Growth and morphology of western red cedar seedlings as affected by photoperiod and moisture stress

Abstract

One-year-old container-grown seedlings of western red cedar (Thujaplicata Donn) were subjected to short days (8 h) and moisture stress, applied separately and in combination, and compared with untreated seedlings. The treatments were applied at various times during the growing season and lasted 2 and 4 weeks. Short days slowed height growth only when applied during the most rapid period of shoot elongation in late June and early July. Short days combined with moisture stress always reduced the final height regardless of the time and duration of applied treatments. Moderate moisture stress applied alone in mid-August hastened root dry weight gain but did not affect other morphological characters. The applied treatments had no lasting effects upon mitotic activity of terminal shoot apices and resulted in no differences in the timing of fall cessation of mitotic activity. The study describes details of the 1st-year growth of containerized western red cedar seedlings that were not subjected to the above specified treatments. It reports on growth rates for several morphological characters, such as height, number of stem units, root collar diameter, and shoot and root dry weights. Also, apical transitions in leaf initiation, stomatal distribution on leaf and cotyledon surfaces, and leaf wax features are described.