© 2000 Heron Publishing—Victoria, Canada
Frost hardening of Pinus radiata seedlings: effects of temperature on relative growth rate, carbon balance and carbohydrate concentration
Dennis H. Greer (1), Linda A. Robinson (1), Alistair J. Hall (1), Karin Klages (2) and Helen Donnison (2)
1. Horticulture and Food Research Institute, Palmerston North Research Centre, Private Bag 11030, Palmerston North, New Zealand / 2. Ruakura Research Centre, Private Bag 3123, Hamilton, New Zealand / Received December 24, 1998
Summary
Pinus radiata (D. Don) seedlings were grown for 100 days at day/night temperatures of 10/1, 15/1, 20/1 and 25/1 °C, to determine whether
temperatures above a threshold of 5 °C influence frost hardiness development. Relationships between hardening and relative
growth rate, carbohydrate concentration and net carbon balance were also investigated. Seedlings hardened at a nearly constant
rate in each treatment, although the rate of hardening was strongly temperature dependent. It increased as the temperature
declined, but in a curvilinear fashion. Temperatures below 9.5 °C were effective in hardening the seedlings. During the daily
temperature cycle, dehardening occurred at temperatures above the threshold, whereas hardening occurred at temperatures below
the threshold. The net difference between the two processes determined the development of frost hardiness. The development
of frost hardiness was negatively correlated with relative growth rate and positively correlated with the accumulation of
starch and sugars. We conclude that frost hardening is a complex process that is causally linked to carbohydrate concentrations.
Keywords:
carbohydrates, hardiness, hardening rate, modeling.
