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Aerosol and Air Quality Research, 16: 2920–2932, 2016 Copyright © Taiwan Association for Aerosol Research ISSN: 1680-8584 print / 2071-1409 online doi: 10.4209/aaqr.2015.04.0272

Deposition and Impact of Urban Atmospheric Dust on Two Medicinal Plants during Different Seasons in NCR Delhi Gyan Prakash Gupta, Bablu Kumar, Sudha Singh, Umesh Chandra Kulshrestha* Jawaharlal Nehru University, School of Environmental Sciences, Delhi 110067, India ABSTRACT

This study reports dustfall deposition on foliar surfaces of two medicinally important plant species i.e., Arjun (Terminalia arjuna) and Morus (Morus alba) in relation with its impact on biochemical constituents and surfaces morphology of the foliar. The study was carried out at a residential (JNU) and an industrial site (SB) of National Capital Region (NCR) Delhi. The results showed that at the industrial site, the dustfall fluxes were almost 2.5 times higher than that at the residential site. Dustfall fluxes were noticed higher on Morus foliar than Arjun foliar as the roughness of Morus foliar is greater. Deposition fluxes of major anions (F–, Cl–, NO3

–, SO42–) and cations (Na+, NH4

+, K+, Ca2+, Mg2+) ions were also calculated by analyzing aqueous extract of dustfall at both the site. The results showed that with the increase in dustfall fluxes on the foliar surfaces, the levels of photosynthetic pigments and soluble sugar decreased while the levels of ascorbic and proline amino acid were increased at both the sites for both the plants. Dustfall fluxes had distinct seasonality having the order of fluxes as winter > summer > monsoon. Surface morphological study revealed that dust deposition adversely affects the foliar surface, cuticle and epidermal layers. Dust particle deposition ruptures and blocks the stomatal pores. As compared to the residential site, the foliar samples collected from the industrial site showed a more significant impact of dust on biochemical constituents and surface morphology. Keywords: Urban dust; Ionic fluxes; Biochemical constituents; Foliar surface; Stomata damage. INTRODUCTION

Generally, dry deposition of gaseous and particulate pollutants takes place through diffusion, Brownian movement and impaction (Finlayson-Pitts and Pits, 1986). However, coarse particles which are generated through disintegration processes are primarily deposited via sedimentation commonly referred as dustfall in a region like India (Rao et al., 1992; Kulshrestha et al., 1995; Kulshrestha et al., 2003; Gupta et al., 2015). The major sources of dust pollution include suspension of soil, agriculture related activities, road dust, vehicular exhaust, power plants, construction activities, brick kilns and cement factories etc. (Karanasiou et al., 2014; Upadhyay et al., 2015). In addition, transboundary and long range transport also contributes a significant amount of atmospheric dust in the south Asian region (Begum et al., 2011). Countries like India have high loading of soil derived dust in the atmosphere under prevailing dry weather conditions. The soil derived particulate matter is rich in CaCO3 and acts as an effective scavenger of atmospheric SO2 forming * Corresponding author.

Tel.: 0091 11 26704320 E-mail address: [email protected]

CaSO4 which is also removed through dustfall (Kulshrestha et al., 2003; Kulshrestha, 2013; Gupta et al., 2015). Deposition of such particulate matter on the foliar may lead to different phytotoxic effects depending on the characteristics of the deposited material. The sulphate, nitrate and heavy metals are the most commonly reported air pollutants responsible for phytotoxic effects (Sheppard, 1994; Reeves and Baker, 2000). Sulphate and nitrate being acidic species have higher aqueous affinity which allows theses ions to mobilize into the foliar mesophyll cells creating stress (Fowler et al., 1989; Grantz et al., 2003; Buchner 2004; Gupta et al., 2015). Dustfall having pH values ≥ 9 might cause direct or indirect injury to the foliar tissues (Vardak et al., 1995; Auerbach et al., 1997).

Deposition of dust on the foliar surface may alter its optical properties, particularly the foliar surface reflectance in the visible and near infrared region (Hope et al., 1991; Keller and Lamprecht, 1995). Dustfall also alters optical properties of snow-cover which can lead to an increase in temperature of vegetation surface (Spatt and Miller 1981; Spencer and Tinnin, 1997), changes in grazing patterns of animal (Walker and Everett 1987; Auerbach et al., 1997; Spencer and Tinnin, 1997). According to Sharifi et al. (1997), the deposition of road dust of 40 g m–2 can cause the 2–3°C increase in leaf temperature in desert environments. The species having stomata in grooves might be less affected

