A laboratory study on O<inf>2</inf>dynamics and photosynthesis in ice algal communities: Quantification by microsensors, O<inf>2</inf>exchange rates,<sup>14</sup>C incubations and a PAM fluorometer

Publication Type:
Journal Article
Citation:
Aquatic Microbial Ecology, 2002, 27 (3), pp. 301 - 311
Issue Date:
2002-04-16
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The present study compared O2exchange measurements, fluorometry and14c incubations for measuring productivity of sea-ice algae. It is demonstrated that brine leaking out of ice during freezing conditions is supersaturated with respect to O2, while the melting water released during thawing is undersaturated with O2. This results in a highly variable O2concentration at the ice-water interface during expanding or shrinking of sea ice. Consequently, great care should be taken when inferring biological activity from O2exchange rates, whether they are obtained via microprofiles, bulk incubations or direct measurement of O2concentrations in water below sea ice. Accounting for the O2dynamics related to changes in sea-ice structure, the photosynthetic activity of a mixed ice algal culture, as measured by net O2exchange rates and14C incubation, co-varied as a function of biomass and irradiance. The ratio between the net O2efflux and the gross C fixation rate (the photosynthetic quotient) was similar for frozen and non-frozen ice algal communities and averaged 1.43 ± 0.48. Quantification of the relative electron transport rate (ETR) from photosystem II (PSII) and the minimum fluorescence yield (F0) by a pulse-amplitude-modulated (PAM) fluorometer offers a fast, simple and non-invasive approach for estimating activity and biomass of ice algal communities. The relative ETR measurements correlated with the other 2 measures for primary production. However, the correlation was non-linear, leading to a poor resolution of the fluorometer approach at higher photosynthetic activities. A similar observation was made for the correlation between measurements and the concentration of chlorophyll a.
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