Light Fluctuations and the Photosynthesis of Marine Algae. II. Photosynthetic Response to Frequency, Phase Ratio and Amplitude

Abstract

Photosynthesis of three marine macroalgae (Hormosira banksii [Turn.] Dene., Carpophyllum maschalocarpum [Turn.] Grev., Ecklonia radiata [C.Ag.] J.Ag.) was measured by ?2 electrode and infra-red gas analysis (IRGA) methods in both steady and fluctuating light regimes Using immersed material of Carpophyllum or Ecklonia in the 02 electrode the response of mean photosynthetic rate (P) to changes in the frequency (i.e. phase period, TJ at different relative amplitudes of fluctuating light was examined. P was also compared to rates predicted from steady state responses on the basis of either integration of photosynthate (Ps) or integration of irradiance (Pf). In alternations of saturating and limiting light (defined with reference to steady P-I response of the same plant material) P was > Ps at T Ps at T> 300s and P -> Pfat T< 0 25s. Enhancement of P at high and intermediate frequencies is attributed to the integrated influence of two transients of CO2 exchange viz. induction loss and post-illumination fixation. The complex interaction of these and other transients such as post-illumination bursts of CO2 means that previous models of the P versus T response based only on two time constants are probably inadequate. However, for these macroalgae, a modified form of the Thornley (1974) model can be used to predict P at the extremes of the frequency range. Key-words: Fluctuating light, photosynthetic rate, marine algae, Hormosira, Ecklonia, Carpophyllum, P-I responses, induction, post-illumination CO2 fixation