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Response of Soybean to Two Levels of Mineral Nutrition in CO₂-Enriched Atmosphere¹

Studies conducted with increased atmospheric CO₂ usually have the nutritional supply being either optimal or not monitored. The expected increase in growth rate and production by plants in an enriched CO₂ atmosphere that is predicted for the future could be limited through the rapid depletion of mineral nutrients in the root media. The objective of this study was to investigate the effect of atmospheric CO2 enrichment on soybean (Glycine max L. Merr. cv. Ransom) plants grown under two nutritional levels. Plants were grown from seed in a mixture of gravel, vermiculite, and tnrface in controlled environment chambers at 350 or 675 ppm CO₂ and were irrigated with one-eighth or one-half strength Hoagland's solution No. 1. The temperature was 26 C during the 12-hour day, and 20 C during the 12-hour dark period. The photosynthetic photon flux density was 550 µE m^-2 sec^-1. Plants grown in one-half strength Hoagland's solution produced more branches, total leaf area, and total blomass at each CO₂ concentration than those grown in one-eighth strength Hoagland's solution. Specific leaf weight increased with increased CO₂ concentration in both nutritional levels. Plants grown in low nutrient supply at low CO₂ concentration had a shorter flowering period and produced fewer towers, pods, and seeds due to the abortion of some flowers and senescence of pods. Total plant weight and seed number were greater with the high nutrient level than with the low nutrient level under similar CO₂ concentrations. Plants grown at 675 ppm CO2 and receiving one-eighth strength Hoagland's solution produced more biomass and total seed yield than plants grown at 350 ppm CO₂ and one-half strength Hoagland's solution. Therefore, the limiting effect of nutrient supply could partly be overcome by the increase in atmospheric CO₂ concentration.

Key Words: Glycine max L. Merr. • Soybean growth • CO₂ x nutritional level • Seed production

² Senior research scientist, Botany Dep., Duke Univ., Durham, N.C.

Received for publication April 15, 1982.