Nutrient allocation in mycorrhizal-plant-herbivore interactions

Arbuscular mycorrhizal fungi (AMF) engage in complex interactions with plants and both aboveground (AG) and belowground (BG) herbivores, collectively shaping plant fitness, defense strategies, and AM fungal community assembly. A central question within these interactions concerns the role of nutrients. Nutrient allocation within the AMF-plant-herbivore triad is a pivotal yet poorly understood driver of multitrophic interactions. This review synthesizes evidence on how carbon, nitrogen, and phosphorus are partitioned between plant mutualistic and antagonistic partners, highlighting critical knowledge gaps regarding the distribution of AMF-mediated nutrients across ecological compartments under combined AG and BG herbivory. Further, this review states that nutrient-derived primary and secondary metabolites exert systemically asymmetric effects on AG and BG herbivores through the plant’s metabolic network. These changes can trigger cascading responses in plants and herbivores, altering their performance in concert with abiotic and biotic factors such as plant and herbivore identity, feeding mode, arrival sequence, and damage intensity. Finally, we conclude that plant defense strategies (resistance vs. tolerance) and herbivore performance are shaped by context-dependent nutrient allocation, necessitating the integration of isotopic tracing, metabolic analysis, and mechanistic modeling to quantitatively analyze the underlying pathways and predict these dynamics under global change.