Abstract: Herbaceous plants have encroached into tundra area of Changbai Mountain under warming climate, which has severely changed the tundra vegetation. We analyzed soil microbes, soil enzyme activity and soil fertility at different stages of herbaceous encroachment. We also analyzed subsequent changes of soil microbial community structure and enzyme activity and the effects of soil microbial community structure and enzyme activity on soil fertility as well as the effects of changes in soil fertility on vegetation changes. Results showed that: (1) Soil microbes and soil enzyme activity changed as the vegetation changed. Among these changes, soil microbial PLFAs and enzyme activity continued to increase with the level of herbaceous encroachment. However, soil microbial PLFAs and enzyme activity decreased when the herbaceous plants dominated the plant communities. (2) The decomposition of soil organic matter was accelerated and the available nutrients increased with the increase of soil microbial PLFAs and enzyme activity under high level of herbaceous encroachment. (3) A transformation process from positive feedback to negative feedback occurred between soil microbes, enzyme activity and the level of herbaceous encroachment. Therefore, the changes of soil microbes and enzyme activity significantly affected herbaceous plant encroachment of the tundra vegetation of Changbai Mountain.

Key words: IAA oxidase, tuberization, Bacillus amyloliquefaciens YTB1407, sweet potato, indole acetic acid