Effects of elevated CO<SUB>2</SUB> on growth, calcification and spectral dependence of photoinhibition in the coccolithophore <I>Emiliania huxleyi</I> (Prymnesiophyceae)

Abstract

We studied the effects of elevated CO<SUB>2</SUB> concentrations on cell growth, calcification and spectral variation in the sensitivity of photosynthesis to inhibition by solar radiation in the globally important coccolithophore Emiliania huxleyi. Growth rates and chlorophyll a content per cell showed no significant differences between elevated (800 ppmv) and ambient (400 ppmv) CO2 conditions. However, the production of organic carbon and the cell quotas for both, carbon and nitrogen, increased under elevated CO2 conditions whilst particulate inorganic carbon production rates decreased under the same conditions. Biometric analyses of cells showed that coccoliths only presented significant differences due to treatments in the central area width. Most importantly, the size of the coccosphere decreased under elevated CO2 conditions. The susceptibility of photosynthesis to inhibition by ultraviolet radiation (UVR) was estimated using biological weighting functions (BWFs) and a model that predicts photosynthesis under photosynthetically active radiation (PAR) and UVR exposures. BWF results demonstrate that the sensitivity of photosynthesis to UVR was not significantly different between E. huxleyi cells grown under elevated and present CO2 concentrations. We propose that the acclimation to elevated CO2 conditions involves a physiological mechanism of regulation and allocation of energy and metabolites in the cell, which is also responsible for altering the sensitivity to UVR. In coccolithophores this mechanism might be affected by the decrease in the calcification rates. This article is protected by copyright. All rights reserved.