Nitrogen Nutrition and Temporal Effects of Enhanced Carbon Dioxide on Soybean Growth
1990
Vessey, J Kevin | Henry, Leslie Tolley | Raper, C. D.
Plants grown on porous media at elevated CO₂ levels generally have low concentrations of tissue N and often appear to require increased levels of external N to maximize growth response. This study determines if soybean [Glycine max (L.) Merr. ‘Ransom’] grown hydroponically at elevated CO₂ requires increases in external NO⁻₃ concentrations beyond levels that are optimal at ambient CO₂ to maintain tissue N concentrations and maximize the growth response. This study also investigates temporal influences of elevated CO₂ on growth responses by soybean. Plants were grown vegetatively for 34 d in hydroponic culture at atmospheric CO₂ concentrations of 400, 650, and 900 μL L⁻¹ and during the final 18 d at NO⁻₃ concentrations of 0.5, 1.0, 5.0 and 10.0 mM in the culture solution. At 650 and 900 μL L⁻¹ CO₂, plants had maximum increases of 31 and 45% in dry weight during the experimental period. Plant growth at 900 μL L⁻¹ CO₂ was stimulated earlier than at 650 μL L⁻¹. During the final 18 d of the experiment, the relative growth rates (RGR) of plants grown at elevated CO₂ declined. Elevated CO₂ caused increases in total N and total NO⁻₃-N content and leaf area but not leaf number. Enhancing CO₂ levels also caused a decrease in root:shoot ratios. Stomatal resistance increased by 2.1- and 2.8- fold for plants at the 650 and 900 μL L⁻¹ CO₂, respectively. Nitrate level in the culture solutions had no effect on growth or on C:N ratios of tissues, nor did increases in CO₂ levels cause a decrease in N concentration of plant tissues. Hence, increases in NO⁻₃ concentration of the hydroponic solution were not necessary to maintain the N status of the plants or to maximize the growth response to elevated CO₂. Paper no. 12142 of the Journal Series of the North Carolina Agric. Res. Service, Raleigh, NC 27695-7643
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