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Composition and Decomposition of Soybean and Sorghum Tissues Grown under Elevated Atmospheric Carbon Dioxide

Cooperative Ext. Serv., N. Fulton Gov. Annex, Room 203, 7741 Roswell Rd, Dunwoody, GA 30350;

C. W. Wood^*

Dep. of Agronomy and Soils, 202 Funchess Hall, Auburn University, AL 36849-5412;

H. H. Rogers, G. B. Runion and S. A. Prior

USDA-ARS, Natl. Soil Dynamics Lab., P.O. Box 3439, Auburn, AL 36831-3439.

^* Corresponding author (wwood{at}ag.auburn.edu).

ABSTRACT

It has been hypothesized that changes in both quantity and quality of plant residue inputs to soils as atmospheric carbon dioxide (CO₂) concentration increases may alter carbon (C) and nitrogen (N) turnover rates and pool sizes. We determined the effect of elevated atmospheric CO₂ on plant tissue quality, and how modifications in tissue quality affect C and N mineralization. Soybean [C₃; Glycine max (L.) Merr. cv. Stonewall] and sorghum [C₄; Sorghum bicolor (L.) Moen. cv. Savanna 5] were grown under elevated (704.96 ± 0.33 µmol CO₂ mol^–1) and ambient (357.44 ± 0.12 µmol CO₂ mol^–1) atmospheric CO₂ in open-top chambers. Leaf and stem tissues were separated from harvested plants and analyzed for C, N, lignin, and cellulose. Tissues were applied to Norfolk loamy sand (fine-loamy, siliceous, thermic Typic Kandiudult) and aerobically incubated for 70-d to determine C and N mineralization, C turnover, relative N mineralization, and C/N mineralized. Elevated CO₂ had no effect on plant residue C concentration, but N concentration of soybean leaves and stems and sorghum stems was reduced; however, CO₂ enrichment increased C/N ratio and lignin concentration for only sorghum stems and soybean leaves, respectively. Source of plant residue (i.e., produced under either elevated or ambient CO₂) had no impact on soil C turnover, relative N mineralization, cumulative C and N mineralization, and C/N mineralized. These data suggest that increasing atmospheric CO₂ will have little effect on composition or decomposition of field crop residues. Thus, since CO₂ enrichment results in increased photosynthetic C fixation, the possibility exists for increased soil C storage under field crops in an elevated CO₂ world.

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				S. A. Prior, H. A. Torbert, G. B. Runion, H. H. Rogers, D. R. Ort, and R. L. Nelson Free-air carbon dioxide enrichment of soybean: influence of crop variety on residue decomposition. J. Environ. Qual., July 1, 2006; 35(4): 1470 - 1477. [Abstract] [Full Text] [PDF]

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