放牧强度对内蒙古荒漠草原土壤有机碳及其空间异质性的影响

放牧是内蒙古荒漠草原主要利用方式之一，研究不同放牧强度下土壤有机碳分布规律对退化草原恢复以及推广精准放牧技术具有重要的指导意义。基于不同放牧强度长期放牧样地（0、0.93、1.82、2.71羊单位hm^-2（a/2）^-1），采用高样本数量的取样设计并结合地统计学分析方法，研究荒漠草原土壤有机碳及其空间异质性。结果表明：中度放牧会显著降低0-30 cm土层全氮含量（P<0.05），全磷含量随放牧强度增强出现先降低后升高趋势；放牧样地土壤有机碳含量均显著低于对照样地（P<0.05），不同放牧强度处理土壤有机碳含量没有显著差异；土壤有机碳密度受放牧影响在0-20 cm土层出现显著下降（P<0.05），变化趋势同有机碳含量相似，碳氮比在重度放牧区0-10 cm土层显著降低（P<0.05）。土壤有机碳空间异质性和异质性斑块的破碎程度随放牧强度增加而增大；土壤有机碳含量与海拔高度在对照、轻度放牧和中度放牧区均呈极显著负相关（P<0.01），在重度放牧区土壤有机碳含量和海拔无显著相关性；土壤有机碳含量与土壤全氮、全磷含量均呈极显著正相关（P<0.01）。综上所述，放牧降低土壤有机碳含量，提高土壤有机碳空间异质性，土壤有机碳含量的空间变异受海拔和土壤养分含量等因素的共同影响。

Effects of grazing intensity on soil organic carbon and its spatial heterogeneity in desert steppe of Inner Mongolia

Grazing is the main utilization method of desert steppe in Inner Mongolia. It is also one of the main anthropic disturbances contributing to desert steppe degradation. Studying the distribution pattern of soil organic carbon under different grazing intensity has important guiding significance for restoration of the degraded grassland and promotion of precision grazing technology. This experiment was based on long-term grazing plots with different grazing intensities (0, 0.93, 1.82, 2.71 sheep units/hm²/half year), using high-density sampling combined with geostatistics to study soil organic carbon and its spatial heterogeneity in desert steppe. The results showed that the total nitrogen content of 0-30 cm soil layer decreased significantly in moderate grazing (P<0.05), and the soil total phosphorus content firstly decreased and then increased with the increase of grazing intensity. Soil total nitrogen content decreased significantly with the deepening of soil depth in 0-30 cm soil layer of four treatments (P<0.05), but soil total phosphorus did not change significantly. Soil organic carbon content of the control plots was significantly higher than that of other treatments, and there was no significant difference in soil organic carbon content among different grazing treatments. Soil organic carbon content in every treatment decreased gradually with the deepening of the soil layer. The data distribution of organic carbon content in the four treatments was symmetrical, and the degree of data dispersion decreased with the deepening of soil layer. Soil organic carbon density decreased significantly in 0-20 cm soil layer under grazing (P<0.05), and the change trend was similar to that of organic carbon content. The C/N ratio in the 0-10 cm soil layer in heavy grazing area decreased significantly, but there was no significant change in 20-30 cm soil layer. In vertical distribution, the C/N ratio decreased significantly with the deepening of soil layer (P<0.05). The spatial heterogeneity of soil organic carbon and the degree of fragmentation of heterogeneous plaques increased with the increase of grazing intensity, but heavy grazing would change this trend, especially in moderate grazing to achieve a strong class of structural dependence. The nugget values of control and heavy grazing were higher, and the control had the largest base values among the four treatments. Elevation was negatively correlated with soil organic carbon content in control (P<0.01), lightly grazed and moderately grazed, but not with heavily grazed. Soil organic carbon content was positively correlated with soil total nitrogen content (P<0.01). Soil organic carbon content was positively correlated with soil total phosphorus content, and the correlation increased with the grazing intensity (P<0.01). In general, grazing reduced soil organic carbon content and storage, and improved spatial heterogeneity of soil organic carbon. Spatial variability of soil organic carbon content was affected by altitude and soil nutrients.