Interactions Between Mycorrhizal Fungi and Mycorrhiza Helper Bacteria: Mechanisms, Ecological Functions, and Potential Applications in Sustainable Agriculture and Ecological Restoration

The interaction between mycorrhizal fungi and mycorrhiza helper bacteria (MHB) constitutes a critical symbiotic interface that drives key functions within terrestrial ecosystems, profoundly influencing plant nutrient acquisition, stress resilience, and soil ecological processes. Although mycorrhizal symbiosis has been extensively studied, the complex interactive network between these fungi and MHB—which act as functional “enhancers” and “stabilizers”—and its systemic application potential remains insufficiently integrated and elucidated. This review aims to provide a comprehensive overview of advances in this field. First, it delineates the functional traits of major mycorrhizal fungal types and their inherent functional reliance on MHB. Subsequently, it dissects the core mechanisms underlying mycorrhizal fungi–MHB interactions through four interconnected dimensions: signal recognition, nutrient exchange, physical association, and defensive synergy. This analysis reveals the foundation for constructing a stable plant–fungus–bacteria functional continuum. Furthermore, the review comprehensively evaluates the empirical applications and demonstrated efficacy of this interactive system in enhancing agricultural productivity, promoting forestry cultivation, and advancing ecological restoration. Finally, by identifying prevailing research gaps spanning molecular mechanisms to field applications, it offers a critical perspective on future research priorities. It also discusses strategies for fostering interdisciplinary innovation to accelerate biotechnology development based on this symbiotic partnership, aiming to provide novel microbial solutions for addressing global challenges such as agricultural sustainability and ecosystem recovery.