Elevated CO2 levels enhance the uptake and metabolism of organic nitrogen

The effects of elevated CO2 (eCO(2)) on the relative uptake of inorganic and organic nitrogen (N) are unclear. The uptake of different N sources by pak choi (Brassica chinensis L.) seedlings supplied with a mixture of nitrate, glycine and ammonium was studied using N-15-labelling under ambient CO2 (aCO(2)) (350ppm) or eCO(2) (650ppm) conditions. N-15-labelled short-term uptake and N-15-gas chromatography mass spectrometry (GC-MS) were applied to measure the effects of eCO(2) on glycine uptake and metabolism. Elevated CO2 increased the shoot biomass by 36% over 15days, but had little effect on root growth. Over the same period, the N concentrations of shoots and roots were decreased by 30 and 2%, respectively. Elevated CO2 enhanced the uptake and N contribution of glycine, which accounted for 38-44% and 21-40% of total N uptake in roots and shoots, respectively, while the uptake of nitrate and ammonium was reduced. The increased glycine uptake resulted from the enhanced active uptake and enhanced metabolism in the roots. We conclude that eCO(2) may increase the uptake and contribution of organic N forms to total plant N nutrition. Our findings provide new insights into plant N regulation under eCO(2) conditions.