Autotrophic growth and photoacclimation in Karlodinium micrum (Dinophyceae) and Storeatula major (Cryptophyceae)

We compared autotrophic growth of the dinoflagellate Karlodinium micrum (Leadbeater et Dodge) and the cryptophyte Storeatula major (Butcher ex Hill) at a range of growth irradiances (E-g). Our goal was to determine the physiological bases for differences in growth-irradiance relationships between these species. Maximum autotrophic growth rates of K. micrum and S. major were 0.5 and 1.5 div..d(-1), respectively. Growth rates were positively correlated with C-specific photosynthetic performance (PPC, g C.g C-1.h(-1)) (r(2)=0.72). Cultures were grouped as light-limited (LL) and high-light (HL) treatments to allow interspecific comparisons of physiological properties that underlie the growth-irradiance relationships. Interspecific differences in the C-specific light absorption rate (E-a(C), mol photons.g C-1.h(-1)) were observed only among HL acclimated cultures, and the realized quantum yield of C fixation (phi(C(real.)), mol C.mol photons(-1)) did not differ significantly between species in either LL or HL treatments. The proportion of fixed C that was incorporated into new biomass was lower in K. micrum than S. major at each E-g, reflecting lower growth efficiency in K. micrum. Photoacclimation to HL in K. micrum involved a significant loss of cellular photosynthetic capacity (P-max(cell)), whereas in S. major, P-max(cell) was significantly higher in HL acclimated cells. We conclude that growth rate differences between K. micrum and S. major under LL conditions relate primarily to cell metabolism processes (i.e. growth efficiency) and that reduced chloroplast function, reflected in PPC and photosynthesis-irradiance curve acclimation in K. micrum, is also important under HL conditions.