Action spectra of oxygen production and chlorophyll a fluorescence in the green microalga Nannochloropsis oculata

The first complete action spectrum of oxygen evolution and chlorophyll a fluorescence was measured for the biofuel candidate alga Nannochloropsis oculata. A novel analytical procedure was used to generate a representative and reproducible action spectrum for microalgal cultures. The action spectrum was measured at 14 discrete wavelengths across the visible spectrum, at an equivalent photon flux density of 60μmolphotonsm-2s-1. Blue light (~414nm) was absorbed more efficiently and directed to photosystem II more effectively than red light (~679nm) at light intensities below the photosaturation limit. Conversion of absorbed photons into photosynthetic oxygen evolution was maximised at 625nm; however, this maximum is unstable since neighbouring wavelengths (646nm) resulted in the lowest photosystem II operating efficiency. Identifying the wavelength-dependence of photosynthesis has clear implications to optimising growth efficiency and hence important economic implications to the algal biofuels and bioproducts industries. © 2014 Elsevier Ltd