A natural temperature, elevation, and rainfall gradient over the Cascade Mountains drives changes in Populus trichocarpa stress response and microbial community structure

Abstract

Abiotic stresses associated with warming and drought are increasing in frequency and severity due to climate change. However, microbial associations can partially mitigate their adverse effects on plant physiology. We examined the bacterial/archaeal and fungal communities with 16S rRNA and ITS2 gene region amplicon sequencing of bulk soil, rhizosphere soil, and root endosphere samples of Populus trichocarpa trees from 11 sites along a 200 km transect with highly variable precipitation, temperature, and soil conditions over the Cascade Mountains in Washington, USA. Foliar stress response was examined with qRT-PCR and field physiological measurements. Soil conditions were examined with physiochemical sample analysis and site climate conditions were approximated using DAYMET. For each niche sampled, bacterial/archaeal and fungal communities clustered into three distinct micro-climate groups: a high-precipitation, low-stress community on the western side of the range, and two stressed climate communities: a high-elevation community nearer the crest of the pass, and a warmer and drier community along the eastern slope. The differences between these micro-climate communities, though still distinct, were notably diminished within the P. trichocarpa root endosphere, indicating that P. trichocarpa likely has a homogenizing effect on the microbiome under stress, but climate plays a major role in shaping these microbial communities.