Gupta et al., Aerosol and Air Quality Research, 16: 2920–2932, 2016 2921

than the species in which the stomata are located at the outer surface of the leaf. Hence, dustfall on foliar surfaces has significant impacts on the photosynthesis and growth (Sharifi et al., 1997, Wijayratne et al., 2009). Trees and shrubs are considered as efficient filters for road dust (Farmer, 1993; Beckett et al., 2000). Dustfall removal efficiency of a tree species depends on its surface geometry, hairs, cuticle and height (Nowak, 1994). In Indian region, dust is abundant in the atmosphere. Unfortunately, consequences of dustfall on plant health have not been studied comprehensively. Hence, this study was carried out at two sites of different characteristics in National Capital Region of Delhi to find out the effects of dustfall deposition on the biochemical parameters of foliar of two medicinally important plants. The response of these selected plant species to the urban dust pollution has not been reported so far. The study also presents the effects of dustfall on the surface morphology of the foliar.

METHODOLOGY Site Description

Two sites viz. JNU (Jawaharlal Nehru University) and SB (Sahibabad) located in the National Capital Region (NCR) of Delhi were selected for this study. JNU site represents residential characteristics while SB site is a typical representative of industrial characteristics. The locations of both these sites have been shown in Fig. 1.

The meteorological conditions of different seasons of Delhi were given in Table 1.

The campus of the Jawaharlal Nehru University (JNU) is located south of Delhi city. It has huge green cover as part of ridge forest having the abundance of Prosopis plant species. There is no major industry located nearby. However, vehicular traffic and construction activities are important sources of air pollution in and around the campus. In addition, several residential colonies are located in the immediate vicinity of the campus from where air is moved over to JNU influencing the air quality of the campus. Sahibabad (SB) site has several industries in the surrounding area which include paint, plastic, steel, electrical processing units etc. and the site is affected by the emissions of vehicles passing through two national highways i.e., NH-24 and NH-58. In addition, the construction activities, diesel driven heavy duty vehicles are the major contributors of road dust in this area. Besides, transboundary pollution from brick kilns and crop residue burning from nearby states is another source of dustfall and other air pollutants. Sample Collection and Analysis

Dustfall was collected on the foliar surface of two plants i.e., Arjun (Terminalia arjuna) and Morus (Morus alba) trees. Arjun tree is very tall (15–20 m) having smooth, grey bark, simple foliars with opposite to sub-opposite alignment. The petiole of Arjun is short (2–4 cm long), sericeous with

Fig. 1. Map showing the collection of sampling sites.

Table 1. Meteorological parameters during different seasons at Delhi.

Season Temperature (°C) Relative Humidity (%) Mean Wind Speed (km h–1) Wind Direction (Degrees)Monsoon 28.0 ± 1.8 72.5 ± 11.5 7.1 ± 2.0 SW

Winter 15.8 ± 3.0 74.3 ± 10 6.2 ± 1.5 SW Summer 28.5 ± 5.0 44.1 ± 16 9.5 ± 1.3 SW


2 (or 1) prominent two glands at petiole apex. Arjuna plant is used for the heart related disorders such as edema, angina and hypercholesterolemia. The bark of Arjun plant has diuretic and prostaglandin enhancing properties. The Morus tree is relatively short (10–15 m) smooth dark green leaves with alternate arrangement and often lobed. The Morus plant has antibacterial, astringent, diaphoretic, hypoglycaemic, odontalgic and ophthalmic properties.

Foliar dustfall was collected on 10 days exposure basis from both the plants during 2012–2014. The foliar were selected at around 3 m height from the road side which were tagged, cleaned and properly washed with distilled-deionised water. Thorough cleaning of foliar made it free from any dust particles. Each time the foliar were plucked after 10 days and washed with 50 mL distilled-deionised water using surface washing method (Davidson and Wu, 1990). Usually, each sample was collected between 10 and 11 a.m. every tenth day after the cleaning. Total 31 and 35 samples of dustfall on Arjun and Morus plant, respectively were collected during the period (2012–2014) of study. In the aqueous extract of dustfall, major anions (Cl–, F–, NO3

– and SO4

2–) and cations (Na+, K+, NH4+, Ca2+ and Mg2+)

were determined by Ion Chromatography (Metrohm 883 Basic IC Plus) equipped with Anion (Metrosep A SUPP 4, 250/4.0) and Cation (Metrosep C4-100/4.0) columns.

