Global mycorrhizal fungal range sizes vary within and among mycorrhizal guilds but are not correlated with dispersal traits

Aim:

Mycorrhizal fungi associate with the majority of plant species with large consequences on ecosystem nutrient, carbon, and water cycling. Two main types of mycorrhizal fungi, arbuscular mycorrhizal (AM) fungi and ectomycorrhizal (EM) fungi, dominate terrestrial ecosystems. Most global distribution modeling of AM and EM mycorrhizal associations describe the distribution of AM and EM plants, and not fungi directly. However, significant functional trait variation occurs within AM and EM fungal guilds. Therefore, modeling range sizes and determinants of these ranges of fungi directly is likely to be a better proxy of ecosystem function than guild-level lumping of AM and EM plant distributions.

Location:

Global

Taxa:

Arbuscular mycorrhizal and ectomycorrhizal fungi

Methods:

Here, I calculated the ranges of 164 AM and 67 EM fungal taxa at the global scale and related range sizes to differences in spore sizes as a proxy of dispersal potential. If dispersal limitation affects range sizes, I expected that EM fungi with smaller spores would have larger ranges than AM fungi with larger spores. If spore size was not related to range size, this would indicate factors other than passive dispersal control global mycorrhizal fungal ranges.

Results:

Overall, AM fungal taxa had larger ranges than EM fungal taxa. AM fungi also had larger spore sizes than EM fungi. Range sizes within both AM and EM fungal taxa were phylogenetically conserved; closely related AM and EM fungi has similar range sizes. Closely related EM fungi also had similar spore sizes. However, spore size was not related to range size for either mycorrhizal guild after phylogenetic correction, except for EM fungi in the Northern hemisphere.

Main Conclusions:

These findings provide evidence that range size for both mycorrhizal guilds is for the most part not determined by dispersal limitation, suggesting instead that environmental tolerance or plant host distributions determine mycorrhizal fungal ranges. Future surveys of the same plant species across environmental gradients will elucidate abiotic versus host plant influence on mycorrhizal niches.