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Nonstructural Carbohydrates and Nitrogen of Soybean Grown under Carbon Dioxide Enrichment

USDA-ARS, Bldg. 164, Univ. of Florida, Gainesville, FL 32611
USDA-ARS, Horticultural Res. Lab., Orlando, FL 32803

R. R. Valle and K. J. Boote

Agronomy Dep., Univ. of Florida, Gainesville, FL 32611

P. H. Jones

Agricultural Engineering Dep., Univ. of Florida, Gainesville, FL 32611

^* Corresponding author.

Carbon dioxide (CO₂) concentration has been rising in the atmosphere for uver a century. This study was conducted to determine the effects of anticipated future levels of CO₂ on nonstructural carbohydrates and N of soybean [Glycine max (L.) Merr. cv. Bragg]. Plants were grown at Gainesville, FL from seeding to maturity in six sunlit, controlled-environment chambers that maintained CO2 at 330, 330, 450, 600, 800, and 800µmol (CO₂) mol^-1 (air). Attached lysimeters contained Arredondo fine sand (loamy, siliceous, hyperthermic Grossarenic Paleudult). Leaflet blades were sampled five times per day at 48 and 69 d after planting (DAP). At 48 DAP, average daytime starch conc. of leaflets increased with increasing CO₂ from 85 g kg^-1 of dry wt at 330 µmol mol^-1 to 205 g kg^-1 at 800 µmol mol^-1. On each date, the daytime rate of starch accumulation combined over all CO₂ treatments was 6 g kg^-1 h^-1. Specific leaf weight increased significantly throughout the day both at 48 (0.64 g m^-2 h^-1) and 69 DAP (0.29 g m^-2 h^-1) . Total Kjeldahl N (TKN) conc., expressed on a g m^-2 basis, showed no change over the day. Total final dry wet increased 18, 34, and 54% at 450, 600, and 800 µmol mol^-1, respectively. The TKN harvested per plant increased 25, 26, and 45% in the 450, 600, and 800 µmol mo1^-1 CO₂ treatments, respectively. Plants in the 450 µmol mol^-1 CO₂ treatment partitioned more biomass to seed than the other CO₂ treatments. With that exception, we saw no great differences among treatment partitioning at final harvest, and thus interpret the main effect of CO₂ enrichment to be enhanced photoassimilation by soybean canopies while maintaining consistent allometric relationships of the plants.

Key Words: Glycine max (L.) • Carbon dioxide • Starch • Soluble sugars • Protein • Chlorophyll • RuBP carboxylase • Partitioning • Biomass • Yield

Received for publication January 7, 1987.

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