Chlorophyll content of spring wheat flag leaves grown under elevated CO2 concentrations and other environmental stresses within the ‘ESPACE-wheat’ project

Spring wheat cv. Minaret was grown in open-top chambers at four sites across Europe. The effect of different treatments (CO₂ enrichment, O₃ fumigation, drought stress and temperature) on the chlorophyll content of the flag leaf was investigated using the MINOLTA SPAD-502 meter. Under optimum growth conditions the maximum chlorophyll content, which was reached at anthesis, was consistent among the sites ranging from 460 to 500 mg chlorophyll m^?2. No significant effect of elevated CO₂ or O₃ was observed at anthesis. Leaf senescence, indicated by the chlorophyll breakdown after anthesis, was relatively constant in the control chambers. Under control conditions, thermal time until 50% chlorophyll loss was reached was 600°C day. Elevated CO₂ caused a faster decline in chlorophyll content (thermal time until 50% chlorophyll loss was reduced to 500–580°C day) indicating a faster rate of plant development at two experimental sites. The effect of ozone on chlorophyll content depended on the time and dose of O₃ exposure. During grain filling, high O₃ concentrations induced premature senescence of the flag leaves (up to ?130°C day). This deleterious effect was mitigated by elevated CO₂. Drought stress led to faster chlorophyll breakdown irrespective of CO₂ treatment.