Serious Complications in Experiments in which UV Doses Are Affected by Using Different Lamp Heights
Ultraviolet Ground- and Space-based Measurements, Models, and Effects IV
James R. Slusser, Jay R. Herman, Wei Gao & Germar Bernhard
Many experiments examining plant responses to enhanced UV-B radiation simply compare an enhanced UV-B radiation treatment with ambient UV-B (or no UV-B in most greenhouse and controlled environment studies). However, some experiments utilize multiple doses of UV-B radiation. A number of different techniques have been used to adjust the UV dose, each with advantages and disadvantages. One common technique is to place racks of fluorescent UV-B lamps at different heights above the plant canopy. A generally ignored consequence of this technique is that the pattern of shade which plants receive from the lamps is distributed differently over the course of the day at different lamp heights. To determine the effects of using lamps at different heights above the canopy, we grew three species (canola, sunflower, and maize) in the greenhouse under racks of unenergized lamps that were placed at two different heights above the plant canopy. Many plant growth characteristics differed between plants grown under the two lamp heights. These differences can potentially enhance or obscure true UV-B effects. Even more troubling is that changes in leaf mass per foliage area, which were observed in this experiment, could contribute to differences in plant UV-B sensitivity. We recommend the use of other techniques for achieving multiple doses of UV-B radiation. These range from simple and inexpensive approaches (wrapping individual fluorescent tubes in different layers of a neutral density filter such as cheese cloth) to more technical and expensive alternatives (electronically modulated lamp control systems). These choices should be determined by the goals of the particular experiment.
Flint SD, Ryel RJ, Caldwell MM (2004) Serious complications in experiments in which UV doses are affected by using different lamp heights. In: Slusser JR, Herman JR, Gao W, Bernhard G (eds) Ultraviolet Ground- and Space-based Measurements, Models, and Effects IV. Proceedings of SPIE Vol. 5545. SPIE, Bellingham, WA. pp. 56-62.