Abstract: Larix chinensis is a timberline tree species on Mt. Taibai in the Qinling mountains. To better understand climatic and physiological processes that control timberline formation, the eco-physiological characteristics of L. chinensis seeds were investigated in the laboratory by exposing seeds to different treatments of illumination and temperature. The major results are summarized below. An alternating photoperiod of 12 h light∶12 h dark increased phytohormone levels of ABA and GA in imbibed seeds during germination. Under conditions of constant temperatures of 25 ℃ or 12 ℃, constant illumination had a positive affect on phytohormone levels of IAA in imbibed seeds. Under alternating temperatures of 25 ℃ for 12 h and 12 ℃ for 12 h, alternating illumination did not affect phytohormone contents of IAA. Changes in phytohormone levels of CTK showed an opposite response as IAA. Constant temperatures had a positive effect on phytohormone contents in imbibed seeds. Temperature was crucial for seed germination, and the rate of seed germination at a constant temperature of 25 ℃ was greater than at a constant temperature of 12 ℃. Alternating illumination (12 h light∶12 h dark) also had a strong, positive effect on seed germination. Otherwise the results showed that endogenous phytohormone levels were important for seed germination. The results indicated that temperature affected the germination rate and success of L. chinensis seeds, which is crucial for regeneration of L. chinensis, while illumination impacts were weak. Further studies are needed to better understand the underlying mechanisms of how temperature affects timberline formation on Mt. Taibai, Qinling mountains.

Key words: Larix chinensis, Seed germination, Temperature, Illumination, Phytohormones