©2023 International Society of Arboriculture Arboriculture & Urban Forestry 49(6): November 2023 337 The correlation between quantitative variables of leaf (leaf area and SLA) and air pollutants appeared in both of P. orientalis and C. caucasica, only there was a significant negative relationship between leaf area and O3 (Table 4). This relationship was stronger in C. caucasica (R2 = −0.78). In other cases, no signif- icant relationship was observed between quantitative variables of leaf and pollutants. Ozone has been found to cause significant damage to plants worldwide, including crops and natural eco- systems (Grulke and Heath 2020). During the grow- ing season, O3 can harm sensitive vegetation, with over 90% of vegetation damage resulting from tropo- spheric O3 alone. This damage can lead to reductions in crop yield and forest production ranging from 0% to 30% (Adams et al. 1989). Sufficient O3 can reduce photosynthesis in sensitive plants (Watanabe et al. 2018), which is the process that plants use to convert sunlight into energy for growth, and slow down plant growth, increase the risk of disease and damage from insects and other pollutants, and harm plants through severe weather. For example, Hoshika et al. (2013) demonstrated that O3-induced stomatal closure in Siebold’s beech (Fagus crenata Blume) during early summer reduced O3 influx and allowed the maximum photosynthetic capacity to be reached, but was not sufficient in older leaves to protect the photosynthetic system. Certain plants may show visible signs of injury when exposed to O3 under specific conditions, including changes in pigmentation or bronzing, chlo- rosis, premature senescence after chronic exposure to low O3 concentrations, and flecking and stippling after acute exposure to high O3 levels. The deleterious effects of O3 on individual plants can consequently (2011) mentioned that although their data analysis suggests a relationship between SLA and NOx/O3 concentration, the absence of a straightforward rela- tionship between SLA and air pollution still questions the usefulness of this bio-indicator for monitoring air pollution. The results of the Kruskal-Wallis test showed that, in the case of P. orientalis, there was no significant difference in the humidity percent among the study areas (p > 0.05), but the difference of the 2 variables of leaf area and SLA were significant (p < 0.01). The grouping of the mean of the SLA for the P. orientalis is shown in Table 3. As shown, the Jamshidieh Park was in a separate group (a) with the lowest values. Lavizan Park was also placed in a separate group (d) with the highest value. Also, in terms of leaf area variable, 4 groups were divided, so that Jamshidieh and Qeytariyeh Parks with the lowest values arranged in group a, and Lavizan Park with highest value arranged in group d. In the case of C. caucasica, there was no signifi- cant difference in the humidity percent among the study areas (p > 0.05), but the difference between the 2 variables of SLA (p < 0.01) and leaf area (p < 0.01) were significant. Based on the grouping of the mean values of the SLA (Table 3), most of the study areas arranged in same group. Qeytariyeh Park with the lowest value arranged in group a, and City Park and National Botanical Garden of Iran with highest value arranged in group c. Also, 4 groups were separated for leaf area variable, so that Qeytariyeh Park with the lowest value were in group a, and City Park with the highest value were in group d. The other study areas were also in intermediate positions. Table 4. Pearson correlation coefficient between leaf area (cm2) and amount of O3 (ppm) in the study species and study areas. Species Urban forest Qeytariyeh Park Jamshidieh Park Green space of Hemmat Highway 15 Khordad Park Taleghani Park Green space of Al-Zahra University Lavizan Park Shafaq Park City Park National Botanical Garden of Iran P. orientalis −0.71 * −0.70 * −0.60 * −0.66 * −0.70 * −0.67 * −0.71 * −0.65 * −0.70 * −0.61 * C. caucasica −0.73 * −0.71 * −0.66 * −0.68 * −0.71 * −0.70 * −0.78 * −0.74 * −0.74 * −0.71 * * Significant at p < 0.05
November 2023
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