Opening up the algal biofuels black box: Understanding N and P uptake strategies to enhance biodiesel production

Background/Question/Methods

The use of agricultural land for growing food crops to produce biodiesel has serious limitations regarding sustainable development. Thus, biodiesel production has moved into its second generation, and algae are among the leading sources. The commercial development of algal biofuels demands scalable and productive systems in order to be economically competitive with other biofuels, and open systems may provide the most cost-effective approach. We therefore need to address some major obstacles associated with open systems, many of which would benefit from an ecological approach. For example, in nature the most productive systems often consist of complex communities, which enhance resource use efficiency. In an algal pond, however, eutrophic conditions are used that result in the dominance of superior competitors, thereby reducing diversity. High-nutrient outdoor systems are therefore more susceptible to population crashes that leave the systems open to invasion and productivity losses. Ideally, an outdoor system would consist of various productive organisms that can buffer the system from random disturbances. In developing an outdoor algal community, a trait-based approach is necessary in order to determine which combination of taxa will produce the desired outcome. Our goal was therefore to determine the nutrient uptake strategies and lipid contents for five potential algal biofuel strains. This information was then used to inform the outcome of a polyculture experiment.

Results/Conclusions

Growth rates and lipid contents for each algal taxon - Nannochloropsis gaditana, Nannochloris atomus, Chlamydomonas sp. CCMP225, Cyclotella cryptica, and Tetraselmis suecica – varied considerably depending on nutrient concentrations, with most species producing the most biomass with additional N and P. However, the lipid compositions varied by species and by nutrient conditions. Certain species showed evidence of P limitation with only N addition, suggesting that manipulation of N and P concentrations might be an effective strategy for promoting coexistence among algal taxa.