Lack of UV radiation in Biosphere 2 - practical and theoretical effects on plants

UV radiation is an important physical stressor for many exposed organisms. It also has a diversity of positive roles in the biosphere, such as in UVA-dependent vision. In artificial ecosystems where the spectral quality is dramatically altered by the overlying structure these interelationships can be disturbed. Here practical and theoretical measurements are presented for the effects of UV exclusion on desert cacti in Biosphere 2. Cacti inside the biosphere lack flavonoids as a result of the attenuation of UVB and most of the UVA radiation caused by the glass structure. Although the theoretical inhibition to chloroplasts is less than outside, it is much greater than would be expected if the plants inside possessed flavonoids, since the small amount of UVA radiation (385-400 nm) that penetrates has a disproportionately greater theoretical effect. The importance of understanding the effects of UV exclusion in artificial ecosystems and the importance of exercising caution in interpreting the data from artificial enclosed ecosystems in the context of the natural world, is discussed. (C) 2000 Published by Elsevier Science B.V.