INTERACTIVE EFFECTS OF CO2 AND ENVIRONMENT ON NET PHOTOSYNTHESIS OF WATER-LILY

Water-lily (Nymphaea marliac) plants were grown out doors in 570-1 stock tanks contained in plastic-walled, open-topped CO2-enrichment chambers continously supplied with either 640 or 340 (ambient) μl CO21-1 of air. Net photosynthesis (Pn) of water-lily leaves in each CO2 treatment was measured hourly between 0800 and 1600 h MST on 26 October and 10 and 24 November 1987. Air temperature and net solar radiation were measured at the same time. The 3 days on which Pn was measured provided an air temperature range of 10.3-33.2°C and a net solar radiation range of 30-659 W m-2. Significant linear relationships wre established between Pn and air temperature and Pn and net solar radiation for both CO2 treatments. Significant interactive effects of CO2 and air temperature and CO2 and net solar radiation were also found to affect Pn. In conditions unfavorable for Pn (low light and low temperature), there was no difference in Pn rate between the two CO2 treatments. In conditions that were favorable for Pn (high light and high temperature), however, Pn in the 640 μl CO2l-1 of air treatment was as much as 60% greater than in the ambient CO2 treatment. © 1990.