Current World Environment

Introduction

Due to industrialization and urbanization, air pollution has turn out to be a serious problem. Now a day’s particulate matter is the big concern due to their undesirable impact on plant and animal.¹ The recognition and classification of plants into tolerant and sensitive groups is essential because the sensitive plants can use as an indicator and the tolerant as a sink for the pollutants in city and developed habitats.² Plants have a very close relationship with nature and if any altered condition occurs in the atmosphere, it directly affects the physiology and biochemistry of plant. Vegetation works as a sink for air pollution and reduce pollution level in the atmosphere.³ Most plants experience internal changes before showing noticeable injure to leaves when they are open to air pollutants.⁴ Hence, this review was conducted to assess the biochemical changes and its role in air pollution tolerance index, a major factor that gives sensitivity, tolerance to plants. Air pollution tolerance index indicate the potential of vegetation to encounter air pollution.⁵ Plants naturally pure the air by consuming particulate matter and smoke. Sensitive tree species are suggested as bio-indicators.6 Vegetation shows dissimilar behaviour for various pollutants and all components of tree can be used as bio-monitors.7 They are very significant for decisive and balancing ecology by nutrient cycling and gases. Directly and indirectly air pollution can affect plants by leaves and through soil acidification.^8,9 Several researchers agree that air pollutants affect plant growth adversely.^10,11 Plants preliminarily accept air pollution thus, performs like a scavenger for pollutants.¹² As the trees are being continuously exposed to the environment, hence they attract, gather and combine pollutants impinging on their leaf surface; therefore they show noticeable or slight changes depending on their sensitivity level.¹³ Physiological changes take place in plants when open to air pollutants before showing visible damage to the foliage.¹⁴ Even leaves can act as natural filters that can eradicate great number of air borne pollutants and consequently recover the quality of air in polluted atmosphere.¹⁵ On the other hand, this function of pollution abatement can be best performed by the pollution tolerant type.¹⁶ Thus, air pollution tolerance index (APTI) is used to choose tolerant species and helps in monitoring plant tolerance towards air pollution. So assessment of plants on the basis of their level of tolerance to air pollution is essential. Consequently, APTI based on biochemical parameter is generally employed for recognising the tolerance level of plants.

Leaf Biochemical and Physiological Parameters

By using the parameters like chlorophyll content, leaf pH extract, relative water content and ascorbic acid content, the APTI was computed by using the following equation:

R is relative water content (%)

Air Pollution Tolerance Index (APTI)

Tiwari et al.,¹⁷ evaluated the APTI of 52 plant species collected from iron and steel industry which is 11 km away from Raigarh district of Madhya Pradesh. They found that APTI of Acacia nilotica was minimum (5.21) and maximum (15.02) in Ficus glomerata.Lakshmi et al.,¹⁸ examined the APTI of twenty four plant species around industrial area of Visakhapatanam and found that out of 24 plant Ficus religiosa (Peepal) show highest APTI which is 25.77 and Casuarina equisitifolia (Casuarina) show lowest APTI which is 6.51. Peepal, Jujube, Amla and Indian laburnum showed intermediate response to air pollution. Other twenty plants showed APTI value less than 16, so these are under sensitive one. Sulistijorini et al.,¹⁹ selected eight plant species from polluted Jagorawi highway and unpolluted site of Sindangbarang field in Indonesia. Various physiological parameters of the trees were recorded. Lagerstroemia speciosa was found more tolerant towards air pollution, Pterocarpus indicus, Delonix regia, Swietenia macrophylla were less tolerant and Cinnamomum burmanii is sensitive towords air pollution.Tripathi et al.,²⁰ evaluated the APTI of selected plant species growing alongside Moradabad city and Found that Holoptelea integrifolia, Saraca indica and Pithecolobium dulcis having highest APTI value i.e 55.8, 52.0 and 34.8 considered as tolerant species. Ficus rumphii, Azadirachta indica and Grewelia robusta (35.7, 30.5, 34.3) are less tolerant. Alstonia scholaris, Cassia simea and Bauhinia variegata (21.5, 6.09, 18.22) are susceptible species.Begum et al.,²¹ examined the air pollution tolerance index of various tree species around different manufacturing areas of Bangalore city. Seventeen plant species were selected for evaluation and out of these Syzygium cumini showed highest APTI value which is 16.1, 32, and 35 in three different industrial areas and considered as tolerant species followed by Azadirachta indicaand Madhuca latifolia Roxb. Gupta et al.,²² evaluated the APTI of various plant species in Burdwan town, West Bengal. Ashok-Saraca indica, Debdaru-Polyanthia longifolia, Banyan-Ficus benghalensis, Dumur-Ficus hispida, Guava-Psidium guajava, Sisoo-Dalbergia sisoo, Mango-Mangifera indica, Chattim-Alstonia scholaris, Mahagunii-Swietenia mahoganii, Asattha-Ficus religiosa were selected for evaluation and found that Banyan, Mango, Mahagunii and Asoke having highest API value.Tripathi et al.,²³ also studied the APTI of plants commonly growing around the industrial area of Varanasi. APTI was calculated by testing various parameters and API was calculated based on resultant APTI, biological and other socio economic characteristics of plants. Out of these plants Ficus infectoria and Ficus religiosa considered as tolerant species.Deepalakshmi et al.²⁴ evaluated APTI of different plant species growing around the Bangalore city. Ten commonly growing plant species were selected and fresh leaf samples of these plants were collected and analysed. Bougainvillea spectabilis and Ageratum conyzoides are considered as more susceptibletype, while Ficusreligiosa, Bambusabambosand Terminaliacatappa with reasonable changes are regarded as tolerant type.

