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Keywords:

  • anthocyanin;
  • aquatic macrophytes;
  • chlorophyll fluorescence;
  • CO2;
  • excess light energy;
  • nonphotochemical quenching (NPQ);
  • photoprotection;
  • xanthophyll cycle

Summary

  • • 
    In the present study, we investigated the effects of CO2 availability on photosynthesis, photoinhibition and pigmentation in two species of amphibious plants, Lobelia cardinalis and Nesaea crassicaulis.
  • • 
    The plants were grown emergent under atmospheric conditions and submerged under low and high CO2 availability.
  • • 
    Compared with Lobelia, Nesaea had thin leaves and few stomata in all CO2 treatments. While Lobelia expressed no variation in anthocyanin content among treatments, Nesaea produced high concentrations of anthocyanin when submerged. Lobelia photosynthesis increased in response to increasing CO2 availability, and photoinhibition was negatively related to xanthophyll content. By contrast, Nesaea photosynthesis was highest under submerged conditions, and there was no relationship between photoinhibition and the xanthophyll content.
  • • 
    We conclude that the response of Lobelia to varying CO2 availability is similar to that of terrestrial plants and that this species relies on the xanthophyll cycle for nonphotochemical quenching (NPQ) and protection against photoinhibition. By contrast, the thin leaves, few stomata and low levels of chlorophylls and accessory pigments in Nesaea, relative to Lobelia, suggest adaptation to a submerged habitat. While Nesaea does not seem to rely on the xanthophyll cycle or other xanthophylls for NPQ, some role of anthocyanins in the protection against photoinhibition cannot be ruled out, owing to its effect as a sunscreen and as an efficient quencher of free radicals.