Growth of Cotton under Chronic Ozone Stress at Two Levels of Soil Moisture
- Joseph E. Miller *,
- Robert P. Patterson,
- Allen S. Heagle,
- Walter A. Pursley and
- Walter W. Heck
- D ep. of Crop Science, USDA-ARS, 1509 Varsity Drive, North Carolina State Univ., Raleigh, NC 27606;
D ep. of Crop Science, USDA-ARS, North Carolina State Univ., Raleigh, NC 27695;
D ep. of Plant Pathology, USDA-ARS, North Carolina State Univ., Raleigh, NC 27695;
D ep. of Botany, USDA-ARS, North Carolina State Univ., Raleigh, NC 27695.
Recent field research has shown that ambient concentrations of ozone (O3) have the potential to reduce yield of a number of economically important crop species. Soil water levels have been shown sometimes to modify the extent of the reduction. The primary emphasis of most of these studies has been on the plant component that represents economic yield. Less emphasis has been placed on characterization of the effects of O3 on growth of the total plant that ultimately determines yield. In this study, we measured season-long growth of field-grown cotton (Gossypium hirsutum L. ‘McNair-235’) that was exposed to a range of O3 concentrations at two levels of soil moisture, well-watered (WW) and water-stressed (WS). The cotton was exposed for 12 h d−1 throughout the growing season in open-top chambers to five O3 concentrations that ranged from 0.020 to 0.074 µL L−1 (seasonal mean 12 h d−1 concentration). Three cotton plants were sampled from each chamber at 2- to 3- wk intervals during the season, and biomass and growth measurements were made on all major plant parts. Ozone stress reduced leaf and root biomass in particular, while stem tissues were less affected. Partitioning of biomass among plant tissues was affected by O3 at certain times during the season. Leaf area duration (LAD) was reduced by O3 in both WW and WS treatments, but changes in the yield/LAD ratio and net assimilation rate indicated that reduced efficiency of leaves also was responsible for yield reductions in the WW plots. Water stress caused fewer significant effects overall than did O3, although it appeared to reduce the growth of most plant parts, especially at low O3 concentrations. There were no significant O3 × water interactions for the growth variables measured.
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