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

Abstract

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 modelling of AM and EM 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, modelling range sizes and determinants of these ranges of fungi directly is likely to create spatial maps that are 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 have similar range sizes. Closely related EM fungi also had similar spore sizes. However, spore size was not related to range size for either mycorrhizal fungal guild after phylogenetic correction, except for EM fungi in the Northern hemisphere. Main Conclusions These findings provide evidence that range size for both mycorrhizal fungal 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 fungal niches.

Codependency between plant and arbuscular mycorrhizal fungal communities: what is the evidence?

“…Notwithstanding the above, there are reasons why codependency may be counterintuitive: AM fungi are globally distributed (Davison et al ., 2015; but see Bruns & Taylor, 2016) and most AM fungi do not appear to suffer dispersal limitations (Correia et al ., 2019; Kivlin, 2020). If every fungus has the opportunity to occur in every habitat, regardless of plant community identity, specific associations may be less common. The Glomeromycota have significantly fewer taxa than their hosts (<1000 AMF species vs 391 000 plant species) making it improbable that plants develop strict specificity with fungal partners. AM fungi are obligate biotrophs.…”

What drives study‐dependent differences in distance–decay relationships of microbial communities?

“…Additionally, different study taxa are likely to yield variable distance–decay relationships because they differ in traits that are linked to dispersal efficacy. For example, small cells disperse more efficiently over long distances (Norros et al., 2014; Wilkinson, 2001; Wilkinson et al., 2012), meaning that organisms with larger cell sizes, such as microbial Eukarya, should be more strongly dispersal limited than those with small cell sizes, such as Bacteria (although this might not be true for all taxa, e.g., see Kivlin, 2020). Finally, it is known that spatial extent can influence our perception of ecological relationships, which might contribute to variable distance–decay relationships (Steinbauer et al., 2012).…”

Global drivers of obligate mycorrhizal symbionts diversification

“…We found no correlation either between spore size and level of endemism ( Supplementary Fig. 26), suggesting that even AMF with large spores can experience long-distance dispersal 60,62 . Large spores might limit dispersal at smaller (e.g.…”

“…Finally, although spore size is often inversely related to dispersal capacity [87], which can either promote diversification by favoring founder speciation events, or limit diversification by increasing gene flow, we found no significant correlation between spore size and diversification rates, which may be explained either by a weak or absent effect or by the low number of species for which this data is available. In addition, the absence of correlation between spore size and level of endemism suggests that even AMF with large spores experience long-distance dispersal [57, 88]. Thus, if large spores might limit dispersal at smaller (e.g.…”