effects of elevated carbon dioxide concentrations on some morphological and physiological characteristics of sesame (sesamum indicum l.) and amaranthus (amaranthus retroflexus l.)

carbon dioxide is the most important resource for crop growth. in order to investigate the effect of elevated co2 concentration on morphological and physiological characteristics of sesame (sesamum indicum l.) and amaranthus (amaranthus retroflexus l.) an experiment was conducted in greenhouse conditions. the experiment was factorial based on randomized complete block design with six treatments and three replications. different co2 concentrations (including 360, 520 and 750 ppm) on monoculture and mixture of two species were investigated. the results indicated that plant height, node number, internode and stem dry weight had significant differences in the co2 concentrations. elevated co2 concentration caused increasing plant height, node number, internode and stem dry weight in sesame and monoculture was better than mixtures, but in the amaranthus, elevated co2 concentration resulted is decreasing plant height, node number, and internode and stem dry weight. number and length of branches and their dry weight had significant different in co2 concentrations. so, effect of elevated co2 concentration was positive for sesame and negative for amaranthus. in amaranthus, monoculture was more successful than mixture. in the sesame, yield was included number and weight capsule and in the amaranthus was included total seed weight, that both had significant affected. elevated co2 concentration had positive effect on yield of sesame and negative effect on yield of amaranthus. in the sesame, monoculture was more successful. the effect of elevated co2 concentration was significant on transpiration and photosynthesis rates. in the sesame, elevated co2 concentration increased transpiration and photosynthesis rates and decreased them in the amaranthus. in the sesame, shoot total length and root dry weight was significantly different in co2 concentrations and increased by elevated co2 concentration, but in the amaranthus, decreased by elevated co2 concentration . in the both species, monoculture was more successful. r/s ratio had significant difference in co2 concentration. in the sesame, elevated co2 concentration decreased, but in the amaranthus increased. however, results showed that elevated co2 concentration in the sesame as a c3 and thermophilic plant, resulted in successful growth and production. in the amaranthus, there was not effect by elevated co2 concentration, but high temperature due to elevated co2 concentration caused short growth season and decreased production.