Precipitation and temperature shape the biogeography of arbuscular mycorrhizal fungi across a 1500 km latitudinal transect in the Brazilian Caatinga

Arbuscular mycorrhizal fungi (AMF), an important group of plant root
symbionts, remain poorly studied in the Neotropics. We used Illumina LSU
amplicon sequencing to test whether AMF communities in soil and roots are
shaped by deterministic or neutral processes along a 20° latitudinal
transect in the Caatinga of Brazil, a unique dry forest eco-region.
Glomeraceae was the most abundant and diverse family, resembling more
paleotropical Africa and European croplands than other tropical forests
from South America. AMF communities showed strong biogeographic structure
inconsistent with a classical latitudinal diversity gradient, and further
differed between soil and roots. Soil AMF biogeography was best correlated
with precipitation; richness increased towards both ends of the
latitudinal transect where precipitation increased, and community
composition converged. Root AMF diversity weakened towards the equator, at
a latitude where soil AMF diversity was highest. Root AMF biogeography
correlated to temperature, with decreasing diversity at higher
temperatures. We found no evidence of phylogenetic niche conservatism
among AMF taxa. Our results suggest that niche-based processes in relation
to regional climate, most importantly precipitation and temperature, shape
the biogeography of AMF across the Caatinga, with niche
partitioning among closely related AMF taxa. Given the expected decrease
in precipitation and increase in temperature in the future, climate change
may strongly affect AMF biodiversity in neotropical dry forests.