Quantification of nutrient-replete growth rates in five-ion hyperspace for Chlorella vulgaris (Trebouxiophyceae) and Peridinium cinctum (Dinophyceae)

Abstract

The effects of five ions, NO-3, PO3-4, K+, Na+ and Cl-, on growth rates were quantified for Chlorella vulgaris (Trebouxiophyceae) and Peridinium cinctum (Dinophyceae) in batch cultures. A five-dimensional, experimental design hypervolume was defined by five-ion mixture vectors projected across a total ion concentration gradient of 1 to 30 mM to quantify growth rates in relation to N:P ratios and primary bulk solution ions. Both C. vulgaris and P. cinctum exhibited very similar, positive responses to cations and negative responses to anions. It was determined that total ion concentration for these five ions, from 1 to 30mM, did not directly affect growth rate for either alga, although it did play an interactive role with several ions. No truly 'optimal' N: P ratio was identified for either alga. Instead, regions of fast growth rates were mapped within the multivariate experimental design space, or 'hypervolumes', that encompassed relatively broad ranges of N:P ratios. This illustrates the fact that optimality is highly contextual and directly dependent on the total ion complement of any given medium. Our results also show that pH is a poor indicator of growth medium quality and should not be considered an independent factor. This study is the first set of unconfounded, ion-specific experiments with algae that we are aware of. The data suggest that we need to reconsider the discussion surrounding 'optimal' ratios and concentrations of nutrients/ions in relation to growth to encompass the hyperdimensionality of media defined by multiple ion vectors. This 'ionic context' is extremely important to algal physiology, has broad implications for questions of nutrient requirements, and needs to be further explored. © 2010 British Phycological Society.