Could ammonium nutrition increase plant C-sink strength under elevated CO conditions?

Atmospheric carbon dioxide (CO) is increasing, and this affects plant photosynthesis and biomass production. Under elevated CO conditions (eCO), plants need to cope with an unbalanced carbon-to-nitrogen ratio (C/N) due to a limited C sink strength and/or the reported constrains in leaf N. Here, we present a physiological and metabolic analysis of ammonium (NH)-tolerant pea plants (Pisum sativum L., cv. snap pea) grown hydroponically with moderate or high NH concentrations (2.5 or 10 mM), and under two atmospheric CO concentrations (400 and 800 ppm). We found that the photosynthetic efficiency of the NH tolerant pea plants remain intact under eCO thanks to the capacity of the plants to maintain the foliar N status (N content and total soluble proteins), and the higher C-skeleton requirements for NH assimilation. The capacity of pea plants grown at 800 ppm to promote the C allocation into mobile pools of sugar (mainly sucrose and glucose) instead of starch contributed to balancing plant C/N. Our results also support previous observations: plants exposed to eCO and NH nutrition can increase of stomatal conductance. Considering the C and N source-sink balance of our plants, we call for exploring a novel trait, combining NH tolerant plants with a proper NH nutrition management, as a way for a better exploitation of eCO in C3 crops.