Dustfall fluxes (DF) were calculated by using the gravimetric method using the formula: DF = (m2 – m1)/(A × d), where, DF is dustfall fluxes (mg m–2 d–1), m1 is the initial weight of petri dish, m2 is the final weight of the petri dish, A is the surface area of the selected foliar (m2) and d is the number of days. Area of the leaf was calculated by the graph sheet drawing method (Gupta et al., 2015b). Analysis of Biochemical Parameters

The foliar samples were processed and analyzed by optimizing colorimetric standard methods using UV-Vis spectrophotometer techniques (Perkin Elmer LAMBDA 35 and Spectrum SP-UV 500 DB). Photosynthetic pigments- chlorophyll a (Chl a), chlorophyll b (Chl b), total chlorophyll (Total Chl), carotenoids (Car) were determined by Hiscox and Israealtm’s (1979) method, soluble sugar was determined by Dubois et al. (1956) method, ascorbic acid (AsA) content was determined by Keller and Schwager (1977) method and proline amino acid (Pro) was determined by Bates (1973) method. Foliar Surface Morphology Analysis

Selected numbers of foliar were studied for their morphological characteristics by using Scanning Electron Microscope (SEM) (Carl Zeiss EVO 40, Germany) at the Advance Instrumentation Research Facility (AIRF) of the University. The collected foliar samples were washed with distilled-deionised water using a soft hair brush followed by gently wiping with tissue paper. Then four small pieces (1 cm2 approx.) were cut from this leaf (two for adaxial and two for abaxial surface study) and fixed in 2.5% glutaraldehyde (in phosphate buffer, pH 7.2). Further, it was dehydrated twice in 50, 70, 90, 100% ethanol and a sample was chemically dried by HMDS (Hexamethyldisilazane) for

2–3 minutes. Then the sample was mounted on the aluminium stubs with carbon tape and it was sputter-coated with a thin layer of gold (Sputter coater-Polaron SC7640). The coated samples were then observed under scanning electron microscope at an accelerating voltage of 20 kV at variable magnification range.

Quality Assurance and Quality Control (QA/QC)

The quality of sampling and analysis was ascertained by analyzing blank of pertidish used for foliar extraction. Figs. 2(a) and 2(b) show the chromatograms of anion and cation separation in the blank. All the anionic species had area below the detection limit in the balnk while cationic species viz. Na+ and Ca2+ showed negligible area. However, while calculating the net area of the sample, the area of these cations in blank was subtracted. Calibration of methods and quantification of components were carried out using MERCK reference standards (CertiPUR).

The Calibration equation, correlation coefficient, detection limit and analytical precision are given in Table 2. Whereas freshly plucked foliar samples were firstly kept in sealed polythene and in an ice box and then brought to the laboratory for the further investigation. For analysis of different biochemical parameter, the foliar samples were taken as triplicate. During biochemical analysis, the margin and mid rib portions were avoided in all the triplicates to ensure the authenticity of the results. RESULTS AND DISCUSSION Dustfall Fluxes and their Seasonal Variation

The values of dustfall fluxes on Arjun and Morus foliar surfaces have been given in Table 3. Sample wise variation of the dustfall fluxes on Arjun and Morus foliar surfaces has been shown in Figs. FS1 and FS2, respectively. The average dustfall fluxes on Arjun foliar were noticed as 229 ± 12 mg m–2 d–1 and 95 ± 6 mg m–2 d–1 at SB and JNU site, respectively whereas 271 ± 13 mg m–2 d–1 and 108 ± 6 mg m–2 d–1 on Morus foliar at SB site and JNU site, respectively. The results showed that the average dustfall deposition on Morus foliar was around 2.5 times higher at SB than those of JNU site. Higher dust deposition at SB site may be due to its contribution from various sources such as road dust, industrial emissions, construction activities and vehicular exhaust etc. The soot emitted from diesel driven trucks may also increase the dust load at SB site. Unpaved roads and poor road conditions further enhance atmospheric dust load which is settled on the various surfaces including foliar. In addition, transboundary pollution especially the emissions from brick kilns and crop residue burning from nearby states might be contributing to higher pollutant load including dustfall. In general, North India has been reported having high loading of atmospheric dust due to natural sources (Sharma and Kulshrestha, 2015) which contribute to high particulate matter often violating the NAAQS limits and also contributing to high aerosol optical depth (CPCB. 2012; Kulshrestha and Sharma, 2015). The dustfall fluxes of this study have been compared with the values reported at various surfaces and sites worldwide as given in Table TS1.


(a)

(b)

Fig. 2. (a) Chromatogram of a extracted petridish water sample (anions); (b) Chromatogram of a extracted petridish water sample (Cations).

Table 2. Calibration equation, correlation coefficient, analytical precision and detection limit for different ionic species.

