Abstract: Dynamic chlorophyll fluorescence parameters and photosynthetic capacity of Quercus mongolica and Tilia amurensis seedlings were measured immediately after suddenly exposing to 10%, 30% and 100% daylight from greenhouse (5% relative light intensity). The aim of the study was to investigate the light acclimation and photoprotective mechanisms to the change of light environment on the two species. The results showed that: maximal photochemical efficiency of PSⅡ(F_v/F_m) decreased immediately on sudden exposure to 100% daylight, with the maximal decrease occurring 3 days (0.52) after transfer on Q. mongolica and 1 day (0.67) on T. amurensis. The decrease on Q. mongolica was obviously higher than that on T. amurensis. During the light acclimation, the F_v/F_m was followed by a subsequent recovery to the initial value, indicating that photodamage in the two species did not occur in the short term; the value of the photosynthetic capacity (P_max) and actual efficiency of PSⅡ (ФPSⅡ) under 30% daylight was higher than 10% and 100% daylight, indicating that relative to high and low light, moderate light was better to the growth of seedlings; the variation of P_max, F_v/F_m, ФPSⅡ, NPQ between 100% and 30% daylight in Q. mongolica was greater than that in T. amurensis, indicating that Q. mongolica was more susceptible to high light than T. amurensis; and the two species dissipated their excess light energy both depending on the increase of non-photochemical quenching of chlorophyll fluorescence (NPQ) and the Car/Chl ratio, and on the decrease of the Chl content.

Key words: Quercus mongolica, Tilia amurensis, light intensity transfer, photosynthetic capacity, chlorophyll fluorescence, photoinhibition, photoprotection