Global dimming, in addition to affecting the amount of visible radiation, will affect the amount of UV radiation reaching the earth's surface. Our experiment using fava beans (Viciafaba) grown in the high UV environment of Mauna Kea, Hawaii, was designed to detect whether a 13% reduction in visible radiation (and associated reduction in UV radiation), a level similar to global dimming, could influence plant growth and leaf optical properties for UV-transmittance. We found that structural differences were minimal in this high light environment, but changes that can occur in secondary chemistry can affect epidermal transmittance for UV. Our results, and those of other researchers, suggest that the primary effects of global dimming on plants may be mediated through changes in secondary chemistry, and would be most likely to occur with foliage in high-shade environments. Such changes have the potential to affect herbivory, nutrient cycling, and plant response to pathogens. Future research to further understand global dimming effects on ecosystem function should continue with a focus on secondary compounds of plants.
Experiments involving UV filtration need to have sufficient methodological detail that comparisons can be made between different venues. Methodology need not be ponderous, but needs to include: (1) latitude and elevation of the experimental site, (2) dates of plant growth, (3) dosimetry of UV radiation during the experiment, and (4) filter descriptions. Filter transmittance needs mention if non-standard materials are used, and filter geometry should not be neglected. For example, flat filter sheets permit some radiation to reach plants in the filtered wavelength region while tents or tunnels exclude all filtered wavelengths. With this standardized reporting of experimental conditions, comparisons of experiments between locations will be facilitated and may lead not only to generalizations on plant responses, but may also assist in the evaluation of spectral weighting functions.
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