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The Influence of Present-Day Levels of Ultraviolet-B Radiation on Seedlings of Two Southern Hemisphere Temperate Tree Species

John E. Hunt and David L. McNeil
Plant Ecology
Vol. 143, No. 1 (1999), pp. 39-50
Published by: Springer
Stable URL: http://www.jstor.org/stable/20050792
Page Count: 12
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The Influence of Present-Day Levels of Ultraviolet-B Radiation on Seedlings of Two Southern Hemisphere Temperate Tree Species
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Abstract

Seedlings of two Southern Hemisphere temperate trees species (mountain beech: Nothofagus solandri var. cliffortioides (Hook. f.) Poole and broadleaf: Griselinia littoralis Raoul) were grown in the field to determine the effects of present-day levels of ultraviolet-B radiation (UV-B) on growth, biomass, UV-B absorbing compounds, leaf optical properties and photoinhibition. Plants were covered with either UV-B transmitting or UV-B absorbing filters. After 125 days of typical summer weather, total biomass of both species was not affected by the UV-B treatments. Without UV-B, height increased (23%) and the number of leaves produced decreased (-21%) in beech, but broadleaf was unaffected. The effect of UV-B on beech height and leaf number was manifest during a second flush of leaves suggesting differences in response to UV-B of leaves initiated in different seasons and UV-B radiation regimes. Leaves of both species were essentially opaque to the transmission of UV-B. In the absence of UV-B the transmission of photosynthetically active radiation through leaves of both species increased, foliar nitrogen concentrations increased and levels of UV-B absorbing compounds decreased. In the youngest leaves of beech but not of broadleaf, removal of UV-B reduced midday photoinhibition, and did not alter the complete recovery of the fluorescence ratio $F_{V}/F_{M}$ in the evening to predawn levels. As leaves of both species aged, midday photoinhibition decreased, with the result that UV-B had no effect on photoinhibition in mature leaves. Results of this experiment show that even under present-day UV-B levels, UV-B radiation modifies the physiology, optical properties and secondary compounds of leaves of both beech and broadleaf seedlings.

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