The effects of irradiance and phosphorus on batch cultures of Pavlova (= Monochrysis) Lutheri

Abstract

Pavlova (=Monochrysis) lutheri was grown in axenic batch culture at 5 levels of irradiance ranging from 140 to 9 W m-2 (experiments were replicated at three irradiances). The experiments were designed so that phosphorus limited the yield and the final biomass was not greater than 2.5 x 106 cells m1-1. Growth parameters were obtained from the nutrient-saturated, exponential phase and the phosphorus-controlled, transitional phase of each experiment. The nutrient saturated, maximum growth rate, µm¬, varied from .979 to .247 day-1. Growth parameters were “inhabited” at the highest irradiance. The differential form of Droop’s cell-quota model was fitted to the time-series of cell numbers, dissolved phosphorus, and cellular phosphorus (cell quota) obtained from the phosphorus-controlled phase of each experiment. A comparison amongst experiments of the estimates of µm, kQ (the parameters in Droop’s model) and Qm¬1 (the cell quota at the transition point between constant, exponential growth and phosphorus-controlled growth) disproved the hypothesis that phosphorus-controlled growth rate is the same at all irradiances. The results of the experiments are described by a simple modification of Droop’s cell quota model. The changes in chlorophyll-a cell-1 within an experiment and amongst light levels, is discussed. In measuring irradiance , it was decided to make no allowance for self-shading.