Temperature effects on growth rates and fatty acid content in freshwater algae and cyanobacteria

Mass cultivation of algae for biofuel and other bioproduct production in outdoor, open raceway ponds has some considerable economic advantages. However, these systems would be subject to fluctuations in temperature (among other environmental factors), which can have dramatic effects on the growth rates of algal species and impact the overall productivity and quality of targeted algal crops. This study sought to elucidate the effects of temperature on algal growth rates, biomass accumulation, fatty acid production and composition. We surveyed 26 algal species from 5 different functional groups, growing them at 6 different temperatures between 9 and 32 °C. For each surveyed species, we collected eco-physiological trait data including maximum growth rate, thermal optimum (Topt), thermal niche width, and lower and upper temperature limits for growth (CTmin and CTmax, respectively); these data were also pooled for analysis at the functional group level. Responses to temperature varied among species, but at the functional group level we determined that the cyanobacteria have the highest thermal optimum (30.6 ± 2.3 °C), followed by chlorophytes (25.7 ± 0.1 °C) and diatoms (24.0 ± 0.4 °C). Temperature-specific fatty acid (FA) production was mostly controlled by growth rates, though some change in production was attributable to modification of intracellular FA stores. Temperature affected FA profiles in diverse ways, with no consistent trends across species or functional groups. In sum, temperature significantly impacts the overall productivity of algal biofuel systems by influencing species growth rates and fatty acid production. While algal growth rates varied predictably with temperature, we did not find the generalizable trends in temperature dependence of FA composition, suggesting that some aspects of algal cultivation for bioproducts in outdoor, open-air systems may be less predictable. However, a compilation of algal growth and FA composition responses to temperature, such as ours, may be useful for choosing appropriate species for given temperature regimes.