ON THE THEORY OF PHOTOSYNTHESIS AND GROWTH IN PHYTOPLANKTON .1. LIGHTLIMITATION AND CONSTANT-TEMPERATURE

Assuming constant temperature and light limitation, for reversible pho toinhibition and photoadaptation in phytoplankton two new modelling ap proaches are presented. The first follows an idea of JONES and KoK (19 66) and describes photoinhibition as a consequence of the serial struc ture of the Z-scheme. The second interpretes photoadaptation as a dyna mic equilibrium of the intracellular synthesis and dilution of Chlorop hyll by other carbon compounds during cell growth. Together both ideas form a closed system of equations for the dynamical description of ph otosynthesis, photoadaptation, reversible photoinhibition and growth i n phytoplankton. To determine the seven bulk parameters of the model f rom measured data for a given species and temperature, three quasi-ste ady, 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: C hl-carbon ratio, mu: carbon-specific growth rate [s(-1)], I: light int ensity). Given these curves, at compensation light intensity their ini tial slopes alpha, beta, delta and the (maximum) value of gamma have t o be estimated; at saturation level the (minimum) value of gamma is ne eded. 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 adap ted populations. Its dynamic transient behavior exhibits features whic h are known from semi-quantitative studies in the field and in the lab oratory. In particular, the striking asymmetry observed in shift-up an d 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.