Ecophysiological responses of two tropical urban shrub plants to elevated carbon dioxide and water stress

Abstract

Elevated atmospheric carbon dioxide causes changes in most plant species in terms of physiological and morphological properties. In this study, we elucidate the effects of elevated CO2 and water regimes on two species of shrubs which were Melastoma malabathricum and Clidemia hirta. The factor of water stress was also included whereby for each CO2 treatment, the amount of water was given once or twice daily. The treatment of elevated CO2 was at 800 ppm, where the plants were exposed for two hours daily and ambient CO2 at 400 ppm as the control. The growth of plants was monitored through their height, leaf area and biomass that were recorded fortnightly for six months. The physiological changes were determined via stomatal conductance, photosynthetic rate and transpiration rate. The results revealed that each species responded differently to the CO2 treatments. The growth parameters of height and leaf area index showed positive responses on elevated CO2 and twice watering for both species. As for biomass, M. malabathricum exhibited higher below ground biomass compared to above ground biomass in the elevated CO2. In contrast, C. hirta showed the opposite trend. The results of the three physiological parameters demonstrated a bell shape trend for both treatments with the highest rate at the fifth month.