Abstract:

The acclimation of seedlings of three secondary-forest tree species to light regimes was investigated during the growth season in 2007 in the Northeast of China. The seedlings of Juglans mandshurica，Fraxinus mandshurica and Phellodendron amurense　were cultivated under four light intensity regimes (100%， 60%， 30% and 15% of full light， which were termed as FI， II， LI and WI respectively). The photosynthetic characteristics， leaf mass per unit area， and chlorophyll content were determined during the growth season. The results showed that light compensation point (LCP)， light saturation point (LSP)， dark respiration rate (R_d)， maximum photosynthetic rate (P_max). The content of carotenoid， leaf dry mass per unit leaf avea (LMA) of all the three tree species decreased along with decreasing light intensities. And the contents of chlorophyll (Chl) of full light treatment were lower than that of the others for all the tree species. The results suggested that Fraxinus mandshurica was moderately shade tolerant at the seedling stage. Analysis of the plasticity index of eco-physiological parameters， suggested that P. amurense had the ability of adapting to wider light intensity range; and the ability of shade-intolerance for P. amurense was greater than that of Juglans mandshurica. The different adapting characters of eco-physiology to light regimes played an important role in explaining the mechanism of co-existing and succession of different species in secondary forest ecosystem.

Key words: light intensity, net photosynthetic rate, photosynthetic parameters, dark respiration