Photoacclimation, photosynthesis, and growth in phytoplankton

In this study we have followed various aspects of the photoacclimation of Synechococcus leopoliensis, Isocrysis galbana, and Scenedesmus quadricauda grown at different irradiances. These included changes in the biochemistry, physiology, and ecological fitness of the cells. As cells adapted to lower growth-irradiance levels, chlorophyll (chi) a per cell increased 2.3-7.4-fold. The photosynthetic apparatus changed by increasing the photosynthetic unit size, or the number of reaction centers per cell. The values of the in vivo spectral average, effective optical-absorption cross section (°a*) showed an opposite trend, ranging from 0.010 m²mg^-1chi a at 15 pinole quanta nr²s^-1to 0.097 m²mg^-1chi a at 600 pmole quanta m^-2s^-1. The maximum quantum yield, (Φ)^max, increased consistently as growth irradiance decreased from 600 to 15 pmole quanta m²s^-1. Light-saturated rates of photosynthesis were considerably higher in all high-light grown cultures than in low-light ones. Respiration rate is greater at high irradiances than at low. We propose an integrated view, relating the measured parameters and their interrelations in these organisms.