Soil Microbial Diversity Under Different Agricultural Utilizations In Shizishan, Wuhan

Microbial diversities of soils from different agritural utilizations (rice continuouscropping, rice-rape rotation, ramie continuous cropping and cotton continuouscropping) in Shizishan, Wuhan, were investigated by use of microbial plate counting,soil enzyme assay, microbial biomass analysis, and 16s-rDNA V₃ regionPCR-DGGE analysis. The results are shown as below:1. The bacterial number of rice-rape rotation field was 2.2～3.8 times higher thanthe others. The fungal number in this soil was 50～70% of the others, and ratio ofbacteria to fungi (B/F ratio) was 2.6～6.3 times higher than the others. The order ofB/F ratio for different soils was rice-rape rotation＞rice continuous cropping＞ramiecontinuous cropping＞cotton continuous cropping.2. Rice-rape rotation soil showed the highest urease activity (6μg NH₄⁺·g^-1. 24h^-1), the lowest dehydrodenase (22.4μg TPF·g^-1·24 h^-1) and acid phosphataseactivities (1.6μgρ-nitrophenol·g^-1·1 h^-1). It indicates that the cycling of C, N inthis soil is more active than the other soils, while the transformation of phophorus isthe weakest. The lowest urease activity (9.9μg NH₄⁺·g^-1·24 h^-1) and the highestdehydrodenase activity (142μg TPF·g^-1·24 h^-1) were observed in rice continuouscropping soil, suggesting that the turnover of C and N nutrients in this soil is theweakest, and the conversion rate of organic matter is the greatest. Higher acidphosphatase activity (2.3～3.3μgρ-nitrophenol·g^-1·1 h^-1) were found in the soils oframie continuous cropping and cotton continuous cropping.3. Microbial biomass C, N and C/N ratio for different utilization soils followedthe sequence: rice-rape rotation＞rice continuous cropping＞ramie continuouscropping＞cotton continuous cropping.4. The ability of CTAB and Al₂(SO₄)₃ in the removal of soil humic subatancesfor DNA extraction was compared. Better removal efficiency was found at a ratio of350μl 0.1 M Al₂(SO₄)₃ to 0.3 g soil. A modified procedure for the efficient extractionof soil DNA was suggested as follows: SDS and lysozyme to release DNA,phynol/chloroform/isoamyl alcohol to remove protein, and Al₂(SO₄)₃ to remove humic substances.5. Microbial richness for different soils was in the order of: rice-rape rotation＞rice continuous cropping＞ramie continuous cropping＞cotton continuous cropping.Soil microbial similarity index (Jaccard Incidence) between rice-rape rotation and ricecontinuous cropping was the highest (34%), and lower indices were observed betweenrice-rape rotation field and cotton continuous cropping field (16%), and betweenrice-rape crop rotation field and ramie continuous cropping field (17%). UPGMAcluster analysis showed that microorganisms in rice-rape rotation field and ricecontinuous cropping field are in the same cluster, The genetic similarity reached 57%between the two utilization soils and was in accord with the result of similarity index.To sum up, rice-rape rotation has the least impacts on soil microbial richness andmicrobial diversity among the four agricultural utilizations in Shizishan. Thisutilization is relatively efficient in the preservation of soil microbial stability.