Combined effects of CO2 concentration and enhanced UV-B radiation on faba bean

Due to anthropogenic influences, both solar UV-B irradiance at the earth's surface and atmospheric [CO2] are increasing. To determine whether effects of CO2 enrichment on faba bean (cv. Minica) growth are modified by UV-B radiation, the effects of enhanced [CO2] on growth and photosynthetic characteristics, were studied at four UV-B levels. Faba bean was sensitive to enhanced UV-B radiation as indicated by decreases in total biomass production. Growth stimulation by CO2 enrichment was greatly reduced at the highest UV-B level. [CO2] by UV-B interactions on biomass accumulation were related to loss of apical dominance. Both [CO2] and UV-B radiation affected biomass partitioning, UV-B effects being most pronounced. Effects of [CO2] and UV-B on faba bean growth were time-dependent, indicating differential sensitivity of developmental stages. [CO2] and UV-B effects on photosynthetic characteristics were rather small and restricted to the third week of treatment. CO2 enrichment induced photosynthetic acclimation, while UV-B radiation decreased light-saturated photosynthetic rate. It is concluded that the reduction in biomass production cannot be explained by UV-B-induced effects on photosynthesis.