Long-Term Organic Amendment Regimes Reshape Soil Micro-Food Web Structure and Multitrophic Co-Occurrence Networks in a Wheat–Maize Rotation

Abstract

Organic amendments can improve soil C storage, nutrient availability, and crop production, particularly in purple soils with low organic matter and weak nutrient retention. They may also alter soil micro-food web processes. However, how different amendments affect bacteria–fungi–nematode associations remains unclear. We hypothesized that, relative to mineral fertilization alone, organic amendments would improve soil nutrient conditions, reshape bacterial and fungal communities, and increase microbivorous nematode abundance, whereas combined organic–mineral inputs would increase multitrophic co-occurrence network complexity. In a long-term wheat–maize rotation, soils were sampled in both seasons in 2023 under seven treatments: no fertilization (NF), mineral fertilization (NPK), manure (OM), straw return (RSD), mineral fertilization combined with manure (OMNPK), mineral fertilization combined with straw return (RSDNPK), and mineral fertilization combined with biochar (BCNPK). Among the organic amendment treatments, only RSD reduced wheat and maize yields relative to NPK. Fertilization mainly affected microbial community composition and nematode trophic structure, while microbial α diversity changed little. Network organization differed among fertilization regimes and between crop seasons. This study provides new insights into how long-term organic amendment regimes differentially regulate crop productivity, soil resource conditions, and soil micro-food webs, and advances our understanding of belowground multitrophic responses across wheat and maize seasons.