PARENT SESSION
Oral Session # 56: Plant Ecology IV: Plant - Water Relations II.
Presiding: D Rosenthal
Wednesday, August 6. 1:30 PM to 5:00 PM, SITCC Meeting Room 200.
The effects of evaporative demand on the radial distribution of sap flux in tree stems.
Ford, Chelcy *,1, 2, McGuire, Mary Anne*,1, Mitchell, Robert*,2, Teskey, Robert*,1, 1 University of Georgia, Athens, GA2 Joseph W. Jones Ecological Research Center, Newton, GA
ABSTRACT- Earlier work has shown that the radial pattern of sap flux in conifers with deep sapwood can change from tree to tree and throughout the day as evaporative demand changes. We evaluated whether the shape of the sap flux radial profile could be predicted temporally as a function of vapor pressure deficit (D) and photosynthetically active radiation (PAR) in a plantation of mature loblolly pine, Pinus taeda L., growing in Georgia, USA. Granier-style heat dissipation probes spanned the entire sapwood radius with measuring points located every 2 cm in ten trees. These measurements were simultaneously validated with independent 2 cm probes. Temperature differentials were recorded every 5 min at all measurement points, and measurements were averaged into 15 min values. We found that the radial pattern of sap flux varied predictably with evaporative demand. Under higher evaporative demands, the inner xylem conducted disproportionately more water than the outer xylem compared to times when evaporative demands were lower. By knowing D and PAR, stem sap flux at any radial point in the xylem can be predicted, and the total radial flux profile can be used to accurately scale single point-measurements to whole-tree water use. These results indicate that the conducting xylem of pines, and perhaps other conifers, should be considered a variable-area flow path that changes dynamically depending on the atmospheric evaporative demand.
Key words: scaling, Pinus taeda , sapflow, water use