Major ions Calibartion eqaution Correlation coefficient (r2) Precision Detection limit (mg L–1) F– y = 0.186x – 0.004 0.9999 0.79% 0.157 Cl– y = 0.115x + 0.020 0.9999 1.60% 0.323

NO3– y = 0.065x + 0.000 0.9999 2.13% 0.440

SO42– y = 0.086x + 0.003 0.9999 2.18% 0.435

Na+ y = 0.211x + 0.008 0.9999 0.23% 0.045 K+ y = 0.111x + 0.008 0.9999 0.17% 0.074

Ca2+ y = 0.177x + 0.069 0.9999 0.37% 0.250 NH4

+ y = 0.247x + 0.004 0.9999 1.23% 0.034 Mg2+ y = 0.368x + 0.154 0.9999 0.70% 0.138


Table 3. Average (± SE) dustfall flux (mg m–2 d–1) of major ions on Arjun and Morus foliar surface at residential site (JNU) and Industrial site (SB).

Parameter JNU SB

Arjun (n = 31) Morus (n = 35) Arjun (n = 31) Morus (n = 35) Dustfall 95 ± 6 108 ± 6 229 ± 12 271 ± 13

Na+ 0.14 ± 0.02 0.13 ± 0.01 0.69 ± 0.08 0.54 ± 0.04 NH4

+ 0.13 ± 0.02 0.29 ± 0.02 0.50 ± 0.07 0.58 ± 0.04 K+ 0.32 ± 0.02 0.30 ± 0.02 0.79 ± 0.10 0.96 ± 0.27

Ca2+ 4.25 ± 0.39 4.54 ± 0.45 9.29 ± 0.85 12.25 ± 1.24 Mg2+ 0.23 ± 0.02 0.27 ± 0.01 0.75 ± 0.07 0.59 ± 0.04

F– 0.11 ± 0.02 0.14 ± 0.01 0.24 ± 0.02 0.29 ± 0.02 Cl– 0.43 ± 0.06 0.60 ± 0.05 1.89 ± 0.21 1.67 ± 0.16

NO3– 1.26 ± 0.16 1.60 ± 0.05 0.70 ± 0.14 1.49 ± 0.25

SO42– 2.56 ± 0.22 2.84 ± 0.28 10.32 ± 1.38 12.05 ± 1.44

Fig. 3. Dustfall flux (mg m–2 d–1) of major ions (average ± SE) on Arjun (Fig. a) and Morus (Fig. b) foliar surface at residential site (JNU) and Industrial site (SB) in different seasons.


The dustfall fluxes on Morus foliar at JNU site were recorded as 69 ± 2, 138 ± 6 and 119 ± 8 mg m–2 d–1 during monsoon, winter and summer seasons, respectively and 182 ± 5, 349 ± 7 and 285 ± 14 mg m–2 d–1 during monsoon, winter and summer seasons, respectively at SB site. The average dustfall fluxes on Arjun foliar at JNU site were recorded as 57 ± 3, 120 ± 5 and 117 ± 7 mg m–2 d–1 during monsoon, winter and summer seasons, respectively and 151 ± 4, 286 ± 6 and 259 ± 8 mg m–2 d–1 during monsoon, winter and summer, respectively at SB site. Apart from source contribution dustfall at two sites, the higher dust accumulation during the winter season may be due to lower temperature and calm conditions which reduce the mixing height further reducing the dispersion of pollutants. Besides these conditions, high humidity can help in retaining dust particles on the foliar as the available moisture wets the foliar surfaces. The lowest fluxes of dustfall during monsoon season are due to the wash out effect of rain. It is reported that rains effectively scavenge the particulate material in Indian region (Kulshrestha et al., 2009).

Arjun foliar are arranged at right angles to the stem with small petiole whereas Morus foliar are arranged along the axis of the stem with a long petiole. Inspite of this arrangement, it is interesting to note that Morus foliar have higher deposition of dustfall primarily due to surface characteristics. Morus foliar surface is rough with depressions which allow greater adherence of fine and coarse particles while Arjun foliar is smooth where particle adherence to the foliar is lower. In addition, as mentioned earlier, sources and meteorology also play very important role for such variations (Kulshrestha et al., 2010). Ionic Fluxes and their Seasonal Variations

Average values of deposition fluxes of major ions through dustfall on Arjun and Morus foliar surfaces at residential (JNU) and industrial (SB) site have been given in Table 3. Fig. 3 shows the seasonal variation of ionic fluxes on both the foliar surfaces at both the sites during different seasons. The percentage contribution of various ionic species to the total dustfall fluxes for both Arjun and Morus plants at both the sites has been shown in Figs. FS3(a)–FS3(d). The results of seasonal variation of ionic species on Arjun and Morus have been described below- Arjun Foliar

