Reduction of ambient UV-B radiation does not affect growth but may change the flowering pattern of Rosmarinus officinalis L.

The effects of sub-ambient levels of UV-B radiation on the shrub Rosmarinus officinalis L. were investigated in a field filtration experiment in which the ambient UV-B was manipulated by a combination of UV-B transmitting and UV-B absorbing filters. As a result, the plants were receiving near-ambien t or drastically reduced UV-B radiation doses. Drastic reduction of UV-B ra diation had no effect on mean, total and maximum stem length, number of ste ms per plant, dry mass of leaves, stems and roots and leaf nitrogen and phe nolic contents. However, flowering was more pronounced under reduced UV-B r adiation during the winter period which coincides with ascending ambient UV -B radiation. In contrast, during autumn and early winter, a period which c oincides with descending ambient UV-B radiation, flowering was unaffected b y reduced UV-B radiation. We can conclude that natural UV-B radiation does not affect growth of Rosmarinus officinalis, but its reduction could influe nce the flowering pattern of the species.