Growth improvement of rain tree (Albizia saman Jacq. Merr) seedlings under elevated concentration of carbon dioxide (CO2)

Abstract

A study was conducted to determine the growth effects of rain tree (Albizia saman Jacq. Merr) seedlings under elevated concentration of carbon dioxide (CO2) in an automated greenhouse system. The CO2 was injected for two hours daily at 9 am-11 am with mean concentration of 800 μmol mol-1. For control trial, seedlings were placed in another greenhouse with mean ambient CO2 concentration of 400 ± 50 μmol mol-1. A completely randomized block design was used in this study, and growth observations were made in every 30 days for duration of 120 days. The results showed that almost all parameters observed for the seedling growth under elevated and ambient concentrations were significant. Concentrations of chlorophyll b in leaves of seedlings exposed for 30 days and 60 days at elevated CO2 were 941.28 ppm and 993.56 ppm, compared to 492.06 ppm and 635 ppm at ambient CO2. The chlorophyll b content of the leaves at 90 days of ambient CO2 was significantly higher (688.51 ppm) compared to the leaves exposed to the elevated CO2 with chlorophyll b content of 276.23 ppm. Moreover, the roots dry weight at ambient CO2 indicated an average of 9.70 gram, while at elevated CO2, the dry weight of plant roots is higher up to 38.65% of 13.45 gram. Root volume at ambient CO2 showed an average volume of 40.36 ml3, while at elevated CO2 the volume increased to 90.33 ml3 (up 123.81%). The results of this study indicate that the rain tree seedlings growth conditions were improved under the elevated CO2 concentration, which reflect the efficiency in the use of CO2 and water for photosynthesis process.