Estimation of photosynthetic rate from measurements of natural fluorescence: analysis of the effects of light and temperature

We examine the effects of light and temperature on the relationship between photosynthesis and natural fluorescence in oceanic and coastal waters. While a moderately-sized database suggests a strong correlation, there is evidence that light and temperature alter the ratio of the quantum yields of photosynthesis and natural fluorescence. Specifically, we find a reduction of this ratio as light intensity increases and temperature decreases. In this paper, we review the effects of these factors and present empirical equations to account for their behavior. Although these equations significantly improve our ability to predict photosynthetic rate from natural fluorescence, the biophysical and biochemical mechanisms undelying these effects are not understood sufficiently.