While Peltophorum pterocarpumand Portulaca oleraceaewith are regarded as comparatively resistant species. The trees of the previous group can be efficiently used as bio indicators of vehicle exhaust pollution, whereas the resistant trees can be employed as sinks for vehicular pollutants. In a similar investigation at Durgapur, Burdwan District,West Bengal of India, it was found that the highest APTI value (176.14) was noticed at Durgapur College Campus followed by 158.68 at Durgapur Projects Limited.²⁵ Tanee et al.,²⁶ evaluated the APTI of various plant species growing alongside the Umuebulu Gas Flare Station of Nigeria. Ten commonly growing plant species were sleeted for analysis; these are Mallotus oppositifolus,Puerania phaseoloides,Vernonia amygdalina, Cymbopogon citrates, Manihot esculenta,Telfairia occidentalis, Musa paradisiacal, and Talinum triangulare. The results showed that out of these ten plant species Psidium guajava having highest APTI and Ocimum grassitisimum have lowest air pollution tolerance index.Babu et al.,²⁷ evaluated the From two sites, where one site is polluted area of a cement industry and another site is Yogi Vemana University campus. Ten samples were collected from each sites and analysed. In the polluted site APTI values were in the range of (7.38-10.12) and in the control site is (6.44-9.6). Out of the ten sample Aegle marmelos having highest APTI values and Ziziphus zizyphus having lowest APTI values.Wang et al.,²⁸ investigated the Leaf dust holding qualities of three tree species growing around the campus of Xi’an University of Architecture & Technology located in the south of Xi’an. S. japonica, P. acerifolia and C. deodara were selected and found that P. acerifolia having highest particulate matter holding capacity.Bakiyaraj et al.,²⁹ Studied the air pollution tolerance index of 11 plant species growing alongside the industrial area of Neyveli town of Tamil Nadu. Out of these eleven plant species Eucalyptus sp having highest APTI value (6.52 ) and Murrya koenigii showed lowest (0.81).Nwadinigwe³⁰ evaluated the air pollution tolerance index of six plant species around the urban area of Nigeria. Anacrdium occidentale, Bougainvillea spectabilis Mangifera indica, Delonix regia, Ixora coccinea , and Duranta erecta were selected and out of these six plant species Delonix regia gave highest APTI value followed by Bougainvillea spectabilis, Mangifera indica, Duranta erecta, Ixora coccinea and Anacrdium occidentale (5.308 to 0.909, 4.904 to 0.001, 4.577 to 0.166, 4.508 to 0.002, 3.728 to 0.004 and 3.470 to 0.001).Bora et al.³¹studied the APTI of six different plant species viz., Saraca indica (13.71), Azadirachta indica (12.98), Shorea robusta (12.64), Eucalyptus spp. (12.61), Ficus religiosa (12.61) and Tectona grandis (13.33). According to anticipated performance index (API) all species were tolerant i.e. Azadirachta indica, Ficus religiosa, Saraca indica, Shorea robusta and Tectona grandis. Madanet al.³² determinedAPTI and API of Ashok (Polyalthia longifolia), Peepal (Ficus religiosa), Mango (Mangifera indica), Neem (Azadirachta indica), Jamun (Syzygium cumini), Guava (Psidium guajava) growing alongside Haridwar. Out of these six plant species Mango showed highest APTI value and Ashok showed lowest. On the basis of API Peepal found very good type.Dhankar et al.³³ selected 15 plant species (F. religiosa, Syzygium cumini, F. benjamina, Mangifera indica, A. lebbeck, P. guajava, , F.virens, F. benghalensis , A. Indica, Saraca asoca, Z.mauritiana, P. glabra, E. Oblique, A. scholaris and B. Variegate) for evaluation of air pollution tolerance index around Rohtak City. Out of the 15 tree species F.virens and E. Oblique were selected for green belt development.Muhammed Aji et al.³⁴ selected three different sites for evaluation of APTI in Maiduguri. 6 plant species were selected on the basics of their abundance. The study showed that Mangifera indica having highest APTI value which is (30.02) and Cassia angustifolia having lowest (14.24). Khaya senegalensis, Eucalyptus spp and Azadiracta indica are moderate species (28.61, 24.10 and 28.23). Akilanet al.