Modulations in carbon and nitrogen assimilation patterns in rice plants exposed to elevated atmospheric carbon dioxide concentrations

Abstract

Aim: To study the influence of elevated atmospheric CO2 concentrations on the carbon and nitrogen assimilation patterns in rice plants. Methodology: Rice (Oryza sativa) plants were placed in Open Top Chambers (OTCs) and exposed to elevated levels of CO2. The treatments consisted of three levels of CO2 (398, 550 and 750 µmol mol-1) and three levels of nitrogen (0, 150 and 200 kg ha-1) and replicated five times in completely randomized design. Results: Leaf nitrogen was significantly reduced by 10.6 % and 6.5 % during later stages in rice plants exposed to CO2 @ 750 µmol mol-1 and 550 µmol mol-1, respectively over the ambient CO2. Rice plants under elevated CO2 did not exhibit any variations in Nitrate Reductase activity in leaves in comparison to ambient CO2 at tillering stage. Interestingly, NRase activity in leaves decreased at flowering stage whereas NRase activity in roots increased at same stage. The highest mean nitrogen values (0.58, 0.89 and 1.35 %) were observed in Camb (ambient CO2 concentration) and the lowest values (0.51, 0.80 and 1.27 %) in C750 in roots, straw and grains, respectively. Elevated CO2 @ 750 µmol mol-1 significantly increased the above ground biomass (straw and grain) by 15.6 and 40.1 %, respectively, over the ambient CO2 of 398 µmol mol-1. Interpretation: Elevated CO2 enhanced the grain productivity but affected the quality of rice grains. Thus, excessive nitrogen fertilization above the current recommendation is necessary for future high CO2 environments.