Response of Soybean Growth to Elevated CO2 Conditions

The study examined the effects of CO2 enrichment on growth of soybean (Glycine max). Two soybean varieties were used, Taekwang and Cheongja. The plants were grown in growth chambers with a 12-h photoperiod and a day/night temperature of 28/21oC at the seedling stage and 30/23oC from the flowering stage. The plants were exposed to the two elevated CO2 levels of 500 and 700 ppm and the ambient level of 350 ppm. Results of the experiment showed that at the second-node trifoliate stage of the two varieties, the elevated CO2 increased plant height, leaf area and dry weight. The elevated CO2 also raised the photosynthetic rate of soybean as compared to the ambient level. From the beginning bloom stage to the full maturity stage of the two varieties, the elevated CO2 increased plant height, leaf area, seed weight and photosynthetic rate. The stomatal conductance and transpiration rate decreased on long days relative to short days of treatment. Through the entire stages, the elevated CO2 increased the water use efficiency of soybean plants because stomatal conductance and transpiration rate decreased at the elevated CO2 levels relative to the ambient level.