Reconciling disparate responses to grazing in the arbuscular mycorrhizal symbiosis

Grazers and the AM symbiosis share a long evolutionary history, grazing effects on arbuscular mycorrhizal (AM) symbioses remain unresolved despite decades of dedicated research. Studies show fungal growth to increase, decrease and remain unchanged in response to grazing pressure. We argue that studies focusing on single fungal traits may fail to detect the full extent of grazing effects on the AM symbioses. Further, carbon limitation may be mediated by resource levels and grazing intensity and the possibility of herbivory-tolerant AM fungi. In this review, we argue that understanding carbon flux between host and fungus is essential to understand the full extent of grazing on the AM mutualism.