Increase in the CO₂ exchange rate of leaves of Ilex rotunda with elevated atmospheric CO₂ concentration in an urban canyon

It was found that the atmospheric carbon dioxide (CO₂) concentration in an urban canyon in Fukuoka city, Japan during August 1997 was about 30 μmol mol^-1 higher than that in the suburbs. When fully exposed to sunlight, in situ the rate of photosynthesis in single leaves of Ilex rotunda planted in the urban canyon was higher when the atmospheric CO₂ concentration was elevated. A biochemically based model was able to predict the in situ rate of photosynthesis well. The model also predicted an increase in the daily CO₂ exchange rate for leaves in the urban canyon with an increase in atmospheric CO₂ concentration. However, in situ such an increase in the daily CO₂ exchange rate may be offset by diminished sunlight, a higher air temperature and a lower relative humidity. Thus, the daily CO₂ exchange rate predicted using the model based soleley on the environmental conditions prevailing in the urban canyon was lower than that predicted based only on environmental factors found in the suburbs.