Phytostablizing base metal mine tailings storage under semi-arid climatic conditions and with limited availability of topsoils is highly challenging. This has given rise to the necessity to rehabilitate microbial community and activities through organic amendment option for direct revegetation. In this research,we measured microbial biomass induced from substrate supply along toxicity gradients. In addition, three typical organic amendments (Acacia biomass, sugarcane mulch and biochar) were applied in base metal mine tailings revegated with Acacia Chisholmii. Microbial biomass and activities in rhizpheric layer were measured to investigate the relationship among microbes, labile C and N and toxiciity.

Resutls showed that microbial biomass is stimulated by sucrose organic C and mineral N addition, which is also constrained if N is limiting with C/N ratio larger than 32. Besides, it is found significantly stimulated microbial biomass, respiration, mineralization, urease activity, invertase activity and neutral phosphotase activity in sugarcane and acacia biomass amended tailings, which are positively related to labiel C and N pool. Meanwhile, no significant differene were observed in biochar amended one. However, microbial metabolic quotients in all amended tailings are much higher than that found in soil, which may result from tailings toxicity. From the aspect of toxicity, in mixture of tailings and soil, it is found substrate induced microbial biomass is decreased with higher percentage of tailings. In addition, when there are more than 25% of soil in the mixture, no significant differences of metabolic quotient were found in the tailings and soil mixture, indicating an improvement of metabolic efficience or shift of microbial community, which are in need of further investigation.