Diurnal Dynamics of Photosynthetic Parameters in Leaves of Angelica sinensis and Its Relation to Environmental Factors

During the rootstock thickening period,the diurnal dynamics of photosynthetic rate(Pn),transpiration rate(Tr),stomatal conductance(Gs) and internal CO2(Ci) of Angelica sinensis as well as the ecological factors photosynthetically active radiation(PAR),CO2 concentration in field(Ca),relative humidity(RH),air temperature(Ta) and leaf temperature(TL) were measured.The results show that the diurnal net photosynthetic rate of A.sinensis in sunny day exhibited double-peak pattern,and the peaks occurred at 10:00 and 16:00 respectively.There was a significant midday depression with A.sinensis,which was caused principally by stomatal factors such as stomatal conductance.The curves of diurnal variation in Tr,Gs and Ci of A.sinensis leaves had two peaks also,the peaks occurred at 10:00 and 17:00 respectively,and an obvious midday depression from noon to 1pm.The most optimal equation describing diurnal variation of Pn was attained by the method of stepwise multiple-regression as follows:yPn=14.310 8+0.007 6xPAR-0.527 1xTL(R2=0.660 1,P0.05).With analysis of partial correlation and path on Pn and environmental factors,it is concluded that TL and PAR had the greatest effect on the diurnal dynamics of Pn,while Ca,RH and Ta indirectly affected Pn mainly through TL.