Effects of ultraviolet-B radiation on marine phytoplankton Public Deposited

http://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/gm80hz37k

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  • Global increases in ultraviolet-B radiation (UVBR:290- 320 nm) resulting from decreases in stratospheric ozone concentration have the potential to alter marine primary production and affect global climate and marine trophic dynamics. Effects of UVBR on phytoplankton carbon fixation were determined from open ocean exposure studies conducted off the coast of Washington state. Photoinhibition of carbon fixation was a linear function of cumulative UVBR dose weighted by an exponential action spectrum. Comparison of the dose-response for UVBR inhibition of carbon uptake with results of earlier research indicates that a common, short-term photoinhibition response to UVBR may occur. Short-term photoinhibition was also measured for nitrogen uptake by natural plankton assemblages from the North Pacific. Ammonium uptake was inhibited by UVBR exposure to a greater extent than nitrate uptake. The action spectrum for ammonium uptake inhibition had a lower slope and greater relative contribution from wavelengths >320 nm to total biologically effective dose than the action spectrum for total UVR (290-347 nm) inhibition of carbon fixation. Inhibition of ammonium uptake was a linear function of biologically effective UVR dose. Comparison between dose-responses and action spectra for arnmonium and carbon uptake suggest deeper water-column penetration of UVR effects on ammonium uptake than carbon on uptake. Influence of nutritional status on the photoinhibitory effects of UVBR on phytoplankton growth rates and biomass were investigated using monocultures of the marine diatom Phaeodactylum tricornutum. Specific growth rates and biomass were inhibited from 2% to 16% by UVBR during nutrient-replete growth. However, no effect of UVBR was detectable when inhibition of growth rate and biomass by nutrient limitation exceeded the potential for inhibition by UVBR. Thus, a competitive interaction appears to occur between macro--nutrient stress and UVBR stress, such that growth rate and biomass will be determined by the most limiting environmental factor. Results suggest that phytoplankton in nutrient-rich areas of the ocean may be most susceptible to UVBR inhibition of growth and biomass, while these parameters may not be appropriate for measuring UVBR stress in regions of nutrient limitation.
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