Abstract Detail

Ecophysiology

Koepke, Dan [1], Blasini, Davis [2], Grady, Kevin [3], Hultine, Kevin [4].

Leaf and wood xylem traits along an extreme heat to frost tolerance spectrum in Fremont cottonwood.

Current evidence suggests that plants often display functional traits that are highly adapted to local environmental conditions. We evaluated potential patterns of local adaptation in traits related to long-distance water transport in a riparian tree species (Populus fremontii) native to the southwestern United States. We established a Populus common garden to address whether xylem traits varied in genotypes sourced across a broad thermal distribution gradient in the southwestern United States. Similar to a leaf economic spectrum, we hypothesized that this species would display a similar heat-tolerance / frost-tolerance spectrum of leaf and wood traits. Specifically, heat-adapted genotypes would have large vessels and low specific leaf area (SLA, area per mass) to support high transpiration rates required for high canopy evaporative cooling, and cold-adapted genotypes have small vessels to limit freeze-thaw cavitation, and low SLA. As an indirect consequence, we also hypothesized that hydraulic efficiency via maximum stem specific hydraulic conductivity (K_max) is greater in the warm populations. Local adaptation in xylem traits was evident in this study. Results for P. fremontii indicate that SLA (R²=0.64, p=0.05) and specific petiole area (R²=0.39, p=0.09) decreased with increasing elevation, having thinner and smaller leaves to reduce radiative heat load and thermal capacitance. Petiole xylem size did not differ across the gradient. Wood vessel area decreased with climate along an elevation gradient (R²=0.07, p=0.0492). The mean (se) area of individual vessels for P. fremontii was 942 (78.8) µm² and 672 (56.8) µm² for the low and high elevation sites, respectively. The hydraulically weighted mean diameter (D_h) also decreased significantly going up an elevation gradient (p=0.023). Significant differences were also found when populations were grouped into ecoregions. There was a decrease in the mean vessel area and the D_h (p=0.0231) when going from the lower and hotter Sonoran Desert Ecoregion to the higher and cooler Colorado Plateau Ecoregion. This indicates that along an increasing frost event continuum with mean xylem area and D_h decreasing, the K_max should also decrease. This trend was not seen, though, due to the high variability within populations and may suggest a high level of genetic plasticity within this species. Budburst was also recorded and was significantly earlier for populations from the hot environments (R²=0.94, p<0.0001), suggesting the need to reduce vessel size in the colder environments is compensated by the phenology timing. Rapid local adaptation could be a major factor that has allowed for its widespread climate distribution.

1 - Desert Botanical Garden, Research, Conservation, Collections, 1201 N. Galvin PKWY, Phoenix, AZ, 85008, USA
2 - Desert Botanical Garden / Arizona State University, 1201 N Galvin Pkwy, Phoenix, AZ, 85008, United States
3 - Northern Arizona University, School of Forestry, 200 East Pine Knoll Drive, Flagstaff, AZ, 86011, USA
4 - Desert Botanical Garden, Research, Conservation, Collections, 1201 N. Galvin Parkway, Phoenix, AZ, 85008, USA

Keywords:
Populus fremontii
xylem
local adaptation
hydraulic conductance.

Presentation Type: Poster
Session: P, Ecophysiology Posters
Location: Arizona Ballroom/Starr Pass
Date: Monday, July 29th, 2019
Time: 5:30 PM This poster will be presented at 5:30 pm. The Poster Session runs from 5:30 pm to 7:00 pm. Posters with odd poster numbers are presented at 5:30 pm, and posters with even poster numbers are presented at 6:15 pm.
Number: PPE011
Abstract ID:942
Candidate for Awards:None