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Fig. 1. Effect of ozone exposure on above-ground biomass productivity of cotton and nutsedge. Open symbols represent each species grown alone; closed symbols represent the average of all levels of nutsedge competition (All:1). Statistical differences between means within a line are indicated by different lowercase letters and symbols indicating the level of significance. Statistical differences between lines are indicated by uppercase letters and symbols indicating the level of significance. ** indicates P 
0.01.
