XVI International Botanical Congess

Elevated CO2 inhibited shoot nitrate assimilation in the short- and long-term. Wheat plants grown under normal CO2 assimilated nitrate in the shoot only when CO2 concentrations in the leaf were low, whereas plants grown at elevated CO2 conducted little shoot nitrate assimilation at any CO2 concentration. Shoot protein levels declined under elevated CO2 when nitrate was the sole nitrogen source, but remained unchanged when ammonium was the sole source. Elevated CO2 inhibited the activities of nitrate reductase and nitrite reductase in the shoot, but stimulated them in the root. Inhibition of shoot nitrate assimilation helps explain the responses of plants and ecosystems to elevated CO2 including CO2 acclimation, inhibition of respiration, and the dependence on nitrogen availability.