放牧干扰后自然恢复的退化沙质草地土壤性状的空间分布

SPATIAL PATTERN OF SOIL CHEMICAL PROPERTIES IN DEGRADED SANDY GRASSLAND UNDER POST-GRAZING NATURAL RESTORATION IN HORQIN SANDY LAND

用地统计学的方法 ,研究了科尔沁沙质退化草地不同强度放牧干扰 (重度放牧和适度放牧 )后自然恢复过程中 0～ 15cm土层土壤有机碳、全氮、pH和电导率在 10m尺度上的空间异质性特征。结果表明 ,重牧后的恢复草地比适度放牧后的恢复草地呈现出显著低的有机碳和全氮含量及其显著高的变异性。在取样尺度的空间分布上均表现出显著的空间结构特征 ,自相关尺度分别为 2 2 2～ 2 9 4m和 2 5 5～ 39m ,结构性方差占样本方差的 87 2 %～ 88 2 %和 6 5 5 %～ 85 9%。全氮的自相关尺度大于有机碳。土壤pH和电导率在取样的尺度内不存在局部格局 ,而可能受更大尺度的格局控制。放牧引起的植被斑块状分布和沙化裸斑的出现是土壤碳、氮空间变异的主要因素 ;土壤异质性尺度的改变又可能影响着植被的恢复演替和分布格局。

Geostatistics was used in studying spatial variation of soil organic carbon, total nitrogen, pH and electrical conductivity in a degraded sandy grassland ecosystem under two different grazing patterns, heavy grazing (HGR) and moderate grazing (MGR) to examine effect of grazing intensity on spatial heterogeneity of the properties. One hundred soil samples were taken from the soil layer 0～15 cm in depth of a grid of 10 m×10 m under each grazing pattern. The results showed that soil organic carbon and total nitrogen contents were significant lower and their coefficients of variation significant higher under HGR than under MGR. Geostatistical analysis of soil heterogeneity revealed that organic carbon and total nitrogen show strong spatial dependence with exponential or spherical semivariograms on the studied scale. 87.2%～88.2% of the variation in soil organic carbon was found within the distance from 22.2～29.4 m, and 65.5%～85.9% of the variation in total nitrogen was found within the distance from 25.5～39 m. The distance of spatial autocorrelation in soil organic carbon and total nitrogen was greater under HGR than under MGR, suggesting that overgrazing resulted in an increase in soil heterogeneity. Soil pH and electrical conductivity did not show spatial autocorrelation within the studied scale, and they were probably controlled by a bigger scale and process. The distribution of vegetation patchs and the bare sand ones resulting from grazing was the main cause of the increase in soil heterogeneity and indicated extent of desertification of the grassland. The changes in heterogeneity in the distribution of soil properties may in turn influence restoration process and distribution pattern of the vegetation.