Whole-stem water relations in white oak.
Goranson, Carol*,1, Teskey, Robert1, 1 University of Georgia, Athens, GA, 30602
ABSTRACT- Trees often experience water stress diurnally and seasonally. The heartwood of trees can contain appreciable amounts of water, but the role of heartwood to the water status of trees is largely unknown. This study addressed whether the heartwood of trees can be a source of water to help meet transpirational water demand. This study examined sapwood water flux and heartwood water content in white oak (Quercus alba) to determine whether water stored in heartwood was used by trees to reduce daily water stress. Tree water use was measured with Granier-type sap flux probes, and heartwood water content was measured with volumetric water content reflectometer probes in white oak trees in Georgia from June 2004 to January 2005. Volumetric water content of the heartwood ranged from .43 to .69, with a small diurnal (1-2% average) variation. Large increases in heartwood water content followed soil water recharge caused by rain storms. Smaller diameter trees (35-36 cm dbh) used less water than larger trees (53-58 cm dbh) on a daily basis, but the smaller trees had larger percent daily and seasonal heartwood water content fluxes, and generally higher heartwood water contents than larger trees. Although there were daily and seasonal changes in the water content of white oak heartwood, the volume of daily water change was the same in the growing and dormant seasons, and it was concluded that heartwood water content changes were unrelated to transpiration and sap flux. Sharp increases in water content were related to increases in soil moisture due to rainfall, but not other meteorological factors.
Key words: Quercus alba, heartwood, sap flux, water content
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