Hairy Vetch Intercropping Attenuates Mycorrhizal Benefits to Walnut Growth and Soil Organic Carbon Sequestration via Glomalin

Intercropping is a prevalent soil management strategy within walnut orchards, while its impacts on the functionality of arbuscular mycorrhizal fungi (AMF) in walnuts ( Juglans regia ) remain unclear, especially concerning soil carbon (C) sequestration via glomalin-related soil protein (GRSP). This study aimed to explore the effects of inoculation with the AMF species Diversispora spurca and intercropping with hairy vetch ( Vicia villosa ) on walnut biomass accumulation, soil water-stable aggregate (WSA) stability, leaf and root C (C leaf and C root ) content, soil organic carbon (SOC), GRSP, and GRSP-contained C (C GRSP ), in addition to the contribution rate of C GRSP to SOC. The intercropping treatment significantly inhibited root mycorrhizal colonization rate, soil hyphal length, and spore density in AMF-inoculated walnut plants. Individual AMF inoculation, rather than individual intercropping, significantly promoted shoot and root biomass accumulation, WSA stability, SOC, C leaf and C root , the levels of purified easily extractable (EEG), difficultly extractable (DEG), and total GRSP (TG), as well as their C contents. The combination treatment (AMF inoculation + intercropping) displayed limited benefits, improving just WSA stability without yielding synergistic advantages over individual treatments. Arbuscular mycorrhizal fungal inoculation significantly increased C GRSP , especially C DEG , while individual intercropping resulted in a reduction of C DEG . The combination treatment elevated both C DEG and C TG , albeit to a lesser extent than AMF alone. The contribution rates of C EEG , C DEG , and C TG to SOC were 0.33% − 0.53%, 1.16% − 1.78%, and 1.49% − 2.31%, respectively. Although AMF inoculation significantly increased the contribution rates of C DEG and C TG to SOC, this effect was diminished when combined with intercropping. Notably, C DEG , rather than C EEG , exhibited a significantly positive correlation with SOC and WSA stability. The findings provide new insights into the mechanisms of SOC sequestration in walnuts grown in controlled environments and offer a theoretical basis for the application of AMF in walnut cultivation.