Response of photosynthetic plasticity of Paeonia suffruticosa to changed light environments

Temporal changes in gas exchange and chlorophyll fluorescence of Paeonia suffruticosa seedlings acclimated to three levels of light environments were investigated. There was a significant photosynthetic depression in seedlings acclimated to a long time of shading and then suddenly exposed to full ambient radiation. The decreased transpiration (E) resulted from ‘feed-forward effect ’ mechanism [Aust. J. Plant Physiol. 5 (1978) 787]. An obvious photosynthetic plasticity was found when the seedlings were acclimated to respective light regimes for 1 month. The photosynthetic rate (Pn) for seedlings acclimated to high-light regime was significantly higher than that for seedlings acclimated to intermediate- and low-light regimes. The decreased Pn for seedlings acclimated to low-light regime was attributed to non-stomatal limitation when exposed to full ambient light. A significant decrease in Fv/Fm for the seedlings acclimated to low-light regime indicated that the photosystem II (PSII) was inactivated when seedlings were exposed to full ambient light. Nevertheless, the photosynthetic plasticity of the P. suffruticosa seedlings was limited temporally. A long time (2 months) of high-light exposure may damage the photosynthetic apparatus. The Pn for seedlings acclimated to intermediate-light regime was significantly greater than that for seedlings acclimated to high- and low-light regimes