Diurnal changes of photosynthesis in Panax ginseng and Panax quinquefolium under different environmental conditions.

The diurnal changes of photosynthesis in Panax ginseng and P.quinquefolium under different environmental conditions were studied in this paper.As for leaves grown under low light intensity(10% light transmission rate,LTR shade),diurnal changes of net photosynthetic rate(Pn) were showed in single peak,the maximum value of Pn was at 12:00 am—1:00 pm.As the increase of light intensity(grown under 20%,30% and 40% LTR shade),Pn was increased,higher Pn was measured from 9:00—11:00 am to 12:00 am—1:00 pm,and then Pn was declined at 2:00—4:00 pm.However,as for leaves grown under high light(50% LTR shade),maximum Pn were measured at 9:00—11:00 am,then,Pn was decreased from 12:00 am—1:00 pm.Specific leaf mass(dry mass per unit leaf area) and starch content was increased as the increase of light intensity and Pn.Daily depression percentage of Pn was paralleled with daily increase percentage of specific leaf mass and starch content.Maximum apparent quantum yield(AQY) was measured at 9:00—11:00 am,and had slight decline at 12:00 am—1:00 pm,the lowest value was measured at 2:00—4:00 pm.The leaves of P.ginseng and P.quinquefolium grown in Changchun region(relative higher temperature and lower relative humidity) showed higher water vapor pressure deficit(VPD) and greater daily depression percentage of Pn,AQY and Gs than those of grown in Huinan region(relative lower temperature and higher relative humidity).For the leaves grown under Huinan region,Tr did not show decline changes at 2:00—4:00 pm;but it showed greater daily depression for those of Changchun region.The leaves grown under Huinan region had higher WUE than these grown in Changchun region at 9:00—11:00 am,and it was nearly same at 2:00—4:00 pm in two regions.The results indicated that P.quinquefolium had stronger ability in acclimatization to high temperature and acridness than P.ginseng.