In order to explore spatial pattern of soil microbial biomass carbon (MBC) and its environmental driving forces in grassland surface layer (0?10 cm) and subsurface layer (10?20 cm) in the agro-pastoral transition zone in northern China, 456 soil samples (57 sample sites, two soil layers and four replicates) were selected for investigation from Inner Mongolia-Liaoning plain, Bashang on the north of Beijing, the northern foot of Yinshan Mountain and Ningxia-Shaanxi Loess Plateau. The results showed that the spatial pattern of MBC was consistent between the surface and subsurface layer, which increased with latitude and had no significant change with longitude and elevation. With the increase of degradation degree, the reduction of soil microbial biomass in the subsurface layer was smaller than that in the surface layer. The difference of soil pH between the two layers decreased with the degree of degradation. The difference in soil MBC between surface and subsurface soils was regulated by the change of soil pH. The smaller the difference in pH between the two soil layers, the smaller the difference in MBC. Climate, vegetation and soil factors could affect the spatial variation of MBC, and soil factors were the main driving forces for MBC at the regional scale. The main influencing factor of MBC was soil total carbon at surface layer, and soil total nitrogen at subsurface layer. In the context of climate change and the intensification of human activities, the results were useful for predicting the response of soil microorganisms at the regional scale and maintaining and restoring ecological functions of degraded grasslands.

为探究我国北方农牧交错带草地表层(0~10 cm)和次表层(10~20 cm)土壤微生物量碳的空间格局及其环境驱动力, 选择蒙辽平原、京北坝上、阴山北麓和宁陕黄土高原4个区域总计456个土壤样品(两个土层, 57个样点, 每个样点4个样方)进行调查。结果表明, 表层与次表层土壤微生物量碳的空间格局具有一致性, 均随纬度增加而增加, 随经度和海拔增加无显著变化。随着草地退化程度加剧, 次表层土壤微生物量碳的降低幅度小于表层土壤。两层土壤 pH 值的差异随草地退化程度的加剧而缩小, 表层与次表层土壤微生物量碳的差异受土壤pH值调控, 两个土层的pH值差异越小, 微生物量碳的差异越小。气候、植被和土壤因素均会影响微生物量碳的空间变异, 其中土壤因素为区域尺度微生物量碳的主要驱动力, 表层土壤微生物量碳的主要影响因素为土壤总碳, 次表层土壤微生物量碳受土壤总氮的影响最大。在气候变化和人类活动影响加剧的背景下, 研究结果对预测区域尺度土壤微生物的响应规律及退化草地生态功能的维持和修复有重要意义。