³⁵ studied APTI values of the four selected species viz, Tamarindus indicus(Tamarind), Neerium oleander(Oleander), Azadirachta indica(Neem) and Pongamia pinnata(Karanj). Three different study areas were selected for calculation namely Arcot (automobiles),Ranipet (Industries) and College farm (less automobile transport and industries) located in Vellore district, Tamil Nadu. Among the four selected species,higher APTI found in Neerium oleanderwhich is (11.25 20.51 18.01),Tamarindus indicus (10.18 16.55 17.55 ), Azardicta indica (9.73 14.31 12.72 ), Pungamia pinnata (10.79 15.55 13.07). Gholami et al. ³⁶ determined APTI of 6 tree species in Ahvaz, Iran. Plant species were selected from blank area and polluted area and analysed. Out of these six plant species Myrtus has highest APTI value (7.21) and Prosopis having lowest (4.57). Ziziphus was selected as the plant susceptible to air pollution in this study.In addition, the results of assessment of the above mentioned index showed that plants with higher APTI can be used as reducers of pollution and plants with lower APTI can be used to measure air pollution. In Indore city (MP) Patidar et al. ³⁷ studied the impact of vehicular pollution on the plants growing along the A.B road. The study was done by selecting five heavily polluted sites of the Agra-Bombay highway (NH-3).Thevetia neriifolia, Magnifera indica, Psidium guajava plants were selected due to their abundance in that road. Proline and Chlorophyll content are analyzed. They found that at most of the sites chlorophyll content was decreased in the foliage of the studied vegetationas compared with the plants of reference site while proline content was increased when compared with the reference site. Results of the current study shown that chlorophyll contents in all the vegetation varied with the pollution status of the site i.e.chlorophyll content of foliage decreases in the highly polluted area.It was concluded that these parameters are highly significant in understanding the plant-environment interactions and are used for developing of bio-indicator groups.Ogunrotimi et al.³⁸ evaluated the sensitivity and tolerance levels of the 12 tree species from 3 major roads to airpollution using APTI and results showed that the APTI of the tree species ranged between 9.2 and 12.7 the highest in case of the highest value was obtained in Polyalthia longifolia and the lowest value in Psidum guajava. It was concluded that P. longifolia, M. indica, G. arborea, T. grandis and T. catappa were the most tolerant to air pollution of all the tree species.Jyoti et al.³⁹ studied APTI values of the five selected species i.e. Ficus Religiosa, Delonix regia, Polyalthia longifolia, Plumeria sp. And Azadirachta indica on the highly polluted roadside of Noida sector 78.For evaluation of its tolerant limit four physiological and biochemical parameters namely Relative water content, leaf extract pH, Ascorbic acid, and chlorophyll content were analyzed. The results showed that Polyalthia longifolia is very sensitive to pollution and Plumeria and Delonix regia are comparatively less sensitive to air pollutants. Aasawariet al.⁴⁰ evaluated APTI of ten roadside tree species selected from polluted and control area in Thane city. The study shows that the control site has more APTI than the polluted site. The APTI observed minimum in Tectona grandis 5.2±0.3247 and maximum in Azadirachta indica 13.5±0.4404. Reduction in APTI at polluted site shows that Alstonia scholaris (6.6%), Tamarindus indica (8.8%) and Azadirachta indica (10.3%) were the most tolerant tree species, while Tectona grandis (47.5%), Acacia nilotica (27.4%) and Cassia fistula (20.7%) were more sensitive tree species. The results showed the order of tolerance (% difference in APTI) as Alstonia scholaris(6.6%)>Tamarindus indica(8.8%)>Azadirachta indica(10.3%)>Moringa pterygosperma (11.9%)>Mangifera indica(13.9%)>Bahunia variegate(14.3%)>Annona squamosa(18.7%)>Cassia fistula (20.7%)>Acacia nilotica (27.4%)>Tectona grandis (47.5%). Maysoon et al.⁴¹evaluated the Air Pollution Tolerence Index of two plant species in Babylon provinus and The results showed the plant Conocarpus lancifolius can be tolerant towards air pollution in comparison with plant Dodonaea viscosa that consider as sensitivity to air pollution.

