Acclimation to elevated carbon dioxide and ultraviolet radiation in the diatom Thalassiosira pseudonana:: Effects on growth, photosynthesis, and spectral sensitivity of photoinhibition

We studied the effects of elevated CO2 concentrations (0.03% vs. 0.1%) on light absorption, membrane permeability, growth, and carbon fixation under photosynthetically active radiation (PAR) and ultraviolet radiation (UVR) exposures in the diatom Thalassiosira pseudonana. Susceptibility of photosynthesis to UVR was estimated using biological weighting functions (BWFs) for the inhibition of photosynthesis and a model that predicts primary productivity under PAR and UVR exposures. Elevated CO2 concentrations reduced chlorophyll content and increased chlorophyll specific cross section, carbon fixation per chlorophyll, and growth rates. In addition, cells acclimated to high CO2 were more sensitive to photoinhibitory UVR than those under atmospheric levels. Sensitivity to UVR was also related to the growth light regime; despite the fact that no UVR effects were observed on growth, light absorption, or carbon fixation, cells pre-exposed to UVR showed reduced photoinhibition compared to those grown under PAR for both normal and elevated CO2 cultures. Thus, acclimation to UVR partially counteracted the increased susceptibility observed under elevated CO2 conditions.