Effect of elevated CO2 concentration on growth and physiology of selected tropical tree seedlings

Abstract

The present study entitled “Effect of elevated CO2 concentration on growth and physiology of selected tropical tree seedlings.” was carried out in College of Forestry, Kerala Agricultural University, Vellanikkara, Thrissur during the period 2008-2010. There are references that elevated CO2 typically increases tree seedling growth and has also modified physiological processes. Polybag seedlings of five economically important tree species were exposed to 500-550 ppm CO2 concentration and another similar set of plants were raised under ambient atmospheric CO2 condition (370-380 ppm). The growth rates and physiology were observed for eight months. Tree seedlings under elevated CO2 concentration put in more height and collar diameter than the seedlings under atmospheric CO2.A higher leaf production and larger leaf area was recorded in seedlings under elevated CO2 concentration. The different levels of CO2 also showed significant effects on the total dry matter content. However, interactions between two CO2 levels and five tree seedlings had no significant impact on the shoot: root ratios throughout the study period. The different CO2 treatment did not significantly affect the relative growth rate (RGR), net assimilation rate (NAR), specific leaf area (SLA) and the leaf area ratio (LAR) of seedlings. However, both CO2 levels showed significantly different impact on the leaf weight ratio (LWR) of seedlings. Seedlings under elevated CO2 recorded lowest number of stomata compared to seedlings under atmospheric CO2 concentration. The varying CO2 concentrations showed significant effect on the rate of photosynthesis of the tree seedlings. Chlorophyll a and Chlorophyll b in tree seedlings was not significantly influenced under different CO2 concentrations. However, total chlorophyll content showed significant influence. Seedlings under elevated CO2 recorded lowest soluble protein content compared to seedlings under atmospheric CO2 concentration. Hence, CO2 enrichment technique can be used as an economically viable nursery technology for production of more healthy and vigorous planting stock to meet the increasing demand for social forestry /agro forestry programme.