Mechanism of ion homeostasis mediated by arbuscular mycorrhizal fungi in plant responses to saline-alkaline stress.

Against the backdrop of global climate change, soil salinization and alkalization have emerged as major environmental constraints on sustainable agricultural development. Salt-alkali stress primarily disrupts cellular ion homeostasis, resulting in excessive accumulation of ions such as Na+ and Cl- and deficiencies of essential nutrient ions including K+ and Ca2+, with negative consequence on plant growth and development. Arbuscular mycorrhizal fungi (AMF), a widespread group of beneficial soil microorganisms, could establish symbiotic associations with most terrestrial plants and enhance the tolerance of host plants to salt-alkali stress through sophisticated mechanisms of ion regulation. Although increasing attention has been paid on AMF-mediated ion regulation in recent years, a systematic integration of the underlying mechanisms from the microscopic to the macroscopic level remains lacking. We summarized the key mechanisms by which AMF regulate ion uptake, transport, and metabolism of plants under salt-alkali stress, including selective ion absorption and enhanced nutrient acquisition by extraradical structures, nutrient exchange and ion compartmentalization mediated by intraradical structures, improvement of the rhizosphere environment by AMF-derived substances, and the regulation of Na+ efflux and translocation, Na+ and Cl- sequestration, as well as K+ and Ca2+ uptake and allocation. Collectively, these mechanisms elucidate how AMF alleviates ion toxicity and nutrient imbalance under salt-alkali stress, and provide a theoretical basis for the application of AMF in enhancing crop salt-alkali tolerance from the perspective of ion homeostasis.