Photosynthetic characteristics of Gynostemma pentaphyllum under shade.

The study showed that under summer shade condition,the diurnal variation of net photosynthetic rate of Gynostemma pentaphyllum presented nontypical double apex,the first apex being 13.8 μmol CO 2·m -2 ·s -1 at 11:00,and the diurnal net photosynthetic rate was about 176.97 μmol CO 2·m -2 ,3.1 times of that under full sunlight.There was a positive correlation between net photosynthetic rate and photon flux density (PFD),and relative humidity had a small effect on net photosynthetic rate.Under full sunlight,the typical midday depression of photosynthesis was observed,and the diurnal variation of net photosynthetic rate presented double apex,with the first apex being 3.0 μmol CO 2·m -2 ·s -1 at 10:00 and the second being 1.25 μmol CO 2·m -2 ·s -1 at 14:00.There was a positive correlation between net photosynthetic rate and relative humidity,and the latter had a strong effect on net photosynthetic rate.When PFD was higher than 700 μmol CO 2·m -2 ·s -1 ,it had a negative correlation with net photosynthetic rate.Stoma conductance was the main factor affecting the transpiration rate of Gynostemma pentaphyllum.Therefore,Gynostemma pentaphyllum was a typical sciophytic plant,and light factor should be considered firstly in its cultivation.