Abstract: Taking a long-term field experiment on an aquic brown soil in the Shenyang Ecological Station of Chinese Academy of Sciences as a platform, the methods of traditional chloroform fumigation and modern PCR-DGGE were adopted to study the effects of different fertilizations on the changes of soil microbial biomass and bacterial community structure. During the whole period of the experiment, there was a similar trend in the dynamic changes of soil microbial biomass C and N. Long-term application of organic manure increased the soil organic C and the soil microbial biomass C and N significantly, while long-term application of chemical fertilizers had significant negative effects on the soil pH and soil microbial biomass C and N. The DGGE patterns showed that under different fertilizations, the majority of soil bacterial 16S rDNA bands were the same, 18 of the 28 bands being common, suggesting that the bacterial populations in test soil were more stable, but their numbers were affected by different fertilizations. Long-term application of organic fertilizer could promote the diversity of the bacterial community structure in aquic brown soil, while the application of chemical fertilizers was in adverse.

Key words: microbial biomass C and N, bacterial community structure, diversity, DGGE, Alternaria alternata, Erysiphe cichoracearum,  Bacillus pumilus, antagonistic activity.