A mechanistic model of photoinhibition

A mechanistic model was developed, to simulate the main facets of photoinhi bition in phytoplankton. Photoinhibition is modelled as a time dependent de crease in the initial slope of a photosynthesis versus irradiance curve, re lated to D1 (photosystem II reaction centre protein) damage and non-photoch emical quenching. The photoinhibition model was incorporated into an existi ng ammonium-nitrate nutrition interaction model capable of simulating photo acclimation and aspects of nitrogen uptake and utilization. Hence the curre nt model can simulate the effects of irradiance on photosynthesis from sub- saturating to inhibitory photon flux densities, during growth on different nitrogen sources and under nutrient stress. Model output conforms well to e xperimental data, allowing the extent of photoinhibition to be predicted un der a range of nutrient and light regimes. The ability of the model to recr eate the afternoon depression of photosynthesis and the enhancement of phot osynthesis during fluctuating light suggests that these two processes are r elated to photoinhibition. The model may be used to predict changes in biom ass and/or carbon fixation under a wide range of oceanographic situations, and it may also help to explain the progression to dominance of certain alg al species, and bloom formation under defined irradiance and nutrient condi tions.