Primary productivity in the submerged aquatic macrophyte Ceratophyllum demersum

Summary

Primary productivity, respiration and excretion in Ceratophyllum demersum were studied to investigate the role of this species in the carbon cycle of Lake Vechten.

Under experimental conditions, the effects of incubation during different periods in the light — combined with different pre- or postincubations — on photosynthesis were studied, using the ¹⁴C method. In the experiments apices were used from a preconditioned culture. These apices are photosynthetically the most active parts of the plants. Photosynthesis was highest during 2–4 hours after transfer to experimental conditions, ¹⁴C fixation amounting to 0.002% mg dry weight⁻¹ hr⁻¹ (0.3-0.5 mg Cg⁻¹hr⁻¹). Excretion of non gaseous organic compounds was very low, excretion of ¹⁴CO₂ considerable. No correction was used for respiration as the ¹⁴C assay is considered to be a method to measure approximate net photosynthesis in macrophytes, when short incubation periods are used. The data were low compared to those in the literature, probably caused by the late dormant state of the plant material. A seasonal effect in the rate of photosynthesis was detectable. The experiments will be followed by in situ measurements.