Anticipated Performance Index (API)

Gupta et al.⁴² calculated the APTI and API of 10 tree species in Burdwan town, West Bengal. Out of the ten tree species Banyan (Ficus benghalensis), Mango (Mangifera indica), Mahagunii (Swietenia mahoganii), Asoke (Saraca indica) having excellent API value, Guava (Psidium guajava) is very good, Debdaru (Polyanthia longifolia) and Asattha (Ficus religiosa) are good, Sisoo (Dalbergia sisoo) is moderate, Chattim (Alstonia scholaris) and Dumur (Ficus hispida) showed Very Poor API values.Pathak et al.⁴³ evaluated the APTI of some plant species growing alongside Varanasi city, Uttar Pradesh.³⁵ plant species were selected for evaluation of API and out of these species Ficus infectoria, Mangifera indica and Ficus religiosa were classified under the ‘excellent’ category.Mondal et al.⁴⁴ determined the Air pollution Tolerence Index(APTI) of ten plant species collected from Burdwan town, West Bengal. High value of APTI was found in Pisidium guajava which is 31.75% and lowest APTI found in Ficus hispida which is 13.26%. The API was also calculated by considering the APTI and other parameters. On the basis of API Banyan, Mango, Mahagunii and Asoke were suitable for green belt development. Chavanet al.⁴⁵ evaluated the API of different plants growing around the Aurangabad city and found that Azadirachata indica and Mangifera indica were the tree species having good API value because of their biochemical and socioeconomic characters while Polyalthia longifolia and Dalbergia sissoo were having moderate and poor API value respectively. Esfahani et al.⁴⁶ evaluated the anticipated performance index of various plant species in green belt of Isfahan, Iran. Tolerant plant species to air pollution were identified on the basis of their API values. Study showed that air pollution tolerance index in identifying resistant species to air pollution is more appropriate than anticipated performance index in semiarid areas like Isafahan. It has been noted that API is beneficial too, when it is calibrated for arid and semiarid areas. Ogunkunle et al.⁴⁷calculated API of four plant species growing alongside the University of Ilorin, by combining air pollution tolerance index and anticipated performance index. The plant species selected for study were, Vitellaria paradoxa, Acacia nilotica and Prosopis Africana have API value 4 which is good, Prosopis africana,Acacia nilotica and Terminalia catappa shown API value 3 which is moderate. So Vitellaria paradoxa could be used as green belt development.Field study was conducted by Kapoor et al.⁴⁸ to assess the anticipated performance index of plants growing alongside the National Highway 21 revealed that comparison of the grading parameters by their summation for the API showed a variation in the plant species from a very poor to very good scale. Among the four plant species selected Toona ciliata with highest API was in the very good category followed by Ficus carica and Melia azediractain the poor and Morus alba under the very poor category. Toona ciliata was the most tolerant species among the selected plants and also this species has the high economic and aesthetic value. The study further signifies that Toona ciliata can be recommended for plantation in the polluted areas.The study concluded that all the biochemical,physiological, biological as well as socio-economic parameters of the plant species play an important role in determining the sensitivity and tolerance of plants to air pollution. The data related to total chlorophyll content, Ascorbic acid content, Relative water content, pH of leaf extract and APTI have been summarised in Table -3. 

Based upon API, Gupta et al have identified the Arjun and Morus plant species as very good performers out of four plant species viz. Arjun, Morus, Sheesham  and Ashok at Delhi.⁴⁹ Hence, these workers have suggested Arjun and Morus plants can be used for the greenbelt development purpose in the Delhi region. Their study included the dustfall deposition on the foliar in Delhi region. The APTI values of their study suggested that all the four species were sensitive and can be used as biological indicators.

Conclusion

The extensive review has focussed on the measurement and monitoring of APTI and API of plant species growing alongside the Roads and industrial areas. These are useful tools to assess the tolerance level of plant species towards air pollution. The tolerant plant species can be used as pollution sink and help in controlling and mitigating the adverse impacts from air pollution. Plants having high APTI and API value are selected for the green belt improvement and helpful in long term air pollution management in city and developed areas. On the basis of review many plant species are found to be tolerant towards air pollution and are suitable for planting around industrial area and roadsides.

Acknowledgements

The facilities provided by the department of Environmental Science, YSP University of Horticulture & Forestry, Nauni, Solan are highly acknowledged.

Funding Sources

The funds are provided by the department of Environmental Science, YSP University of Horticulture & Forestry, Nauni - Solan.

Conflict of Interest

There is no conflict of interest in the present study. 

References