INFLUENCE OF UV-B RADIATION ON PHOTOSYNTHETIC ACTIVITY AND CHLOROPHYLL FLUORESCENCE KINETICS IN NORWAY SPRUCE [PICEA-ABIES (L) KARST] SEEDLINGS

Norway spruce [Picea abies (L,) Karst.] seedlings were grown in greenh ouses with two supplemental levels of ultraviolet-B (UV-B) radiation. Photochemical efficiency of photosystem II and vitality index were det ermined monthly. At the end of the experiment, growth, chlorophyll con tent and photosynthetic rates were measured, The data indicate that lo w temperature in winter affected light dependent processes in experime ntal plants including control, while the rise of ambient temperatures, moderate this effect. The synergistic effects of UV-B radiation and l ow temperatures could only be observed in the second winter period. Me asurements of net photosynthetic activity in the second winter period showed significant differences between treated and untreated plants.