Effects of Elevated Carbon Dioxide and Chronic Warming on Nitrogen (N)-Uptake Rate, -Assimilation, and -Concentration...

The concentration of nitrogen (N) in vegetative tissues is largely dependent on the balance among growth, root N uptake, and N assimilation. Elevated CO₂ (eCO₂) plus warming is likely to affect the vegetative-tissue N and protein concentration of wheat by altering N metabolism, but this is poorly understood. To investigate this, spring wheat (Triticum aestivum) was grown for three weeks at two levels of CO₂ (400 or 700 ppm) and two temperature regimes (26/21 or 31/26 °C, day/night). Plant dry mass, plant %N, protein concentrations, NO₃^- and NH₄⁺ root uptake rates (using ¹⁵NO₃ or ¹⁵NH₄), and whole-plant N- and NO₃^--assimilation were measured. Plant growth, %N, protein concentration, and root N-uptake rate were each significantly affected only by CO₂, while N- and NO₃^--assimilation were significantly affected only by temperature. However, plants grown at eCO₂ plus warming had the lowest concentrations of N and protein. These results suggest that one strategy breeding programs can implement to minimize the negative effects of eCO₂ and warming on wheat tissue N would be to target the maintenance of root N uptake rate at eCO₂ and N assimilation at higher growth temperatures.