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United States Department of Agriculture

Agricultural Research Service

Research Project: Predicting Impacts of Climate Change on Agricultural Systems and Developing Potentials for Adaptation

Location: Plant Physiology and Genetics Research

Title: Nitrate assimilation is inhibited by elevated CO2 in field-grown wheat.

Authors
item Burger, Martin -
item Kimball, Bruce
item Pinter Jr, Paul
item Bloom, Arnold -

Submitted to: Nature Climate Change
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: February 24, 2014
Publication Date: April 6, 2014
Citation: Burger, M., Kimball, B.A., Pinter Jr, P.J., Bloom, A.J. 2014. Nitrate assimilation is inhibited by elevated CO2 in field-grown wheat. Nature Climate Change. 4:477-480.

Interpretive Summary: In order to determine the likely effects of the increasing atmospheric CO2 concentration on the physiology and productivity of wheat under open-field conditions, free-air CO2 enrichment (FACE) experiments were conducted at Maricopa, Arizona in the 1995-6 and 1996-7 growing seasons. Samples of the wheat tissues were analyzed to determine their total and nitrate nitrogen concentrations and isotopic ratios. The results imply that wheat experiences slower nitrate assimilation under elevated CO2 than under present-day ambient CO2 conditions. These findings confirm that rising CO2 levels in Earth’s atmosphere will degrade food quality unless more sophisticated approaches to N fertilization are employed or crops are bred for enhanced root assimilation of nitrate and ammonium. This research benefits all consumers of food and fiber.

Technical Abstract: To test the hypothesis that the decline in shoot organic nitrogen in C3 plants exposed to elevated carbon dioxide (CO2) atmospheres derives from CO2 inhibition of shoot nitrate (NO3–) assimilation, we analyzed wheat (Triticum aestivum L.), grown under elevated and ambient atmospheric concentrations in the free-air CO2 enrichment (FACE) experiment in Maricopa, AZ. The ratio of NO3– to total N concentrations and the stable isotope ratios (delta 15N) of free NO3– and organic N in leaf tissue indicated the extent of NO3– assimilation under the two CO2 regimes. The NO3– to total N ratio was greater and the delta 15N of free NO3– and organic N were lower in leaves of wheat grown under elevated than ambient CO2 concentrations. These results imply that wheat experiences slower NO3– assimilation under elevated than ambient conditions. This is the first direct evidence from a field experiment that CO2 enrichment inhibits NO3– assimilation. These findings confirm that rising CO2levels in Earth’s atmosphere will degrade food quality unless more sophisticated approaches to N fertilization are employed or crops are bred for enhanced root assimilation of NO3- and NH4+.

Last Modified: 11/21/2014
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