Is cell composition related to the phylogenesis of microalgae? An investigation using Hierarchical Cluster Analysis of Fourier Transform Infrared spectra of whole cells

Fourier Transform Infra-Red (FTIR) spectroscopy was used to investigate whether algae belonging to the green evolutionary lineage and algae belonging to the red evolutionary lineage consistently differ for their biomass composition and for the way their composition responds to changes in NO₃⁻ availability. For this purpose, the FTIR spectra of eleven algal species cultured in media containing different amount of NO₃⁻ were subjected to Hierarchical Cluster Analysis (HCA). The same analysis was conducted on the differential FTIR spectra of cells grown at different NO₃⁻ concentrations. Although the organic composition of cells was affected by the availability of NO₃⁻, the analysis of its change did not elicit a clear relationship with the phylogenetic position of the species used. However, when the two evolutionary lineages, and not the individual species, are compared, some differences emerge: the species belonging to the green lineage reorganize their biomass composition similarly in response to variations in N availability, whereas the species of the red lineage modulate their allocation patterns more heterogeneously. This difference may contribute to the ecological fitness of microalgae and may have had an influence on the evolutionary trajectories of phytoplankton groups.