Eastern Joshua Tree Arbuscular Mycorrhizal Fungi Largely Consistent Across Roots, Soils, and Seasons.

The Mojave Desert is home to iconic Joshua trees threatened by climate change. Most desert plants form mutually beneficial partnerships with arbuscular mycorrhizal fungi (AMF), yet the AMF of the Eastern Joshua tree (Yucca jaegeriana) remain completely uncharacterized. We tested how Y. jaegeriana AMF spore abundance, richness, and composition varied when sampling 20 trees across 4 seasons from roots versus soils. We confirmed root colonisation via staining, assessed spore abundance via microscopy, and used Illumina MiSeq to sequence AMF virtual taxa (VT) with WANDA AML2 primers. We identified 12 spore morphotypes and 47 VTs across 5 families within Glomeromycotina, and the most abundant VT, Glomus VTX00294, appeared in 87% of soil and root samples. The majority of VTs (26/47) were present across all seasons and were shared among soil and roots (38/47), with more VTs unique to soil. In soil, per tree mean spore abundance and AMF richness were lowest in Summer but consistent across other seasons, with richness ranging from 8.8 to 11.5 VTs and mean root richness consistent across seasons. We conclude that sampling from soils rather than roots and any season other than Summer will yield the most diverse AMF communities.