At JNU site, the average deposition flux was the highest for Ca2+ following the order of SO4

2– > NO3– > Cl– > K+ >

Mg2+ > K+ > Na+ > NH4+ > F–. At JNU site, the order of

ionic fluxes during winter season was Ca2+ > SO42– > NO3

– > Cl– > K+ > Mg2+ > NH4

+ > Na+ > F– while during summer season, the order was Ca2+ > SO4

– > NO3– > Cl– >

K+ > Mg2+ > F– > Na+ > NH4+. During monsoon season,

the order of deposition fluxes of the ionic species was Ca2+ > SO4

2– > NO3– > K+ > Cl– > Mg2+ > Na+ > F– > NH4

+. At SB site, the deposition flux was the highest for SO4

2– following the order- Ca2+ > Cl– > K+ > Mg2+ > NO3

– > Na+ > NH4

+ > F–. At SB site, the order of deposition flux was SO4

2– > Ca2+ > Cl– > Na+ > Mg2+ > K+ > NH4+ > NO3

– > F– during winter season while in summer season, the order was

Ca2+ > SO4– > NO3

– > K+ > Cl– > Na+ > Mg2+ > F– > NH4+.

During monsoon season, the order of fluxes was SO42– > Cl–

> Mg2+ > Na+ > NO3– > K+ > NH4

+ > F–. Morus Foliar

At JNU site, the average deposition flux was the highest for Ca2+ following the order SO4

2– > NO3– > Cl– > K+ >

Mg2+ > K+ > NH4+ > F– > Na+. Seasonal variation of ionic

fluxes at JNU site followed the order Ca2+ > SO42– > NO3

– > Cl– > Mg2+ > K+ > NH4

+ > Na+ > F– during monsoon, Ca2+ > SO4

2– > NO3– > Cl– > K+ > Mg2+ > NH4

+ > F– > Na+ during winter while Ca2+ > SO4

2– > NO3– > Cl– > NH4

+ > K+ > Mg2+ > F– > Na+ during summer seasons. At SB site also, the average deposition flux was the highest for Ca2+ and it decreased in the order of SO4

2– > NO3– > Cl– > K+ >

Mg2+ > NH4+ > Na+ > F–. Seasonal variation of ionic fluxes

at SB site followed SO42– > Ca2+ > K+ > Cl– > NO3

– > Mg2+ > Na+ > NH4

+ > F– order during winter, Ca2+ > SO42– > Cl–

> NO3– > K+ > NH4

+ > Na+ > Mg2+ > F– order during summer, Ca2+ > SO4

2– > NO3– > Cl– > Mg2+ > K+ > Na+ > F– > NH4

+ order during monsoon season. Significantly higher deposition of SO4

2– at SB site clearly indicated the impact of emissions from industrial and vehicular sources in the industrial area. Besides this, interstate transboundary pollution is also responsible for elevated fluxes of ionic species.

Data showed that Ca2+ has been the most dominating ion representing as a major constituent of aqueous extract of dustfall. Ions such as SO4

2–, NO3– and NH4

+ are important to discuss as they are formed through the oxidation of their precursor gases and are considered as the indicators of anthropogenic activities. Percent increase of four ions (Ca2+, SO4

2–, NO3– and NH4

+) during summer and winter with respect to monsoon values has been given in Table 4.

Dustfall fluxes (DF) of Ca2+ was the highest during all the seasons indicating its association with calcite and dolomite of this region contributed as soil dust and road dust (Kumar et al., 2014). In addition, long range transport of dust has also been reported from middle-east and African regions (Begum et al., 2011; Ghosh et al., 2014; Kulshrestha and Kumar, 2014). It is worth mentioning that both Ca2+ and SO4

2– are the major ions contributed through dustfall. The possible reasons for very high Ca2+ and SO4

2– are associated with the oxidation of SO2 onto CaCO3 rich dust forming CaSO4 in Indian region (Kulshrestha, 2013; Kulshrestha et al., 2003). The highest fluxes of these ionic species during the winter season can be attributed to meteorological conditions such as lower temperature, lower mixing height and high relative humidity which favor stagnation of pollutants. The lowest fluxes during monsoon could be due to washout effect of rain which removes the pollutants reducing their loadings in the air. Variation of Biochemical Constituents in Morus and Arjun Foliar Extract Photosynthetic Pigments

The average concentration of pigments of Arjun and Morus foliar has been given in Table 5. In case of Arjun foliar, the average concentrations (fresh weight, f.w.) of Chl a, Chl b, total Chl and Car were recorded as 1.73


Table 4. Percent increase in foliar Ca2+, SO42–, NO3

– and NH4+ fluxes during summer and winter with respect to monsoon

season at both the sites.

