Background and aims <p>Salinization poses a significant threat to global agricultural sustainability. While arbuscular mycorrhizal fungi (AMF) are known to enhance plant salt tolerance, their mechanisms for regulating nutrient distribution across plant organs and their impact on soil enzyme activity remain unclear. This study investigates the role of AMF under saline-alkaline stress using <i>Amaranthus hypochondriacus</i> as a model plant.</p> Methods <p>A symbiotic system involving <i>Funneliformis mosseae</i> and <i>A. hypochondriacus</i> was established. Plants were subjected to saline-alkaline stress with at 100&#xa0;mmol/L (pH = 9.38, EC = 5.43 dS/m). Nutrient content, ion balance, and rhizosphere soil enzyme activity in both the plants and soil were measured. Additionally, the chemical stoichiometry of the plants and soil was determined.</p> Results <p>Under saline-alkaline stress: (1) <i>F. mosseae</i> enhanced biomass accumulation in all plant organs and optimized nutrient uptake efficiency, reducing Na⁺ content in the roots and leaves by 4.10% and 5.64%, respectively. (2) <i>F. mosseae</i> increased the Ca²⁺/Mg²⁺ ratio in all plant organs (6.89%—78.60%) and raised the K⁺/Na⁺ ratio in the roots by 10.17%, while decreasing the N/P ratio in the leaves by 22.25%. (3) <i>F. mosseae</i> boosted enzyme activity in the rhizosphere soil (4.23% to 78.68%). It increased olsen phosphorus content in saline-alkaline soil by 45.30%, reduced microbial P limitation, and enhanced C limitation.</p> Conclusions <p><i>F. mosseae</i> enhances <i>A. hypochondriacus</i> tolerance to saline-alkaline stress by modulating nutrient allocation in plant organs and improving rhizosphere soil enzyme activity. This study provides a new theoretical basis for utilizing AMF to improve plant growth in saline-alkaline soils.</p>