AM fungi reshape rhizosphere microbiome and N-cycle genes under soda saline-alkali stress, implying nitrogen retention

Soda saline-alkali stress severely constrains soil nitrogen availability, yet the mechanisms by which arbuscular mycorrhizal (AM) fungi regulate nitrogen cycling through the rhizosphere microbiome remain poorly understood. In this study, a microcosm experiment was established using one-year-old Elaeagnus angustifolia L. seedlings as the host plant, and inoculation with Rhizophagus intraradices resulted in mycorrhizal colonization rates of 72.80% and 78.00% under mild and moderate soda saline-alkali stress, respectively. Metagenomic sequencing revealed that inoculation significantly increased NH 4 + -N, microbial biomass nitrogen, and the activities of nitrogen-acquiring enzymes, while decreasing NO 3 − -N concentrations. Community analysis revealed that AM fungi enriched nitrogen mineralizing and DNRA related bacterial genera, and concurrently suppressed ammonia oxidizing taxa. At the gene level, inoculated treatments exhibited higher abundances of assimilatory nitrate reduction and DNRA genes, lower abundances of nitrification genes across all steps, and greater representation of amino acid metabolism pathways. These findings indicate that AM fungal inoculation is accompanied by a reconfiguration of the rhizosphere microbiome and nitrogen-cycling gene abundance. The observed pattern of enriched DNRA potential and depressed nitrification potential coincides with ammonium accumulation and microbial nitrogen retention, suggesting a microbial-mediated capacity to alleviate nitrogen limitation under soda saline-alkali stress.