Effects of plant functional group and reclamation treatments on microbial networks and nutrient limitation in initial soil developed on spoil heaps after hard coal mining

Plant functional groups (PFGs), together with the type of reclamation treatment applied, can influence the changes in soil nutrient availability. The stoichiometric imbalance between resources can alter the activity and structure of microbial communities which play a crucial role in regulating carbon and nutrient cycling in initial soil ecosystems. However, the response of microbial networks within the soil food web in spoil heaps to stoichiometric imbalances has not yet been investigated. In this study, we examine how soil microbial networks webs respond to elemental limitation in unreclaimed sites on carboniferous bare rock and reclaimed with topsoiling in the presence of two PFGs, i.e. grasses and forbs, which are commonly used in the spoil heap reclamation processes. To understand these relationships, soil physicochemical properties, enzyme stoichiometry, abundances and community compositions of soil bacteria and fungi were investigated. We found that the availability of P most limited the formation of soil microbial networks. Both types of PFGs stimulated the formation of complex soil microbial networks but didn't affect the nutrient limitation of the soil microbial community differently. Soil microbiome in bare rock was P-limited and characterized by disturbed structure and lower diversity. Topsoiling increased biodiversity and improved the structure of soil microbial communities. The application of topsoiling showed no positive effect on the stability and complexity of the soil microbial networks. Our findings indicate that P-limitation needs to be considered in understanding and predicting biogeochemical cycles on unreclaimed heaps where spontaneous succession occurs. Topsoiling appears to be a good way to reclaim heaps with an adequate nitrogen supply to the soil.