Nitrogen assimilation and growth of wheat under elevated carbon dioxide

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Abstract
Simultaneous measurements of CO2 and O2 fluxes from wheat (Triticum aestivum) shoots indicated that short-term exposures to elevated CO2 concentrations diverted photosynthetic reductant from NO or NO reduction to CO2 fixation. With longer exposures to elevated CO2, wheat leaves showed a diminished capacity for NO photoassimilation at any CO2 concentration. Moreover, high bicarbonate levels impeded NO translocation into chloroplasts isolated from wheat or pea leaves. These results support the hypothesis that elevated CO2 inhibits NO photoassimilation. Accordingly, when wheat plants received NO rather than NH as a nitrogen source, CO2 enhancement of shoot growth halved and CO2 inhibition of shoot protein doubled. This result will likely have major implications for the ability of wheat to use NO as a nitrogen source under elevated CO2.