Effect of Elevated Concentration of Atmospheric Carbon Dioxide on Some traits of Three Rapeseed (Brassicc napus L.) Varieties Under Saline Conditions

In order to evaluate the effect of increasing atmospheric CO2 concentration on salinity tolerance in rapeseed an experiment was conducted at the greenhouse of Tarbiat Modares University in 2010. The experiment consisted of three rapeseed varieties, four levels of salinity and three levels of atmospheric CO2 concentrations. Three levels of atmospheric CO2 concentrations (350, 700 and 1050 µmol mol-1), four levels of salinity (0, 5, 10 and 15 dS.m-1) were applied on three rapeseed varieties Okapi, Zarfam, and RGS003. Three levels of CO2 concentrations were considered as three environments. Results indicated that CO2 concentrations had significant effect on shoot fresh and dry weight, leaf dry weight, plant height, leaf area, chlorophyll fluorescence, membrane ion leakage, and grain yield. Salinity had significant effect on shoot fresh and dry weight, plant height, leaf area, leaf specific weight, leaf relative water content, leaf chlorophyll fluorescence, membrane ion leakage, chlorophyll content and grain yield. The highest seed yield (2800 kg ha-1) was obtained in control and minimum (1130 kg ha-1) at salinity level of 15 dS.m-1.The CO2 concentration level of 1050 µmol mol-1 had the highest effect on shoot fresh and dry weight, leaf dry weight, plant height and leaf area, but no effect on grain yield. CO2 concentration had no significant effect on chlorophyll content. Effect of salinity on different traits of rapeseed varieties varied at different levels of CO2 concentrations and significant differences observed in leaf fresh and dry weight, shoot fresh and dry weight and membrane ion leakage. Membrane ion leakage increased with salinity, but was lowest in 1050 µmol mol-1 CO2 concentration and highest in 350 µmol mol-1. This study showed that elevated CO2 concentration could partially ameliorate some of adverse effects of salinity on vegetative growth of rapeseed, but not grain yield.