Improvement of soil organic carbon turnover and microbial community niche differentiation with the addition of commercial organic fertilizer in wheat–green manure systems

Abstract

Background and Aims Green manure and commercial organic fertilizer are widely used in agricultural production to improve farmland soil carbon reserves; however, their combined impact on soil organic carbon (SOC) turnover is not yet fully understood. Methods We designed a potted wheat-soybean green manure system to investigate the impact of different fertilization treatments on SOC content and structure, extracellular enzyme activity community characteristics of fungi and bacteria after wheat harvest in 2021 and 2022. Results The results indicated that compared to chemical fertilization (CF), following the addition of soybean green manure, organic fertilization (OF) led to a 12.5% increase in SOC content, 19.3% increase in the highly active organic carbon (HAOC) fraction and 10.2% increase in the recalcitrant organic carbon (ROC) fraction. Additionally, there was a 16.1% increase in the alkyl-C to O-alkyl-C ratio and a 63.4% decrease in aliphatic C to aromatic C ratio. Significant increases were observed in the contents of extracellular enzyme, soil total nitrogen, alkali-hydrolyzable nitrogen, available phosphorus, available potassium, microbial carbon and microbial nitrogen. The abundance of observed species of fungi and bacteria significantly decreased in OF compared with that in CF, with the symbiotic network indicating a higher level of positive interaction between fungi and bacteria in OF. Conclusion OF primarily altered soil enzyme activity by influencing soil nutrient contents, resulting in the decomposition of labile organic carbon and an increase in microbial residue biomass, without affecting ROC formation or humification degree. These findings can maximise SOC content in organic agriculture through land use and fertilization techniques.