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  • Author or Editor: Richard E. Melious x
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In a greenhouse experiment, Malus hupehensis (Pamp.) Rehd. seedlings were treated weekly with simulated acid rain solutions ranging from pH 2.25 to pH 7.0. Necrotic lesions developed on leaves at pH 2.25 and pH 2.50 immediately after the first application at the 8-node stage. Following the 9th weekly application on seedlings with 23 to 26 nodes, lesions developed at pH levels up to 3.25. At final destructive harvest, 20% of the leaf area at pH 2.25 and 8% of the leaf area at pH 2.50 was injured. Significant growth reduction occurred at these 2 pH levels. Regression analysis indicated extensive growth inhibition at <pH 3.0, no growth inhibition around pH 3.5, some inhibition between pH 4.5 and pH 5.6, and normal growth at pH 7.0 in comparison to the unsprayed control. Growth was negatively correlated with lesion formation at 3 destructive harvest dates. Relative growth rates were reduced only at pH 2.25 and pH 2.50 and reduction in the unit leaf rate was also observed. Lesion development continued to increase on the basal leaves through the 6th weekly application but leveled off during the final applications. Negative correlations of photosynthesis rate to lesion percentage and dry weight to lesion percentage were observed.

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