Algal photosynthesis and physiology

Algae, herein referring to microalgae including cyanobacteria, occur in almost all environments, exhibiting a wide range of specific growth rates and productivities. The diversity of algae includes genotypes that can, through evolution, grow over large ranges of mean and extreme values of flux in photosynthetically active radiation (PAR) of both low and high concentration of dissolved nutrients and of wide ranges in temperature (Raven and Geider 2003). They can also deal with the influences of both abiotic factors, such as salinity and mixing in the water column, and biotic factors, such as grazers and parasites/parasitoids, including viruses (Falkowski and Raven 2007). Biotechnological applications require algae adapt to the light, nutrient, and temperature conditions in the cultivation system, allowing relatively high growth rates of individual cells and overall high culture productivity. In addition, such biotechnological processes must yield the desired outputs, from oils for use as fuels to nutritional supplements, such as carotenoids, polysaccharides, and other cell wall components and even the whole organisms as biomass for use in feed and food. The need for high culture productivities as well as the desired product composition and quality imposes significant limitations on the algal species and strains to be cultivated (Borowitzka 2013; Raven and Ralph 2015).