Assessing Global Dimming and UVB Effects on Plant Growth

To provide some insight into the effects of global dimming on plant growth, the 372

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Ultraviolet Plant Growth

Atmospheric transparency (%)

TRENDS in Ecololgy % & Evolution

Figure 13.1 Idealized changes in diffuse and direct beam radiation reaching the Earth as a function of atmospheric transparency (reprinted from Roderick 2006). Solid lines represent standard atmospheric conditions; dotted lines show the immediate effect of the Mt. Pinatubo volcanic eruption in June 1991

Atmospheric transparency (%)

TRENDS in Ecololgy % & Evolution

Figure 13.1 Idealized changes in diffuse and direct beam radiation reaching the Earth as a function of atmospheric transparency (reprinted from Roderick 2006). Solid lines represent standard atmospheric conditions; dotted lines show the immediate effect of the Mt. Pinatubo volcanic eruption in June 1991

role of UV-B in this response, and a comparison of the magnitude of the responses to dimming and UV-B, we conducted a field experiment using minimal shading levels approximating the reduction in solar radiation observed under these conditions (e.g., Stanhill and Cohen, 2001). We specifically examined whether there could be direct influences of global dimming and altered solar UV-B on various aspects of leaf development (e.g., leaf optical properties or leaf mass per unit area), which are important traits that influence light penetration into the canopy and which often influence plant responses to UV-B. We further evaluated whether these possible changes in light penetration or other effects of shade could influence overall plant growth in this experiment. These effects were put into perspective with UV-B radiation effects by simultaneously conducting a UV-B screening experiment at the same site (Mauna Kea, Hawaii). This served two purposes: (1) it permitted comparisons between these two global environmental factors, and (2) enabled us to assess whether UV radiation effects are sufficiently large such that a potential reduction in UV accompanied by global dimming could have measurable effects on plants. Finally, we examined whether reports in the literature suggest trends in the effects of UV-B radiation, contrasting UV screening experiments at higher latitudes (lower UV-B) with lower-latitude (higher UV-B) sites, and we compared the responses of other species at high-UV sites with our results.

13.2 Methods

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