Photosynthetic Characteristics in Wheat Exposed to Elevated O3 and CO2
1996
Rudorff, B. F. T. | Mulchi, C. L. | Lee, E. | Rowland, R. | Pausch, R.
Tropospheric trace gases such as CO₂ and O₃ have progressively increased over the past century and are predicted to increase to levels at which they may have a significant impact on agricultural production. The effects of CO₂ enrichment and O₃ air pollution on leaf photosynthesis (Pₙ) and stomatal conductance (g₅) were investigated. Two soft winter wheat (Triticum aestivum L.) cultivars, Massey in 1991 and Saluda in 1992, were studied in field experiments at Beltsville, MD, by means of open-top chambers to mimic atmospheric environments predicted for the first half of the 21st century. Plants were exposed to two levels of O₃ (charcoal filtered air and ambient air + an average of 40 nmol O₃ mol⁻¹ from Monday–Friday of every week). Ozone treatments were superimposed on two CO₂ treatments (350 μmol CO₂ mol⁻ and 500 μmol CO₂ mol⁻¹). Averaged over O₃ treatments, Pₙ was stimulated during the early and late growing season under enriched CO₂. Averaged over CO₂ treatments, high O₃ exposure had a negative impact on Pₙ early in the season of 1992 and a major impact late in the season of 1991 and 1992 due to premature senescence. Decreases in gₛ occurred under the enriched CO₂ environment and to a lesser extent with high O₃. Interactive effects on Pₙ and gₛ were mostly absent. It is likely that if CO₂ and O₃ concentrations continue to increase, the beneficial effect of CO₂ enrichment on Pₙ may be partially negated by O₃-induced stress. Conversely, damaging effects of O₃ on Pₙ may be compensated by elevated atmospheric CO₂. Contribution of the Maryland Agric. Exp. Stn. Scientific article no. A6668, contribution no. 8887.
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