title: Regulation of photosynthetic rates of submerged rooted macrophytes.
abstract: Fourteen temperate, submerged macrophytes were cultivated in the laboratory at high DIC levels (3.3-3.8 mM), 10.4-14.4 mol photons (PAR) m-2d-1and 15°C. Photosynthesis at photosaturation ranged between 0.59 and 17.98 mg O2g-1DW h-1at ambient pH (8.3) and were markedly higher between 1.76 and 47.11 mg O2g-1DW h-1at pH 6.5 under elevated CO2concentrations. Photosynthetic rates were significantly related to both the relative surface area and the chlorophyll content of the leaves. Consequently, the photosynthetic rate was much less variable among the species when expressed per surface area and chlorophyll content instead of dry mass. The chlorophyll content was probably a main predictor of photosynthesis of submerged leaves because of the direct relationship of chlorophyll to the light harvesting capacity and/or a coupling to the capacity for photosynthetic electron transport and carboxylation. A comparison with terrestrial leaves characterized the submerged leaves by their low chlorophyll concentrations and low photosynthetic rates per surface area due to the thin leaves. Photosynthetic rates per chlorophyll content in submerged leaves at CO2saturation, however, were at the same level as photosynthesis in terrestrial leaves measured at ambient CO2when appropriate corrections were made for differences in incubation temperature.
authors.affiliation: Freshwater Biological Laboratory, University of Copenhagen, 51 Helsingørsgade, DK-3400, Hillerød, Denmark.
authors.forename: Søren Laurentius
authors.initials: SL
authors.lastname: Nielsen
authors.affiliation: Freshwater Biological Laboratory, University of Copenhagen, 51 Helsingørsgade, DK-3400, Hillerød, Denmark.
authors.forename: Kaj
authors.initials: K
authors.lastname: Sand-Jensen
keywords: CO2 limitation; Chlorophyll content; Photosynthetic rates; Relative surface area; Submerged macrophytes