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Sensitivity of ragweed (Ambrosia artemisiifolia) growth to urban ozone concentrations.

Although the sensitivity of growth and yield to ground-level ozone (O3) has been determined for a variety of agronomic crops and trees, little information is available for weedy species. Common ragweed (Ambrosia artemisiifolia L.) is recognized both as a common agricultural weed and the principle source of pollen for Fall (late August to November) allergies in North America. To quantify the extent to which ambient O3 limits growth and reproduction, ragweed was grown from germination to floral initiation at control [carbon filtered (CF), 15.8 nL O3 L-1 air] and treatment levels (63.5 nL O3 L-1 air) of tropospheric O3. This 8-h treatment average is similar to the average 1-h O3 peak values from May through September in urban areas of Washington D.C. and Baltimore, MD. By 48 d after sowing, during floral initiation, no significant differences in total plant or floral biomass were observed as a function of O3 concentration, relative to the CF control. Analysis of leaf area ratio, relative growth rate and net assimilation rate at approximately 10-d intervals during early vegetative growth also did not demonstrate any significant effect of O3. Data from this experiment indicate that ragweed is insensitive to O3 levels up to four times that of the CF control, and suggests that O3 levels associated with urban environments may not limit the growth or reproductive development of ragweed.