Fungal-bacterial composition and network complexity determine soil multifunctionality during ecological restoration

Ecological restoration has been considered an efficient strategy for improving ecosystem functioning. However, the patterns and driving forces of soil multifunctionality (MF) during ecological restoration are poorly understood. Here, we examined multiple soil functions related to climate regulation (carbon [C] stock and C mineralization), nutrient supply (nitrogen [N] stock, phosphorus [P] stock, total inorganic N, and available P concentration), and biogeochemical cycling (net N and P mineralization), and explored how the soil MF developed during ecological restoration (i.e., grassland → shrubland → forest) after agricultural abandonment. Our results showed that forest supported significantly higher soil MF than grassland and shrubland. The development of soil MF could not be explained by microbial α-diversity, as we did not observe significant changes in bacterial and fungal α-diversity during ecological restoration. Microbial community composition altered significantly during ecological restoration. Notably, the changes in abundant taxa (i.e., Alphaproteobacteria and Agaricomycetes) positively affected soil MF, whereas the rare taxa negatively correlated with soil MF across different stages of ecological restoration. In addition, our result showed that the complexity of meta-community co-occurrence networks declined with ecological restoration. We further demonstrated that higher soil MF was supported by a less complex microbial network, and this influence was held when soil abiotic drivers (pH and stability of soil aggregates) were included simultaneously. In conclusion, our work suggests that ecological restoration after agricultural abandonment plays an essential role in improving soil MF, and it emphasizes the importance of soil microbial composition and network complexity in regulating the soil MF.