Biogeography of root fungi in grasslands

Aim: Roots and rhizospheres host diverse microbial communities that
can influence the fitness, phenotypes, and environmental tolerances
of host plants. Documenting the biogeography of microbiomes can
detect the potential for a changing environment to disrupt
host-microbe interactions, particularly in cases where microbes,
such as root-associated Ascomycota, buffer hosts against abiotic
stressors. We evaluated whether root-associated fungi had poleward
declines in diversity as occur for many animals and plants, tested
whether microbial communities shifted near host plant range edges,
and determined the relative importance of latitude, climate, edaphic
factors, and host plant traits as predictors of fungal community
structure. Location: North American plains grasslands Taxon: Foundation North American grass species ⎯ Andropogon
gerardii, Bouteloua eriopoda, B. gracilis, B. dactyloides, and
Schizachyrium scoparium and their root-associated fungi Methods: At each of 24 sites representing three replicate
latitudinal gradients spanning 17° latitude, we collected roots from
12 individual plants per species along five transects spaced 10 m
apart (40 m × 40 m grid). We used next-generation sequencing of the
fungal ITS2 region, direct fungal culturing from roots, and
microscopy to survey fungi associated with grass roots. Results: Root-associated fungi did not follow the poleward declines
in diversity documented for many animals and plants. Instead, host
plant identity had the largest influence on fungal community
structure. Edaphic factors outranked climate or host plant traits as
correlates of fungal community structure; however, the relative
importance of these environmental predictors differed among plant
species. As sampling approached host species range edges, fungal
composition converged among individual plants of each grass species. Main conclusions: Environmental predictors of root-associated fungi
depended strongly on host plant species identity. Biogeographic
patterns in fungal composition suggested a homogenizing influence of
stressors at host plant range limits. Results predict that
communities of non-mycorrhizal, root-associated fungi in the North
American plains will be more sensitive to future changes in host
plant ranges and edaphic factors than to the direct effects of
climate.