Hydration of Eastern Hemlock as Influenced by Waxing and Weather
Abstract:The xylem pressure potential and stem diameter of small, container-grown, eastern hemlock (Tsuga canadensis (L.) Cart.) trees placed in an open field were measured several times between 6 January and 1 May 1972. Some trees had been sprayed with one or two coats of either 20 percent (v/v) or 40 percent Mobileaf, a wax-film antitranspirant. The wax provided no significant thermal insulation for the needles. On days when the air temperature was above 0°C, the xylem pressure potential was lower in unwaxed trees than in waxed trees and decreased with increasing vapor pressure deficit of the air in the unwaxed but not in the waxed trees. Those treated with 40 percent Mobileaf had only slightly higher potentials than those treated with 20 percent Mobileaf, and trees with a second film of wax maintained only slightly higher potentials than those with a single film. On days when air temperatures were below 0°C, the potentials of the waxed and unwaxed foliage were very similar but differed after warming for 1 hr at 19°C. Warming the foliage initially increased the potentials in all treatments. At temperatures below 0°C the trees had lower potentials at equivalent vapor pressure deficits than those sampled at above 0°C. Temperatures below 0°C also significantly reduced the diameter of the stems in both waxed and unwaxed hemlocks. Apparently, low potentials and stem shrinkage at temperatures below 0°C arise from extra-cellular freezing which antitranspirants affect little, but antitranspirants can reduce dehydration markedly on warm spring days. Forest Sci. 20:19-24.
Document Type: Journal Article
Affiliations: The Department of Soil and Water, The Valley Laboratory, P.O. Box 248, Windsor, Conn. 06059
Publication date: 1974-03-01
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