土壤粒径分布及空间变化对土壤溶质和水盐运移、土壤肥力状况等有重要意义，是土壤重要物理特性之一。基于新疆准噶尔北部、阿勒泰山南麓不同管理模式下的草地(荒漠草地、天然草地、弃耕草地、季节草地和禁牧草地)，运用质地分类和分形理论探讨草地粒度特征。结果发现：研究区土壤颗粒中黏粒含量最低，最小值仅有0.17 g/kg，砂粒含量最高，最大值可达900.37 g/kg，粒径分布呈现单峰特征，表明土壤发育较差；砂粒和粉粒含量之间呈极显著负相关关系，相关系数为0.999 8(P<0.01)，推测成土母质和地域差异导致土壤中砂粒和粉粒几乎占了全部；荒漠草地、天然草地和弃耕草地黏粒含量的平均值随着土层深度增加而减小，呈现出负相关特征，而季节草地和禁牧草地并无此特征；荒漠草地的分形维数D值最大，可能是因为灌木作为该生态系统中的优势植物，能有效地减缓荒漠草地逆向演替和消亡的进程，对土壤颗粒具有一定的细化作用；所有土壤样品分形维数D与黏粒含量均具有较强相关性，天然草地、荒漠草地和弃耕草地的分形维数D分别与粉粒和砂粒含量的相关性较强，与禁牧和季节草地的相关性较差，说明春、秋轮牧对土壤的干扰可能超过了土壤本身承载能力，对土壤颗粒组成破坏比较大，影响了土壤发育，放牧向禁牧转化时期的长短可能决定了土壤的发育是否良好。

As one of the important physical properties of soil, particle size distribution (PSD) and spatial variation is of great significance not only to the transport of soil solute, water and salt, but also to soil fertility status and so on. Based on the grasslands (desert grassland, natural grassland, abandoned grassland, seasonal grassland and forbidden grassland) under the different management modes in the northern Junggar and southern Altay Mountains, the texture classification and fractal theory were used to study PSD characteristics of grasslands. The results showed that clay content in the study area was the lowest with the minimum value of only 0.17 g/kg while sand content was the highest with the maximum value of 900.37 g/kg; PSD showed a single peak, indicating that the soil is poorly developed; Silt and sand contents showed significant negative correlation with the correlation coefficient of 0.999 8 (P<0.01), suggesting that soil parent material and geographical differences lead to sand and silt particles almost accounted all of the soils. Mean clay content decreased with the increase of soil depth in desert grassland, natural grassland, and abandonment grassland, while no such tendency was found in the seasonal grassland and forbidding grazing grassland. The fractal dimension of D in desert grassland is the highest, which may be because the shrubs, as dominant plants in the ecosystem, can effectively slow down the process of reverse succession and extinction and had a certain effect in the accumulation of fine particles; Fractal dimension D had significant correlation with and clay content of all soils and with silt and sand contents of desert grassland, natural grassland, and abandonment grassland, whereas not with those of seasonal grassland and forbidding grazing grassland. The above results showed that the interference of spring and autumn grazing on soil may exceed soil bearing capacity, damage largely soil particles and hinder soil development, and the length of grazing transforming into prohibition may determine whether the development of the soil is good or not.

S152

国家科技支撑计划项目(2014BAC15B04)资助。