Data from: Tree-fungal interactions across climatic gradients: What is the potential for tree niche expansion via varying fungal associations?

Tree species persist across wide climatic gradients, potentially
facilitated by varying species interactions. We investigated how tree
species’ associations with fungal communities varied with climatic
gradients across their range. We partnered with volunteers to
sample tree roots across the eastern United States, with >1000
participants providing samples from 20 states. We characterized fungal
communities via amplicon sequencing and tested how fungal guilds and
individual taxa varied across climate gradients, as well as how fungal
guilds and taxa correlated with seedling performance in a field experiment
representing four climate conditions. Relative abundance of
non-mycorrhizal endophytes (NME) increased in hotter and drier locations,
guild-wide and for individual taxa. Relative abundance of ectomycorrhizal
(EM) fungi declined in drier sites, while that of many individual EM fungi
increased with colder temperatures. Seedling performance increased with
greater relative abundance of arbuscular mycorrhizal (AM) fungi and
intermediate abundance of NME in hot, dry conditions, and individual NME
taxa had, on average, positive correlations with seedling growth in these
conditions. One of the NMEs, Cladosporium, emerged as a candidate taxon
for niche expansion in Acer trees due to its increased abundance and
positive association with seedling growth in hot, dry conditions in the
field. Synthesis: Climatic niche breadth may reflect both
intrinsic tree traits and varying relationships with microbes. NME
represents an intriguing group whose impact on current and future tree
ranges deserves further investigation.