Nitrate for Me, Ammonium for You The interdependence of plant nitrogen uptake and plant responses to carbon dioxide is well established, but the influence of inorganic nitrogen form—i.e., whether nitrate or ammonium—has been largely ignored. Bloom et al. (p. 899 ) present evidence from five independent methods in both a monocot and dicot species that carbon dioxide inhibition of nitrate assimilation is a major determinant of plant responses to rising atmospheric concentrations of carbon dioxide. This finding explains several phenomena, including carbon dioxide acclimation and decline in food quality. The large variation in these phenomena among species, locations, or years derives from the large variation in the relative dependence of plants on nitrate and ammonium as nitrogen sources among species, locations, or years. The relative importance of ammonium and nitrate for plant N nutrition in future cropping systems will be critical for quantity and quality of food.

Carbon Dioxide Enrichment Inhibits Nitrate Assimilation in Wheat and Arabidopsis