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In contrast to former experiments conducted under greenhouse conditions, in the presented study innovative materials (such as ETFE foil) with a high transmittance in the UV-B and also in the visible range were used, which allows to omit any additional source of UV-B radiation. The aim was to investigate the growth behaviour under these conditions. The effects of UV-B radiation under more realistic field conditions are smaller than expected from the growth chamber experiments (Searles 2001). Ultraviolet-A radiation, similar to UV-B, can induce a reduction of aboveground biomass and leaf area (Krizek et al. 1998).
One aspect of the work was to investigate the influence of preadaptation of lettuce plants to UV-B radiation in greenhouses and the effect after transfer to field conditions. Many of the above-described responses have direct impact for horticultural applications. It is preferable to have UV-B adapted plants for sale and the possibility to transfer these plants directly to field conditions with an increased likelihood of survival under ambient conditions. Together with our research partner from University of Bonn we found significantly higher quercetin and cyanindin content during the greenhouse phase in response to enhanced UV-B radiation. But six days after transfer to field conditions the secondary metabolites of UV-B pre-treated lettuce plants are levelled (Behn et. al. 2010).
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