Date of Award:

5-2000

Document Type:

Dissertation

Degree Name:

Doctor of Philosophy (PhD)

Department:

Natural Resources

Department name when degree awarded

Rangeland Resources

Committee

Martyn M. Caldwell

Abstract

The severity of stratospheric ozone depletion in the temperate and polar latitudes has raised concerns about the sensitivity of terrestrial vegetation and ecosystems to solar ultraviolet (UV-B) radiation. This dissertation examined the responses of plants and microbes to solar UV-B for 3 years in Tierra de! Fuego, Argentina (55° S). This region is under the influence of the Antarctic "ozone hole" during the austral spring. Additionally, a quantitative review of the UV-B literature was conducted using a set of statistical techniques known as meta-analysis.

For the field studies in Tierra de! Fuego, plots were established in a Sphagnum moss peatland and a Carexsedge fen during the spring of 1996. These plots received either near-ambient solar UV-B (90% of ambient) or reduced UV-B (20% of ambient) using specially designed plastic films. At the end of the first field season, no effects of the solar UV-B treatments were apparent on the growth and pigmentation of the plant species in either community The height growth of the moss Sphagnum mageffanicum was less under near-ambient solar UV-B than reduced UV-B during the second and third growing seasons. In contrast, volumetric density of the moss was greater under nearambient UV-B. The growth of the vascular plants did not respond to the solar UV-B treatments even after 3 years although UV-B-absorbing compounds were greater under near-ambient UV-B in some species. Populations of testate amoebae (i.e., shelled amoebae) inhabiting S. magellanicum had greater numbers under near-ambient UV-B than reduced UV-B throughout the 3 years. This response may be an indirect effect of solar UV-B mediated by the direct effect of UV-Bon S. mageffanicum height growth. Fungi on the leaf surfaces of the tree Nothojagus antarctica appeared to be directly inhibited by solar UV-B.

The quantitative literature review of plant field studies simulating stratospheric ozone depletion assessed the effects of elevated UV-B on 10 plant response variables from papers published between 1976 and mid-1999. Modest significant inhibitions of leaf area, aboveground biomass, and plant height were apparent due to increased UV-B using meta-analysis. An increase in UV-B-absorbing compounds appears to be the most robust general response to increased UV-B radiation.

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