Characterization of diurnal photosynthetic rhythms in the marine diatom Skeletonema costatum grown in synchronous culture under ambient and elevated CO2

Abstract

Photosynthetic performance was examined in Skeletonema costatum (Greville) Cleve. under 12 : 12-h light : dark (LD) cycle at ambient CO₂ (350 μL L^–1) and elevated CO₂ (1000 μL L^–1). At ambient CO₂, the cellular chlorophyll a content, the light-saturated photosynthetic rate (P_m), the initial slope of the light saturation curves (α), the photochemical efficiency of PSII (F_v / F_m), the apparent carboxylating efficiency (ACE) and the photosynthetic affinity for CO₂ [1 / K_m(CO₂)] all showed rhythmical changes with different amplitudes during the light period. The P_m had similar changing pattern in the light period with the ACE and 1 / K_m(CO₂) rather than with the α and F_v / F_m, indicating that rhythmical changes of photosynthetic capacity may be mainly controlled by the activity of C-reduction associated with CO₂ uptake during the light period. The CO₂ enrichment reduced the ACE and the affinity to CO₂, and increased the α, cellular chlorophyll a content and P_m based on cell number. By contrast, the changing patterns of all photosynthetic parameters examined here during the light period had almost the same for cells grown at ambient CO₂ and elevated CO₂, suggesting that the photosynthetic rhythms of S. costatum are not affected by CO₂ enrichment.