title: Chlorophyll content and fluorescence responses cannot be used to gauge reliably phytoplankton biomass, nutrient status or growth rate.
abstract: 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. FV/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.
authors.affiliation: Institute of Environmental Sustainability, Wallace Building, University of Wales Swansea, Swansea SA2 8PP, UK.
authors.forename: Mikaela
authors.initials: M
authors.lastname: Kruskopf
authors.forename: Kevin J
authors.initials: KJ
authors.lastname: Flynn
mesh_terms: D018533:Biomass; D002244:Carbon / Q000032:analysis; D002734:Chlorophyll / Q000032:analysis* / Q000302:isolation & purification; D000077194:Chlorophyll A; D009584:Nitrogen / Q000378:metabolism; D010758:Phosphorus / Q000378:metabolism; D010788:Photosynthesis; D010839:Phytoplankton / Q000737:chemistry* / Q000254:growth & development*; D013050:Spectrometry, Fluorescence / Q000379:methods
chemical_list: D002734:Chlorophyll; D010758:Phosphorus; D002244:Carbon; D009584:Nitrogen; D000077194:Chlorophyll A