591 mm的降水量范围内，表层土壤有机碳含量表现为草地（8.70 g·kg^-1）>林地（7.88 g·kg^-1）>农地（7.73 g·kg^-1），土壤有机碳密度表现为草地（20.28 kg·m^-2）>农地（19.34 kg·m^-2）>林地（17.14 kg·m^-2）.林地、草地、农地的土壤有机碳含量无显著差异，综合3种土地利用类型的数据分析表明，不同降雨梯度下土壤有机碳含量差异显著（P<0.001），土壤有机碳含量（r=0.838，P<0.001）与年均降水量间存在显著线性正相关关系；由北向南（以最北端鄂尔多斯为起点），土壤有机碳含量沿着368～591 mm的年均降水量梯度的递增速率为0.04 g·kg^-1·mm^-1，土壤有机碳密度的递增速率为0.08 kg·m^-2·mm^-1.年均降水量、土壤黏粒含量、林下枯落物蓄积量和农作物根系密度可较好地模拟表层土壤有机碳分布.

Distribution of soil organic carbon in surface soil along a precipitation gradient in loess hilly area.

Along the 368-591 mm precipitation gradient, 7 survey sites, i.e. a total 63 investigated plots were selected. At each sites, woodland, grassland, and cropland with similar restoration age were selected to investigate soil organic carbon distribution in surface soil (0-30 cm), and the influence of factors, e.g. climate, soil depth, and land uses, on soil organic carbon distribution were analyzed. The result showed that, along the precipitation gradient, the grassland (8.70 g·kg^-1) > woodland (7.88 g·kg^-1) > farmland (7.73 g·kg^-1) in concentration and the grassland (20.28 kg·m^-2) > farmland (19.34 kg·m^-2) > woodland (17.14 kg·m^-2) in density. The differences of soil organic carbon concentration of three land uses were not significant. Further analysis of pooled data of three land uses showed that the surface soil organic carbon concentration differed significantly at different precipitation levels (P<0.001). Significant positive relationship was detected between mean annual precipitation and soil organic carbon concentration (r=0.838, P<0.001) in the of pooled data. From south to north (start from northernmost Ordos), i.e. along the 368-591 mm precipitation gradient, the soil organic carbon increased with annual precipitation 0.04 g·kg^-1·mm^-1, density 0.08 kg·m^-2·mm^-1. The soil organic carbon distribution was predicted with mean annual precipitation, soil clay content, plant litter in woodland, and root density in farmland.