Does ectomycorrhizal fungal biodiversity affect tree growth?

Abstract

Ectomycorrhizal fungi (EMF) are ubiquitous tree-associated symbionts aiding plant nutrition and growth in forests from the tropics to the boreal zone. They colonize tree roots and provide >70% of growth limiting nutrients, but with >10,000 EMF species, tree growth rates may vary depending on the composition and diversity of associated EMF communities as a consequence of the diversity of fungal functions and niches. While ample research demonstrates that EMF species differentially influence host plant growth in experimental inoculation studies, disparate insights from experimental and observational studies in the field must be integrated to evaluate the ecological relevance of EMF species, compositional, and biodiversity differences. In this short review, I evaluate whether EMF species identity, composition, and richness affect tree growth during early plant life stages. I first show that EMF species often, but not always, differentially effect seedling and sapling growth, both in the greenhouse and under field condition where other factors determine plant growth, such as variation in soil fertility and climate. Effects of EMF species richness on plant growth are context dependent, and stimulated tree growth in 37% of the cases identified (11/30 cases). Evidence to date suggests that differences in EMF composition more than richness affect tree growth. Limitations of current experimental studies and challenges interpreting observational patterns make it difficult to tease apart causality and directionality, but I provide a list of possible solutions for future research to address outstanding questions. Understanding how mycorrhizal biodiversity affects plant growth is not only an important frontier in ecological research, it also has implications for embedding fungi into forest management, conservation, and ecosystem restoration agendas.