Tree species with limited geographical ranges show extreme responses to ectomycorrhizas

Abstract

Aim At continental scales, abiotic factors such as climate are typically used to explain differences in plant ranges. Although biotic interactions also underlie the biogeography of plants, the importance of plant‐associated microbes is often overlooked when predicting ranges. In particular, symbiotic microbes may influence the distribution of plants that engage in strong interactions with them. We tested whether seedling response to inoculation by ectomycorrhizal fungi explains range size of trees. To examine mechanisms underlying the relationship between range size and response to inoculation, we also examined to what extent sympatry between host and fungi influenced this relationship. Location Global. Time period Contemporary. Major taxa studied Trees and fungi forming ectomycorrhizas. Methods Using a dataset of 1,275 observations from 126 papers, we calculated mean biomass response (effect size) of 59 tree species to fungal inoculation. We extracted host range area from digitized maps of native distributions, and determined whether hosts were naturally sympatric with fungal species used as inoculum by searching herbaria databases with geospatially referenced data. Results Tree species with seedling effect sizes falling above or below the average response tended to have small ranges and those with average responses, large ranges. Moreover, hosts inoculated with fungi whose ranges were allopatric to their own had higher biomass compared to those that were inoculated by sympatric fungi, suggesting that the extent of geographical overlap between trees and symbiotic fungi may attenuate the mutualism. Main conclusions We demonstrate that mycorrhizas may underlie host biogeographical patterns at the continental scale. Our study is novel in the scope of species and scale tested, and points to a possible mechanism underlying this pattern related to the process of mutualism breakdown accruing over time at local geographical scales. For ectomycorrhizal tree species, performance may increase when exposed to fungal partners without a recent shared evolutionary history.

Host Phylogenetic Relatedness and Soil Nutrients Shape Ectomycorrhizal Community Composition in Native and Exotic Pine Plantations

“…However, other studies have found that ECM host specialization contributes significantly to the composition of ECM communities [25,56]. Although the reason(s) for these opposing responses are not clear, they may reflect differences in the evolutionary co-adaptation between ECM fungi and their host [25,30], or differences in host range [57].…”

Variations in Soil Functional Fungal Community Structure Associated With Pure and Mixed Plantations in Typical Temperate Forests of China

“…ECM fungi can excrete extracellular enzymes that degrade complex organic nitrogen compounds, thereby providing benefits to forest trees by enhancing the mobilization and uptake of soil nutrients (Nygren et al, 2007; Courty et al, 2010; Li et al, 2016; Luo et al, 2018). Additionally, ECM symbiosis is usually viewed as promoting nutritional mutualism and providing resources for host trees to withstand harsh conditions (Peay, 2016; Karst et al, 2018). Previous studies have shown that plants likely form different root symbioses via mycorrhizal networks, such as those associated with ECM fungi, to promote the growth of their neighbors (Simard et al, 2012; Teste et al, 2014; Luo et al, 2018).…”

Highly invasive tree species are more dependent on mutualisms

“…We calculated an effect size (ES) for each study using log response ratio aswhere EMF P is the biomass of seedlings in the presence of EMF and EMF A is the biomass of seedlings in the absence of EMF. We calculated a mean effect size for each Pinus species using an unweighted average of all the contrasts for each species, following Karst et al (). A positive effect size indicates that Pinus seedlings benefit from the presence of EMF, whereas if the effect size is negative seedlings are negatively affected by EMF.…”

“…Additionally, working with species within the same genus minimizes confounding effects arising from phylogenetic relatedness. Here we focus on the seedling stage because: (1) Pinus species vary greatly in their growth response to EMF at the seedling stage (Karst et al ), (2) it is the most vulnerable stage in the life cycle of a plant (Harper , Baskin and Baskin , Fenner and Thompson ), and (3) patterns of growth at the seedling stage are very good predictors of patterns of growth at maturity for woody species (Cornelissen et al ).…”