Functional trait-dependent variation in the distribution and climate tolerance of North American soil fungi

Clara Qin and Kai Zhu, University of California, Santa Cruz, Peter Pellitier, Stanford University, Kabir G. Peay, Biology, Stanford University, Stanford, CA

Background/Question/Methods
The responses of fungi to climate change may depend on their traits. A trait-based approach to fungal ecology, then, can improve earth system modeling by accounting for the role of fungal functional traits in regulating ecosystem feedbacks. However, little is known about the macroecological distribution of fungal traits in the environment, or variation in climate niches between and among fungal functional guilds. We use FungalTraits—an expert-derived, trait-based classification of fungal genera—to examine the macroecological patterns of fungal functional guilds across a synthetic, continental-scale dataset. We developed and implemented an R package, neonMicrobe, to process the National Ecological Observatory Network’s (NEON) ITS amplicon sequences, and combined them with sequences from a previous NSF Dimensions of Biodiversity project on North American soil fungi (DoB-FUN). We explore the functional guild composition of soil fungal communities across habitat types. For each guild, we also estimate the degree of endemism by calculating its total richness across the dataset and then the proportion of its total richness at each spatial unit (sample, plot, site, eco-climatic domain). In addition, we estimate the temperature niche breadths of functional guilds by calculating the range of mean annual temperature among the sites where each species was found to occur.
Results/Conclusions
The combined NEON-DoB dataset includes 59 sampling locations spanning the US and Canada. Approximately 30% of all species-level taxa, representing 80% of sequences, were assigned a functional guild. We found that fungal guild composition varies significantly with vegetation cover type. In particular, the soil fungal communities collected from pine forests are predominantly ectomycorrhizal (79% of sequences), whereas the fungal communities from other sites consist of more soil saprotrophs than any other specified guild. We find that mycoparasites display the highest degree of endemism (proportion of total richness at eco-climatic domain scale, mean = 11%) and soil saprotrophs the lowest (19%), with ectomycorrhizal fungi (15%) and other guilds falling in between. Temperature niche breadth varies significantly between guilds (Kruskal-Wallis test, P < 0.001). Ectomycorrhizal fungi have significantly narrower temperature niches (pairwise Wilcoxon test, BH-adjusted P < 0.05) than arbuscular mycorrhizal fungi, plant pathogens, and especially soil saprotrophs, which have the broadest temperature niches. Our results demonstrate that ectomycorrhizal fungal species are generally less tolerant to temperature changes than species in other guilds, and corroborate recent findings highlighting the vulnerability of ectomycorrhizal fungal species to changing climates. Furthermore, our analysis provides a novel summary of fungal distribution and climate response across functional guilds.