THE COMBINED EFFECTS OF CO2 CONCENTRATION AND ENHANCED UV-B RADIATIONON FABA BEAN .3. LEAF OPTICAL-PROPERTIES, PIGMENTS, STOMATAL INDEX AND EPIDERMAL-CELL DENSITY

Seedlings of Vicia faba L. (cv. Minica) were grown in a factorial expe riment in a greenhouse. The purpose of the study was to determine whet her CO2 enrichment and supplemental UV-B radiation affect leaf optical properties and whether the combined effects differ from single factor effects. Seedlings were grown at either 380 mu mol mol(-1) 750 mu mol mol(-1) CO2 and at four levels of W-B radiation. After 20 and 40 days of treatment, absorptance, transmittance and reflectance of photosynt hetically active radiation (PAR) were measured on the youngest fully d eveloped leaf. On the same leaf, the specific leaf area on a fresh wei ght basis (SLA(fw)), chlorophyll content, UV-B absorbance, transmittan ce of UV light and stomatal index were measured. W-B radiation signifi cantly increased PAR absorptance and decreased PAR transmittance. The increased PAR absorptance can be explained by an increased chlorophyll content in response to W-B radiation. Leaf transmittance of UV radiat ion decreased with increasing UV-B levels mainly caused by increased a bsorbance of UV absorbing compounds. UV-B radiation decreased both the stomatal density and epidermal cell density of the abaxial leaf surfa ce, leaving the stomatal index unchanged. Effects of CO2 enrichment we re less pronounced than those of W-B radiation. The most important CO2 effect was an increase in stomatal density and epidermal cell density of the adaxial leaf surface. The stomatal index was not affected. No interaction between CO2 and UV-B radiation was found. The results are discussed in relation to the internal light environment of the leaf.