Periodicities of photosynthesis and cell division: behavior of phase-lagged replicate cultures of Ditylum brightwellii in a diurnally varying photic regime

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Abstract
Diel periodicities of photosynthetic capacity (light-saturated photosynthesis = Pmax) and cell division were studied for the marine centric diatom D. brightwellii grown in a light environment that varied in intensity. A method was used to phase-lag replicate cultures of D. brightwellii to a light-dark schedule by offsetting subjective dawn at successive 1 h intervals. Control experiments were conducted using a more traditional protocol of around-the-clock sampling. Both approaches documented the periodicities of Pmax and cell division for this species in a diurnally varying light cycle, demonstrating the usefulness of the phase-lagging technique in reproducing time-dependent patterns in photosynthesis and growth. Comparative data on the photosynthetic periodicity of D. brightwellii in a photic regime of constant intensity are presented from earlier work. An explanation is offered for differences in amplitude and timing of photosynthetic rhythms, focusing on light loading and the coupling of integral photosynthetic performance to the maximum growth rate.