Light and atmospheric pollution affect photosynthesis of street trees in urban environments

The gas exchange of leaves of the Ilex rotunda trees planted at thirteen sites in the city of Fukuoka, Japan, with various sun light conditions and air pollutant concentrations was studied. The highest maximum photosynthetic rate and the stomatal conductance of single leaves were measured under controlled conditions and analyzed with the environmental variables by correlation analysis. The photosynthetic rate of the urban core was highest and that of the suburban area was lowest. The results from the correlation analysis showed that the photosynthetic rate was negatively correlated with sun light conditions and positively correlated with air pollutant concentrations. The reasons for the higher photosynthetic rate in the urban core with poor sun light condition and higher air pollutant concentrations were discussed in relation to stimulation by air pollutant and avoidance of photoinhibition.