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ARS Home » Research » Publications at this Location » Publication #61797
Title: EFFECT OF ATMOSPHERIC CO2 CONCENTRATION ON PHOTOSYNTHETIC PERFORMANCE OF C3 AND C4 PLANTS.

Author
item CHEN, X - AGRONOMY, UNIV OF IL, CHA
item ALM, D - BIOLOGY, UNIV OF IL, CHA
item Hesketh, John

Submitted to: Biotronics
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/28/1995
Publication Date: N/A
Citation: N/A

Interpretive Summary: Carbon dioxide is increasing in the atmosphere because of the burning of fossil fuels and rain forest trees. Crop yields are increasing because of increased CO2 uptake by leaves. We need to know if there are associated problems, or if we can increase yields further by genetic or management manipulations of leaf CO2 uptake rates. Corn, soybean, sunflower and pigweed crop stands were exposed to CO2-enriched atmospheres (one and two times current levels) in the field at Urbana, IL. Leaf CO2 uptake rate comparisons were made among treatments to determine the importance of stomatal (leaf surface pores) and chemical limitations inside the leaf. Leaves performed very well at the enriched CO2 levels over the course of a day, although there was an afternoon decline in performance at both CO2 levels, probably due to an effect of water stress on the chemical processes involved. The row crop farmer can expect increasing yields as the atmospheric CO2 increases, but we don't know yet how to exploit further this new resource.

Technical Abstract: Four C3 and C4 plant species (soybean, sunflower, pigweed, and corn) were grown in the field to test photosynthetic performance at ambient (350umol CO2 mol-1 air or ppm) and enriched (700ppm) atmospheric CO2 (CA), particularly after plants were switched from the 700 to 350ppm treatment and back. At 700ppm steady-state photosynthetic gas exchange (Pn) values were the same for C4 species and were greater for C3 species, while stomatal conductances (gs) were reduced in all comparisons, compared to plants at ambient CO2 levels. Short term Pn values taken immediately after switching treatments were not signifi-cantly different from long term values for the same treatment, except for pigweed, where in both cases Pn after switching was 73 percent of the long term values. In all tested species, gs values were lowered when measured directly after being transferred to the other treatment. Pn at 700ppm continued at a rapid pace throughout the day for the C3 species, that for the C4 species being the same as at 350ppm. Pn declined over the course of the day for the same light levels for all species and treatments, except for pigweed at 350ppm. The decrease in Pn at 700ppm suggested nonstomatal control in the C3 species.