Abstract: Mycorrhizal fungi serve as key regulators of underground common networks of plants, playing a critical role in maintaining plant species coexistence and biodiversity through “carbon-nutrient/water” exchange and multi-species interconnections. With advances in mycorrhizal ecology, research on the effects of mycorrhizal fungi on plant-plant interactions and their underlying mechanisms has deepened. To systematically summarize the roles and mechanisms by which mycorrhizal fungi maintain plant species coexistence, this review synthesizes current research on how mycorrhizal fungi influence plant species coexistence and analyzes emerging trends in this field. Mycorrhizal fungi maintain plant species coexistence primarily through the following pathways: (1) driving differentiation in plant strategies for water and nutrient uptake and utilization, thereby enhancing resource use efficiency, (2) mediating nutrient redistribution via common mycorrhizal networks to alleviate competition among plants, (3) enhancing plant resistance to biotic and abiotic stresses through physical barriers, induced resistance, and defensive signal transfer, and (4) recruiting mycorrhizal helper bacteria (MHB) to form multi-scale mutualistic networks, thereby contributing to the stability of soil ecosystems. At the same time, mycorrhizal fungi are themselves influenced by plant species coexistence. The diversity and coexistence context of host plants can regulate fungal diversity, promote diversification in mycorrhizal resource acquisition strategies, and further enhance the stability of the plant fungal symbioses. Future research should focus on in situ experiments and multifactor coupling studies, elucidate molecular signaling and nutrient exchange mechanisms within mycorrhizal symbiosis, quantify the ecological functions of mycorrhizal networks, and validate their modes of action. Additionally, more attention should be directed toward understudied types of mycorrhizal associations.

Key words: species coexistence, mycorrhizal networks, nutrient allocation, plant stress resistance, mycorrhiza helper bacteria