Comparison of the two methods for primary production measurement

Abstract

We compared the primary production rates estimated by 14C uptake and fast repetition rate fluorometery (FRRF) in the Korean waters. The FRRF-derived primary production rates well correlated with the 14C-based primary production rates despite the differences in methodology and time scale of the measurements (r2=0.86, slope=1.67, p<0.001, n=23). However, the relationship between the two methods differed depending on season and place. The discrepancy between the two methods may be attributed to the responses of physiological processes (cyclic electron flow, the Mehler reaction and photorespiration) to high irradiance, and the uncertainties in the parameters such as photosynthetic unit size ( ), photosynthetic quotient ( ) used in the equations of FRRF-derived primary production estimation. Furthermore, the bottle effects can influence the measurements by the 14C method. To check this possibility, short-term (two hours) experiments were conducted with three phytoplankton species (Skeletonema costatum, Heterocapsa circularisquama, Coscinodiscus oculoides) in the same way as with the 14C method. Fluorescence variables were measured by using a Fluorescence Induction and Relaxation (FIRe) fluorometer at time intervals during the course of the two-hour experiments. On average, 10-20% of the primary production rates from the FIRe measurement decreased after short-term incubations under high light intensity.e the differences in methodology and time scale of the measurements (r2=0.86, slope=1.67, p<0.001, n=23). However, the relationship between the two methods differed depending on season and place. The discrepancy between the two methods may be attributed to the responses of physiological processes (cyclic electron flow, the Mehler reaction and photorespiration) to high irradiance, and the uncertainties in the parameters such as photosynthetic unit size ( ), photosynthetic quotient ( ) used in the equations of FRRF-derived primary production estimation. Furthermore, the bottle effects can influence the measurements by the 14C method. To check this possibility, short-term (two hours) experiments were conducted with three phytoplankton species (Skeletonema costatum, Heterocapsa circularisquama, Coscinodiscus oculoides) in the same way as with the 14C method. Fluorescence variables were measured by using a Fluorescence Induction and Relaxation (FIRe) fluorometer at time intervals during the course of the two-hour experiments. On average, 10-20% of the primary production rates from the FIRe measurement decreased after short-term incubations under high light intensity.