Higher host plant specialization of root-associated endophytes than mycorrhizal fungi along an arctic elevational gradient.

Nerea Abrego,Gleb Tikhonov,Niels Martin Schmidt,Tomas Roslin,Otso Ovaskainen,Panu Somervuo,Tea Huotari,Ayco J M Tack,Björn D Lindahl

doi:10.1002/ece3.6604

Abstract

How community‐level specialization differs among groups of organisms, and changes along environmental gradients, is fundamental to understanding the mechanisms influencing ecological communities. In this paper, we investigate the specialization of root‐associated fungi for plant species, asking whether the level of specialization varies with elevation. For this, we applied DNA barcoding based on the ITS region to root samples of five plant species equivalently sampled along an elevational gradient at a high arctic site. To assess whether the level of specialization changed with elevation and whether the observed patterns varied between mycorrhizal and endophytic fungi, we applied a joint species distribution modeling approach. Our results show that host plant specialization is not environmentally constrained in arctic root‐associated fungal communities, since there was no evidence for changing specialization with elevation, even if the composition of root‐associated fungal communities changed substantially. However, the level of specialization for particular plant species differed among fungal groups, root‐associated endophytic fungal communities being highly specialized on particular host species, and mycorrhizal fungi showing almost no signs of specialization. Our results suggest that plant identity affects associated mycorrhizal and endophytic fungi differently, highlighting the need of considering both endophytic and mycorrhizal fungi when studying specialization in root‐associated fungal communities.

Highlights

Measuring specialization in interaction networks has important implications for understanding co-evolutionary dynamics (Thrall, Hochberg, Burdon, & Bever, 2007) and the mechanisms shaping species distributions (Mariadassou, Pichon, & Ebert, 2015)
We evaluated whether the network-level specialization changed along elevation by adding an interaction term between plant species and elevation in the joint species distribution model
While we expected a low degree of host specialization in the root-associated fungal community in general, we found a clear signal of specialization on host plant species

Summary

| INTRODUCTION

Measuring specialization in interaction networks has important implications for understanding co-evolutionary dynamics (Thrall, Hochberg, Burdon, & Bever, 2007) and the mechanisms shaping species distributions (Mariadassou, Pichon, & Ebert, 2015). Root-associated fungi (RAF) comprise highly species rich communities that have important consequences on the fitness of the associated plants (Bacon & White, 2000; Smith & Read, 2008) These associations are of particular importance in arctic environments with low nutrient availability (Hobbie & Hobbie, 2006). We ask (a) whether host plant specialization differs between mycorrhizal and root-associated endophytic communities and (b) whether the level of specialization of RAF on plant species changes along elevation. For this purpose, we acquired molecular data on RAF of five plant species that were equivalently sampled along an elevational gradient in the Zackenberg Valley (Northeast Greenland). We hypothesized a lower specialization of plant–RAF associations at higher elevations, because a lower degree of specialization could improve colonization in harsh climatic conditions and with low nutrient availability, in which the impact of RAF associations on plant survival can be expected to be especially critical

| MATERIALS AND METHODS

| DISCUSSION