The effect of elevated CO2 concentrations in the atmosphere on plant transpiration and water use efficiency. A study with potted carnation plants

Transpiration rates of potted spray carnation plants Cerise Royalette decreased about 0.04% per vpm CO₂ between ambient atmospheric CO₂ concentration and 1500 vpm CO₂ at several light flux densities and leaf temperatures. Measurements of daily water losses of potted spray carnation plants placed under high solar radiation conditions in two minigreenhouses with 300 and 5000 vpm CO₂ demonstrated that elevated CO₂ concentrations reduced water losses by 20–30%. The effect of the increase in global CO₂ concentration on stomatal closure was calculated to have decreased the yearly transpiration rate of an outdoor crop by 1.6% in this century and is expected to cause a decrease of 10% within the next 50 years if all other factors remain unchanged. From a model of CO₂ uptake of carnation plants it was calculated that the expected water use efficiency (net photosynthesis rate/transpiration rate) will increase by about 40–50% over the next 50 years due to the expected increase in global CO₂ concentration.Contribution No. 205-E, 1979 series.Presented at the Eighth International Congress of Biometeorology 8–14 September 1979, Shefayim, Israel.