Using chlorophyll a fluorescence for assess of primary production of phytoplankton
Rubin A B, Konev Yu N, Antal T K, Venedictov P S, Kazimirko Yu V
Russia, Moscow, Lomonosov MSU , Faculty of Biology, Dept. of Biophysics.
Evaluation of the productivity of aquatic biosystems is needed to understand mechanisms underlying the enviromental changes both on local and global scale. Thus, a primary target of oceanological research is to develop an approach for rapid, convenient, and accurate estimation of the productivity of aquatic systems, which is largely determined by phytoplankton (PP) productivity.
As a rule, photosynthesis of natural phytoplankton is estimated by measuring the rate of light-dependent incorporation of radioactive inorganic carbon into organic substance (Steemann Nielsen, 1952) or, less frequently, changes in oxygen concentration (Williams and Jenkinson, 1982; Langdon, 1984; Bender et al., 1987). These direct methods are technically difficult and associated with phytoplankton incubation in small isolated volumes, which leads to artifacts (so-called 'bottle effects'). These artifacts are difficult to correct, thus, researchers turned to noninvasive nondirect methods of PP assessment. These methods are based on empirical or theoretical models of photosynthesis and allow to calculate the primary production on the basis of variables (algal biomass, radiant energy within the spectral range l=400 to 700 nm, etc.) that can be measured more simply than direct estimation of PP (Ryther&Yentsch, 1957; Koblentz-Mishke, 1985; Falkowski&Kolber, 1995; Antoine&Morel, 1996).
Chlorophyll fluorometry is the most popular among such nondirect methods (Herman, Platt, 1986; Samuelsson, Oquist, 1977; Keller, 1987). It provides for simple, fast and noninvasive measurements and excludes "the bottle effect" (Kolber et al, 1990; Falkowski et al., 1991; Geider et al,1993; Green et al, 1994). Falkowski et al. (1984) developped a submersible fluorometer based on the pump-and-probe technique (Mauzerall, 1972), which provides for measuring the vertical distribution of PP in real time. In the author's original model, photosynthetic rate was lineary related to the absorption cross-section and the quantum yield of photosystem II, both of which can be estimated by measuring chlorophyll fluorescence. PP calculated by this method fairly well correlated with PP obtaned by direct methods. However, the measurement of variable fluorescence of chlorophyll in the presence of ambient solar radiation requires rather sophisticated equipment.
Here, we report results of calculating PP from the data obtained with a simple submersible chlorophyll fluorometer, which measures chlorophyll fluorescence Fo and Fv/Fm ratio in situ in a dark chamber by the pump and probe method. The calculation of primary production bases on the suggested by Kiefer&Mitchell (1983) model, which describes primary reactions of photosynthesis such as harvesting of light by algae pigments, transportation of exitons to reaction centers of PS II, where primary charge separation and stabilization occure.