Effects of Salinity on Yield Quantity and Quality of Three Rapeseed (Brassicc napus) Cultivars Under Different Atmospheric Carbon Dioxide Concentrations

Background and objectives
Soil and water salinity is the main limitations of cultivation in hot and dry regions such as Iran. Approximately 36% (6.8 million hectars) of arable land in Iran have suffered various degrees of soil salinity. About 90 percent of edible oil consumption in Iran has imported. Rapeseed with special growth habit can be cultivated in different area in Iran and is the best crop rotation for cereals that are include about 70 percent of crops cultivation area. On the other hand the concentration of atmospheric carbon dioxide due to human activities is increasing. Increasing of CO2 concentration can affect on growth of plants. Laboratory studies have shown that increasing CO2 concentration, will increase water use efficiency, net photosynthesis, biomass production and yield in most plants. The effects of free-air CO2 enrichment on the growth of summer rapeseed was investigated and showed that at the end of the flowering, shoot biomass significantly increased to 40%. But in the final harvest, biomass and grain yield increase was not significant. Therefore, the effect of increasing carbon dioxide concentration on the response of canola varieties under saline conditions is essential.
Materials and Methods
The experiment was conducted in Faculty of Agriculture, Tarbiat Modares University, Tehran, Iran, at the 2010, 2011 growing season. Four levels of salinity (0, 5, 10 and 15 dS.m-1) on three cultivars of rapeseed (Okapi, Zarfam, and RGS) at three levels of atmospheric CO2 concentration (350, 700 and 1050 µmol mol-1) were studied. Three levels of CO2 concentrations have been considered as three environments that two other treatments (salinity and cultivar) carried out in them in a completely block design with factorial arrangement. 20Kg black pots were prepared. Pots were filled with silty loam soil (58% sand, 28% silt and 14% clay) to its final weight was 18kg. To preparation of saltwater, natural salt and Tap water with electrical conductivity of 588 micro-Siemens per centimeter was used.
In order to apply the CO2 treatment, growth chamber in greenhouse (9 m long, 2 meters in width and height of 2.5 m) were established. The top of chambers were covered with plastic film about 20 cm over the walls.CO2 was supplied from a CO2 cylinder gas purchased from commercial sources.
Results and Discussion
Results indicated that effect of salinity on grain yield was highly significant and yield decreased from 2800 kg/ha in level 0 to 1130 kg/ha in level of 15 dS m-1 salinity. Number of pod per plant was affected by salinity more than other yield component. Elevated CO2 has no significant effect on yield and yield component, only in the second year of experiment, elevated CO2 (1050 ppm) has been able to partially ameliorate the negative effect of salinity. Grain yield significantly affected by cultivar and RGS003 had the highest yield (2300 kg ha-1) and zarfam and okapy had the second and third rank respectively. Oil and protein content of grain has been decreased and increased by salinity respectively. CO2 concentration had no effect on oil content. Oil content in cultivars reduced in all CO2 concentration with increasing of salinity. Protein content was increased by increasing of salinity and CO2 concentration.
Conclusion
Elevated CO2 has no significant effect on yield and yield component, only in the second year of experiment, elevated CO2 (1050ppm) has been able to partially ameliorate the negative effect of salinity. Oil and protein content of grain has been decreased and increased by salinity respectively. Protein content was increased by increasing of salinity and CO2 concentration.