Photosynthetic efficiency as a function of thermal stratification and phytoplankton size structure in an oligotrophic alpine lake |
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Authors: | Christina Kaiblinger Sonja Greisberger Katrin Teubner Martin T Dokulil |
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Institution: | (1) Institute for Limnology, Austrian Academy of Sciences, Mondseestrasse 9, 5310 Mondsee, Austria |
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Abstract: | Allometric relationships of phytoplankton communities were studied on the basis of a five-year data-set in a deep oligotrophic
alpine lake in Austria. The seasonal phytoplankton succession in Mondsee is characterised by diatoms during winter mixing
and a distinct metalimnetic population of Planktothrix rubescens during stratification in summer. The variation of phytoplankton photosynthetic efficiency between seasons was assessed using
in situ carbon-uptake rates (5 years data) and Fast Repetition Rate Fluorometry (FRRF) (2 years data). The light-saturated,
chlorophyll-specific rate of photosynthesis (P*max), irradiance at the onset of saturation (E
k) and maximum light-utilisation efficiency (α*) were determined for winter mixing and summer stratification. Fluorescence-based parameters as the functional absorption
cross section of Photosystem II (σ
PSII) and the photochemical quantum yield (F
v/F
m) were additionally analysed in 2003 and 2004 to study the underlying physiological mechanisms for the variability in photosynthetic
performance. Beyond their sensitivity to changing environmental conditions like thermal stratification, phytoplankton populations
differ in their photosynthetic behaviour according to their size structure. Therefore Photosynthesis vs. Irradiance (P/E)-relationships
were analysed in detail within a 1-year period from size fractionated cell counts, chlorophyll-a and carbon-uptake. |
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Keywords: | Primary productivity P*max E k Alpha FRRF Size classes |
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