Original paper

Relationships between electron transport rates determined by pulse amplitude modulated (PAM) chlorophyll fluorescence and photosynthetic rates by traditional and common methods in natural freshwater phytoplankton

Goto, Naoshige; Miyazaki, Haruna; Nakamura, NaNa; Terai, Hisayoshi; Ishida, Noriko; Mitamura, Osamu

Abstract

The relationships between the electron transport rate (ETR) measured by pulse amplitude modulated (PAM) fluorometer and the rate of O2 production and 14C fixation by traditional and most common methods were estimated in natural phytoplankton communities to determine the molar ratio of oxygen produced and carbon fixation per electron transported. The observations were carried out in Lake Biwa, Japan approximately once a month for a year. A remarkable linear relationship was observed between the rate of O2 production and C fixation to ETR at low-to-medium irradiances during the sampling period, but not at higher irradiances. The annual average O2 production/ETR and C fixation/ETR ratios at low-to-medium irradiances were 0.117 and 0.095, respectively, and the photosynthetic quotient (O2 production/C fixation) calculated from the two ratios was 1.23, which is the most common value as the photosynthetic quotient. The same was true for cultured algal species. These results indicate that the O2 production/ETR and C fixation/ETR ratios are reliable values at low-to-medium irradiances, and that PAM measurements can be used to quantify primary production rates based on traditional methods using the ratios. However, it must be noted that the determination of the average O2 production/ETR and C fixation/ETR ratios in a natural phytoplankton community requires long-term observation because those ratios change seasonally over a certain range.

Keywords

pulse amplitude-modulated (pam) fluorescenceelectron transport rate (etr)oxygen evolutioncarbon fixationphytoplankton