Microbial control of soil DOM transformation during the vegetation restoration in the Loess Plateau

This study focuses on the changes and associations between soil dissolved organic matter (DOM) and microbial communities during the vegetation restoration process (abandoned farmland, 5, 15, 20, and 40 years of vegetation restoration) in grasslands on the Loess Plateau of China. High-throughput sequencing was used to determine microbial community and composition, and Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR-MS) was used to obtain specific information on DOM molecules, explored the specific relationship between DOM chemical diversity and microbial communities during vegetation restoration. Vegetation restoration promotes increased diversity and complexity of soil DOM molecules. During vegetation restoration, the content of recalcitrant DOM components (lignin/carboxyl-rich alicyclic molecules (CRAM)-like structures, aromatic structures, tannins) increased, but the content of labile DOM (aliphatic/proteins, carbohydrates, lipids) decreased. The alpha diversity of microbial communities varied significantly with niche width. Stochastic processes shaped the bacterial community, while deterministic processes dominated the fungal community. Chloroflexi, Actinobacteria, and Ascomycota were negatively correlated with most lignin/CRAM-like structures and tannins, whereas Acidobacteria and Proteobacteria were positively correlated. Vegetation restoration promotes an increase in recalcitrant DOM content (difficult for microorganisms to degrade) and facilitates soil carbon sequestration. Microorganisms are able to consume and form DOM molecules and play a huge role in the transformation of soil DOM. This study increases the understanding of the potential link between microbes and DOM fate during grassland vegetation restoration, and emphasizes the necessity of “Grain-for-Green” project to reduce carbon emissions in the context of global climate change.