Interactions between functionally diverse fungal mutualists inconsistently affect plant performance and competition

Madhav P Thakur,Arjen Biere,Christiane Roscher,Vera Quast,Ainhoa Martinez‐Medina,Nicole M Van Dam,Nico Eisenhauer

doi:10.1111/oik.06138

Abstract

Plants form mutualistic relationship with a variety of belowground fungal species. Such a mutualistic relationship can enhance plant growth and resistance to pathogens. Yet, we know little about how interactions between functionally diverse groups of fungal mutualists affect plant performance and competition. We experimentally determined the effects of interaction between two functional groups of belowground fungi that form mutualistic relationship with plants, arbuscular mycorrhizal (AM) fungi and Trichoderma, on interspecific competition between pairs of closely related plant species from four different genera. We hypothesized that the combination of two functionally diverse belowground fungal species would allow plants and fungi to partition their symbiotic relationships and relax plant–plant competition. Our results show that: 1) the AM fungal species consistently outcompeted the Trichoderma species independent of plant combinations; 2) the fungal species generally had limited effects on competitive interactions between plants; 3) however, the combination of fungal species relaxed interspecific competition in one of the four instances of plant–plant competition, despite the general competitive superiority of AM fungi over Trichoderma. We highlight that the competitive outcome between functionally diverse fungal species may show high consistency across a broad range of host plants and their combinations. However, despite this consistent competitive hierarchy, the consequences of their interaction for plant performance and competition can strongly vary among plant communities.

Highlights

Species interactions within one trophic or functional group may affect species interactions at other levels or organization (Menge and Sutherland 1976, Agrawal et al 2007, Bascompte and Jordano 2007, Tylianakis et al 2008, Valiente-Banuet et al 2015)
We studied how interactions between two common fungal symbionts of plant that form mutualistic relationships with plants affect the performance of and competition between several pairs of closely related plant species
While our results show a consistent negative effect of one fungal species (AM fungi) on the other (Trichoderma) independent of host plant communities, the net effects of such competitive fungal interactions on plant performance and competition were inconsistent

Summary

Introduction

Species interactions within one trophic or functional group may affect species interactions at other levels or organization (Menge and Sutherland 1976, Agrawal et al 2007, Bascompte and Jordano 2007, Tylianakis et al 2008, Valiente-Banuet et al 2015). Plants associate with a variety of mutualist organisms both above- and belowground. These associations can increase plant fitness by increasing their ability to acquire resources and boosting their resistance to herbivores (Bronstein et al 2006, Van Dam and Heil 2011, Philippot et al 2013). Among the vast diversity of belowground mutualists, two fungal groups are widely recognized for their symbiotic associations with plants: arbuscular mycorrhizal (AM) fungi (Bonfante and Genre 2010, van der Heijden et al 2015) and fungi in the genus Trichoderma (Harman et al 2004, MartinezMedina et al 2016)

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