CLONAL VARIATIONS IN THE WATER RELATIONS OF RED OSIER DOGWOOD DURING COLD ACCLIMATION

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Abstract
The water relations of six climatic races of red osier dogwood (Cornus sericea L.) were followed during cold acclimation in St. Paul, Minnesota in the fall of 1977. The following year, a similar study was completed on three of the climatic races. The clones originated from Alaska, Washington, Oregon, Montana, Idaho and North Dakota. By November, differences in rates of acclimation could be distinguished. Races could be divided into two groups: Oregon, Idaho and Montana became hardy to between − 25 and − 30 °C and Alaska, North Dakota and Washington became hardy to between − 37 and − 42 °C. After the initial frost, daytime stomatal resistance increased first in Alaska and then in Washington, Montana and North Dakota, but not in Idaho and Oregon. Differences among the races could be distinguished by this trait. The remaining water relations parameters measured did not show differences among the races. Stem water content of all clones decreased into mid-October when they reached a similar water content of approximately 1 g H2O/g dry weight. Midday leaf xylem pressure potential of all clones increased during acclimation. Relative water content of the stems decreased during acclimation but later increased. The water relations parameters of the outdoor acclimation process were very similar to those reported for growth chamber studies.