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

• Published in: Nature climate change 2014-06, Vol.4 (6), p.477-480
• Main Authors: J. Bloom, Arnold, Burger, Martin, A. Kimball, Bruce, J. Pinter, Jr, Paul
• Format: Article
• Language: English
• Subjects: 631/158/2165; 631/158/2455; Biological and medical sciences; Carbohydrates; Carbon dioxide; Climate Change; Climate Change/Climate Change Impacts; Environment; Environmental Law/Policy/Ecojustice; Food quality; Fundamental and applied biological sciences. Psychology; Leaves; letter; Metabolism; Nitrates; Nitrogen; Nitrogen metabolism; Organic nitrogen; Plant physiology and development; Plant tissues; Rhizosphere; Stable isotopes; Wheat
• ISSN: 1758-678X; 1758-6798
• DOI: 10.1038/nclimate2183

Reductions in the protein and nitrogen content of plants grown under enhanced atmospheric CO 2 concentrations could adversely affect the quality of food grown in the future, but the mechanisms of change remain unclear. Now research investigating plant responses to enhanced levels of atmospheric CO 2 under field conditions finds that wheat nitrate assimilation was slower for elevated CO2 than for ambient CO 2 . Total protein and nitrogen concentrations in plants generally decline under elevated CO 2 atmospheres 1 , 2 . Explanations for this decline include that plants under elevated CO 2 grow larger, diluting the protein within their tissues 3 , 4 ; that carbohydrates accumulate within leaves, downregulating the amount of the most prevalent protein Rubisco 2 ; that carbon enrichment of the rhizosphere leads to progressively greater limitations of the nitrogen available to plants 4 ; and that elevated CO 2 directly inhibits plant nitrogen metabolism, especially the assimilation of nitrate into proteins in leaves of C 3 plants 5 . Recently, several meta-analyses have indicated that CO 2 inhibition of nitrate assimilation is the explanation most consistent with observations 6 , 7 , 8 . Here, we present the first direct field test of this explanation. We analysed wheat ( Triticum aestivum L.) grown under elevated and ambient CO 2 concentrations in the free-air CO 2 enrichment experiment at Maricopa, Arizona. In leaf tissue, the ratio of nitrate to total nitrogen concentration and the stable isotope ratios of organic nitrogen and free nitrate showed that nitrate assimilation was slower under elevated than ambient CO 2 . These findings imply that food quality will suffer under the CO 2 levels anticipated during this century unless more sophisticated approaches to nitrogen fertilization are employed.