The Root Race: Does Stream Type Affect Belowground Architecture of a Riparian Tree Species? Jackie Parker

 

 

 

 

Jackie Parker¹*, Abraham Cadmus², Catherine Gehring³, Thomas Whitham⁴

 

¹Northern Arizona University, Flagstaff, Arizona; jaclyn.parker@nau.edu

² Northern Arizona University, Flagstaff, Arizona; abraham.cadmus@nau.edu

³Northern Arizona University, Flagstaff, Arizona; catherine.gehring@nau.edu

⁴Northern Arizona University, Flagstaff, Arizona; thomas.whitham@nau.edu

 

 

 

To understand how rooting architecture influences the biomass and survivorship of Fremont cottonwood (Populus fremontii), we conducted an experiment to measure differences between perennial and ephemeral stream adapted genotypes. Differential rooting strategies may be genetically driven, as such it is imperative to understand the impacts of architecture on tree success. To quantify architecture, we collected cuttings from eight natural populations of Fremont cottonwood from paired ephemeral and perennial streams. These cuttings were grown in one of three drought treatments one meter from a mock water table for six weeks then analyzed for biomass and architecture. Three patterns emerged: 1. Ephemeral adapted trees allocated 4x more biomass to root tissue under high drought stress compared to perennial trees. 2. Fine root mass and complexity was greatest in perennial trees under low drought stress, and conversely, ephemeral trees under high drought stress. 3. The length of the longest roots at the end of the experiment revealed that ephemeral adapted trees were superior at reaching a mock water table under drought conditions. We conclude that the rooting structures of perennial and ephemeral stream adapted trees may be controlled by a gene-by-environment interaction. These findings suggest that Fremont cottonwood trees may be locally adapted to a specific hydrological regime. As such, root dynamics and architecture may an essential consideration for future restoration projects as rivers and streams transition to a more ephemeral state with the progression of climate change.