Competition between three submerged macrophytes, Elodea canadensis Michx, Elodea nuttallii (Planch.) St John and Lagarosiphon major (Ridl.) Moss

Abstract

During photosynthesis, submersed aquatic plant stands create ‘envelopes’ of raised pH and dissolved O₂ concentrations and depleted dissolved CO₂ concentrations. These may extend beyond the plant stands, suppressing the photosynthetic performance and increasing the photorespiratory stress of adjacent species. In competition between three aquatic macrophytes, Elodea canadensis, Elodea nuttallii and Lagarosiphon major, we hypothesised that a competitive advantage is achieved by those species that have the best stress generation/toleration mechanisms. pH and free CO₂ conditions were measured under laboratory conditions at two plant densities and compared with measurements of photosynthesis and respiration at various pH and free CO₂ concentrations. L. major raised pH faster and photosynthesised at a greater rate under the experimental conditions and may gain competitive advantage at high pH. No clear differences in photosynthetic behaviour were observed between the Elodea spp. and it is concluded that a wider range of factors than those studied here are probably involved in competition between the three species.