Prediction of photo-protective carotenoids at global scale

As phytoplanktoncells are exposed to natural dynamic light fields, they develop various combined mechanisms in order to optimize their light harvesting and photosynthetic electron transport. Especially under high light conditions algal cells evolve various physiological protective mechanisms to dispose excess light energy to prevent damage of the photosynthetic apparatus. Among these mechanisms the so-called xanthophyllcycle (XC) is one of the most important one, which avoids overexcitation of the photosynthetic systems by thermal dissipation of the excess energy. In response to high light phytoplanktoncells accumulate XC- pigmentsto avoid the photodamage, which would cause photoinhibition. The mechanistic model for photoinhibitionproposed by (Marshall, Geider & Flynn 2000) predicts how changes in light, nutrients and temperature influence the parameters of the photosynthesis-irradiance relationship. The model does not parameterize a variable XC- pigmentspool size, hence, it predicts the changes in light absorption parameters that would take place with a constant XC- pigmentspool. We inserted this model in the global biogeochemical model REcoM2 to predict the photo-protective needs of phytoplanktonin terms of the XC- pigmentspool size. Two global scale databases of HPLC pigmentsshowed how the predicted photoprotectiveresponse correlates with photo-protective carotenoids pool at global scale, with the advantage that the model prediction is separable per phytoplanktongroup. Our results show higher concentration of XC- pigmentsin lower latitudes being non-diatom phytoplanktonthe main contributor. XC- pigmentspool size and its relation to photosynthetic pigmentsare relevant when describing the light harvesting by phytoplanktonat the global scale.