Environmental variables and their effect on photosynthesis of aquatic plant communities

Abstract

Environmental variables affect both photosynthetic pigments and enzymes and instantaneous photosynthetic rates of aquatic plants. Environmental conditions have been better described for pelagic phytoplankton than for littoral communities of macrophytes and attached microalgae which, furthermore, live in a structurally more complex and dynamic environment. Phytoplankton in well-mixed surface waters is circulated in a light gradient over a long distance, and this makes precise light adaptation difficult. Light is rapidly attenuated with depth in dense communities of macrophytes and attached algae, but the light climate is nevertheless more predictable and light adaptation simpler because of the fixed vertical position of a macrophyte leaf or an attached microalga. Dense communities of macrophytes and attached algae have high rates of photosynthesis in light and respiration in the dark per unit volume of the medium they live in. Because of reduced exchange of dissolved metabolites with the more uniform pelagial waters, they experience marked variations in dissolved inorganic carbon (DIC), CO 2 and O 2 with depth and light and darkness. The simultaneous depletion of DIC and CO 2 and build-up of O 2 which occur in the light within the diffusive boundary layers that surround leaf surfaces and attached algal communities call for particularly efficient mechanisms to assimilate inorganic carbon.