Ash-leaf maple (Acer negundo L.) is one of the most active invasive species in ecosystems of the Siberian region, which transforms their structure and functioning. As ashleaf maple is actively invading natural plant communities, its study has gained relevance. The purpose of this study is to assess the biological activity of the soil through the level of activity of soil enzymes (invertase, protease, phosphatase) and the main ecologicaltrophic groups of microorganisms (microorganisms that utilize organic forms of nitrogen; microorganisms that utilize mineral forms of nitrogen; microscopic fungi) in meadow plant coenoses under the influence of ash-leaf maple. The object chosen for the study is natural meadow communities of Kuzbass comprising ash-leaved maple. The census
plots were located within the invasive species’ crown projection area, the control plots were located outside the tree crown projection. Invertase activity was determined by the method suggested by V. F. Kuprevich and T. A. Shcherbakova, protease activity – by the method of A. Sh. Galstyan and E. A. Arutyunyan, phosphatase activity – as suggested by A. Sh. Galstyan. The abundance of soil microorganisms was studied using standard methods by inoculating a soil suspension on agar media. Experimental data were treated statistically using Microsoft Office Excel 2007 and Statistica 10 programs. In meadow phytocoenoses, ash-leaf maple invasions raise the level of enzymatic and microbiological activity of the soil. The activity of soil enzymes in the studied plant communities was 10–12 % higher within the A. negundo crown projection area than outside of it. There prevailed the microorganisms that utilized mineral nitrogen, especially in communities dominated by U. dioica, 1.8-fold versus the control, on average. The diversity of plant communities had no significant effect on the level of soil biological activity. A comparison of enzymatic and microbiological activity indices of soil between communities with different
dominant species – U. dioica, T. officinale, V. lobelianum – showed the soil activity parameters were generally similar. The resultant data can be used as diagnostic indicators of soil condition and in biomonitoring of soils in natural ecosystems.