| dc.description | Effects of varying nitrogen and light regimes on the bio-optical properties of four phytoplankton species, belonging to three Phytoplankton Functional Types (PFT), namely cyanobacteria, chlorophytes and diatoms, were investigated. Significant decreases in intracellular chlorophyll-a and photosynthetic carotenoid concentrations with increasing nitrogen-limitation and light intensity were observed in all four phytoplankton species. The peak height of the Gaussian band at 635 nm, representing absorption by phycocyanin in S. bacillaris , showed the same trend as those shown by chlorophyll-a and photosynthetic carotenoids under the different treatments. Species-specific changes were observed in the intracellular concentrations of photoprotective pigments under the changing nitrogen and light environment. The abundance of photoprotective pigments relative to chlorophyll-a increased under high light in all four phytoplankton species. The chlorophyll-a specific-absorption coefficient increased under low-ambient nitrogen and high-light conditions. Variability in the chlorophyll-a specific-absorption coefficient is caused by changes in the pigment packaging and in the abundance of accessory pigments relative to chlorophyll-a. The observed changes in the absorption properties in my study are consistent with the predictions of theoretical models of package effect. Inter-taxa and intra-species variability were also observed in the unpackaged chlorophyll-a specific-absorption coefficient at 676 nm. Significant increases in carbon per cell volume, carbon-to-nitrogen and carbon-to-chlorophyll-a ratios occurred under nitrogen-limited and high-light conditions in the four phytoplankton species. The ranges of the various bio-optical properties of the different PFTs obtained from the culture study were compared with mean values of the same properties retrieved from the field samples dominated by the same PFT. The field samples of the two PFTs cyanobacteria and chlorophyte corresponded well with the values obtained from nitrogen-limited, high-light grown cultures of the same PFTs, whereas the field samples of diatoms agreed well with nitrogen-sufficient low-light cultures of diatoms. The results obtained from this study can be used to improve the parameterization of PFT-based ecosystem models. | en_US |
