Soil microbial communities associated with giant sequoia: How does the world's largest tree affect some of the world's smallest organisms?

Giant sequoia (Sequoiadendron giganteum) is an iconic conifer that lives
in relic populations on the western slopes of the California Sierra
Nevada. In these settings, it is unusual among the dominant trees in that
it associates with arbuscular mycorrhizal fungi rather than
ectomycorrhizal fungi. However, it is unclear whether differences in
microbial associations extends more broadly to non-mycorrhizal components
of the soil microbial community. To address this question, we
characterized microbiomes associated with giant sequoia and co-occurring
sugar pine (Pinus lambertiana) by sequencing 16S and ITS1 of the bulk soil
community at two groves with distinct soil parent materials. We found
tree-associated differences were apparent despite a strong grove effect.
Bacterial/archaeal richness was greater beneath giant sequoia than sugar
pine, with a unique core community that was double the size. The tree
species also harbored compositionally distinct fungal communities. This
pattern depended on grove but was associated with a consistently elevated
relative abundance of Hygrocybe species beneath giant sequoia. We conclude
that the effects of giant sequoia extend beyond mycorrhizal mutualists to
include the broader community, and that some but not all host tree
differences are grove-dependent.