Coapplication of biochar and nitrogen fertilizer affects soybean yield by regulating the microbiome and metabolite profile of rhizosphere soil

Biochar has been recognized as an effective soil amendment in recent years. Biochar combined with nitrogen fertilizer has been proven to solve the problem of low nitrogen fertilizer utilization efficiency, thereby increasing crop yield. However, how biochar combined with nitrogen fertilizer affects the growth of soybean is not clear. Therefore, in this study, high-throughput sequencing and nontargeted metabolomics techniques were used to investigate the changes in soil physicochemical properties, soybean yield and yield components under different ratios of combined biochar and nitrogen fertilizer. The results revealed that, at equal nitrogen levels, cation exchange, conductivity and microbial carbon content increased at the beginning of the increase in biochar dosage but began to decrease after a certain level was reached; biochar with nitrogen fertilizer altered the diversity and composition of microbial communities and affected bacteria to a greater extent than fungi did. Metabolomic analysis revealed that most of the metabolites upregulated after biochar and nitrogen fertilization were lipids, lipid-like molecules and organoheterocyclic compounds, and the differentially abundant metabolites were significantly enriched in metabolic pathways such as glycerophospholipid metabolism, ABC transporters and other metabolic pathways. Partial least squares pathway modeling analysis revealed that the application of biochar combined with nitrogen fertilizer significantly promotes soil physicochemical properties and soybean yield. This study can bridge the gap in the current assessment of the effects of biochar and nitrogen fertilization on the soil microenvironment and crop yield and provides important scientific value and guidance for soybean cultivation strategies.