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Productivity and Resource Use Efficiency in a Microalgal Polyculture under Different Levels of Co2 and Phosphorus Supply

Wulfers, Tristan A.
Although decades of research in the field of ecology have shown that productivity is a product of both species richness and resource supply, few studies have investigated the potential application of these principles to the production of biofuels. Recent studies provide evidence that species richness of microalgal communities is positively related to biomass production and resource use efficiency (RUE), but it is unclear how this relationship is affected by resource supply. Species differ in their ability to acquire resources and in how efficiently they are able to convert them into biomass. Therefore, changes in resource supply may alter the composition of algal communities, thus affecting productivity. I conducted an experiment in which I grew polycultures consisting of two algal species from different major taxa, Chlorophyceae and Cyanophyceae, at different levels of CO2 and phosphorus (P) supply in order to investigate how resource supply affected species abundance. I compared the growth and elemental composition of mixed cultures to that of species grown in monoculture to evaluate the effects of increased species richness on productivity and RUE. The results show that species relative abundance was dependent on resource supply. There was no evidence for effects of increased richness on RUE, but the productivity of mixed cultures was greater than that of either monoculture when P supply was high. The increased productivity of mixed species cultures under high P supply appeared to be due to the weakening of negative competition effects by increased resource supply. These results suggest that growing multi-species cultures may be an effective way to enhance biomass yields and improve biofuel production.