草地灌丛化是我国草地生态系统面临的重要生态环境问题，内蒙古干旱半干旱地区是我国生态环境最为脆弱的地区之一，灌丛化现象十分普遍，严重威胁当地国民经济和农牧生产。本论文选取内蒙古小叶锦鸡儿灌丛化草地为研究对象，采用野外剖面观测、分层采集土样和磷脂脂肪酸（PLFA）法，测定土壤微生物群落结构及空间分布格局；结合CT扫描测定的土壤大孔隙结构特征参数，分析土壤微生物与土壤大孔隙的相关性，探讨土壤微生物对土壤大孔隙的影响。研究结果如下： （1）内蒙古小叶锦鸡儿灌丛化草地的土壤微生物包括细菌、真菌、放线菌、原生动物、革兰氏阳性菌、革兰氏阴性菌。灌丛斑块中各类微生物量都有大小顺序：细菌>革兰氏阴性菌>革兰氏阳性菌>放线菌>真菌>原生动物；草本斑块中，细菌生物量最大，原生动物生物量最小。 （2）灌丛斑块的总微生物量大于草地斑块，随灌丛化程度加剧，灌丛斑块和草地斑块的差值增大，由1.25 nmol/gDW增大到39.27 nmol/gDW，增长了31倍。 （3）随灌丛化程度加剧，草地斑块中的细菌、真菌、革兰氏阳性菌、革兰氏阴性菌、原生动物的总生物量先减小后增大，灌丛斑块中的细菌、革兰氏阴性菌、原生动物的总生物量呈现增加趋势，真菌、革兰氏阳性菌、放线菌的总生物量先减小后增大。 （4）灌丛斑块中的革兰氏阳性菌和放线菌总生物量大于草地斑块。中度和重度灌丛化草地中，细菌、真菌、革兰氏阴性菌在灌丛斑块中的总生物量大于草地斑块，在轻度灌丛化草地中灌丛斑块小于草地斑块。轻度和中度灌丛化草地中，原生动物在灌丛斑块中的总生物量小于草地斑块，在重度灌丛化草地中，草地斑块大于灌丛斑块。 （5）草地斑块中，土壤微生物在垂向上主要分布在0-10cm土壤深度；灌丛斑块中，土壤深度0-50cm皆有分布，范围更广、分布更均匀、层间差异较小。 （6）草地斑块中，土壤大孔隙主要分布在土壤深度0-10 cm，灌丛斑块中，土壤大孔隙在土壤深度0-45 cm均有分布，空间分布范围更广。 （7）草地斑块中，细菌、革兰氏阴性菌与土壤大孔隙度呈显著正相关，与孔隙平均水力半径呈显著正相关。灌丛斑块中，土壤微生物都与孔隙网络密度呈显著正相关，与土壤大孔隙数量呈显著正相关，其中真菌与土壤大孔隙数呈极显著正相关。 （8）草地斑块中土壤微生物对土壤大孔隙影响更大，灌丛斑块中土壤微生物对土壤大孔隙的影响相对较小。随灌丛化程度的加剧，土壤微生物对土壤大孔隙的影响下降。

Shrub encroachment is an important ecological environment problem in China's grassland ecosystem. Arid and semi-arid area in Inner Mongolia is one of the most vulnerable areas in China, where the phenomenon of encroachment is very common, which seriously threatens the local national economy and agriculture and animal husbandry. Therefore, by the means of the methods of soil profile observation, mixed soil samples collected in layers and phospholipid fatty acid (PLFA) biomarkers method, we select the Caragana microphylla encroached grassland as study area to investigate soil microbial community structure, and spatial distribution pattern of soil microorganism. Combined with parameters of soil macropore structure measured by CT scanning, we analyze the interactions between soil microorganism and soil macropore, reveal the correlation between them. (1) There are seven kinds of soil microorganism, bacteria, fungi, actinomycetes, protozoa, Gram-positive bacteria and gram negative bacteria in Inner Mongolia Caragana microphylla grassland. At each site, there are relationship between the quantity of various microorganism, Bacteria > Gram-negative bacteria > Gram-positive bacteria > actinomycetes > fungi > protozoa, in the shrub patches; the quantity of bacterial maximum, the quantity of protozoa minimum in the interspace grass patches. (2) Form state 2 to state 4, the total biomass under shrub patches is larger than that of the interspace grass patches. The difference of total biomass between the shrub patches and the adjacent interspace grass patches increased with the exacerbation of shrub encroachment, from 1.25 nmol/gDW to 39.27 nmol/gDW, which increased 31 times. (3) With the exacerbation of shrub encroachment, the total biomass of bacteria, fungi, Gram-positive bacteria, Gram-negative bacteria and protozoa decreased first and then increased in the shrub patches; the total biomass of bacteria, Gram-negative bacteria and protozoa increased in the interspace grass patches; the total biomass of fungi, Gram-positive bacteria, actinomycetes decreased first and then increased. (4) The total biomass of Gram-positive bacteria and Actinomyces in shrub patches is larger than that of the interspace grass patches. In state 3 and 4, the total biomass of bacteria, fungi and Gram-negative bacteria in the shrub patches was larger than that of the interspace grass patches, and the patches were smaller in state 4 than in the interspace grass patches. In state 2 and 3,The total biomass of protozoa in shrub patches was smaller than that of the interspace grass patches, and in state 4, in the interspace grass patches were larger than that of shrub patches. (5) The vertical spatial distribution characteristics of bacteria, fungi, actinomycetes, protozoa, Gram-positive bacteria and Gram-negative bacteria are centrally distributed in the 0-10cm soil layer under the interspace grass patches, while widely distributed in the 0-50cm soil layer in shrub patches, more broadly and little difference between soil layers. (6) Soil macropores are mainly distributed in the 0-10cm soil layer under the interspace grass patches, while widely distributed in the 0-45cm soil layer in shrub patches, more broadly. (7) Bacteria and Gram-negative bacteria are significantly positively correlated with porosity， and the same with the average hydraulic radius of the pores under the interspace grass patches. Bacteria, fungi, actinomycetes, Gram-positive and Gram-negative bacteria are positively correlated with the pore network density, and significantly positively correlated with the number of macropores, moreover, fungi is very significantly positively correlated with the number of macropores under the shrub patches. (8) Soil microbes had greater influence on porosity under the shrub patches, the influence of soil microbes on soil macropores is relatively small. The effect of soil microbes on soil macropores decreased with increasing degree of shrub.