Environment-Microbiome-Plant Interactions Drive Root Microbiome Assembly Outcomes and Impact Conifer and Shrub Seedling Performance in Post Wildfire Soils
Authors
Tanya E. Cheeke1* (tanya.cheeke@wsu.edu), Geoff Zahn2, Brittany LeTendre3, Kevan Moffett3, Emily Graham4, Stephanie S. Porter3
Institutions
1Washington State University–Tri-Cities, Richland, WA; 2Utah Valley University, Orem, UT; 3Washington State University–Vancouver, WA; 4Pacific Northwest National Laboratory, Richland, WA
Abstract
Temperate conifer forests are faced with unparalleled challenges from anthropogenic climate change. Rising temperatures contribute to increasing frequency of wildfire, and prolonged drought can result in shifts from forest-to shrub-dominated ecosystem states. However, few studies explore ecoevolutionary hypotheses to predict how soil and root microbiome attributes shape the growth and drought tolerance of conifer and shrub seedlings, two traits that are critical to early competitive dynamics during revegetation after fire. In a greenhouse, researchers grew Grand fir (Abies grandis) and Snowbrush (Ceanothus velutinus) with live soil inocula from native conifer forests after various numbers of recent, high-severity wildfires (zero, one, and three wildfires within 25 years), with and without a drought treatment. The team used plant performance data and amplicon sequencing (16S, ITS, 18S) of root microbiomes to test predictions of how root microbiome attributes, such as guild abundance, microbial network connectivity, and the source of inocula, influenced early conifer and shrub seedling performance. Researchers hypothesized that environment-microbiome-plant interactions would play a key role in driving root microbiome outcomes and plant performance. The team found that root microbiomes from soils that experienced very different recent fire impacts had contrasting effects on root microbiome community assembly after one year of growth and soil microbiomes from different sites resulted in contrasting effects on seedling growth. The proportions of mutualistic and pathogenic fungi predicted stronger and weaker growth for Grand fir, respectively, but not for Snowbrush. Bacterial pathogens had a negative effect on the growth of Snowbrush, but only under drought conditions. Root microbiomes with greater fungal network connectivity were associated with stronger plant performance. This study shows that changes in microbiome assembly processes can impact microbiome function and may translate into changes in seedling performance in post-wildfire soils.