©2023 International Society of Arboriculture 336 surfaces, such as soil and crown conditions, it is rec- ommended that future studies address these aspects. Regarding the SLA of P. orientalis, the highest and lowest values were related to Lavizan Park (12.42 cm2/g) and Jamshidieh Park (7.14 cm2/g), respectively. In the case of C. caucasica, City Park with an average of 9.69 cm2/g and Qeytariyeh Park with an average of 3.31 cm2/g had the highest and lowest amount, respectively. The average of SLA in all study areas were estimated 9.2 and 6.5 cm2/g for P. orientalis and C. caucasica, respectively. According to the equation of SLA, in 2 leaves with the same dry weight, the large the leaf area, the lower the SLA. In the case of the present study, although the area of P. orientalis leaves was about 6 times of the area of C. caucasica leaves, this ratio was not observed in the SLA. The SLA of P. orientalis leaves was slightly higher than C. caucasica. The range of SLA of P. orientalis are reported between 122 and 194 cm2/g in other research in Iran (Rafiee et al. 2014; Khosropour et al. 2018; Rashidi and Jalili 2018; Abbasi et al. 2021). In the only research conducted on the SLA of C. caucasica in Iran, the average of this variable is estimated to be 103.5 cm2/g in an urban forest of Sanandaj City (Pourhashemi et al. 2012). In the present study, although there was no signifi- cant relationship between SLA and air pollutants, the SLA values were lower in more polluted areas than in less polluted areas. So, it can be said that in most cases, with the increase of pollutants, the SLA of 2 study species has decreased. Rashidi et al. (2017) also achieved similar results in the study of air pollution stress on F. rotundifolia in Tehran parks. Gratani et al. (2000) also showed a 25% increase in SLA values in areas with high pollution compared to the control area in Italy. Balasooriya et al. (2009) on Traxacum officinale Weber showed that a large amount of SLA in a less polluted location could indicate the sensitiv- ity of this characteristic to the type of management such as pruning method. They noted that tree shading could explain the large amount of leaf area in a less polluted area, and that this reaction could be due to the plant’s response to less light and the presence of shade. In some studies, the results have been contra- dictory. For example, for Melia azedarach L. in Argentina (Pignata et al. 1999) and Ligustrum lucidum W. T. Ation (Carreras et al. 1996) and P. orientalis in Iran (Rafiei et al. 2014), increases in SLA were observed in areas with more pollution. Wuytack et al. urban areas. For example, 5 studied plant species— Azadirachta indica A. juss., Calotropis procera (Ait.) R. Br., Catharanthus roseus (L.) G. Don, Nerium ole- ander L., and Tabernaemontana divaricata L.— reportedly had decreased leaf area in the polluted area when compared with the non-polluted area (India) (Madhumonisa and Saradha 2021). Rashidi et al. (2017) reported that with increasing SO2, the leaf area decreases on Fraxinus rotundifolia Mill. in different areas of Tehran. The leaf area of Cinnamomum cam- phora (L.) Nees & Eberm., Lawsonia inermis L. and Bougainvillea spectabilis Willd. was decreased sig- nificantly in the industrial zone compared with the control area (Saudi Arabia)(Shaheen et al. 2016). Areington et al. (2015) showed that the leaf area of plants that had the closest distances to pollutants had a significant decrease compared to plants located far- ther away. Leaf surface is influenced by multiple factors, such as light competition (crown light exposure), varying conditions across different sites, and soil factors (e.g., soil type, nutrient availability, and plant-soil nutrient interactions). The spatial distribution and morpholog- ical variations of foliage within tree crowns reflect the tree’s adaptation to different microenvironments within crowns and stands. These factors significantly impact light use efficiency, carbon assimilation, and photosynthetic capacity of the entire tree (Wang et al. 2019). Foliar morphology, quantity, and spatial distri- bution play crucial roles in crown structure and tree growth as they strongly influence the interception and penetration of light within the crown (Alcorn et al. 2013). Accurate quantification of leaf morphology, quantity, and spatial distribution within crowns is thus vital for enhancing forest productivity (Čermák et al. 2008; Koester et al. 2014). Numerous studies have demonstrated the influence of soil parameters on leaf traits, particularly leaf area and SLA. For instance, Khanom et al. (2008) observed that Stevia rebaudiana (Bert.) grown in noncalcareous soil exhibited a maximum leaf area of 1401 cm2, whereas in calcareous soil, the minimum leaf area was 754 cm2. Ordoñez et al. (2009) established associations between leaf traits (SLA, leaf nitrogen concentration, leaf phosphorus concentration, and leaf nitrogen-to- phosphorus ratio) and soil fertility on a global scale using data from 474 species across 99 sites (809 records in total). However, since this study did not comprehensively explore the factors influencing leaf Mousavi Javardi et al: Relationships Between Leaf Characteristics and Air Pollutants
November 2023
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