Photochemical responses to changing light or nutrient conditions were examined in three phytoplankton communities by in vivo chlorophyll fluorescence before (F a ) and after (F b ) the addition of the electron flow inhibitor 3(3,4‐dichlorophenyl)‐1,1‐dimethyl urea. These values were used to calculate an index called “cellular fluorescence capacity” (CFC), defined as (F b – F a )/F b . CFC varied markedly throughout the day and night in the spring community of diatoms and green algae in Lake Taupo, New Zealand. Morning and afternoon maxima were separated by a pronounced depression during the midday peak irradiance. Under continuous low light Taupo plankton demonstrated a circadian rhythm in CFC, but the amplitude of variation was much lower than that recorded under natural or controlled light/dark regimes. In an oligotrophic water body (Wastwater) in the English Lake District a bimodal relationship between CFC and depth was observed when surface features indicated Langmuir circulation. Photochemical capacity measured as CFC could be raised or lowered in samples from this lake by exposure to bright or dim light for 4–8 h. Phytoplankton from a eutrophic lake with a history of nitrogen limitation (Lake Rotorua, New Zealand) responded to nitrogen enrichment after a lag of 4–6 h by an increase in CFC. This was correlated with enhanced rates of carbon fixation and, at longer time intervals, increased growth rates. These CFC data are consistent with the hypothesis that the capacity for non‐cyclic electron transport in natural phytoplankton communities is highly responsive to short‐term changes in light or the availability of nutrients.
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Warwick F. Vincent (1980) studied this question.
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