Differential effects of roots and symbiotic fungal hyphae on soil organic carbon under straw incorporation

Plant roots and their associated microbes, for example, arbuscular mycorrhizal fungi (AMF) regulate soil organic carbon (SOC) dynamics through microbial mediation and physical stabilization of organic matter. However, the relative contribution of roots and AMF to SOC formation and how agricultural practices affect the effects of root pathway and AMF hyphae pathway remain poorly quantified. The net effects of root pathway and hyphae pathway on SOC fractions were explored using in vivo in‐growth core technique under three farming scenarios (no‐till straw removal, rotary tillage straw return and ditch‐buried straw return). Root pathway decreased SOC but hyphae pathway increased it under straw removal. In contrast, under straw incorporation, SOC increased in the root pathway but was decreased in the hyphae pathway. Compared to the hyphae pathway, the root pathway exhibited higher cellulase activity and microbial biomass carbon but lower peroxidase activity. Notably, the hyphae pathway consistently suppressed SOC mineralization, whereas the root pathway had minimal or inconsistent effects on it. Furthermore, negative correlations were observed between the root pathway and hyphae pathway regarding SOC content, its fractions and enzyme activities, highlighting their contrasting roles in regulating carbon dynamics. Synthesis and applications . These findings indicate that AMF and crop roots adopt distinct mechanisms influencing SOC accumulation. Moreover, agricultural management practices, such as straw incorporation, can alter the magnitude of these contrasting effects by differentially regulating root pathway and hyphae pathway processes.