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Published online 1 May 2008
Published in J Environ Qual 37:865-870 (2008)
DOI: 10.2134/jeq2006.0511
© 2008 American Society of Agronomy, Crop Science Society of America, and Soil Science Society of America
677 S. Segoe Rd., Madison, WI 53711 USA
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TECHNICAL REPORTS

Plant and Environment Interactions

Seasonal Variation of Leaf Dust Accumulation and Pigment Content in Plant Species Exposed to Urban Particulates Pollution

Santosh Kumar Prajapati and B. D. Tripathi*

Pollution Ecology Research Lab., Dep. of Botany, Banaras Hindu Univ., Varanasi, 221005, India

* Corresponding author (sntshprjpt{at}rediffmail.com).

Received for publication November 23, 2006.

   ABSTRACT
TOP
 NOTES
 ABSTRACT
INTRODUCTION
 Experimental
 Results
 Discussion
 Conclusions
 REFERENCES
 
To assess the dust interception efficiency of some selected tree species and impact of dust deposition on chlorophyll and ascorbic acid content of leaves the present study was undertaken. The plant species selected for the study were Ficus religiosa, Ficus benghalensis, Mangifera indica, Dalbergia sissoo, Psidium guajava, and Dendrocalamus strictus. It was found that all species have maximum dust deposition in the winter season followed by summer and rainy seasons. Chlorophyll content decreased and ascorbic acid content increased with the increase of dust deposition. There was significant negative and positive correlation between dust deposition and chlorophyll and ascorbic acid content, respectively. Maximum dust interception was done by Dalbergia sisso and least by Dendrocalamus strictus. Thus plants can be used to intercept dust particles which are of potential health hazards to humans.


   INTRODUCTION
TOP
 NOTES
 ABSTRACT
 INTRODUCTION
Experimental
 Results
 Discussion
 Conclusions
 REFERENCES
 
PARTICULATE matter (PM) has been widely studied in recent years and the United Nations estimated that over 600 million people in urban areas worldwide were exposed to dangerous levels of traffic-generated air pollutants (Cacciola et al., 2002). Atmospheric PM with aerodynamic diameter <10 µm (PM10) or <2.5 µm (PM2.5) are of considerable concern for public health (NEPC, 1998; Schwartzet al., 1996; Beckett et al., 1998; Borja-Aburto et al., 1998). Vehicle-derived particulates were monitored using magnetic properties of leaf dust (the magnetic minerals derived from vehicular combustion and street trams which are mainly maghemite and metallic iron and get deposited on plant leaves, imparting magnetic character to leaves) and it has been established that they are particularly dangerous to human health (Prajapati et al., 2006). Indian cities are facing serious problems of airborne particulate matter (Agarwal et al., 1999). Agricultural activities and vehicular traffic may generate local dust concentrations close to the source that exceed environmental guideline values (Leys et al., 1998; Manins et al., 2001). The deposition of gaseous pollutants and particulate matter and their interception are greater in woodlands than in shorter vegetation (Fowler et al., 1989; Bunzl et al., 1989). It has been established that leaves and exposed parts of a plant generally act as persistent absorbers in a polluted environment (Samal and Santra, 2002). Presence of trees in the urban environment can thus improve air quality through enhancing the uptake of gases and particles (McPherson et al., 1994; Beckett et al., 1998, 2000; Freer-Smith et al., 2005) near roadways (Smith 1971) and in agricultural situations (Raupach et al., 2001). Trees act as a sink for air pollutants and thus reduce their concentration in the air. Dust interception capacity of plants depends on their surface geometry, phyllotaxy, and leaf external characteristics such as hairs, cuticle etc., height, and canopy of trees. Removal of pollutants by plants from air is by three means, namely absorption by the leaves, deposition of particulates and aerosols over leaf surfaces, and fallout of particulates on the leeward side of the vegetation because of the slowing of the air movement (Tewari, 1994; Rawat and Banerjee, 1996). Leaf petioles are more efficient particulate impactors than either twigs (stems) or leaf lamina (Ingold, 1971). Green belts also reduce noise pollution (Pal et al., 2000b; Fang and Ling, 2005; Martínez-Sala et al., 2006).

The direct physical effects of mineral dusts on vegetation became apparent only at relatively high surface loads (e.g., >7 g m–2) (Farmer, 1993) as compared with the chemical effects of reactive materials such as cement dust which may become evident at 2 g m–2 (Grantz et al., 2003). Air pollutants damage plants leaves, impair plant growth, and limit primary productivity according to the sensitiveness of the plants to pollutants (Ulrich, 1984). The most noticeable damage occurs in the leaves. Limestone and cement dusts, with pH values of 9 or higher, may cause direct injury to leaf tissues (Vardaka et al., 1995) or indirect injury through alteration of soil pH (Hope et al., 1991; Auerbach et al., 1997). Damages caused by air pollutants to plants include chlorosis, necrosis, and epinasty (Katiyar and Dubey, 2000). Air particulates affect the overall growth and development of plants according to their physical and chemical nature (Gupta and Ghouse, 1987; Pandey et al., 1999), and morphology and anatomy of the leaves are altered (Gupta and Mishra, 1994; Trivedi and Singh, 1995; Somashekar et al., 1999; Singh and Sthapak, 1999; Farooq et al., 2000; Pal et al., 2000a; Shrivastava and Joshi, 2002; Garg et al., 2000). Surface dust deposits may alter the optical properties of leaves, particularly the surface reflectance in the visible and short wave infrared radiation range (Eller, 1977; Hope et al., 1991; Keller and Lamprecht, 1995). In response to these adverse effects various biochemical changes also occur such as decreased chlorophyll content and increased ascorbic acid content (ascorbic acid is an antioxidant and thus scavenges the oxidants of leaves) (Balsberg-Pahlsson, 1989; Pandey and Sinha, 1991; Krishnamurthy et al., 1994; Senapati and Misra, 1996; Joshi et al., 1997; Pandey et al., 1999; Mandal and Mukherji, 2000; Garty et al., 2001; Mashitha and Pise, 2001; Gavali et al., 2002). These responses ultimately accelerate the process of senescence (Lee et al., 1981; Kohert et al., 1986).

