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Photosynthetic response of Scandinavian kelp forests to stratospheric ozone depletion

by 1970- Miller, Harlan Laurence

Abstract (Summary)
Direct quantification of photosynthetic carbon assimilation in seaweeds provides a valuable measure of primary production by these abundant macrophytes. Most photosynthetic studies with macroalgal are based on oxygen evolution. This approach is preferred over traditional 14C tracer techniques since oxygen electrodes are generally inexpensive and radioactive wastes are not produced. Nevertheless, oxygen techniques do not directly measure carbon assimilation; thus, primary production estimates rely on the conversion of oxygen units to carbon units via a photosynthetic quotient, which may vary depending on physiological state and nutrient status of the alga. Here, I present two methods for measuring photosynthesis in macroalgae, both of which should greatly enhance prospects for photosynthetic research, particularly under field conditions. First, a carbon uptake procedure is described which relies on incorporation of a stable 13C isotope label. Important advantages of the 13C method include simplicity of sample processing, avoidance of environmental hazards and restrictions of radioactive 14C, and ability to be used as a dual tracer with 15N. Second, I employed a fiber-optic micro-optode system for measurement of dissolved oxygen. The fluorescence-based optodes stabilize quickly ( < 15 s), do not consume oxygen, and are simple to set-up and maintain. Oxygen and carbon photosynthesis were assessed concurrently in a light/dark chamber design. Both techniques resolved significant decreases in light-saturated photosynthesis (Pmax) 10 in the kelp Laminaria hyperborea collected subtidally at 10 m compared to kelp at 0 m (from mean low tide). Oxygen and carbon photosynthetic rates agreed well with published values and were mutually consistent, considering a reasonable photosynthetic quotient. Estimated measurement errors ( < 2%) associated with the 13 C technique were less than intrinsic variation ( > 20 %) in photosynthetic rates (and lamina dry weights) between kelp individuals with similar light histories. Both techniques should provide an alternative to traditional photosynthetic protocols and stimulate further primary production research in macrophytes.
Bibliographical Information:

Advisor:

School:The University of Texas at Austin

School Location:USA - Texas

Source Type:Master's Thesis

Keywords:ozone layer depletion kelps photosynthesis scandinavia

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