Microbial diversity drives soil multifunctionality along reclamation chronosequence in an opencast coal mine

Plantation reclamation can improve soil microbial diversity and soil multifunctionality in the reclaimed coal mine. However, with the reclamation years, how restoration of microbial communities promotes restoration of soil multifunctionality is not clear. Here, we investigated the microbial diversity and soil physicochemical properties and soil enzyme activities of different reclamation years in the reclaimed coal mine afforested with Chinese pine (Pinus tabuliformis). We chose six soil physicochemical properties (soil BD, pH, TC, TN, soil labile carbon [LC1], and [LC2]) pools and four soil enzyme activities (invertase, dehydrogenase, polyphenol oxidase, and urease) as soil multifunctionality indicators. Firstly, we compared the difference of soil microbial alpha diversity and soil physicochemical properties and soil enzyme activities of the different reclamation years and studied the changes of soil multifunctionality with the reclamation years. Secondly, the relationship between soil microbial diversity and soil multifunctionality was compared by fitting five different functions (logarithmic, linear, M-M, power, and exponential). Thirdly, we analyzed the driving effects of soil microbial diversity on soil multifunctionality at different threshold levels. Finally, the important driving factors on soil multifunctionality were explored. The results confirmed there were significant differences in soil microbial alpha diversity of different reclamation years, and the later stage was significantly higher than the initial stage of reclamation. Soil multifunctionality increased significantly with the reclamation years, and the soil multifunctionality related to carbon and nitrogen cycle increased more significantly. Microbial communities have strong driving effects on soil multifunctionality. Bacterial diversity was positively correlated with soil carbon cycle and nitrogen cycle function and soil multifunctionality in a nonredundant fashion. Random forest and structural equation modeling analyses showed that bacterial diversity was the most important biotic factor. Reclamation years had indirect effects on soil multifunctionality by affecting microbial communities. Soil microbial diversity had strong driving effects on soil multifunctionality. The results provided empirical evidence that the protection of biodiversity is crucial for maintaining ecosystem functions in reclaimed coal mine ecosystem.