Interactive effects of elevated CO2, nitrogen and drought on leaf area, stomatal conductance, and evapotranspiration of wheat

Atmospheric CO2 enrichment may bring different effects on plant growth and evapotranspiration if plants are under N and water deficient conditions. In this study, spring wheat (Triticum aestivum L.) was grown in pots at two atmospheric CO2 concentrations (ambient and elevated), two levels of soil moisture (well-watered and droughted to 45–60% of field capacity) and five nitrogen (N) fertilization treatments (0, 112.5, 225.0, 337.5, 450.0 kg hm−2) in growth chambers. Leaf growth, leaf area, and tiller increment were largely a function of N application and water supply. Elevated CO2 increased 23–45% in leaf area only with the N-added treatments 55 days after sowing. Elevated CO2 also reduced stomatal conductance more in droughted treatments (−51%) than in well-watered treatments (−41%), and more with zero N application (−60%) than with the adequate N (−35 to 44%). Evapotranspiration (ET) was also reduced by CO2 enrichment in a similar way. Our results showed that the CO2-enrichment-induced decrease in transpiration almost compensated for the increase in ET brought by the higher leaf area under adequate N and water supply, such that ET was similar for control and CO2-enriched plants. Under reduced N and water supply, CO2 enrichment had limited effect on either leaf growth or ET.