Chlorophyll concentration of potatoes grown under elevated carbon dioxide and/or ozone concentrations

Potato cv. Bintje was grown in open-top-chambers and free-air-CO2-enrichment systems at 7 sites across Europe for 2 years (1998-99). The effect of different treatments (CO2 enrichment and O-3 fumigation) on the chlorophyll content of fully expanded upper and lower canopy leaves was investigated collecting Minolta SPAD-502 meter readings. In both CO2 treated and O-3 fumigated plants, leaves had lower chlorophyll content than those in ambient air controls; season-long chlorophyll averages were 9.3% lower in the 'CO2' treatments, 9.1% lower in 'O-3' treatments and 12.3% lower in 'CO2+O-3' treatments. The analysis of chlorophyll content in three different growth phases (Emergence-Tuber Initiation; Tuber Initiation-Maximum Leaf Area; Maximum Leaf Area-Harvest) showed that in the early growth period, i.e. before tuber initiation there was a slight indication for an higher chlorophyll content at elevated CO2 (+ 3.8%) or O-3 (+1.7%). However, from tuber initiation onwards the leaves of plants grown under elevated CO2 or O-3 showed a progressively lower chlorophyll content (-4.8% for CO2 treatments and -2.6% for O-3 treatments) indicating a faster senescence of leaves that increased during the late growth period (-12.8% for CO2 treatments and -12.7% for O-3 treatments) and that was enhanced by CO2-O-3 interaction (-17.8%).