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 correla...