Abstract: The stomatic resistance of 9 woody species in different functional areas of Chengde City, North China, was measured with an automatic porometer and the effect of total suspensible particles (TSP) on the plugging of stomata was observed under SEM. It was found that plants in the heavy traffic area and the residential area had relatively higher stomatic resistance, with a mean value (averaged from the upper and lower epidermis) of 10. 5±5.1 s · cm-1. The stomatic resistance of the heavy traffic area was twice as much as that of the relativey clean area, even 8 times more in some species. The great difference, as much as 25 times more, was also found between the upper and lower epidermis even in the same species. In some species such as Fraxinus americana, the stomatic resistance of the upper epidermis was so high that it was beyond the limit of measurement. There was a very good correlation between the stomatic resistance of the lower epidermis and the air TSP, especially in F. americana and Salix matsudana, with r=0. 9968 (<0. 001) and 0. 9951 (<0. 001) respectively. Such relation was very poor for the upper epidermis. Stomata plugging with TSP was studied under SEM. It was noticed that small particles (<5 μm) could enter the stomta to cause plugging and large particles (>30 μm) could plug the stomata by covering the whole orifices, both of which cause stomatic resistance. The findings indicate the main mechanism of monitoring air TSP pollution by stomatal resistance measurement.

Key words: Stomatic resistance, TSP, Air pollution