The interaction effect of temperature and drought on seed germination of Cypress (Cupressus sempervirens var. horizontalis)

The current experiment was done on Cypress, as one of the most important species in urban forestry, to provide a hydrothermal time model under controlled conditions in a laboratory. The model is designed with respect to stress tolerance thresholds for seed germination. Five different temperature (10, 15, 20, 25, 30 C°) and drought (0, -0.5, -1, -1.5 and -2 MPa) treatments were applied on the seeds. The optimum temperature (To) and basic temperature (Tb) were obtained 21/05 C° and 6/041 C° respectively. The hydrotime constant (θH) for this species was 0/35. The results showed that the decreasing in water potential and temperature caused germination percentage decrease. Temperature and water potential factors had independent and interaction effects significantly on time and percent germination. Finally hydrothermal time model is provided for the species.