Parameter JNU SB

Arjun Morus Arjun Morus Winter Summer Winter Summer Winter Summer Winter Summer

Ca2+ 98% 42% 163% 17% 59% 23% 120% 33% SO4

2– 89% 51% 115% 16% 187% 37% 229% 42% NO3

– 88% 4% 22% 23% 229% 47% 70% 47% NH4

+ 329% 55% 137% 192% 118% 26% 68% 128%

Table 5. Average value of biochemical constituents (mg/g) and dustfall fluxes ((mg/m2/d) on Arjun and Morus at JNU and SB sites. (Average value ± SE).

Parameters JNU SB

Arjun (n = 31) Morus (n = 35) Arjun (n = 31) Morus (n = 35) Chlorophyll a 1.73 ± 0.06 2.93 ± 0.12 1.45 ± 0.04 2.38 ± 0.11 Chlorophyll b 0.68 ± 0.03 0.66 ± 0.02 0.44 ± 0.03 0.43 ± 0.03

Total Chlorophyll 2.41 ± 0.07 3.58 ± 0.13 1.89 ± 0.06 2.81 ± 0.13 Carotenoids 0.89 ± 0.07 1.35 ± 0.13 0.80 ± 0.02 1.06 ± 0.05

Soluble sugar 131 ± 4 153 ± 4 110 ± 3 123 ± 4 Ascorbic acid 0.79 ± 0.03 1.03 ± 0.04 1.16 ± 0.04 1.64 ± 0.08

Proline amino acid 0.65 ± 0.03 3.45 ± 0.19 0.80 ± 0.04 4.72 ± 0.23 Dustfall Fluxes 95 ± 6 108 ± 6 229 ± 12 271 ± 13

± 0.06, 0.68 ± 0.03, 2.41 ± 0.07 and 0.89 ± 0.07 mg g–1 respectively at JNU and 1.45 ± 0.04, 0.44 ± 0.05, 1.89 ± 0.06 and 0.80 ± 0.02 mg g–1 (f.w.), respectively at SB. In case of Morus foliar, average concentrations of Chl a, Chl b, total Chl and Car were recorded as 2.93 ± 0.12, 0.66 ± 0.02, 3.58 ± 0.13 and 1.35 ± 0.13 mg g–1 (f.w.), respectively at JNU site and 2.38 ± 0.11, 0.43 ± 0.03, 2.81 ± 0.13 and 1.06 ± 0.05 mg g–1 (f.w.), respectively at SB site. As shown in Fig. 4, the concentrations of Chl a, Chl b, total Chl and Car decreased with an increase in dustfall fluxes at SB site. Trendlines clearly show a reduction in pigment levels at SB site. The seasonal variation of pigment content has been presented in Fig. FS4. The results showed that the chlorophyll a; chlorophyll b; total Chlorophyll and carotenoid were the highest during monsoon season and the lowest during winter season at both the sites.

At SB site, a decrease in the chlorophyll content of the foliar as compared to JNU site might be due to the development of alkaline condition due to mobilization of soluble content to the meosphyll cell. Also, the shading effect of dust could also reduce sunlight availability further reducing the chlorophyll synthesis (Anthony, 2001; Singh et al., 2002). Reduction in chlorophyll content of leaves in polluted areas has been reported by other workers at different sites worldwide (Somashekar et al., 1999; Singh, 2000; Samal and Santra, 2002). In addition, the photosynthesis process is SO4

2– sensitive because it acts as a competitive inhibitor of ribulose-1, 5- biphosphate carboxylase inhibiting the photophosphorylation process (Kaiser et al., 1986). Soluble Sugar

Carbohydrates are important components of storage and structural material in plant species. On an average, the concentrations of total soluble sugar in Arjun foliar were

noticed as 131 ± 4 and 110 ± 3 mg g–1 (dry weight, d.w) whereas, in Morus foliar the concentrations were recorded as 153 ± 4 and 123 ± 4 mg g–1 (d.w) at JNU and SB, respectively (Fig. FS5 and Table 5). Results showed that the relative decrease in soluble sugar content with the increase in dustfall fluxes at SB site was more as compared to JNU site (Fig. 4). Further, the greater reduction was observed in a case of Morus. The decrease in soluble sugar content may correspond to a lower photosynthetic rate and higher energy requirements due to high dust loadings. A decrease in sugar content of plant foliar with an increase in air pollutant level in industrial and urban areas has been reported by other workers too (Tzvetkova and Kolarvo, 1996; Sharma and Tripathi, 2009).

