New cell-based model of photosynthesis and photo-acclimation: accumulation and mobilisation of energy reserves in phytoplankton

In this study, we present a new model of acclimation to light under nutrient-replete con ditions based on the photo-acclimation model by Geider et al. (1998; Limnol Oceanogr 43:679-694). Rather than being solely carbon (C)-based, the new model employs the cell as the basic unit, which makes it more amenable for application in individual-based (Lagrangian) modelling approaches. The model differentiates between a functional C pool which also contains nitrogen (N) and an energy reserve pool which does not contain N. The cell-specific light-saturated photosynthetic rate is assumed to scale with the size of the functional pool, and the light-limited photosynthetic rate with the cellular chlorophyll content. Through the explicit inclusion of a C (energy) storage pool, an improved regulatory term for chlorophyll synthesis, and the addition of an optional acceleratory term, the dynamics of the model in comparison to the original model could be improved. This is demon strated by observations during a light-shift experiment on the diatom Skeletonema costatum.