Abstract:

Camptotheca acuminata was an important medicinal tree as its camptothecin with anti-tumor activity. The diurnal changes of net photosynthesis rate (Pn) in leaves of C. acuminata under natural condition were studied in this paper by CI-301 CO₂ analyzer. The results showed that the curve of diurnal variation of Pn was demonstrated two peaks in clear day, which appeared at 10:00 and 16:00 respectively. The first peak value was 7.9075 μmol CO₂·m^-2s^-1 and the second one was 3.7340 μmol CO₂·m^-2s^-1. There was a clear depression at noon, which was 2.4470 μmol CO₂·m^-2s^-1 appeared at 14:00. Only one peak had the curve of Pn in cloudy day, which occurred at 12:00 Daily average Pn in clear day was 4.3300 μmol CO₂·m^-2s^-1, and that of cloudy was 3.7500 μmol CO₂·m^-2s^-1 Photon flux density (PFD) and relative humidity played very important roles in Pn changes among the ecological factors. Depression of Pn was not caused by the decreasing of stomatal conductance that would decrease the CO₂ supply. Factly it was regulated by nostomatal factors.

Key words: Camptotheca acuminata, Net photosynthesis rate, Diurnal variation