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 Pnof seedlings at 9: 00 am was significantly higher than that at 15: 00 pm. Pnunder F2 light condition was the highest,and the Pnvalue under the F1 light condition was higher than that under the full light condition.It was clear that Pnof 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 Pnvalues. The variations of Gsvalues of the seedlings under F2 light condition was lower than the other two groups; the Trunder F2 light condition reached the highest value in the morning,and the Trunder FL condition was the highest in the afternoon. The intercellular carbon dioxide concentration( Ci)showed a Vcurve trend. The Ciof seedlings under F2 had the highest value in the morning,and the Cireached the opposite trend in the afternoon,significantly different from the FL trend. The trend of thediurnal variation of stomatal limitation( Ls) was opposite to that of Cicompletely. In general,the net photosynthetic rate of the seedlings decreased with the increase of light intensity during the daytime obviously.