Application of fast repetition rate fluorometry to phytoplankton photosynthetic parameters in freshwaters |
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Authors: | Christina Kaiblinger 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: | Fast repetition rate fluorometry (FRRF) was successfully applied to various studies in modern oceanography. In this study, for the first time, the seasonality of phytoplankton photosynthetic parameters in a deep alpine lake was observed using FRRF in combination with the traditional 14C incubation technique. Special attention was given to the differences in photosynthetic behaviour during mixed and stratified conditions, characterised especially during summer by a deep chlorophyll maximum (DCM) dominated by the filamentous cyanobacterial species Planktothrix rubescens. Maximum light-utilisation efficiency (α*14C) was in the range of 0.01–0.03 mgC (mg Chl-a)−1 h−1 (μmol phot. m−2 s−1)−1, while maximum quantum yields for carbon fixation (ΦC,max) varied from 0.01–0.07 molC (mol phot.)−1. Higher values occurred during thermal stratification indicating acclimation of the phytoplankton assemblage. These findings were supported by FRRF-based estimates, although cyanobacterial blooms could not be characterised by FRRF-excitation due to methodological deficiencies. In general, however, instantaneous photosynthetic rates measured by FRRF-excitation correlate well at sub-saturating light-intensities with conventional 14C-uptake rates, although they operate on different time-scales. |
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Keywords: | freshwater FRRF photosynthesis primary productivity quantum yield of fluorescence seasonality thermal stratification |
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