Study on Diurnal Variation of Photosynthesis of Medicinal Plant Blumea balsamifera

In order to explore the characteristics of diurnal variation of photosynthesis and key influencing factors of medicinal plant B.balsamifera,the eco-physiological photosynthetic characteristics of B.balsamifera and the environmental factors were measured using Li-6400portable photosynthesis system,also the systematic analysis was carried out.The results showed that the diurnal variation of stomatal conductance(Gs)and leaf transpiration(Tr)of B.balsamifera both showed a double peak curve.The diurnal variation pattern of intercellular CO2 concentration(Ci)showed aV-type curve.The diurnal change of net photosynthetic rate(Pn)of B.balsamiferapresented a typical bimodal pattern,the first peak[Pn=20.39μmol/(m2·s)]appeared at 10o'clock and the second peak[Pn=19.44μmol/(m2· s)]appeared at 15o'clock,and in midday there was an obvious photosynthetic depression,but the extent was gentle.The diurnal variations of Pn related significantly positively to all the eco-physiological factors except atmospheric CO2 concentration(Ca).The main reason of midday photosynthetic depression was stomatal limitation factors based on stomatal closure.Gs,Ci and photosynthetically active radiation(PAR)were the key influencing factors on Pn of B.balsamifera,and Gs produced more influence than Ci and PAR.