Chiang Mai Journal of Science

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This study was performed to examine the CO₂ uptake of Azadirachta indica A. Juss. var. stamensis (Valeton), a fast-growing tree species, and Pterocarpus macrocarpus Kurz, a slow-growing tree species, both grown in Kanchanaburi province. Field data were taken using the Li-Cor 6200 portable photosynthetic system in December 1999 and February 2000. The results showed that the CO₂ uptake rate of A. siamensis was significantly higher than of P. macrocarpus in early winter (December). The highest CO₂ uptake of A. siamensis was 13.86 mgCO₂ dm^-2.hr^-1 at around noon, whereas that of P. macrocarpus was only 8.68 mgCO₂ dm^-2.hr^-1. Nevertheless, no differences in the CO₂ uptake were observed at the end of the winter (February) in both tree species. Furthermore, the water use efficiency (CO₂ uptake per one unit of transpiration) of A. siamensis was lower than that of P. macrocarpus in both periods. In conclusion, the water use efficiency of P. macrocarpus was higher thant of A. siamensis whereas the CO₂ uptake rate of A. siamensis was greater than of P. macroparpus.

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