Competition of planktonic and benthic microalgae for phosphorus and light.
Floeder, Sabine*,1, Kombuechen, Anja1, Pasternak, Annika1, Hillebrand, Helmut1, 1 University of Cologne, Cologne, Germany
ABSTRACT- In freshwater systems, production of both, planktonic and benthic microalgae tend to be limited by phosphorus and light. However, the availability of these resources to planktonic and benthic communities differs, due to differences in habitat structure. Light intensity in the water depends on the intensity of incoming light and on light attenuation. Assuming a well mixed epilimnion, individual phytoplankton cells should receive similar light intensities per unit time. Comparable to nutrient competition, the phytoplankton collectively consumes the light resource. Benthic microalgae colonize substrates forming three-dimensional mats. Access to nutrients and light is structured by the vertical architecture of the assemblage and often possible only for canopy layer algae. Light attenuation within the mats may be considerable. Additionally, algal mats will always be shaded by the phytoplankton inhabiting the layer above. We investigated the competition of planktonic and benthic microalgae in a three factorial design, manipulating phosphorus concentration (15 and 150g P L-1), light intensity (15 and 150 mol photons m-2s-1) and inoculum (planktonic, benthic and benthic-planktonic). We found significant and interacting effects of phosphorus, light and inoculum on biomass production, diversity and growth of microalgae. In singular culture, both benthic and planktonic microalgae benefited from the enhanced supply of phosphorus and light. In combined culture, planktonic microalgae benefited from the increased light supply and became dominant regardless whether high or low phosphorus concentrations were added. In contrast, benthic microalgae profited from low light intensity combined with high nutrient concentrations.
Key words: nutrient competition, light competition, benthic microalgae, planktonic microalgae
All materials copyright The Ecological Society of America (ESA), and may not be used without written permission.