## 4 Discussion  
Soil microorganisms play a key role in many soil processes and the delivery of essential soil ecosystem services. The development of microbial diversity is crucial to facilitate a sustainable ecosystem in post-mining soils [6; 18]. In this study, the overall microbial diversity was low and only the treatments with river sediment (lime1 + Rs, lime1 + NPK + Rs, lime2 + Rs, lime2 + NPK +  
Figure 3: Bioplot of the principal components on soil nutrient and microbial properties (n = 48). (**a**) Microbial properties, (**b**) Nutrient profiles. PC1: the first principal component; PC2: the second principal component. The most important parameters for the definition of the two components are shown on the edge of each axis, indicating the direction in which the value of the parameter increases. Symbols: control1 (\(\Circuit\)), control 2 (\(\blacksquare\)), lime1 (\(\triangle\)), lime1 + NPK (\(\triangledown\)), lime1 + P (\(\triangledown\)), lime1 + Rs (\(\Box\)), lime1 + NPK + Rs (\(\Diamond\)), lime2 (\(\blacktriangle\)), lime2 + NPK (\(\blacktriangledown\)), lime2 + P (\(\bigstar\)), lime2 + Rs (\(\blacksquare\)), lime2 + NPK + Rs (\(\bullet\)). Rs) significantly increased microbial diversity relative to the controls (Figure 1a). In river sediment, organic matter-decomposing _Escherichia_, nitrogen-metabolizing _Nitrosopumillus_ and sulphate-reducing _Desulfococcus_ genera were reported to be abundant and their abundance were found to be statistically associated with the redox state of soil and C and N turnover [36]. Therefore, the addition of river sediment cannot only ameliorate the mine soil physic-chemical conditions (Table 1), but also speed up the shift of soil microbial community (Figure 1a). It was argued in the literature that driving factors for the evolution of a microbial community structure largely depend on the environmental gradient to which the communities are subjected or imposed under experimentally [16]. Organic C, N availability, pH, salinity and many other abiotic factors influence the microbial community in soil [37; 38; 39]. A similar result was also reported by [PERSON] et al. [9] who found that the addition of native soil to Cu-Pb-Zn tailings significantly changed the composition and structure of microbial communities. Therefore, incorporation of amendments may fast-track the establishment of microbial community and initiate the rehabilitation of biogeochemical process of mine soils [2; 9]. In addition, soil microbial activity and biomass all vary with different types of remediation. In this study, the added amendments significantly increased microbial activity and microbial biomass C (Figure 1). This is in accordance with the findings of [PERSON] et al. [40], who employed calcium carbonate and pig slurry manure as amendments to restore a bare acidic tailings pond. These authors found that the amendments increased pH up to neutrality and significantly enhanced both soil microbial biomass and activity. The explanation for their results was that the amendments ameliorated soil conditions such as pH, metal availability, organic matter and nutrient status, all of which impact on ecosystem function [40]. In our study, the application of amendments successfully reduced acidity and heavy metal availability (see [PERSON] et al., [17] for details) and increased the values of OM, TN, TP, TK, NH\({}_{4}\)+-N, NO\({}_{3}\)-N, AP and AK (Table 3). A suitable pH, low heavy metal toxicity and enhancement of nutrient status after remediation were the most determining factors for soil microbial community responses. Soil enzymes play a fundamental role in nutrient mineralization, organic matter decomposition and nutrient cycling and their activities have increasingly been used to evaluate the success of remediation efforts [14]. In the present study, the application of amendments significantly increased dehydrogenase, cellulase and urease activities (Figure 2), probably attributable to neutralization and amelioration by lime, river sediment and NPK fertilization or phosphate alone.