The effects of acclimation to cold (4 A degrees C) and heat (36/38/40 A degrees C) on corresponding freezing and heat tolerances of one-year-old Trigonobalanus doichangensis seedlings were studied. In addition, the effects of abscisic acid (ABA) and salicylic acid (SA) pretreatments on the tolerance of this species to temperature extremes were tested. The results show that the content of soluble sugars increased with the duration of acclimation to cold (4 A degrees C), and the relative electrical conductivity and malondialdehyde content increased significantly after 7 d; however, the content of proline did not vary significantly. After acclimation to cold for 3 and 7 d, the semilethal low temperature (LLT50) was 0.8 and 1.1 A degrees C lower, respectively, compared with that of the control. The maximum quantum yield of photosystem II (measured as variable to maximum fluorescence ratio, F-v/F-m) decreased significantly after freezing treatments (-4 to -8 A degrees C), however, less when the plants were pretreated with 1-100 mg dm(-3) ABA. Acclimation to heat did not increase the semilethal high temperature (LHT50). A low concentration (1 mg dm(-3)) of SA increased LHT50, but medium and high concentrations (10 and 100 mg dm(-3)) decreased it. F-v/F-m decreased significantly after a heat shock (45-54 A degrees C). The pretreatment with 1-50 mg dm(-3) SA ameliorated a subsequent heat (48 A degrees C) stress.