The influence of irradiance and genotype on the change in carbon allocation by four species of microalgae under increasing nutrient stress

Abstract

During nutrient-replete growth of microalgae, new photosynthate is allocated toward three different biochemical pools: light harvesting compounds, the biosynthetic apparatus and energy storage. The mechanisms governing allocation of photosynthate between the energy storage compounds carbohydrate and lipid are not well understood. For biofuel production, it is desirable to identify conditions and algal strains that allocate maximum amounts of photosynthate to lipid. This thesis assessed the allocation of photosynthate toward the energy storage pool, and to lipid vs. carbohydrate, at two light levels and during ongoing nitrogen-starvation, for two diatoms and two chlorophytes. Nitrogen-starvation resulted in an increase in the photosynthate allocated toward energy storage, however the magnitude of change was determined by a combination of species and light level. Of the four species studied, the diatom Chaetoceros muelleri, grown in high light, accumulated lipid during N-starvation at a relatively high rate, making it a good candidate for biofuel production.