Arbuscular mycorrhizal fungi and hydraulic-thermal coordination under combined drought and heat stress in soybean.

Concurrent drought and heat waves impose a non-additive physiological constraint on soybean (Glycine max (L.) Merr.), creating a physiological trade-off between hydraulic preservation, which favors stomatal closure to prevent cavitation, and evaporative cooling, which requires sustained stomatal opening to mitigate thermal damage. This review synthesizes physiological and molecular evidence to develop a conceptual framework for understanding how arbuscular mycorrhizal fungi (AMF) may influence plant responses under combined stress. Available evidence indicates that improved plant water status is the most direct explanation for higher stomatal conductance in mycorrhizal plants under combined stress, which may in turn support transpirational cooling. Signaling responses may also contribute, but their roles have not been tested independently of differences in plant water status, particularly in soybean. Ultimately, integrating AMF-mediated physiological resilience into agricultural management may support strategies for maintaining crop performance under increasingly frequent climate extremes.