What was done
Hedera helix L. plants produce both variegated foliage, which contains large sectors of non-photosynthetically-active yellow and white leaf area, and non-variegated foliage.  In this study, cuttings of both foliage types were grown for 28 days at ambient CO2 before being subjected to 46 days of exposure to atmospheric CO2 concentrations of 355 and 720 ppm, to determine the effects of elevated CO2 on photosynthesis in this ornamental plant.

What was learned
After two days of differential CO2 treatment, photosynthetic rates in all CO2-enriched plants were about 90% greater than those observed in plants maintained at ambient CO2.  After 32 days of elevated CO2 exposure, however, photosynthetic acclimation was evident in all plant cuttings; but the phenomenon was not uniform.  The completely green CO2-enriched non-variegated cuttings exhibited photosynthetic rates that were not significantly different from those displayed by their respective controls growing at ambient CO2.  The CO2-enriched variegated cuttings, on the other hand, displayed much less photosynthetic acclimation, maintaining photosynthetic rates that were still 48% greater than their respective control plants growing at 355 ppm CO2.

Because variegated plants contain leaf tissue sections lacking chlorophyll, these leaf parts may serve as substantial sinks for photosynthetically-derived sugars produced in neighboring leaf sections containing chlorophyll, which sugars would otherwise accumulate in the green areas of the leaves producing a greater degree of CO2-induced photosynthetic acclimation.  Devoid of this impediment, or possessing it to a much-reduced degree, the variegated plants are able to maintain greater rates of photosynthesis in response to atmospheric CO2 enrichment, allowing them to produce more biomass.  After the 46-day experiment was ended, for example, the CO2-enriched variegated plants had a total dry weight that was 33% greater than that of their counterparts growing at ambient CO2, while the CO2-enriched non-variegated plants had a total dry weight that only 13% greater than that of their control plants.

What it means
As the atmospheric CO2 concentration rises, it is likely that Hedera helix - and perhaps many of the other 700 species known to possess variegated leaves - will respond by significantly increasing their photosynthetic rates and biomass production.  Thus, in the future, one can anticipate the growth of variegated ornamental plants, so often used in landscape designs, to respond quite dramatically to the increasing CO2 content of the air.