Document: THO-3-34-7

Physiological and morphological responses of three Nothofagus species to UV-B radiation resulting from Antarctic ozone depletion in Tierra del Fuego, southern South America.

ROBSON, T.M.* ¹, M.M.CALDWELL ¹, J.G.ZALLER ¹, C.L.BALLARÉ ², O.E.SALA ² and A.L.SCOPEL ²

Utah State University, Logan, UT 84322-5230. USA ¹
Universidad de Buenos Aires, Buenos Aires, Argentina. ²

Abstract:
The extensive forests of southern South America, in particular those of Tierra del Fuego, are comprised almost exclusively of three Nothofagus species. The Antarctic ozone depletion known since the early 1980's, currently causes Tierra del Fuego to receive more UV-B radiation during the Austral Spring (Sept-Dec) than it has over the estimable past. This research aims to elucidate the mechanism by which Nothofagus species respond to this unprecedented change in their light environment. Plastic filters were used to regulate UV-B radiation, to near-ambient UV-B and attenuated UV-B radiation. Appropriate branch filter structures were developed, to allow branches under different light regimes on the same tree to be compared whilst minimising resultant stress and perturbation of growth. These filters were installed before bud-swelling, and branches were monitored throughout the growing season in trees of each of the closely related species, the deciduous Nothofagus antarctica, N. pumilio and the evergreen N. betuloides , near Ushuaia, Tierra del Fuego. This allowed the different patterns and timing of growth in these species to be contrasted. Measurements of leaf physiology and morphology were carried out. Rates of leaf expansion were compared, by fitting leaf measurements repeated in time over the course of expansion to a piece-wise linear polynomial equation. Final leaf size was not shown to be significantly affected by UV-B radiation. Concentration of UV-B absorbing compounds, and leaf thickness were both observed to increase in response to near-ambient levels of UV-B radiation. The seasonal changes in parameters such as stem elongation; leaf development; and branching frequency under the two treatments, did not show a distinct trend with altered UV-B radiation flux. These findings relate to other work being done on the effects of UV-B radiation on the natural ecosystems of Tierra del Fuego, and interactions between Nothofagus and associated organisms. The results have the potential to indicate how increased UV-B radiation could affect competition between the three co-existing Nothofagus species, if extrapolated over many years of increased UV-B exposure.

Keywords: UV-B radiation, global climate change, Nothofagus ecology, ecophysiology, leaf morphology, ozone depletion,

This abstract is being presented at: 9:30 AM in session:
Oral Session #69: UV-B.