Ascorbic Acid (AsA)

Ascorbic acid is a cellular antioxidant and a strong reducing agent. It reduces the effect of air pollution and protects the plant against oxidative damage. The average AsA content of Arjun foliar was estimated 0.79 ± 0.03 and 1.16 ± 0.04 mg g–1 (f.w) whereas, in case of Morus foliar 1.0 ± 0.05 and 1.64 ± 0.08 at JNU and SB site, respectively (Fig. FS6 and Table 5). Results showed that AsA content increased with the increase in dustfall fluxes at the SB site as compared to the JNU (Fig. 4), the greater increase was observed in Morus foliar. Seasonal variation indicated that the increase in AsA content in the Arjun and Morus foliar from the SB site was greater as compared to the JNU site. The higher levels of ascorbic acid AsA may be attributed to the greater oxidative stress due to a greater accumulation of dust at SB site. Increased rate of production of reactive oxygen species (ROS) during photo-oxidation of SO2 to SO3

– results in higher levels of ascorbic acid content (Smirnoff, 2005, Athar et al., 2008).


Fig. 4. Effects of dustfall fluxes (DF) on biochemical parameter of Arjun (a, b) and Morus (c, d) plant foliar at JNU and SB site.

Proline Amino Acid (Pro) Amino acid proline (Pro) is a stress-indicator which

plays a major role in plant defense mechanisms, in particular oxidative damage, and its greater accumulation in stressed plants (Van-Assche and Clisjsters, 1990; Sinha and Saxena, 2006). The average proline (Pro) content was estimated as 0.65 ± 0.03 and 0.80 ± 0.03 mg g–1 (f.w.) whereas, in case of Morus foliar it was 3.45 ± 0.19 and 4.72 ± 0.23 mg g–1 (f.w.) at JNU and SB site respectively (Fig. FS7 and Table 5). Results showed that increase in Pro content with the increase in dustfall fluxes at SB site was greater as compared to JNU site (Fig. 4). It was noticed that the foliar of both the plant species from the industrial site (SB) showed greater increase in Pro content during different seasons than at the residential site (JNU). This is probably due to greater stress at SB site which affects nitrogen metabolism in plants resulting in increased Pro levels (Atanasova, 2008). Relative Change in Biochemical Constituent Levels during Different Seasons: JNU vs. SB Sites

In order to compare the concentrations of different biochemical parameters during different seasons at residential site and the industrial site, the relative difference has been calculated in term of percent difference with respect to the

level of corresponding parameter during corresponding seasons at the industrial site (SB) using the formula: ((Aj – As)/Aj) × 100), where Aj is the concentration of biochemical constituent at JNU site and As is the concentration of biochemical constituent at SB site.

The calculation showed that the percent difference in biochemical constituent levels between JNU and SB foliar was the lowest during monsoon season (Table TS2). This is probably due to the wash out effect of rain during monsoon season which results in clearing off dust particles from the foliar surface reducing the dustfall deposition further resulting in the lowest difference in dust deposition at both the sites. Besides this, atmospheric dust loadings are the lowest during monsoon season due to scavenging of particulate matter by rain as mentioned earlier (Figs. FS1 and FS2). The results showed that during winter and summer seasons, urban dusts play a significant role in determining the levels of biochemical constituents of the plants. These levels are more affected at the industrial site (SB) as compared to the residential site (JNU). Changes in Foliar Surface Morphology

Plants act as pollution receptors as these are directly exposed to air. Both gases as well as particulate pollutants are


deposited onto the foliar surfaces affecting their physiological and morphological characteristics (Rai et al., 2010). Sedimentation of coarse particles has more effect on the upper surfaces of foliar (Kim et al., 2000; Chaturvedi et al., 2013) while finer particles affects lower surfaces (Ricks and Williams, 1974; Krajickova and Mejstrik, 1984; Fowler et al., 1989; Beckett et al., 2000). Smaller particles are entered through the stomata while larger size particles are piled up on the foliar surfaces and block the stomata further affecting photosynthesis, water retention, gaseous exchange and finally plant growth and yield (Thompson et al., 1984; Tomasevic et al., 2010; Rai et al., 2010). Deposition of dust particles on the foliar can cause a decrease in stomatal diffusive resistance and increase in leaf temperature (Fluckinger et al. 1979). According to a study reported by Stevovic et al. (2010) more damage in upper and lower epidermis along with the reduction in palisade parenchyma cells was noticed in the polluted area than that of the non-polluted area.

