Elevated CO2atmosphere significantly increased photosynthesis and productivity in a fast growing tree species,Gmelina arboreaRoxb.

Abstract

Sequestering atmospheric carbon and storing it in the terrestrial biosphere is one of the option that has been proposed to compensate greenhouse gas emissions. Young fast growing tree species are believed to be a major potential sinks and could absorb large quantities of CO2. The ongoing enrichment of the atmosphere with CO2 found to stipulate a positive effect on tree species due to increasing availability of carbon. The present study dissects out the CO2 fertilisation effects on photosynthetic gas exchange characteristics, key responses of photosynthetic enzymes consorted with overall plant growth performance in a fast growing tree species, Gmelina arborea Roxb (Verbenaceae). Gmelina plants were grown under ambient (360 μmol/mol) and CO2-enriched conditions (460 μmol/mol) in open top chambers and studied for two marked growth seasons subsequently for 3 years (2006 to 2008). Growth characteristics string along with biochemical measurements were carried out at regular intervals. Photosynthetic rates (Pn) were correlated with other leaf gas exchange and biochemical variables to localise bottlenecks for acclimatory response. Carbonic anhydrase (CA; EC 4. 2. 1. 1) activity showed positive linear correlation (r2 = 0.947) with Pn and RUBP case activity (r2 = 0.952). Gmelina plants were harvested and biomass measured at the end of two growth seasons for three consecutive years. Gmelina significantly responded to CO2 enrichment with periodic and potential increase in biomass, which was also espied with almost 32% higher Pn and a radical increase in CA (60.82%). Our findings clearly demonstrate that Gmelina plants are highly suitable for agroforestry projects for efficient long-term carbon sequestration and to mitigate elevated CO2 levels in the near unprecedented global climate change.