Interaction of spatial sulfur patterns between urban air and woody species of the Pearl River Delta, southern China

Sulfur (S) uptakes by woody plants might indicate the presence of urban air pollution in the form of sulfur dioxide (SO₂), which is one of the most important pollutants worldwide. The present study detected total carbon (C) and S contents in the leaf and stem (dry mass) of 53 common woody species in representative forest plots in five cities across the Pearl River Delta (PRD), a densely urbanized region in Southern China. Coupling analysis explored whether spatial patterns of S content in woody species were relatively consistent with atmospheric SO₂ concentration in the five PRD cities. Total S content varied in leaves and stems with averages of 2.0 g/kg and 0.8 g/kg, respectively, while air SO₂ concentration ranged from 9.0 to 108.0 g/m³. However, total C content was relatively constant among all the species across the diverse forest plots, with an average of 443.5 g/kg and a median of 448.0 g/kg in leaves and 437.0 g/kg in stems. This suggests that air SO₂ pollution did not influence tree growth, so afforestation may be an effective method of eliminating urban air pollution in the PRD.