Effects of carbon dioxide fertilization and copper exposure on photosynthesis in hornwort

Abstract

As global carbon dioxide (CO₂) emissions continue rising to unprecedented levels, photosynthetic efficiency of terrestrial plants is also increased. This phenomenon is known as CO₂ fertilization. While advantageous to aid in the removal of excess greenhouse gases, CO₂ fertilization may be offset by the simultaneous increase in heavy metal pollutants, such as copper, cadmium, lead, and mercury. The purpose of this experiment was to investigate whether heavy metal pollution, modelled through copper II sulfate (CuSO₄), may significantly impair CO₂ fertilization and photosynthesis in marine plants. We examined the volume of O₂ produced and the rates of photosynthesis in Ceratophyllum demersum (hornwort). Plants were placed in tubes of pre-boiled water with dissolved baking soda (NaHCO₃) as the CO₂ source. There were five treatment groups: no hornwort, hornwort control, hornwort + CO₂ fertilization, hornwort + CuSO₄, and hornwort + CuSO₄ + CO₂ fertilization. We found that CO₂ fertilization increased O₂ production and photosynthetic rate, while the addition of CuSO₄ inhibited photosynthesis and the positive effects of CO₂ fertilization. These results imply that although CO₂ fertilization can increase photosynthesis and eliminate some of the excess CO₂ in our atmosphere, this effect will be eliminated if we do not also control the amount of heavy metal pollution ejected into the environment.