Effects of enhanced UV-B irradiation on plants. The importance of leaf characteristics, canopy architecture and nitrogen distribution

The destruction of the ozone layer will result in increasing UV-B irradiation at the earth's surface. This can influence both animal and plant life. Although there are numerous publications concerning the effects of UV-B on terrestrial plants, there are still many unanswered questions. It is very important for agricultural purposes to find (or breed) resistant cultivars. Knowledge of the plant characteristics that determine the sensitivity to UV-B, however, is mainly lacking. In this thesis three questions are raised: (1) Which characteristics determine the sensitivity of plants? Is canopy architecture (planophyle vs. erectophyle leaves) important? (2) Do UV-B induced changes in morphology increase the plant's resistance to UV-B? (3) Does UV-B change the biomass and N-allocation? What are the consequences?; Experiments were conducted on rye (Secale sereale L., erectophyle leaves) and bean (Phaseolus vulgaris L., planophyle leaves). In the field experiments only natural sunlight was used, with different thicknesses of the greenhouse Plexiglas resulting in two UV-B levels. Growthchamber experiments were conducted under high light intensities of metal-halide lamps. Experiments were conducted under various intensities of both visible and UV-B light, and under varying temperature and N-supply (optimal and 50% reduced). In all experiments growth, photosynthesis, N content and pigmentation of the plants were measured. An additional experiment on the flowering and pod formation in bean was conducted. By measuring all parameters in function of the height in the canopy, enough data were acquired to construct and program a photosynthesis and growth model, "Plagro", for rye. This computer model was used to investigate the importance of leaf angles, N distribution and root/shoot ratio in determining plant sensitivity to UV-B.