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Water Relations of Differentially Irrigated Cotton Exposed to Ozone

Statewide Air Pollution Res. Cent., Univ. of California, Riverside, CA 92521

^* Corresponding author.

This field study was conducted to test the hypothesis that plants chronically exposed to O₃ may be more susceptible to drought kcause OM₃ typically inhibits root growth and increases shoot-root ratios in plants. Cotton (Gossypium hirsutum L. cv. Acala SJ-2) was grown in open-top chambers on Hanford coarse sandy loam (coarseloamy, mixed, non-acid, thermic, Typic Xerorthents) in Riverside, CA. Plants were grown under three irrigation regimes: optimum water for lint production (OW), suboptimum or moderate drought stress (SO), and severely drought stressed (SS) and were exposed to seasonal 12 h (0800–2000) O₃ concentrations of 0.015, 0.074, 0.094, or 0.111 µL L^–1. Leaf xylem pressure potentials (₁) and soil water content (_v) were measured weekly from June to October. Mean seasonal ₁ increased from –1.89 MPa to –1.72 MPa in low to high O₃ treatments, averaged across soil water regimes. Ozone had no effect on seasonal water use of cotton, but water use efficiency was significantly reduced by O₃ in OW and SO, but noit in SS treatments. Drought-stressed plants extracted proportionally greater amounts of water from deeper in the soil profile than OW cotton, and O₃ had no apparent effect on this redistribution of roots in the soil. Since O₃ had no apparent effect on the ability of droughtstressed cotton to maintain ₁ and to increase root growth relative to shoot growth, this suggests that O₃ may have little or no effect: on the potential of cotton to adapt to or tolerate drought.

Received for publication January 23, 1989.

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