Nitrogen assimilation and growth of wheat under elevated carbon dioxide

Simultaneous measurements of CO 2 and O 2 fluxes from wheat ( Triticum aestivum ) shoots indicated that short-term exposures to elevated CO 2 concentrations diverted photosynthetic reductant from NO [12pt]{minimal} {amsmath} {wasysym} {amsfonts} {amssymb} {amsbsy} {mathrsfs} {}{-69pt} {document} {equation*}{{₃⁻}}{equation*}{document} or NO [12pt]{minimal} {amsmath} {wasysym} {amsfonts} {amssymb} {amsbsy} {mathrsfs} {}{-69pt} {document} {equation*}{{₂⁻}}{equation*}{document} reduction to CO 2 fixation. With longer exposures to elevated CO 2 , wheat leaves showed a diminished capacity for NO [12pt]{minimal} {amsmath} {wasysym} {amsfonts} {amssymb} {amsbsy} {mathrsfs} {}{-69pt} {document} {equation*}{{₃⁻}}{equation*}{document} photoassimilation at any CO 2 concentration. Moreover, high bicarbonate levels impeded NO [12pt]{minimal} {amsmath} {wasysym} {amsfonts} {amssymb} {amsbsy} {mathrsfs} {}{-69pt} {document} {equation*}{{₂⁻}}{equation*}{document} translocation into chloroplasts isolated from wheat or pea leaves. These results support the hypothesis that elevated CO 2 inhibits NO [12pt]{minimal} {amsmath} {wasysym} {amsfonts} {amssymb} {amsbsy} {mathrsfs} {}{-69pt} {document} {equation*}{{₃⁻}}{equation*}{document} photoassimilation. Accordingly, when wheat plants received NO [12pt]{minimal} {amsmath} {wasysym} {amsfonts} {amssymb} {amsbsy} {mathrsfs} {}{-69pt} {document} {equation*}{{₃⁻}}{equation*}{document} rather than NH [12pt]{minimal} {amsmath} {wasysym} {amsfonts} {amssymb} {amsbsy} {mathrsfs} {}{-69pt} {document} {equation*}{{₄⁺}}{equation*}{document} as a nitrogen source, CO 2 enhancement of shoot growth halved and CO 2 inhibition of shoot protein doubled. This result will likely have major implications for the ability of wheat to use NO [12pt]{minimal} {amsmath} {wasysym} {amsfonts} {amssymb} {amsbsy} {mathrsfs} {}{-69pt} {document} {equation*}{{₃⁻}}{equation*}{document} as a nitrogen source under elevated CO 2 .