Leaf water relations of cotton in a free-air CO2-enriched environment

Abstract

As part of an intensive study of crop response to CO2 enrichment in a free-air CO2 enrichment (FACE) experiment in the field, we determined aspects of the water relations of a cotton crop on selected dates in 1991. The atmosphere was enriched from 370 μmol CO2 mol−1 (control) to about 550 μmol mol−1 in free air during daylight hours. Under full irrigation, CO2 enrichment decreased stomatal conductance and single-leaf transpiration only toward the end of the season, and these changes led to increased leaf water potentials only at that time of year. Under water-stressed (deficit irrigation) conditions, CO2 enrichment decreased conductance throughout the season but there was no corresponding consistent effect on leaf water potentials. As with the fully irrigated controls, CO2 enrichment increased leaf water potentials only at the end of the season. CO2 enrichment increased season-long biomass accumulation 39% under full irrigation and 34% under deficit irrigation. These results are consistent with previous studies of cotton in open-top chambers that found only small effects of CO2 enrichment on internal water relations of cotton, and no water stress-induced increase in crop responsiveness to elevated CO2.