Diurnal changes of photosynthetic characteristics of Taxus cuspidata seedlings under different light conditions.

In order to understand the characteristics of light adaptation of Taxus cuspidata for efficient cultivation, we selected 5-year-old seedlings to study the diurnal changes of photosynthetic characteristics under three different light conditions, i.e., full light (FL), 60% FL (F1) and 30% FL (F2), and measured the physiological responses of the seedlings to the change of light and temperature. The results showed that the photosynthetic rate (Pn) of all three groups had a double-peaked curve, and Pn of seedlings at 9:00 am was significantly higher than that at 15:00 pm. Pn under F2 light condition was the highest, and the Pn value under the F1 light condition was higher than that under the full light condition. It was clear that Pn of seedlings was restrained by the increase of light intensity. The diurnal changes of stomatal conductance (Gs) and the transpiration rate (Tr) showed a similar double-peaked pattern of the Pn values. The variations of Gs values of the seedlings under F2 light condition was lower than the other two groups; the Tr under F2 light condition reached the highest value in the morning, and the Tr under FL condition was the highest in the afternoon. The intercellular carbon dioxide concentration (Ci) showed a “V” curve trend. The Ci of seedlings under F2 had the highest value in the morning, and the Ci reached the opposite trend in the afternoon, significantly different from the FL trend. The trend of the diurnal variation of stomatal limitation (Ls) was opposite to that of Ci completely. In general, the net photosynthetic rate of the seedlings decreased with the increase of light intensity during the daytime obviously.