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Abstract Detail


Blasini, Davis [1], Koepke, Dan F. [2], Grady, Kevin C [3], Bush, Susan E  [2], Hultine, Kevin R [2].

Whole-tree water relations are correlated with exposure to Frost and/or heat waves in a dominant riparian tree species: Populus fremontii.

Increases in extreme weather events, including drought and intense mid-summer heat waves, is having a world-wide profound impact on ecosystem structure and function. Southwestern riparian forest is expected to be critically impacted by the effects of these extreme weather events. The resilience of these ecosystems to weather extremes may depend on the capacity for foundation tree species, like Populus fremontii, to persist under a broad range of hydro-climatological conditions. In order to better understand the capacity for P. fremontii to persist, we investigate intraspecific differences in morpho-physiological traits along this species’ entire thermal gradient. Simultaneously, we studied the role that these functional traits play on the physiological mechanisms responsible for adaptation at local and regional level. This investigation took place in an experimental garden placed at the mid-elevation point of P. fremontii’s thermal distribution, with an even representation of populations coming from warmer and cooler provenances. We measured a broad suite of leaf functional and structural traits, including whole-plant leaf area (Al), sap-flux-scaled transpiration (E), canopy stomatal conductance (gs) specific-leaf area (SLA), specific-stem density (SSD), xylem area (Ax), sapwood area (As), characteristic-leaf dimensions (cld), stomatal density (SD), water potential (Ψ), canopy area (Ac) and the difference between leaf to air temperature (Tl-Ta). We observed negative relationships between provenance elevation and SLA (r2=0.54, p=0.037), SD (r2=0.59, p=0.022) and Al:As (r2=0.65, p=0.016). Simultaneously, we found positive trends between provenance elevation and cld (r2=0.61, p=0.021), Ψ (r2=0.74, p=0.006), and Tl-Ta (r2=0.69, p=0.010). These results suggest that populations from the hottest edge of this species distribution display a set of coordinated morpho-physiological traits that support higher transpiration rates as a strategy to maintain leaf temperature at an optimal level for photosynthesis. Thus, smaller/thinner leaves found in these populations reduce sensible heating and capacitance from solar radiation while greater sapwood to leaf area, xylem area, and stomatal density may be increasing the potential ability of these trees to transpire at higher and faster rates. Additionally, by having open/smaller canopies with lower leaf area to sapwood area ratios, these low-elevation populations display lower canopy boundary layer conductance and water potentials. We also found significant opposite morpho-physiological characteristics in the high elevation populations. It indicates a functional trade-off between minimizing the risk of losing hydraulic conductivity from freeze-thaw cavitation and displaying lower transpiration rates. These results imply water availability will be essential for the hot temperature-adapted populations to endure the projected Increases in extreme weather events.

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1 - Arizona State University, School of Life Sciences, Tempe, AZ, 85281, USA
2 - Desert Botanical Garden, Department of Research, Conservation and Collections, Phoenix, AZ, 85008, USA
3 - Northern Arizona University, School of Forestry, Flagstaff, AZ, 86011, USA

functional traits
Sap Flux
Leaf Thermoregulation
Populus Fremontii.

Presentation Type: Oral Paper
Session: ECOPH1, Ecophysiology I
Location: San Pedro 2/Starr Pass
Date: Tuesday, July 30th, 2019
Time: 10:30 AM
Number: ECOPH1007
Abstract ID:476
Candidate for Awards:None

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