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The Love-Hate Relationship of CO2 & Plant Protein Concentration
Volume 17, Number 19: 7 May 2014

Nitrogen assimilation is inhibited by elevated CO2 in field-grown wheat. So states the title of a paper by Bloom et al. (2014) that was recently published in Nature Climate Change, and which is providing delicious fodder for those who continually castigate the nefarious air pollutant that each of us adds to the atmosphere with every breath we exhale.

The bulk of the paper is devoted to describing a number of complexities of the multi-faceted relationship that exists between the nitrogen/protein concentrations of wheat leaves and grain, which narrative provides numerous opportunities for rather esoteric discussions of the subject. But the ultimate result is what grows in the field and is harvested. And it doesn't take a Ph.D. biochemist to appreciate what was found in the fields that provided the data for the paper we here discuss.

In the words of Bloom et al., "in the low-N treatment at Maricopa [Arizona], elevated CO2 increased grain yields by 9% (Pinter et al., 1997), but decreased grain protein concentrations by 11% (Kimball et al., 2001), and so grain protein yields decreased by about 2%." Continuing, they say that "in the high-N treatment, elevated CO2 increased grain yields about 16% (Pinter et al., 1997), but had an insignificant effect on grain protein concentrations (Kimball et al., 2001), and so grain protein yields increased about 16%," all of which suggests that a little N fertilization helps a whole lot, and that it can readily overcome whatever problem wheat plants might have in extracting nitrogen from N-deficient soils.

Last of all, Bloom et al. conclude their paper by noting that "breeding crops for enhanced root NO3- and NH4+ assimilation has the potential to compensate for lower shoot NO3- assimilation rates and likely losses in food quality as atmospheric CO2 rises," which they describe as an approach that "is yet untapped."

So start tapping, you biochemists! We'd like to see even more grain protein produced.

Sherwood, Keith and Craig Idso

References
Bloom,A.J., Burger, M., Kimball, B.A. and Pinter Jr., P.J. 2014. Nitrate assimilation is inhibited by elevated CO2 in field-grown wheat. Nature Climate Change 10.1038/NCLIMATE2183.

Kimball, B.A., Morris, C.F., Pinter Jr., P.J., Wall, G.W., Hunsaker, D.J., Adamsen, F.J., LaMorte, R.L., Leavitt, S.W., Thompson, T.L., Matthias, A.D. and Brooks, T.J. 2001. Elevated CO2, drought and soil nitrogen effects on wheat grain quality. New Phytologist 150: 295-303.

Pinter Jr., P.J., Kimball, B.A., Wall, G.W., LaMorte, R.L., Adamsen, F. and Hunsaker, D.J. 1997. Effects of Elevated CO2 and Soil Nitrogen Fertilizer on Final Grain Yields of Spring Wheat. Annual Research Report: U.S. Water Conservation Laboratory, Agricultural Research Service, U.S. Department of Agriculture, pp. 71-74.