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 12ptminimal amsmath wasysym amsfonts amssymb amsbsy mathrsfs -69pt document equation*₃^{-}equation*document or NO 12ptminimal 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 12ptminimal amsmath wasysym amsfonts amssymb amsbsy mathrsfs -69pt document equation*₃^{-}equation*document photoassimilation at any CO 2 concentration. Moreover, high bicarbonate levels impeded NO 12ptminimal 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 12ptminimal amsmath wasysym amsfonts amssymb amsbsy mathrsfs -69pt document equation*₃^{-}equation*document photoassimilation. Accordingly, when wheat plants received NO 12ptminimal amsmath wasysym amsfonts amssymb amsbsy mathrsfs -69pt document equation*₃^{-}equation*document rather than NH 12ptminimal 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 12ptminimal amsmath wasysym amsfonts amssymb amsbsy mathrsfs -69pt document equation*₃^{-}equation*document as a nitrogen source under elevated CO 2.