INFLUENCE OF PHOTOPERIOD AND TEMPERATURE ON GROWTH, GAS-EXCHANGE, ANDCOLD-HARDINESS OF YELLOW CYPRESS STECKLINGS

Yellow cypress (Chamaecyparis nootkatensis (D. Don) Spach) stecklings (rooted cuttings) were acclimated for approximately 8 weeks under one of the following photoperiod-temperature treatments: 18 h/10 degrees C , 18 h/20 degrees C, 9 h/10 degrees C, 9 h/20 degrees C followed by de acclimation in a common environment of 12 h/20 degrees C for approxima tely 6 weeks. During acclimation and deacclimation, steckling morpholo gical development, net photosynthesis, transpiration and leaf conducta nce, and midday shoot water potential were measured. Hardiness was det ermined by freeze-induced electrolyte leakage. Shoot growth was reduce d more by short photoperiods (9 h) than by cool temperature (10 degree s C) as were net photosynthesis, stomatal conductance, transpiration, and photosynthetic efficiency. Photoperiod-induced cold hardening of s hoots and height growth cessation were reversible in warm temperatures (20 degrees C) and 12-h days, indicating that hardiness induction tre atments had no lasting effects on the growth or cold hardiness of this tree species.