Comparative studies of the photosynthesis of the submerged macrophyte Elodea canadensis and the filamentous algae Cladophora glomerata and Spirogyra sp.

Abstract

The photosynthetic and respiratory responses of Elodea canadensis Michx., Cladophora glomerata (L.) Kütz. and Spirogyra sp. to oxygen, temperature, HCO 3 −1 concentration, pH and irradiance were determined. Photosynthesis was inhibited by O 2 in all three species under all conditions and inhibition was greatert in E. canadensis. This inhibition was not caused solely by an accelerated rate of dark respiration and this suggests that photorespiration may be an important factor controlling productivity, particularly in E. canadensis. Photosynthetic performance was impaired much more in E. canadensis than in either of the filamentous algae conditions of high pH and low CO 2 concentrations. In the field photosynthesis of these algae may increase the pH and reduce the CO 2 content of the water sufficiently to exert deleterious effects on macrophyte photosynthesis. Such a plant-induced change in water quality could give C. glomerata a competitive advantage over E. canadensis and be a factor in the replacement of the vascular plant by the alga in some waters.