Evaluation of Freezing Tolerance of Thuja and Arizona Cypress under Controlled Conditions

Arizona Cypress (Cupressus arizonica L.) and Thuja (Thuja orientalis L.) are very important evergreen and mainly used as ornamental trees. This study was carried out in two independent experiments with the main purpose of evaluating of freezing tolerance of Arizona Cypress and Thuja with eight levels of temperatures (control, -10, -15, -20, -25, -30, -35, -40℃) in a completely randomized design. Proline, Electrolyte leakages, Soluble carbohydrate and Re-growth were measured. Result showed that, in both species Proline and Electrolyte leakages increased. Re-growth percentage decreased dramaticaly in both species with lowering temperature level. so that any Re-growth was observed for Thuja and Arizona Cypress in the -30 and -20℃, respectively. Interactions between Soluble carbohydrate and temperature were not significant for Thuja but decreased significantly (P>0.01) in Arizona Cypress. There was a negative significant correlation between Re-growth, in Thuja (-0.895ôô) and Arizona Cypress (-0.646ôô) with temperature. According to the results, Arizona Cypress was more susceptible to freezing compared to Thuja