Time-dependent effects on phytoplankton performance under dynamic light environments

Light is an inherently variable resource in nature. Aquatic phototrophs like phytoplankton experience fluctuations ranging from limiting to supra-saturating light. Phytoplankton exhibit substantial physiological plasticity to persist in dynamic light environments although it may vary among functional groups. We investigated the impact of flashing light of various frequencies on the growth performance of six eukaryotic phytoplankton species from different taxa. We were particularly interested in determining their growth strategies under constant versus variable light. Phytoplankton performance varied widely across the range of frequencies. Performance under low frequencies was well predictable based on observations under constant light while under high-frequency light flashes, organisms were able to efficiently time-integrate light as a resource. Intermediate frequencies revealed species-specific responses that suggested both physiological and morphological constraints. We suppose that differences in cell size essentially controlled physiological and thus metabolic rates under flashing light, reinforcing the role of environmental fluctuations on phytoplankton community structure.