FUNCTIONAL GROUP RICHNESS: IMPLICATIONS OF BIODIVERSITY FOR LIGHT USE AND LIPID YIELD IN MICROALGAE 1 Maria Stockenreiter, 2,3 Florian Haupt, Anne-Kathrin Graber Biology II, Aquatic Ecology, Ludwig-Maximilians-Universit€ at M€ unchen, Großhaderner Straße 2, Planegg-Martinsried 82152, Germany Jukka Seppa¨la¨, Kristian Spilling, Timo Tamminen Marine Research Centre, Finnish Environment Institute, P.O. Box 140, Helsinki 00251, Finland and Herwig Stibor Biology II, Aquatic Ecology, Ludwig-Maximilians-Universit€ at M€ unchen, Großhaderner Straße 2, Planegg-Martinsried 82152, Germany European Institute for Marine Studies, Technop^ ole Brest-Iroise, Place Nicolas Copernic, Plouzan e 29280, France Currently, very few studies address the relationship between diversity and biomass/lipid production in primary producer communities for biofuel production. Basic studies on the growth of microalgal communities, however, provide evidence of a positive relationship between diversity and biomass production. Recent studies have also shown that positive diversity– productivity relationships are related to an increase in the efficiency of light use by diverse microalgal communities. Here, we hypothesize that there is a relationship between diversity, light use, and microalgal lipid production in phytoplankton communities. Microalgae from all major freshwater algal groups were cultivated in treatments that differed in species richness and functional group richness. Polycultures with high functional group richness showed more efficient light use and higher algal lipid content with increasing species richness. There was a clear correlation between light use and lipid production in functionally diverse communities. Hence, a powerful and cost-effective way to improve biofuel production might be accomplished by incorporating diversity related, resource-use-dynamics into algal biomass production. Key index words: Algal neutral lipids; Biofuel; Diver- sity; Functional groups; Light use; Nile Red; PAR absorbance; Phytoplankton; Resource-use-efficiency; Species richness Algae are important components of aquatic eco- systems, accounting for more than half of the total global primary production, with their lipids serving as major dietary sources for primary consumers (Guschina and Harwood 2009). Lipids are vital for maintaining somatic and population growth, sur- vival, and reproductive success (Brett and M€ uller- Navarra 1997). Microalgal lipids have also received increasing attention in recent years, as they may provide a new, renewable feedstock for biofuel pro- duction in times when fossil fuels are running out (Chisti 2007). At present, extensive effort is being invested toward identifying the best microalgal strain or species that could provide the highest growth and lipid yields for biofuel production (Sheehan et al. 1998, Miao and Wu 2004, Li et al. 2008, Griffiths and Harrison 2009, Tran et al. 2009). The most common growth systems for the mass production of microalgae are either closed photobi- oreactors or open ponds. Closed systems are not easily contaminated, but are expensive to build and operate. In comparison, open ponds are relatively inexpensive but are usually open to the environ- ment, and monocultures of selected strains do not persist for very long (Sheehan et al. 1998). Recent studies have shown that the monocultures of selected microalgal strains may not be superior, in terms of lipid production, compared to diverse microalgal communities. For instance, in controlled growth experiments, diverse microalgal communities showed higher lipid production and biomass specific lipid content compared to corresponding monocultures (Stockenreiter et al. 2012). However, to incorporate these findings into potential cultivation systems for microalgal biomass production that generate lipids, a more mechanistic insight into the biodiversity– lipid productivity relationship is required. In general, two mechanisms operating in tandem are believed to be responsible for diversity–productivity 1 Received 7 February 2012. Accepted 21 May 2013. 2 Present address: W.K. Kellogg Biological Station, Michigan State University, 3700 E Gull Lake Dr, Hickory Corners, Michigan, 49060, USA. 3 Author for correspondence: e-mail stockenr@msu.edu. Editorial Responsibility: A. Buschmann (Associate Editor) J. Phycol. 0, 1–10 (2013) © 2013 Phycological Society of America DOI: 10.1111/jpy.12092 1