Effects of free-air CO2 enrichment (FACE) on N, P and K uptake of soybean in northern China

The objective of this study was to investigate the effect of elevated (550 ± 19 μmol mol−1) [CO2] on uptake and utilization of nitrogen (N), phosphorus (P) and potassium (K) by soybean (Glycine max (L.) Merr) at the free-air carbon dioxide enrichment (FACE) experimental facility in northern China. The above-ground biomass and root biomass were significantly increased under elevated [CO2]. Elevated [CO2] significantly decreased the N concentration of the above-ground part at the beginning bloom (R1) stage, but had no effect at the beginning pod (R3), beginning seed (R5) or harvest stage. The concentration of ureide in the upper most fully-expanded leaf was not significantly affected by elevated [CO2] at any growth stage. Elevated [CO2] increased P concentration of the above-ground plant parts at the R1 and R5 stages, but did not affect P concentration at the R3 stage or at harvest. However, K concentration of the above-ground plant parts and root was not affected by elevated [CO2] at any growth stage. At harvest, elevated [CO2] significantly increased N, P and K uptake in soybean seed. Results indicate that more N, P and K fertilizers may be required to maintain the availability of these elements in the soil for soybean under future elevated [CO2] environments.