C4 Acid Metabolism and Dark CO2 Fixation in a Submersed Aquatic Macrophyte (Hydrilla verticillata) 1

摘要

The CO2 compensation point of the submersed aquatic macrophyte Hydrilla verticillata varied from high (above 50 microliters per liter) to low (10 to 25 microliters per liter) values, depending on the growth conditions. Plants from the lake in winter or after incubation in an 11 C/9-hour photoperiod had high values, whereas summer plants or those incubated in a 27 C/14-hour photoperiod had low values. The plants with low CO2 compensation points exhibited dark 14CO2 fixation rates that were up to 30% of the light fixation rates. This fixation reduced respiratory CO2 loss, but did not result in a net uptake of CO2 at night. The low compensation point plants also showed diurnal fluctuations in titratable acid, such as occur in Crassulacean acid metabolism plants. However, dark fixation and diurnal acid fluctuations were negligible in Hydrilla plants with high CO2 compensation points.