Physiology of carbon photoassimilation by <i>Oscillatoria thiebautii</i> in the Caribbean Sea1

Abstract

Surface populations of Oscillatoria thiebautii (Gom.) Geitler in the Caribbean Sea are exposed to photoinhibiting irradiances throughout most of the 12‐h light period. Oxygen inhibition of carbon assimilation at high irradiance suggested that photoinhibition was partly due to photorespiration. The pattern of carbon flow into the major end products of photosynthesis appeared to be the same for a given photosynthetic rate regardless of irradiance level. At one station, enhanced relative rates of protein synthesis were observed at low rates of photosynthesis. At another station, this effect was not observed but the proportion of 14 C in polysaccharide was low while that in metabolites was high. On the basis of previous findings, colonies at the second station were interpreted to have been in a nutritionally poor state. The rates at which intracellular macromolecular pools approached saturation seemed to depend on the rate of photosynthesis. Diel estimates of in situ carbon photoassimilation rates and dark carbon loss rate lead to an estimate of carbon doubling time for surface Oscillatoria populations of 18 days.