EFFECT OF FREE-AIR CO2 ENRICHMENT ON THE CHLOROPHYLL CONTENT OF COTTON LEAVES

In vivo chlorophyll concentrations were estimated using a Minolta SPAD 502 meter on upper-canopy leaves of cotton plants exposed to air enri ched to an atmospheric CO2 concentration of approximately 550 mumol mo l-1 in a free-air CO2 enrichment (FACE) study. Measurements were made on 27 days during the final 90 days of the 1991 growing season. In bot h well-watered and moderately water-stressed plants, leaves in the FAC E plots had greater chlorophyll a concentrations than leaves in the am bient air control plots (about 370 mumol CO2 mol-1): season-long chlor ophyll a averages were 7.1% greater in the 'wet' treatment and 8.2% gr eater in the 'dry' treatment. This finding differs from what has been observed in a number of studies where experimental plants were grown i n small pots. It is, however, typical of what has been observed in stu dies employing larger pots and open fields, and is a compelling ration ale for conducting additional studies of this nature in FACE projects.