Abstract: The photosynthetic characteristics of Aegiceras comiculatum seedlings respectively cultivated in fresh water and artificial sea water were measured in different months with Li-6400 photosynthetic system. Results showed that in July and October, the net photosynthetic rate of A.comiculatum seedlings demonstrated a “double peak pattern” of daily change along with the phenomenon of noon break. In July, the maxium net photosynthetic rates（P_max）of the artificial sea water group and the fresh water group were respectivley 9.97 and 11.95 μmol·m^-2·s^-1；and in October the P_max of the two groups were respectively 12.2 and 12.9 μmol·m^-2·s^-1. After fresh water adaptation, A.comiculatum demonstrated higher net photosynthetic rates than those cultivated in artificial sea water. From the light response curves, the maxium net photosynthetic rate（P_max）, light saturated point（LSP）, light compensated point（LCP）and apparent quantum yield（AQY） were obtained, which were respectively 7 μmol·m^-2·s^-1，1 477 μmol·m^-2·s^-1，30 μmol·m^-2·s^-1，0.031 3 for the artificial sea water group；and respectively 8.69 μmol·m^-2·s^-1，980 μmol·m^-2·s^-1，40 μmol·m^-2·s^-1，0.011 for the fresh water group. Of the physiological and ecological factors that have been measured, the photosynthetic active radiation and stomatal conductance had the largest effects on the photosynthesis of A.comiculatum, which exhibited highly significant correlationships with net photosynthetic rate and transpiration rate. After fresh water adaptation, A.comiculatum demonstrated a narrower range of utilizable light intensity, but higher net photosynthetic rate, which indicated that A.comiculatum had a strong adaptability to fresh water environment.

Key words: Aegiceras comiculatum, fresh water adaptation, net photosynthetic rate, stomatal conductance, transpiration rate