Deckmyn, G., Caeyenberghs, E. and Ceulemans, R. 2001. Reduced UV-B in greenhouses decreases white clover response to enhanced CO2. Environmental and Experimental Botany 46: 109-117.
What was done
The authors grew white clover plants (Trifolium repens L., cv. Mervi) in four small greenhouses, two of which allowed 88% of the incoming UV-B radiation to pass through their roofs and walls and two of which allowed 82% to pass through. One of the two greenhouses in each of the UV-B treatments was maintained at ambient CO2 (371 ppm) and the other was maintained at elevated CO2 (521 ppm). Midway through the four-month summer growing season, flower numbers were counted; and at the end of the season, total shoot and root biomass was determined.
What was learned
At the mid-season point of the study, the 40% increase in atmospheric CO2 concentration stimulated the production of flowers in the low UV-B treatment by 22% and in the slightly higher UV-B treatment by 43%; while at the end of the season, the extra CO2 was determined to have provided no stimulation of biomass production in the low UV-B treatment, but it significantly stimulated biomass production by 16% in the high UV-B treatment.
What it means
The results of this study indicate that, at least for the crop investigated, the positive effects of atmospheric CO2 enrichment on flower and biomass production are greater at more realistic or natural values of UV-B radiation than what are characteristic of many greenhouses. The authors thus say their results "clearly indicate the importance of using UV-B transmittant greenhouses or open-top chambers when conducting CO2 studies." If this is not done, their work suggests the results obtained may not depict the true magnitude of biological benefits to be received from atmospheric CO2 enrichment.