A theoretical analysis and field evaluation of a light and temperature model of production by Ecklonia cava

Abstract

The dependence of photosynthesis on light and temperature is modelled through analysis of transition probabilities of photosystems. In the model, two transition probabilities are functions of light, and one transition probability is a function of temperature. The estimated light-saturated photosynthesis of Ecklonia cava blades at 20 °C was 0.037 mg C cm⁻² h⁻¹. The value of the activation energy, the standard enthalpy and the standard entropy were estimated to be 56.5 kJ mol⁻¹, 204 kJ mol⁻¹ and 678 J mol⁻¹ K⁻¹, respectively. A production model (an integral photosynthesis model) for an E. cava stand was developed using the photosynthesis model. Production calculated by the model agreed well with observed data during the growing period of an E. cava stand at a field observation site on the west side of Miura Peninsula, Japan. Results of the analysis of the effects of irradiance and temperature on the production of the E. cava community by the model are:

1. Production decreased with irradiance decrease. The estimated compensation irradiance was 26.5 μmol photons m⁻² s⁻¹ when the biomass was 3 kg wet mass m⁻² (blade:stipe ratio = 2 kg m⁻²:1 kg m⁻²) and the temperature was 20 °C.

2. The optimum temperature decreased when irradiance decreased and when biomass increased. The highest estimated value for the optimum temperature was 24.0 °C. The estimated optimum temperature was 18.2 °C when the biomass was 12 kg wet mass m⁻² and the photon irradiance was 200 μmol photons m⁻² s⁻¹.

3. The amount of biomass that resulted in the maximum production was influenced by irradiance and temperature. At 400 μmol photons m⁻² s⁻¹ and 20 °C, the estimated value of the biomass (blade:stipe = 2:1) giving the maximum pr oduction was about 5.3 kg wet mass m⁻². However, at 100 μmol photons m⁻² s⁻¹ and 24 °C, the estimated value was about 3.0 kg wet mass m⁻². The estimated values of the maximum production under the two conditions were 1.05 and 0.30 g C m⁻² h⁻¹, respectively.