Light absorption and size scaling of light-limited metabolism in marine diatoms

Previous studies have found that the size-scaling exponent of metabolic rates in unicellular algae often deviates from the exponent of -1/4 usually found for heterotrophs. This study confirms a significant linear relationship between log cell volume (mum(3)) and log intrinsic growth rate (h(-1)), carbon-normalized photosynthetic capacity and performance (h(-1)), and carbon-normalized respiratory rate (h(-1)) for eight marine centric diatoms under nutrient-saturated, light-limited conditions. The intrinsic growth rate and carbon-normalized respiratory rate have size-scaling exponents not significantly different from -1/4, whereas the carbon-specific photosynthetic rates deviate from -1/ 3. The size dependence of the optical absorption cross section (m(2) mg chlorophyll a(-1)) due to the package effect provides a mechanistic model that explains the anomalous size scaling of the anabolic rates of unicellular phytoplankton.