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.