title: Carbon allocation under light and nitrogen resource gradients in two model marine phytoplankton(1).
abstract: Marine phytoplankton have conserved elemental stoichiometry, but there can be significant deviations from this Redfield ratio. Moreover, phytoplankton allocate reduced carbon (C) to different biochemical pools based on nutritional status and light availability, adding complexity to this relationship. This allocation influences physiology, ecology, and biogeochemistry. Here, we present results on the physiological and biochemical properties of two evolutionarily distinct model marine phytoplankton, a diatom (cf. Staurosira sp. Ehrenberg) and a chlorophyte (Chlorella sp. M. Beijerinck) grown under light and nitrogen resource gradients to characterize how carbon is allocated under different energy and substrate conditions. We found that nitrogen (N)-replete growth rate increased monotonically with light until it reached a threshold intensity (~200 μmol photons · m(-2)  · s(-1) ). For Chlorella sp., the nitrogen quota (pg · μm(-3) ) was greatest below this threshold, beyond which it was reduced by the effect of N-stress, while for Staurosira sp. there was no trend. Both species maintained constant maximum quantum yield of photosynthesis (mol C · mol photons(-1) ) over the range of light and N-gradients studied (although each species used different photophysiological strategies). In both species, C:chl a (g · g(-1) ) increased as a function of light and N-stress, while C:N (mol · mol(-1) ) and relative neutral lipid:C (rel. lipid · g(-1) ) were most strongly influenced by N-stress above the threshold light intensity. These results demonstrated that the interaction of substrate (N-availability) and energy gradients influenced C-allocation, and that general patterns of biochemical responses may be conserved among phytoplankton; they provided a framework for predicting phytoplankton biochemical composition in ecological, biogeochemical, or biotechnological applications.
authors.affiliation: Marine Laboratory, Nicholas School of the Environment, Duke University, 135 Duke Marine Lab Road, Beaufort, North Carolina, 28516, USA.
authors.forename: Thais B
authors.initials: TB
authors.lastname: Bittar
authors.affiliation: Marine Laboratory, Nicholas School of the Environment, Duke University, 135 Duke Marine Lab Road, Beaufort, North Carolina, 28516, USA.
authors.forename: Yajuan
authors.initials: Y
authors.lastname: Lin
authors.affiliation: Marine Laboratory, Nicholas School of the Environment, Duke University, 135 Duke Marine Lab Road, Beaufort, North Carolina, 28516, USA.
authors.forename: Lara R
authors.initials: LR
authors.lastname: Sassano
authors.affiliation: Marine Laboratory, Nicholas School of the Environment, Duke University, 135 Duke Marine Lab Road, Beaufort, North Carolina, 28516, USA.
authors.forename: Benjamin J
authors.initials: BJ
authors.lastname: Wheeler
authors.affiliation: Center for Marine Microbial Ecology and Diversity, University of Hawaii, POST 105, 1680 East-West Road, Honolulu, Hawaii, 96822, USA.
authors.forename: Susan L
authors.initials: SL
authors.lastname: Brown
authors.affiliation: Romberg Tiburon Center for Environmental Studies, San Francisco State University, 3152 Paradise Dr, Tiburon, California, 94920, USA.
authors.forename: William P
authors.initials: WP
authors.lastname: Cochlan
authors.affiliation: Marine Laboratory, Nicholas School of the Environment, Duke University, 135 Duke Marine Lab Road, Beaufort, North Carolina, 28516, USA.
authors.forename: Zackary I
authors.initials: ZI
authors.lastname: Johnson
keywords: Redfield ratio; carbon; cell quota; light; nitrogen; resource allocation