CO2 enrichment on biomass accumulation and nitrogen nutrition of spring wheat under different soil nitrogen and water status

Atmospheric CO2 increase may bring unexpected consequences on field crops with less nitrogen (N) and water supply. This study investigated biomass accumulation and N nutrition of spring wheat (Triticum aestivum L.) grown under two atmospheric CO2 concentrations (350 and 700 mumol mol(-1)), two soil moisture treatments (well-watered and droughted) and five N fertilizer treatments (0, 50, 100, 150, 200 mg kg(-1)). Results showed that the effects of elevated [CO2] on shoot and total biomass accumulation depended largely on the soil N levels. Shoot and total biomass increased significantly in responding to CO2 enrichment only in moderate to high N treatments. With either the droughted or the well-watered treatments; CO2 enrichment didn't show any significant enhancement in biomass accumulation. Thus, elevated CO2 concentrations did not relieve any adverse effects of droughted and N stress on the dry matter accumulation. Enriched [CO2] levels reduced the shoot N contents, shoot and total N uptake significantly but only slightly decreased the root N content. and uptake. Shoot critical N concentrations were lower for spring wheat grown at 700 mumol mol(-1) than at 350 mumol mol(-1) CO2 concentration in both well-watered and droughted treatments. The critical N concentrations were 1.6% and 2.1% for the well-watered and droughted treatment at enriched [CO2], and 1.9% and 2.6% at ambient [CO2], respectively. Our results showed that CO2 enrichment increased both the water use efficiency (WUE) and nitrogen use efficiency (NUE), possibly due to the reduced mass flow to the roots and thus reduced shoot and root N concentrations. The decrease in N uptake by spring wheat due to enriched [CO2] could not be explained in this experiment.