Greenhouse-grown plants of Zinnia elegans Jacq. were exposed to simulated sulfuric acid rain 30 minutes per day twice a week for 6 weeks at pH 2.8, 4.0, and 5.6. Injury occurred primarily to older, mature leaves and cotyledons at pH 2.8 and 4.0 and to ray flowers at pH 2.8. Plants supplied with higher levels of Hoagland’s nutrient solution grew more rapidly, contained greater quantitities of foliar K, P, and Ca, and exhibited more foliar injury after exposure to acidic simulated rain (SR). Dry weight of plants given full-strength nutrient solution (highest level) was depressed at pH 2.8 and increased at pH 4.0 relative to pH 5.6. Loss of 86Rb by leaching from foliage was significantly increased at pH 2.8, but no differences in total foliar content of K, P, and Ca were detected.
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.
Mature ‘McIntosh’, ‘Empire’, and ‘Golden Delicious’ apple trees (Malus domestica Borkh.) were sprayed with simulated acid rain solutions in the pH range of 2.5 to 5.5 at full bloom in 1980 and in 1981. In 1981, weekly sprays were applied at pH 2.75 and pH 3.25. Necrotic lesions developed on apple petals at pH 2.5 with slight injury appearing at pH 3.0 and pH 3.5. Apple foliage had no acid rain lesions at any of the pH levels tested. Pollen germination was reduced at pH 2.5 in ‘Empire’. Slight fruit set reduction at pH 2.5 was observed in ‘McIntosh’. The incidence of russetting on ‘Golden Delicious’ fruits was ameliorated by the presence of rain-exclusion chambers but was not affected by acid rain. With season-long sprays at pH 2.75, there was a slight delay in maturity and lower weight of ‘McIntosh’ apples. Even at the lowest pH levels no detrimental effects of simulated acid rain were found on apple tree productivity and fruit quality when measured as fruit set, seed number per fruit, and fruit size and appearance.
respective pH (pH 2.3 and pH 2.1 at 70 m m for malic and citric acid, respectively). The phosphate buffer (70 m m K 2 HPO 4 ) was prepared by titration using H 2 SO 4 . Fruit incubated in deionized water served as control. Fruits were inspected for cracks
-pure water. Sample and standard preparation. To extract organic acids, we precision-weighed 5.0 g of V. uliginosum fruit from each sample and added 5 mL of mobile phase (0.01 mol·L −1 K 2 HPO 4 , pH 2.5) before grinding the sample into a homogenate. We
pathway ( Forkmann, 1991 ; Holton and Cornish, 1995 ; Mol et al., 1998 ; Wiering and deVlaming, 1984 ). Additionally, genetic differences in flower color resulting from modifications in the pH were explained by genes Ph1, Ph2 , and Ph6 ( Griesbach
described by Nour et al. (2010) . Chromatographic separation was performed with an HPLC system (1260 Series; Agilent Technologies, Santa Clara, CA), using 50 m m potassium dihydrogen orthophosphate buffer, pH 2.8, as a mobile phase (flow rate of 0.7 mL
was carried out on a 250 × 4.6-mm, 5-μm column (Diamonsil C18; Dikma Technologies, Foothill Ranch, CA). Detection was operated at 214-nm wavelength with 0.1 mmol·L −1 KH 2 PO 4 (pH = 2.6) as mobile phase passed through a 0.45-μm membrane filter. The
(pH 2.0, using 6 M HCl). With a separatory funnel, the free phenolic compounds were extracted with diethyl ether (5 × 20-mL portions). The extractant was composed of acetone, water, and acetic acid. The organic phase (acetone) was removed using the
of 5.8 ( Lien and Rognes, 1997 ); a pH increase from 3.5 to 9.2 causes a reduction in glycine uptake in Lolium perenne ( Thornton, 2001 ), and glycine uptake by Pisum sativum shows little change between pH 2 to 9 ( Dureja et al., 1984 ). Glycine