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In this study, the characteristics of soil bacterial composition and diversity were investigated under four land-use types (afforestation land, FL; abandoned land, SL; native grassland, GL; cultivated land, CL) to explore correlations between land-use types and the bacterial communites in soil in a subtropical mountainous region of southwestern China. The results showed that the dominant taxonomic genera were Actinobacteria and Proteobacteria. Land-use type influenced the bacterial richness and diversity, and ranked as follows: FL>CL>SL>GL. Marked differences in the distribution of taxon assemblages among the different land-use types in soil were found. The relative abundances of Acidobacteria in SL, Proteobacteria in FL, and Chloroflexi in GL presented as being higher than in other land-use types. Among all the physicochemical properties, significant pearson linear correlations between soil bacterial taxonomic genera (Flavobacterium, Sphingomonas, Blastocatella, Zymomonas, Pedomicrobium, Reyranella, Rhodanomonas, Flavisolibacter, Candidatus and Telmatobacter ) and physicochemical properties (pH, TP and LAP) were observed. These findings suggested that land-use type is a major factor that affects the bacterial composition and diversity, and that changes in soil bacterial composition and diversity are associated with shifts in physicochemical properties.

To understand the response mechanism of soil microbial biomass carbon content, soil microbial biomass nitrogen content and soil enzyme activities to intercropping pattern, an experiment consisting of three cropping patterns: Sophora davidii Skeels monocropping pattern, Pennisetum sinese Roxb monocropping pattern and S. davidii and P. sinese intercropping pattern had established in the southern region of Guizhou Province, China. The results showed that soil microbial biomass carbon content, microbial biomass nitrogen content and enzyme activities were gradually reduced with the depth (0-30 cm) of the soil layer increased under the three cropping patterns. The microbial biomass carbon and nitrogen content of S. davidii and P. sinese intercropping pattern were significantly higher than those of S. davidii monocropping and P. sinese monocropping pattern in 0-20 cm soil layer (P P. sinese monocropping > S. davidii and P. sinese intercropping > S. davidii monocropping in most soil layers. The soil nutrient contents (soil organic matter, total nitrogen, total phosphorus, and total potassium) and soil microbial biomass content (microbial biomass carbon and nitrogen) were highly significant positive correlation (P 0.05), but the activiies of β-N-acetylglucosidase, the activiies of soil nitrogenase, the activiies of soil Leucine aminopeptidase and the activiies of soil glutamine synthetase were showed a significant (P S. davidii and P. sinese has a significant effect on soil quality improvement in shallow soil (0-20cm), and the microbial biomass carbon, soil microbial biomass nitrogen and soil enzymes can be used as an important index for evaluating the changes of soil quality.