COMBINED EFFECTS OF ENHANCED UV-B RADIATION AND NITROGEN DEFICIENCY ON THE GROWTH, COMPOSITION AND PHOTOSYNTHESIS OF RYE (SECALE-CEREALE)

The interactive effects of N-deficiency and enhanced UV-B radiation on growth, photosynthesis and pigmentation of rye were studied. The plan ts were grown for 5 weeks in growth chambers with high (700 mu mol m(- 2) s(-2)) irradiance levels. A 30% difference in UV-B at plant level w as achieved by using different thicknesses of UV-B transparent Plexigl ass. One half of the plants received optimal N nutrition, while the ot her received half of this dose. Both enhanced UV-B and N deficiency st rongly decreased production (from 24-33%). The combined effect was add itive (no interaction) on most parameters, including total dry weight production which was 52% lower than in the control series. Significant interaction was found on the root/shoot ratio. While reduced N supply induced an increase in the ratio at normal UV-B irradiation, under th e increased UV-B, N deficiency had no effect on the root/shoot ratio. The reduced biomass due to UV-B was clearly correlated to a reduction in photosynthesis. At optimal N supply the plants increased the produc tion of protective pigments in response to UV-B, but at reduced N supp ly this response was lacking. The increased N content of the high UV-B /high N plants could be a result of increased flavonoid production as well as changes in light penetration in the canopy.