Bicarbonate use in three aquatic plants

Our study aimed to test the ability of aquatic plants to use bicarbonate when acclimated to three different bicarbonate concentrations. To this end, we performed experiments with the three species Ceratophyllum demersum, Egeria densa, Lagarosiphon major to determine photosynthetic rates under varying bicarbonate concentrations. We measured bicarbonate use efficiency, photosynthetic performance and respiration. For all species, our results revealed that photosynthetic rates were highest in replicates grown at low alkalinity. Thus, E. densa had approx. five times higher rates at low (264 ± 15 μmol O2 g−1 DW h−1) than at high alkalinity (50 ± 27 μmol O2 g−1 DW h−1), C. demersum had three times higher rates (336 ± 95 and 120 ± 31 μmol O2 g−1 DW h−1), and L. major doubled its rates at low alkalinity (634 ± 114 and 322 ± 119 μmol O2 g−1 DW h−1). Similar results were obtained for bicarbonate use efficiency by E. densa (136 ± 44 and 43 ± 10 μmol O2 mequiv. L−1 g−1 DW h−1) and L. major (244 ± 29 and 82 ± 24 μmol O2 mequiv. L−1 g−1 DW h−1). As to C. demersum, efficiency was high but unaffected by alkalinity, indicating high adaptation ability to varied alkalinities. A pH drift experiment supported these results. Overall, our results suggest that the three globally widespread worldwide species of our study adapt to low inorganic carbon availability by increasing their efficiency of bicarbonate use.

► Bicarbonate uptake in aquatic plants is an important factor for species distribution.
► We investigate the ability in using bicarbonate in three species.
► All three species have a high efficiency in using bicarbonate.
► These plants acclimate successfully to various alkalinities.