INFLUENCE OF NURSERY CULTURE ON GROWTH, COLD-HARDINESS, AND DROUGHT RESISTANCE OF YELLOW CYPRESS

The influence of short-day (9 h) and long-day photoperiods (18 h), and three levels of plant moisture stress (none and dried to predawn shoot water potentials of -1.0 or -1.8 MPa), applied for 7 weeks beginning in mid-July 1990, were studied on greenhouse-grown stecklings (rooted cuttings) of yellow cypress (Chamaecyparis nootkatensis (D. Don) Spach). A series of morphological and physiological measurements were made on the stecklings during and after the treatment period. Moisture stress significantly reduced steckling shoot growth and shoot dry weight by lowering net photosynthesis rates, while short-day photoperiods did not. The most pronounced growth reductions occurred when the treatments were combined, but effects were short-lived, with shoot growth resuming soon after the treatments ended. The short-day and moisture-stress treatment had no significant effect on root dry weight, shoot/root ratio, or water balance ratio. The risk of using moisture stress to control shoot growth in the nursery was low; mortality did not occur until the stecklings had been without water for at least 9 days. Moisture-stress treatments increased steckling root growth potential but had little effect on osmotic adjustment, cell elasticity, dry weight or symplastic fractions, cuticular transpiration, resistance to plant water movement, and relative water content of the shoots; short-day treatments had no influence on any of these parameters. Short days and moisture stress, singly or combined, had little effect on steckling cold hardiness. Steckling gas exchange rates were reduced significantly by low root temperature. In a 6-week controlled-environment simulation of planting-site moisture conditions, no significant differences in steckling net photosynthesis, transpiration, or stomatal conductance were found among nursery treatments; those that had been subjected to moisture stress in the nursery had small growth increases after planting in both wet and dry soil moisture regimes. We conclude that shoot growth of yellow cypress stecklings was controlled in the nursery using 9-h photoperiods and -1.8 MPa predawn shoot water potentials. Improved cold hardiness of the stecklings was not achieved using these nursery cultural methods, but moisture stress did confer some measure of drought resistance immediately after treatment, with higher root growth potential and lower shoot mass.