Response of O. cordata Floating Leaves to Different CO2 Concentrations

In the different CO₂ acclimated experiments, the pots of O. cordata plants were put into the white plastic tanks (65 cm × 45 cm × 35 cm) containing tap water and incubated at two CO₂ concentrations as described previously (Huang et al., 2018). In the high CO₂ treatment (HC), the target pH of 7.0 was maintained between 6.52 and 7.06 by bubbling the medium with pure CO₂ under the control of a microcomputer pH controller (model 6311, Jenco Instruments, USA), producing CO₂ concentrations between 380~1603 μM with a mean of 941 μM. A low CO₂ (LC) concentration was produced by the natural photosynthesis of the plants which depleted the inorganic carbon of the water, and increased pH from 8.09 to 8.91, with a CO₂ concentration range of 3~28 µM and a mean of 15 µM. The acclimation of different CO₂ with four replicate pots per treatment, lasted four weeks in the growth room. Over the whole period of acclimation, alkalinity, pH and temperature were measured to calculate the CO₂ concentration using the equations reported in Maberly (1996). More information of the conditions in the treatments is shown in Table 1 . Following the different CO₂ acclimation, there were newly floating leaves emerged, which were harvested for anatomical structure observation and physiological parameters measurement.

Conditions in the low and high CO₂ treatments.

Mean values are given with s.d. and ranges are in parentheses. ^# calculated as a geometric mean.