Effect of free-air CO2 enrichment on the chlorophyll content of cotton leaves

Abstract

In vivo chlorophyll concentrations were estimated using a Minolta SPAD 502 meter on upper-canopy leaves of cotton plants exposed to air enriched to an atmospheric CO2 concentration of approximately 550 μmol mol−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 both well-watered and moderately water-stressed plants, leaves in the FACE plots had greater chlorophyll a concentrations than leaves in the ambient air control plots (about 370 μmol CO2 mol−1): season-long chlorophyll a averages were 7.1% greater in the ‘wet’ treatment and 8.2% greater in the ‘dry’ treatment. This finding differs from what has been observed in a number of studies where experimental plants were grown in small pots. It is, however, typical of what has been observed in studies employing larger pots and open fields, and is a compelling rationale for conducting additional studies of this nature in FACE projects.