Untargeted metabolomics to study changes in soil microbial community in response to tillage practices

Soil microbes are the main drivers of nutrient turnover in agro-ecosystems. The series of biochemical processes involved by these microorganisms are inseparable from the regulation of metabolites in the root-zone soils. Therefore, understanding the evolution of microbial communities driven by root-zone soil metabolites will help optimize agricultural management practices. Based on a field experiment, we explore the changes in soil properties, microbes, and metabolites under three tillage practices such as no-tillage with straw mulching (NTS), rotary tillage, and plough tillage with straw returning (RTS and PTS) based on untargeted metabolomics. We found that NTS helped to enhance nutrient contents and enzyme activities in the 0-20 cm soil layer. Specifically, compared with RTS and PTS, NTS increased grain yield by 6.4 % and 8.5 %, and SOC by 13.3 % and 5.7 %, respectively, but decreased pH by 2.8 % and 1.1 %. In addition, compared with NTS, RTS and PTS decreased the fungal richness by 16.5 % and 8.1 %, and decreased the fungal shannon index by 16.4 % and 9.2 %. However, tillage practices did not result in substantial differences in the alpha diversity of bacterial community. Both bacterial and fungal community composition were substantially affected by tillage practices and they were both significantly correlated with soil metabolites. In the symbiotic networks, NTS significantly increased the abundance of microorganisms with high connectivity, while RTS significantly increased the concentration of metabolites with high connectivity. Amino acids, as the main drivers, were significantly and positively associated with bacterial and fungal community composition, mainly enriched in the metabolic pathways of D - glutamine and D - glutamate metabolism and arginine and proline metabolism, and correlated with soil properties negatively and carbohydrates positively, directly or indirectly affecting soil microbial community composition. Our findings would provide new insight into metabolomics for the in-depth understanding of the metabolic mechanism for soil microbial community changes in dryland wheat fields under different tillage practices.