Reduced UV-B in greenhouses decreases white clover response to enhance <tex>CO_{2}$</tex>

The interaction between reduced UV-B radiation and elevated CO 2 on the growth, allocation and physiology of white clover ( Trifolium repens ) was studied in greenhouses of different UV-B transmittance (82 and 88% of ambient) with either ambient (371 ppm) or elevated (521 μmol mol −1 ) CO 2 concentration. The 88% UV-B levels in increased growth and flowering, indicating an important role for ambient UV-B levels in plant functioning and growth. High CO 2 increased growth significantly only under the 88% UV-B level. The interaction between UV-B and CO 2 effects on total biomass was significant. Allocation was affected significantly by both UV-B (increased root growth, increased flowering) and CO 2 (increased flowering, reduced stem weight). The results clearly indicate the importance of using UV-B transmittant greenhouse or open-top chamber when conducting CO 2 studies, or at least stating the reduction in UV-B within greenhouses.