The Mechanism Of Inorganic Carbon Assimilation Of Three Common Submerged Macrophytes

Potamogeton pectinatus, Potamogeton maackianus and Myriophyllum spicatum is three common submerged macrophytes in our country. They are ideal materials for the re-vegetation of submerged plants in eutrophic lakes and rivers. There have been a lot of researches on the growth and photosynthetic characteristics of the three common submerged macrophytes all around the world. However, the dissolved inorganic carbon use efficiency,the influencing factors and the mechanisms involved in carbon use of them are not fully elucidated. In this paper, we chose Potamogeton pectinatus Potamogeton maackianus and Myriophyllum spicatum as the experimental materials. The inorganic carbon utilization efficiency of them was compared using pH drift technique. The extracellular carbonic anhydrase activity was monitored, and the extracellular carbonic anhydrase inhibitors were used to determine the contribution of extracellular CA pathway to the inorganic carbon use of the three species, as such pathway was suggested to be important in the inorganic carbon use of plants.The impacts of natural level of inorganic carbon concentration in the water-column on their inorganic carbon use efficiency and growth were investigated at different pH valuesThe results of the pH drift experiment shows that, all of the three submerged aquatic plants can use HCO3- as inorganic carbon resources, but significant differences showed in the use efficiency. Comparing with Potamogeton pectinatus, Potamogeton maackianus and Myriophyllum spicatum showed stronger HCO3- use capabilities. As pH value increased and the natural concentration of inorganic carbon in the water-column was kept, the ability of inorganic carbon use of the three species all decreased, and so was their biomass and chlorophyll content. The results indicated that inorganic carbon concentration decreased with the high pH level,witch was responsible for the growth of the three submerged plants.The inorganic carbon utilization ability of the three kinds of submerged plants decreased by 50% or even more by the addition of the extracellular CA inhibitors, indicating that extracellular CA played an important role in the process of inorganic carbon utilization for the three species. But their contributions to the inorganic carbon use of them were different. And the maximum decline rate was 62% for Myriophyllum spicatum.The extracellular CA activity of the three species all increased at first and then decreased with the increase of the pH level. Maximum values occurred when pH was 8, indicating that extracellular CA activity is greatly activated then. When pH level further increased and the inorganic carbon concentration decraesed,the activity showed a downward trend. The results suggested that the enzyme activity of the three common submerged macrophytes was greatly induced by inorganic carbon concentration.We proved Myriophyllum spicatum and Potamogeton maackianus have a stronger ability to use water DIC through the experiment. Myriophyllum spicatum showed better growth rate than the other two species in a wide pH range, indicating that Myriophyllum spicatum is more suitable for the restoration of submerged plants in the eutrophic waterbody.