Increased nitrogen accumulation in mulberry trees due to the secretion of glomalin-related soil protein induced by arbuscular mycorrhizal fungi

In the initial stages of restoring areas affected by rocky desertification, plant survival is strongly influenced by nitrogen nutrition. Mycorrhization is a unique type of inter-root engineering that improves nitrogen acquisition efficiency by plant roots. We selected potted mulberry trees inoculated, two dominant arbuscular mycorrhizal fungi (AMF) with Funneliformis mosseae (Fm) and Rhizophagus intraradices (Ri), to clarify the effects of AMF on the root nitrogen content of mulberry trees. Meanwhile, the key factors of soil nitrogen changes caused by AMF were analyzed, based on the primary role of soil nitrogen as the source of root nitrogen. Simultaneously, the potential of AMF to promote the acquisition of different forms of nitrogen by mulberry roots was investigated. Our findings indicate that the inoculation of mulberry plants with Fm and Ri, improved plant height and increased nitrogen accumulation in the roots and shoots. Additionally, AMF regulates nitrogen transformation, significantly increasing soil nitrate nitrogen (NO₃⁻-N) and dissolved organic nitrogen (DON) levels. The results indicated that soil NH₄⁺-N, NO₃⁻-N, and DON contributed to the observed changes in root nitrogen accumulation. The largest contribution (22.0 %) to the overall effect size was made by NO₃⁻-N. AMF stimulated soil microbial activity and significantly increased soil glomalin-related soil protein (GRSP), enzyme activity, and soil microbial biomass (SMB). Urease activity and microbial biomass carbon (MBC) both increased exponentially by 118.7 % and 115.2 %, respectively. Higher GRSP, enzyme activity, and SMB were positively correlated with changes in soil nitrogen patterns, and GRSP had the most significant effect on changes in the soil nitrogen dynamics. Our study confirmed that inoculation with AMF not only regulates soil nitrogen dynamics but also diversifies plant nitrogen sources. This is achieved by increasing plant growth and enhancing soil microbial activity. Ultimately, this enhances plant root nitrogen nutrition. Therefore, AMF promote root nitrogen accumulation and enhance root nitrogen uptake through GRSP-regulated soil nitrogen, providing a theoretical basis for the management of rocky desertification.