Returning farmland to forests and grasslands promotes soil quality restoration in Northeast China: Evidence from soil nitrogen cycle

Soils contain a diversity of microbial communities involved in the nitrogen cycle (N-cycling), which are essential for maintaining the quality and health of soil. However, agricultural intensification has led to land use conversion, which has had a negative impact on ecosystems. There is a lack of research on the whole N-cycling process in land use change under the context of ecological restoration. Here, we utilized qPCR (Quantitative Real-time PCR) and MiSeq techniques to analyse the functional genes related to nitrogen fixation (nifH), nitrification (AOA and AOB) and denitrification (norB and nosZ) to explore whether the conversion of farmland to forest and grassland affects changes in microbial communities involved in the N-cycling. We reveal the potential effects of ecological restoration on microbial community function in the N-cycling through soil properties. Specifically, land use conversion increased N-cycling gene abundance and changed in the N-cycling microbiome exhibited. The ecological restoration has increased the importance of stochastic processes in the assembly of AOA and AOB communities and affected the ecological cluster of soil N-cycling microbial network. Overall, these findings reveal specific microbial processes and interactions that influence the soil N-cycling and provide insights for future research on sustainable land management approaches that support soil health.