Air Pollution Tolerance Index (APTI) of ،Three Tree Species of Morus alba L., Ailanthus altissima (Mill.) Swingle and Salix babylonica L. in Different Areas of Tehran City

Introduction
Air pollution is one of the top environmental concerns and illness of human health (She et al., 2017). Experts concluded that contents of outdoor air pollution (emphasis particulate matter) have adverse effects to human health (Carvalho-Oliveira et al., 2017). Air pollution associated with lung cancer, cardio vascular systems that threat human health (Carvalho-Oliveira et al., 2017). In some countries, for instance in the China, air pollution is the fourth concern and death in this country (She et al., 2017) .
Pollutants which are in urban areas respectively, P.M (2.5,10), ozone, SO2, NO, Pb, CO causes injure in plant leaves and effects the size of leaves and stomatal characteristic. The release of pollutants cause many threat for plants and other organisms. (Achakzai, Khalid et al. 2017). The Plants more resistance than of other organism (human, animal) for environmental pollutants. The APTI (air pollution tolerance index) value select plant species by their tolerance or sensitivity to pollution source by means of biochemical and physiological parameters (Achakzai, Khalid et al. 2017). leaf trees used for monitoring air quality and more affordable method in compared with traditional techniques(Carvalho-Oliveira et al., 2017)
There are 22 air quality monitoring stations in Tehran city. According to air quality monitoring, P.M 2.5 is the main air pollutant that threats public health and other organisms (plants, animals) . Industrial factories, carcinogen and phytotoxic air pollutants that emitted from vehicle motor, use of low quality fuels (Benzene etc), lack of proper monitor for Air pollution are the main causes of Air pollution in Tehran. The current research was conducted with the aim of study of air pollution tolerance index of three tree species such ( Morous alba , Ailanthus altissima , salix babylonica ) in different areas of Tehran city .
Material and methods
The city of Tehran (35035 / N to 350 48/ N and 51 0 17/ E to 51 0 33 /E., area 800 km2, Iran) has 22 air quality monitoring stations. According to this stations, four sites selected for collection of three tree such as Morous alba, Ailanthus altissima, Salix babylonica, respectively Area 3(site1), Area5 (site2), Area6 (site 3) and Area9 (site 4).
Leaf samples of three tree species with similar heights and age were collected on Monday, September 17, 2017. Ten leaves of each plants collected and stored in sealed plastic bags and kept in a portable ice- box and transferred to the lab for physiological and biochemical analyze. In the lab four biochemical parameters such as total chlorophyll, ascorbic acid (was measured by spectrophotometer), Extract pH leaf samples, relative water contents evaluated (Achakzai, Khalid et al. 2017).
The air pollution tolerance index of the plant species is determined using the formula given by Singh and Rao (1983):
APTI = ([A (T + P)] + R) / 10
In this formula, A is the content of leaf ascorbic acid in mg.g-1Fw; T, total leaf chlorophyll content in mg g-1Fw, P, pH of leaf extract, and R is the percentage of relative water content of leaf.
According to the criteria provided by Pandy et al. (2015), which is confirmed by many researchers, plants with APTI values ranging between 17-30 (tolerance), 13-16 (average), 13 (sensitive), and plants with APTI 1> are very sensitive (Pandey , Pandey et al. 2015).
Results and Discussion

Total chlorophyll content (TCH )
Results of measuring of chlorophyll contents indicated that the total chlorophyll content of the Morus alba was highest (site 4) in the selected sites. While Ailanthus altissima at site 1 had the lowest chlorophyll contents.
In this study, total chlorophyll contents in three tree species studied were ranged between 2.52 to 7.10 mg.g-1 Fw.
Chlorophyll is a photosynthetic pigment which indicate photosynthetic activity and dependent to factors such as age of plant species, environmental conditions, pollution level (Katiyar and Dubey, 2001; Ninave et al., 2001; Achakzai et al., 2017).
Morus alba at polluted sites 4 and 3 (according to Tehran's air quality monitoring data) showed the highest chlorophyll content (7.1 and 6.4), while Salix babylonica, Ailanthus altissima at site 1 and 2 have the lowest chlorophyll content (3.26 and 52.2). According to capabilities of each tree, the response of three trees in sites 1 and 2 was less, but at sites 3 and 4 responded to air pollution by increasing the contents of Total chlorophyll. Therefore, all three trees have increased their chlorophyll content against air pollution, but the Morus alba tree has been more successful than other trees.
The results of this study are consistent with the results of other researchers that plants with higher chlorophyll content are high resistant to air pollution (Shannigrahi et al., 2003; Prajapati and Tripathi, 2008; Rai and Panda, 2014.(
Ascorbic acid
Results of measuring of Ascorbic acid concentration indicated that Ascorbic acid concentration of the Morus alba was highest (site 4) in the selected sites. While Salix babylonica at site 2 had the lowest Ascorbic acid concentration. In this study , Ascorbic acid concentration in three tree species studied were ranged between 3.66 to 7.80 mg.g-1 Fw. Ascorbic acid levels in selected trees increase in contaminated areas(site 3,4). The results of this study are consistent with the results of other researchers, with high amount of stress, increase antioxidants such as ascorbic acid ((Mächler et al., 1995; Krishnaveni, 2013; Kaur and Nayyar, 2014).
Relative Water Content (RWC)
Results of measuring of Relative water contents indicated that Relative water contents of the Morus alba was highest (site 2) in the selected sites. While Ailanthus altissima at site4 had the lowest Relative water contents.
In this study, Morus alba showed the highest RWC at site 3,4 , its value was even higher than the other trees. which is a sign of a better response of the Morus alba to contamination. The results are consistent with the results of other researchers(Ritchie et al., 1990; Chaves et al., 2003).
pH leaf samples
Results of measuring of pH leaf samples indicated that pH leaf samples of the was highest (site 3) in the selected sites. While Ailanthus altissima at site2 had the lowest Relative water contents. In this study pH leaf samples in three tree species studied were ranged between4.9 to 7.4. Morus alba showed a better resistance than to the other tree species by trying to neutralize the alkaline pH. Ailanthus altissima and Salix babylonica, showed Acidic pH content (approximately 5.5).
Air Pollution Tolerance Index (APTI)
Results of measuring of APTI Values indicated that APTI Value of the Morus alba was highest (site 4) in the selected sites. While Salix babylonica at site4 had the lowest Relative water contents.
According to the results of this study, White mulberry seem to be a good alternative to planting in Tehran and Tolerant to seasonal air pollution (summer and early autumn).
In order to recommend the planting of this tree in different areas of Tehran, it is necessary to consider other criteria such as the water need for this tree, its transpiration rate, resistance to insects, such as aphids and whitefly. Also, its seedlings to test the maximum tolerance to air polluted in the appropriate greenhouses.