Growth Responses of Melastoma malabathricum to Elevated Carbon Dioxide and Water Regime

摘要

Elevated atmospheric CO_2 has significant effects on plant growth depending on the species and the interaction between treatments given. In other words, the impacts vary among species, depending on differences in photosynthetic pathways, intrinsic growth rates and other properties. In this research we studied the effects of increased carbon dioxide concentration and water regimes on a shrub species, Melastoma malabathricum in a shade house at ambient CO_2 and open roof greenhouse at elevated CO_2. The factor of water stress was also included, in which for each CO_2 treatment, the amount of water was given once or twice daily. The treatment of elevated CO_2 was at 800 ppm, when the plants were exposed daily from 0900h until 1100h. The plant growth was monitored through their biomass, height and leaf area that were recorded fortnightly for six months. The results showed that the height of M. malabathricum stem in elevated CO_2 was significantly higher than those in ambient CO_2. Similarly, leaf area in the elevated CO_2 showed a big difference with a value of 46.24 cm~2 for elevated CO_2 with twice watering, but only 17.94 cm~2 for ambient CO_2 with twice watering. Even for once watering, we can see the values of leaf area were higher with 32.06 cm~2 for elevated and 24.35 cm~2 in ambient CO~2. The above ground and below ground biomass differed significantly between ambient and elevated CO_2. Above ground biomass in ambient CO_2 was higher than that in elevated CO_2 with a percentage of 25.7%. In contrast, the below ground biomass in elevated CO_2 was higher than that in ambient CO_2 with a percentage of 17.4%. The results suggested that the increment of CO_2 concentrations and water regime in the natural environment may influence the growth and ultimately the abundance and distribution of this shrub species in urban forest.