LEAF STRUCTURE AND GAS EXCHANGE CHARACTERISTICS OF PTEROCARPUS INDICUS PLANTED IN THE CITY

Abstract

Pterocarpus indicus, which is the most common ornamental trees planted in Bangkok, was selected for leaf anatomy and gas exchange characteristics studics. Six study sites in Bangkok were selected: Silom, Ladprao and Bangkhen as heavy-polluted area; Kasctsart University, Chatuchak Park and Lumpini Park as mild-polluted area. Anatomical study of P. indicus leaf indicated that there were no differences in leaf structurc among sites. Slight differences in leaf thickness and palisade thickness were observed between heavy-polluted and mild-pollutcd sites. P. indicus leaf was found to be hypostomatous. The stomata were found evenly distributed throughout the leaf. Stomatal frequency varied differently among six study sites, but no statistical difference was found. Stomatal frequency varied between 153-173 stomata/mm2. The average stomatal size was 24.24 um, no any differences were observed. The diurnal course of the net photosynthetic rates of P. indicus of all sites showed the similar pattern. The photosynthetic rates increased in the morning and remained relatively constant or dropped a little in the afternoon. The net photosynthetic rates reached the maximum between 8.00-9.00 h. The average daily photosynthetic rates varied differently among study sites. Highly significant differences were observed (p<0.01). The lowest net photosynthetic rate (2.64 umol m-2s-l) was found in the trees planted at heavy-polluted sites while the highest rates (6.21 pmol m-2s') was found at the mild-polluted sites. Net photosynthetic rates did not increase with the light intensity or carbon dioxide.