Chlorophyll content and fluorescence responses cannot be used to gauge reliably phytoplankton biomass, nutrient status or growth rate
2006
Kruskopf, Mikaela | Flynn, Kevin J.
• To consider the relationship between chlorophyll a (Chl a) content and phytoplankton growth and nutrient status, four phytoplankton species were grown in nitrogen (N)‐limited [and, for one species, phosphorus (P)‐limited] culture and measurements were made of CNP biomass, in vivo and in vitro Chl a content, the ratio of variable to maximum fluorescence (FV/FM) and the performance index for photosynthesis, PIABS (a derivative of the O‐J‐I‐P analysis of photosystem II functionality). • Interspecies differences plus the development of intraspecies differences during nutrient stress produced c. 10‐fold variations in Chl : C. Estimates of C from in vivo Chl content were better than those from extracted Chl content, as the decline in Chl : C during nutrient stress was offset in part by increased Chl fluorescence. • F V/FM was not a robust indicator of nutrient status or relative growth rate. Responses of FV/FM in cells re‐fed the limiting nutrient showed no consistent pattern with which to gauge nutrient status. PIABS showed some promise as an indicator of nutrient status and relative growth rate. • Chl a content and fluorescence parameters do not deserve the unquestioned status they usually enjoy as indicators of biomass and physiological status.
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