Johnson, Daniel M. , Woodruff, David R. , McCulloh, Katherine A. , Meinzer, Frederick C. .
Leaf hydraulic conductance, measured in situ, declines and recovers daily: leaf hydraulics, water potential and stomatal conductance in four temperate and three tropical tree species.
Adequate leaf hydraulic conductance (Kleaf) is critical for preventing transpiration-induced desiccation and subsequent stomatal closure that would restrict carbon gain. A few studies have reported midday depression of Kleaf and its subsequent recovery in situ, but the extent to which this phenomenon is universal is not known. The objectives of the current study were to measure Kleaf, 1) in the lab (under controlled conditions) across a range of water potentials to construct vulnerability curves and 2) over the course of the day in the field along with leaf water potential and stomatal conductance. We chose two broadleaf (one evergreen, Arbutus menziesii, and one deciduous, Quercus garryana) and two coniferous species (Pinus ponderosa and Pseudotsuga menziesii) as representative of different plant types. In addition, we measured Kleaf in the lab and leaf water potential in the field for three tropical species (Protium panamense, Tachigalia versicolor, and Vochysia ferruginea) to predict their daily changes in field Kleaf in situ. We hypothesized that in the field leaves would close their stomata at water potential thresholds at which Kleaf begins to decline sharply in lab-generated vulnerability curves, preventing substantial losses of Kleaf. The temperate species showed a 15 to 66% decline in Kleaf by midday, prior to stomatal closure. Although there were substantial midday declines in Kleaf, recovery was nearly complete by late afternoon. Stomatal conductance began to decrease once Kleaf began to decline. Predicted Kleaf in the tropical species decreased by 74% percent of maximum Kleaf in Tachygalia, but only 22 to 31% in Vochysia and Protium. The results presented here, from our work and from other published studies, were consistent with two different strategies regarding daily maintenance of Kleaf: 1) a substantial loss and recovery, or 2) a more conservative strategy of loss avoidance.
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1 - Dept. of Wood Science and Engineering, Oregon State University, Corvallis, OR, 97331, USA
2 - USDA Forest Service, Pacific Northwest Research Station, 3200 SW Jefferson Way, Corvallis, OR, 97331, USA
Presentation Type: Oral Paper:Papers for Topics
Location: Cottonwood A/Snowbird Center
Date: Monday, July 27th, 2009
Time: 8:30 AM