Hydrobiologia (2007) 578:65–77 DOI 10.1007/s10750-006-0434-3
P H Y T O P L A N K T O N W O RK S H O P
Phytoplankton morphological response to the underwater light conditions in a vegetated wetland Ine´s O’Farrell Æ Paula de Tezanos Pinto Æ Irina Izaguirre
Springer Science+Business Media B.V. 2007 Abstract This study analyses the influence of the underwater light climate on the morphometric characteristics of the phytoplankton at the population and community levels. The differences in light conditions across the floodplain were mainly defined by the patchiness of floating macrophytes and humic acids concentration. A morphometric response at the community level to the underwater PAR was registered. Sites with strong light constraints were characterised by non-flagellated organisms or with a small proportion of unicellular flagellates. Short organisms (2) were the morphotypes related to poorly illuminated environments. Moreover, the organisms showed forms more slender under these limiting conditions. This
pattern was different to that registered in wellilluminated sites where longer and larger organisms, with a smaller S/V and frequently flagellated, coexisted with the previously mentioned organisms. The autotrophic picoplankton, the smallest phytoplankton fraction, revealed lower abundances at sites with higher humic substances. Short term morphological changes were additionally studied for the dominant species by means of mesocosm experiments simulating different light climates. Intraspecific morphological plasticity was observed with respect to the filament length and the vacuolization of cells.
Guest editors: M. Albay, J. Padisa´k & L. Naselli-Flores Morphological plasticity of phytoplankton under different environmental constraints.
Introduction
Electronic supplementary Material Supplementary material is available for this article at http://dx.doi.org/ 10.1007/s10750-006-0434-3 and is available for authorized users. I. O’Farrell (&) P. de Tezanos Pinto I. Izaguirre Lab. Limnologı´a, Dpto. Ecologı´a, Gene´tica y Evolucio´n, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires. CONICET, Buenos Aires, Argentina e-mail:
[email protected]
Keywords Phytoplankton Morphology PAR Macrophytes South American wetland
Reynolds (1984) relates the success of the algae in exploiting the potential advantages offered by pelagic habitats with a certain degree of preadaptation to a dispersed existence. This capability is connected to the low level of structural organization and the morphological plasticity of algal cells, and is evidenced by the existence of a diversity of form, function and adaptive strategies. Algal growth depends upon intercepting sufficient light energy to perform the photosynthesis needed to sustain carbon fixation. The
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photosynthetic response of algae will be dependent upon the quality, intensity and subsurface attenuation of the solar radiation, and the efficiency of the pigment light trap among other factors. The in vivo absorbance spectrum is determined by the pigment composition, as well as the size and shape of the chloroplasts, cells or colonies (Kirk, 1994). This author asserts that either very long and thin filaments, or small spheres (
