## 4 Discussion  
Soil nutrient conditions, pH levels, and heavy metal types and content typically affect the community structure of soil microbes [19]. A large number of studies have reported that soil fungal communities are affected by many environmental factors [20]. [PERSON] et al. [21] found that the most important factors that affect the quantity and diversity of soil fungi in a _Taxus chinensis_ forest in Tianshui City, Gansu Province, China, were soil pH and SWC. In our study, we found that the relative abundance of Zygomycota was affected by soil pH (Figure 4), which is consistent with results from [PERSON] et al. We found that the order of relative abundance of soil fungi on a phylum level was Ascomycota, having the highest relative abundance, followed by Zygomycota, Basidiomycota, and Chytridiomycota (Figure 2A). The main reason for this could potentially be that most Ascomycota members are saprophytic and therefore the main decomposers in soil. Saprophytic Ascomycota are able to decompose large amounts of refractory organic matter, such as lignin and keratin, and also play an important role in nutrient cycling. Accordingly, Ascomycota were found to be the dominant fungal species in the soil of the tailings dam and they were also the dominant phylum in most soils [22; 23]. Some studies reported that TN and pH played very important roles in changes of soil fungal community composition and fungi prefer to live in slightly acidic environments [21; 24]. In our study, the pH level of the tailings dam soil was 7.9, which was weakly alkaline. Our results showed that the relative abundances of Ascomycota and Basidiomycota were negatively correlated to soil pH and the relative abundance of Ascomycota was also positively correlated to TN (Figure 4). In addition, [PERSON] et al. [20] also found that pH decreased with an increase in TN content; thus, Ascomycota decreased significantly. However, Ascomycota was still the dominant phylum in soil, with the highest relative abundance. The reason for this could potentially be that Ascomycota is significantly affected by TN content. On the other hand, Ascomycota is one of the most abundant fungal phyla, which is able to access nutrition through various means, including saprophytic, parasitic, and symbiotic methods. In addition, N is the main source for microbial nutrition in soil [25], taking part in the synthesis of proteins, nucleic acids, and macromolecular substances as well as supplying a large number of essential elements for microbial growth and its metabolic processes [26]. At the same time, N also plays an important role in the material cycle, energy flow, and multi-element balance of ecosystems and its effect on microbial growth exceeds that of soil pH and other environmental factors [27]. Therefore, Ascomycota can still be the dominant phylum in a weakly alkaline environment. In addition, the C/N ratio of soil has been reported to be an important influencing factor of microbial communities [28]. In our study, the C/N ratio of soil was 27.41, and results from PCA showed that the C/N ratio of soil was not the main influencing factor for fungi on a phylum level (Figure 4). The soil of the tailings dam was formed by means of the accumulation of ore sand, which contains a significant amount of heavy metals. According to the third-level of the soil quality standard, soil Cd (5.27 mg\(\cdot\)kg\({}^{-1}\)) and Cu (553.53 mg\(\cdot\)kg\({}^{-1}\)) exceeded the standard in this region. The relative abundance of Basidiomycota was positively correlated to Cd and negatively correlated to Cu. The main reason was that Cd is a nonessential element for microbial growth. Moreover, heavy metals could promote a certain range of microbial growth before growth is inhibited as concentrations increase [29]. Although both Cd and Cu exceeded the standard, Cd did not reach the maximum concentration of Basidiomycota tolerance and hence still promoted the phylum's growth.