Carbon dioxide absorption rate by urban trees in Chulalongkorn University Centenary Park

Abstract

Nowadays many city governments have adopted policies promoting urban greening because of urban greening provide ecosystem services. One of services is to mitigate the increasing carbon dioxide in atmosphere through photosynthesis. In this study, we studied carbon dioxide absorption rate ( A ) by urban trees in Chulalongkorn University (CU) Centenary Park in wet and dry season and selected urban trees species which are Lagerstroemia floribunda (Crepe Myrtle), Afzelia xylocarpa (Black rosewood), Homalium tomentosum (Moulmein lancewood) and Bauhinia purpurea (Orchid Tree). We measured stomatal conductance ( s g ), the ratio of leaf intercellular CO₂ concentration and atmospheric CO₂ concentration ]Equation] and then calculated carbon dioxide absorption rate. The results showed that A in all species showed no seasonal difference (p › 0.05). Overall, A increased with vapor pressure deficit ( VPD ) until it reached approximately 2 to 30 kPa and then decreased with VPD . Because VPD is calculated from relative humidity (RH) and temperature, we examined the relationships between these two variables and A to see which one contributed more to the VPD responses. Results showed that RH seemed to affect the VPD in A. xylocarpa, L. floribunda and B. purpurea while temperature contributed more to the response in dry season of H. tomentosum. We conclude that A was the highest in L. floribunda, B. purpurea, H. tomentosum, and A. xylocarpa, respectively and all species were no statistically significant differences of A between wet and dry season. The results from this study will be important to increase planting trees that can choose maximize carbon dioxide absorption rate by selecting appropriate species for improve CO₂ mitigation of this park.