Cottonwood Trees Vary in their Leaf Hydraulic Architecture Traits when Grown at the Extreme Hot Edge of their Range
Iris Garthwaite1*, Rebecca Best2
1. School of Earth and Sustainability, Northern Arizona University, Flagstaff, AZ USA;
2. School of Earth and Sustainability, Northern Arizona University, Flagstaff, AZ USA;
Climate means, extremes, and variability are shifting rapidly, which will likely result in mismatches between climate and locally adapted plant traits. Phenotypic plasticity, the ability for a plant to respond to environmental conditions within a lifetime (e.g., by adjusting the types of leaves they make each year), may provide a buffer for plants to persist under rapid environmental change. We used three common gardens to investigate phenotypic plasticity for six populations of Fremont cottonwood (Populus fremontii), an important riparian tree. We focused on the plasticity of leaf venation, a multivariate trait that is linked to plant performance and tolerance to environmental stress. We found that 1) Populations responded differently to a hotter growing environment, with some increasing and some decreasing the density of their leaf venation; 2) Even within populations, vein density also differed among genotypes in the hottest environment; 3) Locally adapted hot populations trended toward greater vein density and higher growth in the hottest environment compared to northern populations. Past studies indicate that high vein density is associated with a suite of characteristics that are likely to support survival in hotter and drier climates (i.e., high leaf hydraulic conductance, high stomatal density, and drought resistance). Results from this study suggest that different P. fremontii populations will vary in their capacity to adjust their leaf venation and support growth in a novel hot environment.  Survivorship modeling efforts, restoration project managers, and assisted migration initiatives should consider genetic stock, growing conditions, and multiple dimensions of environmental stress early in the research and planning process to improve predictions and enhance restoration outcomes.