On the causes of interspecific differences in the growth-irradiance relationship for phytoplankton. Part I. A comparative study of the growth-irradiance relationship of three marine phytoplankton species: Skeletonema costatum, Olisthodiscus luteus and Gonyaulax tamarensis
Three marine phytoplankton species (Skeletonema costatum, Olisthodiscus luteus andGonyaulax tamarensis) were grown in batch cultures at 15°C and a 14:10 L:D cycle at irradiance levels ranging from 5 to 450 μEinst m−2 s−1. At each irradiance, during exponential growth, concurrent measurements were made of cell division, carbon-specific growth rate, photosynthetic performance (both O2 and POC production), dark respiration, and cellular composition in terms of C, N and chlorophyll a. The results indicate that the three species were similar with respect to chemical composition, C:N (atomic) = 6.9 ± 0.4, photo-synthetic quotient, 1.43 ± 0.09, and photosynthetic efficiency, 2.3 ±0.1 × 10−3 μmol O2 (μg Chl a)−1 h−1 (μEinst m−2 s−1)−1. Differences in maximum growth rate varied as the −0.24 power of cell carbon. Differences in growth efficiency, were best explained by a power function of Chl a:C at μ = 0. Compensation intensities, ranged from 1.1 μEinst m−2 s−1 for S. costatum to 35 forG. tamarensis and were found to be a linear function of the maintenance respiration rate. The results indicate that interspecific differences in the μ−I relationship can be adequately explained in terms of just three parameters: cell carbon at maximum growth rate, the C:Chl a ratio (at the limit as growth approaches zero) and the respiration rate at zero growth rate. A light-limited algal growth model based on these results gave an excellent fit to the experimental μ−I curves and explained 97% of the observed interspecific variability.