The deposition of dust is seen higher at SB site as compared to JNU site. The same is the case for SB site where adaxial and abaxial surfaces of the foliar show more number of particles. In case of Arjun foliar, the adaxial surface of foliar is seen with restructuring of cuticle and epicuticular wax due to abrasive effect of the dust deposition (Rocha et al., 2014) (Figs. 5(a)–5(b)). These effects are more prominently

seen at SB site (Fig. 5). As shown in Fig. 5, the number of dust particles per unit area is seen higher at SB site as compared to JNU site. The size of stomatal pore is seen narrow and shrinked at SB site as compared to JNU site, probably due to the formation and deposition of secondary particles which might be the cause of more damaged upper and lower epidermis and guard cells at SB site as compared to JNU site (Figs. 5(e)–5(f)). At SB site, ruptured and swollen guard cells are seen which are raised from the epidermis at the abaxial surface (Figs. 5(c)–5(f)). Figs. 5(c)–5(f)) shows the dust particles deposited in and around stomata on abaxial leaf surface clogging the stomatal pores.

Fig. 6 shows the morphological changes in Morus foliar surface. As shown in Figs. 6(a)–6(b), the adaxial surface is seen more rough, degraded having highly disturbed striations of an epidermal surface at the industrial site (SB). The size of stomatal pore is normal at JNU as compared to SB (Figs. 6(c)–6(f)) which is probably due to more stress of air pollution at the industrial site, because of the same reasons the guard cells are seen more damaged at SB site as compared to JNU site. The guard cells and the epidermal cells are seen ruptured and swollen at the abaxial surface (Figs. 6(d) and 6(f)). As seen in Fig. 6(f), the stomata are clogged due to deposition of the particles on the abaxial surface in and around stomata.

Fig. 5. SEM images of Arjun foliar showing dust particles and ruptured epidermal cells (a, b-adaxial surface); dust particles clogged stomata and ruptured the guard cells (c, d, e, f- abaxial surface) with different size of stomatal pores (e, f- abaxial surface) at JNU and SB.


Fig. 6. SEM images of Morus foliar showing dust particles and ruptured epidermal cells (a, b-adaxial surface); dust particles clogged stomata and ruptured the guard cells (c, d, e, f-abaxial surface) with different size of stomatal pores (e, f- abaxial surface) at JNU and SB.

CONCLUSIONS

The foliar dustfall fluxes were almost 2.5 times higher at industrial site than at residential site due to higher emissions of dust from industrial sources, road dust, heavy duty vehicle, construction activities etc. in Sahibabad area. At JNU site, the average dustfall fluxes were recorded as 95 ± 6 mg m–2 d–1 and 108 ± 6 mg m–2 d–1, respectively for Arjun and Morus foliar, respectively. At SB site, the average dustfall fluxes were recorded as 229 ± 12 mg m–2 d–1 and 271 ± 13 mg m–2 d–1 for Arjun and Morus foliar respectively. These fluxes had distinguished variations during different seasons. Apart from local and transported pollution, winter season had the highest fluxes which were probably due to meteorological conditions such as low temperature, high humidity, lower mixing height etc. which favored dust deposition while the lowest fluxes as observed during monsoon season were probably due to the wash out effect of rain which reduced the dust loadings in the atmosphere. The dustfall fluxes were noticed higher on Morus foliar as compared to the Arjun foliar. This is probably due to suitable foliar arrangement and surface characteristics of Morus plant. Morus foliar surface is rough while Arjun foliar is smooth. The rough surface of Morus foliar allows greater adherence of dust particles. At JNU site, both Morus as well as Arjun foliar had the highest fluxes for Ca2+ followed by SO4

2–

and other ions. But at the SB site, SO42– flux was the

highest at Arjun foliar while Ca2+ flux was the highest at Morus foliar following the same order of remaining ions very similar to that at the JNU site. In case of both the plants, the dust deposition had significant impact on biochemical constituents. The levels of chlorophyll, carotenoids and soluble sugar have decreased while the levels of ascorbic acid and proline amino acid which are considered as stress indicators have increased with the increase in dustafall fluxes at both the sites. SEM results of surface morphology also verified that the deposition of industrial and road dust has affected the foliar surface of both the plants particularly damaging the cuticle and epidermal layer at adaxial site, and guard cells and stomatal pores at abaxial site. ACKNOWLEDGEMENT

The authors thank the University Grant Commission (UGC), New Delhi for financial support to conduct this research work. The author also would like to thank the Advance Instrumentation Research Facility (AIRF), JNU, New Delhi for analytical assistance.

SUPPLEMENTARY MATERIALS

Supplementary data associated with this article can be


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Received for review, April 29, 2015 Revised, August 19, 2015

Accepted, September 30, 2015

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