The Diurnal Variations of Photosynthesis in Panax stipuleanatus

The diurnal variations of photosynthesis in Panax stipuleanatus was investigated with Ci-310PS portable photosynthetic system under 12% light transmission rate in shady shed. The results were shown as follow: The curves of the diurnal variations of the net photosynthetic rates in May were different from those in September, the former with one peak and the latter with two peaks. In May,the net photosynthetic rates reached a maximum((2.73μmol/(m~2·s))at 13∶00; while in September, two peaks happened separately at about 12∶00 and 14∶00 hour with a midday suppression at 13∶00 hour. The diurnal variations of the transpiration rates had the same tendency as those of the stomatal conductance; the correlative coefficient between them was 0.445 in May and 0.909 in September separately, reaching the significant levels. In comparison, P. stipuleanatus and P. notoginseng (two-year-old) were most significantly different from each other in the net photosynthetic rates, but their transpiration rates were significantly different.