On the theory of photosynthesis and growth in phytoplankton .1. Light limitation and constant temperature

Assuming constant temperature and light limitation, for reversible photoinhibition and photoadaptation in phytoplankton two new modelling approaches are presented. The first follows an idea of JONES and KoK (1966) and describes photoinhibition as a consequence of the serial structure of the Z-scheme. The second interpretes photoadaptation as a dynamic equilibrium of the intracellular synthesis and dilution of Chlorophyll by other carbon compounds during cell growth. Together both ideas form a closed system of equations for the dynamical description of photosynthesis, photoadaptation, reversible photoinhibition and growth in phytoplankton. To determine the seven bulk parameters of the model from measured data for a given species and temperature, three quasi-steady, fully adapted light curves are needed: the P-l, gamma-I and mu-I curves (P: specific photosynthetic rate [gC (gChl)(-1)s(-1)], gamma: Chl-carbon ratio, mu: carbon-specific growth rate [s(-1)], I: light intensity). Given these curves, at compensation light intensity their initial slopes alpha, beta, delta and the (maximum) value of gamma have to be estimated; at saturation level the (minimum) value of gamma is needed. The last bulk parameters of the model are the compensation light intensity and the optimum-growth light intensity. The model performs well compared with laboratory measurements of quasi-steady, fully adapted populations. Its dynamic transient behavior exhibits features which are known from semi-quantitative studies in the field and in the laboratory. In particular, the striking asymmetry observed in shift-up and shift-down adaptation experiments is explained by the equations. In an appendix a detailed comparison between target and queuing theory is given and it is shown that the former appears to be more adequate for describing the primary reactions of photosynthesis.