Asymmetric patterns of global diversity among plants and mycorrhizal fungi

Abstract

Questions Although the roles of mycorrhizal fungi in different vegetation types are widely acknowledged, it is still largely unknown how the diversity and frequency of different symbiotic partners vary among plant assemblages globally. We asked (1) how the global distribution of vascular plants correlates with the diversity (i.e. number of species) and frequency (i.e. relative abundance) of different plant mycorrhizal types (i.e. arbuscular mycorrhizal [AM], ectomycorrhizal [ECM], ericoid mycorrhizal [ERM], orchid mycorrhizal [ORM] and non‐mycorrhizal [NM]); and (2) how the diversities of the most dominant plant mycorrhizal types (AM and ECM) correlate with those of their respective mycorrhizal fungal partners. Location Worldwide. Methods We retrieved all vascular plant occurrences available in the Global Biodiversity Information Facility database from sites worldwide where AM and ECM fungal diversity has been examined. Plant mycorrhizal types were assigned to plant species using expert‐based imputation. Diversity and frequency indices were calculated using extrapolation and bootstrapping procedures in order to account for the heterogeneity and uncertainty of the datasets. Results Each plant mycorrhizal type correlated differently with the global diversity pattern of vascular plants, with higher total plant diversity in AM‐dominated vegetation, compared with vegetation containing a larger share of ECM, ERM or NM plant species. The diversities of AM and ECM fungi were positively correlated with the frequency, but not diversity, of their respective plant mycorrhizal types; and weakly correlated with the frequency and diversity of other plant mycorrhizal types. Conclusions At the global scale, vascular plant distribution correlates, among other factors, with the frequency, and to a lesser extent diversity, of different mycorrhizal types of plants and fungi. Recognizing these relationships may help to predict changes in the frequency of ECM and AM plant mycorrhizal types under the different ongoing global changes.

Global macroecology of nitrogen‐fixing plants

“…However, trees can also fix N in boreal forests via association with actinobacteria. Similarly to the turnover in the major symbiotic guilds (high abundance of arbuscular mycorrhizal plants near the equator, followed by high abundance of N‐fixers at mid‐latitudes and ectomycorrhizal plants at higher latitudes; Soudzilovskaia et al., 2019; Steidinger et al., 2019; Toussaint et al., 2020), there also seems to be a turnover in the N‐fixer types, with cyanobacterial associations dominating in the tropics, followed by rhizobial associations peaking at the 20–30 degree latitudinal band and actinorhizal associations dominating at higher latitudes.…”

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

“…Noncausal covariation among AM partner taxon richness has been shown in some (Landis et al ., 2004; König et al ., 2010; Hiiesalu et al ., 2014) but not all studies (Johnson et al ., 2010; Antoninka et al ., 2011; Lekberg et al ., 2013; Chaudhary et al ., 2018; Toussaint et al ., 2020). One may predict that more plant species provide more niches for AM fungi, or vice versa, but carbon availability, fungal competition and priority effects may have an equally strong or even stronger effect on AM fungal species richness than on plant species richness (Waldrop et al ., 2006; Antoninka et al ., 2011; Werner & Kiers, 2015).…”

Global drivers of obligate mycorrhizal symbionts diversification

“…We found no effect of latitude, regardless of the AMF delineation or the minimum number of sequences per species (MCMCglmm: P>0.05), even though AMF are more frequent and diverse in the tropics ( Supplementary Fig. 27, 18,23,52 ) and their speciation rates are positively affected by global temperature. We did not find any effect of habitat or climatic zone either ( Supplementary Fig.…”

“…Looking at the correlates of AMF present-day diversification rates, we found no effect of habitat or climatic zone, even though AMF are more frequent and diverse in the tropics (Supplementary Fig. 32)[20, 25, 81] and their speciation rates are positively correlated with global temperature. Further work, including a more thorough sampling of the distribution of AMF species across latitudes and habitats, would be required to confirm these patterns and to distinguish whether speciation events are indeed no more frequent in the tropics or, if they are, whether long-distance dispersal redistributes the new lineages at different latitudes over evolutionary time scales [25].…”

“…Two prevailing hypotheses are the evolutionary speed hypothesis, stipulating that high temperatures entail high mutation rates and fast speciation 50 , and the productivity hypothesis, stating that resources and associated ecological niches are more numerous in warm and productive environments, especially when the tropics are large 51 . The latter hypothesis is particularly relevant in the case of AMF, which have many host plant niches in the tropics and potentially less in temperate regions 52 , where a higher proportion of plant species are non-mycorrhizal 53 or associated with ectomycorrhizal fungi 30,40 . Hence, the observed effect of past global temperature could reflect the shrinkage of tropical areas and the associated diminution of the relative proportion of plants relying on AMF.…”