Facilitation and Antagonism in Mycorrhizal Networks

Abstract

Arbuscular mycorrhizal (AM) fungi are a group of soil and root inhabiting fungi that represent an ancient plant-fungi symbiosis. These fungi interconnect multiple plant individuals and species simultaneously generating a complex fungal network belowground that plays a significant role in shaping plant community composition and ecosystem productivity. However, the underlying mechanisms as to how AM fungal networks and their diversity influence plant performance and community structure are not always predictable and are frequently debated. Although all potential plant hosts may be able to associate with all AM fungi, plant-AM fungal associations can result in a range of AM fungal facilitative and antagonistic effects on plants. Although the facilitative effects of AM fungi have long been studied, the extent and mechanisms of AM fungal antagonistic effects are much less understood. Moreover, AM fungi are observed to vary in their functional properties and temporal patterns adding further complexity to the potential mechanisms by which AM fungi and the diversity of AM fungi determine plant community composition and productivity through their facilitative and antagonistic effects on plants. Here we review the potential mechanisms by which AM fungal communities facilitate greater diversity and productivity in plant communities, as well as the potential mechanisms by which AM fungi may be antagonistic to plant performance. Specifically we address how AM fungal communities might facilitate greater plant community performance through functional complementarity among AM fungi as a result of functional, spatial and temporal niche segregation. We also address facilitative and antagonistic aspects of AM fungi through their ability to allocate resources among plant community members that consequently facilitates plant recruitment and alters plant-plant competitive outcomes. By considering the multiple facets by which AM fungi may be facilitative or antagonistic to plants we identify potential knowledge gaps in mechanistically predicting how AM fungal communities shape plant community composition and maintain ecosystem productivity.