We are using a PAM fluorometer to measure the quantum yield of chlorophyll fluorescence in an intact microalga culture. When the culture is dark-adapted for 20-30 minutes, the quantum yield is rather low (0.4), while if it's measured under low light (~50uM quanta) the yield will increase to about 0.6. The alga medium is not agitated and the cells form a biofilm on the bottom of the flask. Could this be a result of a low-oxygen layer forming around the biofilm after being in the dark, inhibiting PQ pool oxidation? Is there another explanation?
Funnily enough, I've recently asked the same question.
https://www.researchgate.net/post/Why_might_PSII_fluorescence_yields_PAM_fluorometry_be_lower_in_dark-adapted_samples_than_in_the_same_samples_under_lights?_tpcectx=qa_overview_asked&_trid=1cxiZvKMUUvcdbXHxKt9xQ06_
Thanks Tom. As a first attempt I will change the instrument settings.
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