| Summary: | Photosynthetic rates of three marine picoplankton species were measured as a function of both photon flux density (P-I response) and photon wavelength (action spectra or P-S response). The picoplankton species examined included two prokaryotes, the marine cyanobacteria Synechococcus sp. WH 7803 and Synechococcus sp. WH 5701, and one eukaryote, the prymnesiophyte Pavlova sp. (clone NEP). The wavelength dependence of photosynthesis was also measured in natural phytoplankton assemblages, collected from latitudes ranging from the sub-tropical North Atlantic Ocean to the eastern Canadian Arctic. The abilities of previous P-I formulations to provide a quantitative description of the P-I response of the picoplankton were compared. Three new P-I models are introduced that provide an improved overall fit (fidelity) to the P-I data. Two of these models, a simple geometrical description and a rational model based on target theory, accommodate the spectral dependence of photosynthesis by way of a simple spectral weighting function. The third model, a kinetic description involving two spectrally distinct photosystems, also includes the effects of Emerson enhancement at low PFDs. The photosynthetic action spectra of both cyanobacterial species revealed the importance of the phycobiliproteins and Emerson enhancement. In contrast, the photosynthetic action spectra of natural phytoplankton assemblages closely resembled those of Chromophytic algae such as Pavlova sp., where chlorophyll is the dominant light-harvesting pigment and Emerson enhancement is minimal. For the natural phytoplankton assemblages the photosynthetic rate under polychromatic irradiance could be approximated using a suitable spectral weighting function. Absorption by detritus in natural phytoplankton assemblages eliminated the absorption spectrum as a suitable spectral weighting function. Using the photosynthetic action spectrum to predict rates of light-limited photosynthesis at depth shows that the ability of the phytoplankton to utilize underwater spectral distributions increases with depth. Furthermore, photosynthetic rates measured under artificial light significantly under-estimate the predicted photosynthetic rate at depth. Thesis (Ph.D.)--Dalhousie University (Canada), 1990.
|
|---|