Original paper

Can Chlorophyll-a in-vivo fluorescence be used for quantification of carbon-based primary production in absolute terms?

Toepel, Jörg Gilbert; Wilhelm, Christian

Abstract

We tested the Chlorophyll-a in-vivo fluorescence technique as a method to measure absolute values of primary production by the application of a bio-optical model. In this model, absolute values of gross photosynthetic oxygen evolution were calculated on the basis of Chlorophyll-a in-vivo fluorescence, such as photosystem II quantum yield and the amount of absorbed light quanta per time (QPhar). Simultaneous measurements of photosynthesis rates, as measured by a Clark-type electrode and estimated via the fluorescence based model, yield similar results. The P-I-curves measured by these two independent methods are nearly identical under light limitation, whereas maximal photosynthetic activities under saturating light are found to be higher using the bio-optical model. Furthermore, we determined the relationship between carbonbased biomass formation and the photosynthesis rate under low and high light. The quantity of electrons consumed for C and N assimilation is the same as the quantity of electrons produced by the photosystems under low light. Under high light, the electron production exceeds the electron consumption for N and C assimilation. We found that an oxygen production of 55 – 60 μmol O2 is equivalent to the production of 1 mg dry matter. We conclude that the photosynthetic electron transport rate represents a fairly good estimated measure of newly synthesised organic matter under the applied conditions. Therefore, the use of fluorescence data in an appropriate bio-optical model is a powerful tool for measuring biomass formation in absolute terms but is restricted to replete nutrient and medium light conditions. The validity of this experimental approach for measuring primary production under stress conditions still needs to be elaborated.

Keywords

biomass formationphotosynthesis ratebio-optical model