The present work was planned to assess dust deposition on leaves of some selected plants growing along the side of a city road having high traffic density, to observe the variation in dust deposition on leaves with respect to species and seasons and observe seasonal variation in leaf pigments, i.e., "total chlorophyll" and "ascorbic acid" in the plant species.


   Experimental
TOP
 NOTES
 ABSTRACT
 INTRODUCTION
 Experimental
Results
 Discussion
 Conclusions
 REFERENCES
 
Study Area
Varanasi is a holy city and also one of the oldest cities in the country "(82°15' E to 83°30' and 24°35' to 25°30' N, India). The city has more than one million people and thus a sizeable volume of traffic exists. The study site for sampling dust and leaves was selected near the center of the city on an important city road with high traffic density.

Sampling of Dust and Leaves
This study was conducted during 2005–2006 in three seasons, i.e., winter (December), summer (May), and rainy (August). Six species of roadside plants growing on both sides of the road were selected. A total of six plants, with one individual from each species, were taken into account. These plants were common and thus selected for the study. The selected plant species and their characteristics, including leaf characteristics, are given in Table 1 . From each plant species nine young leaves were selected for the study of different parameters. The upper surface of all these leaves was cleaned using a fine brush and leaves marked for identification. All the leaves were left for 24 h to allow dust to accumulate on their surface. After 24 h the surface of all these previously selected leaves were cleaned using a fine brush and the dust was collected on pre-weighed tracing paper with utmost care. After this leaves were cut from the petiole, kept in an icebox, and brought to the laboratory for determination of chlorophyll and ascorbic acid content. The individual leaf area (m2) was calculated by tracing out the leaves on graph paper. The samples were weighed using an electronic balance and the amount of dust was calculated using the equation W = (w2 – w1)/a, where W is dust content (g m–2), w1 is initial weight of tracing paper, w2 is final weight of tracing paper with dust, and a is total area of the leaf (m2).


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  		Table 1. Characteristics of selected plants at study site with their leaf characteristics.

 
Biochemical Analysis
Photosynthetic Pigments
A 0.5 g fresh leaf sample was crushed in 0.025 L 80% acetone (acetone/water, 4:1 v/v). Tightly plugged flasks were refrigerated for 24 h. Finally, volume was maintained at 0.040 L by 80% acetone and a pinch of MgCO3 to buffer the extracting medium. Extraction was performed in the dark to avoid photooxidation of pigments. Extract was filtered and centrifuged at 314.1 rads–1 for 15 min. Optical densities of the solution were measured at 645 and 663 nm wavelengths. Pigment content was computed by the following formulae given by Maclachlan and Zalic (1963) for chlorophyll ‘a’ and ‘b’.

Formula

Formula

Ascorbic Acid
Ascorbic acid content of leaf sample was determined with the help of a spectrophotometer. 5 g of fresh leaf sample was homogenized in 0.020 L extracting solution, prepared by dissolving 5 g oxalic acid and 0.75 g sodium salt of EDTA in 0.1 L distilled water. The homogenized leaf sample was centrifuged for 15 min at 628.2 rads–1. 0.001 L homogenate was mixed thoroughly with 0.005 L Dichlorophenol indophenol (DCPIP) (0.02 g L–1) with constant shaking. Optical density of the pink colored solution was measured at 520 nm (Es). For this reason, one drop of 1% ascorbic acid solution was added to bleach the pink color completely. Then optical density of the turbid solution (Et) was measured at the same wavelength. A calibration curve was plotted using ascorbic acid solution of varying strength (0. 01–0.05 g L–1) Ascorbic acid content was calculated by the formula given by Keller and Schwager (1977).

Formula
where, Eo, Es, and Et are optical densities of blank sample, plant sample, and sample with ascorbic acid, respectively, V = volume of extract, and W = weight of the leaf sample (g).


   Results
TOP
 NOTES
 ABSTRACT
 INTRODUCTION
 Experimental
 Results
Discussion
 Conclusions
 REFERENCES
 
Dust Fall
The seasonal variation in dust accumulation on leaves of different plants under study is presented in Fig. 1 . It is evident from the figure that all plants showed higher dust deposit in winter followed by summer and lowest in rainy season. It is also clear that the seasonal variation in dust deposition is also prominent. It shows Dalbergia sisso to have maximum and Dendrocalamus strictus to have minimum dust accumulation. The trend of dust deposition among the species was D. sisso > M. indica > P. guajava > F. benghalensis > F. religiosa > D. strictus.


Figure 1
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  		Fig. 1. Dust accumulation per day in different plants under study (g m–2 leaf area).

 
Pigment Content
The seasonal variations in leaf pigment content of different plant species under study are presented in Fig. 2–7GoGoGoGoGo . It is evident from the figures that the total chlorophyll content in all the plant species was maximum in the rainy season followed by summer and winter seasons. It is clear that there is significant difference in chlorophyll content between rainy and summer season. The study also clearly shows that there is an increase in ascorbic acid content in leaves with a decrease in chlorophyll content. The concentration of ascorbic acid in plant species were maximum in winter followed by summer and rainy seasons. ANOVA (significant at P < 0.01) showed that there is a significant variation in pigment content among plant species and between seasons for both chlorophyll and ascorbic acid.


Figure 2
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  		Fig. 2. Seasonal variation in leaf pigment content of Ficus religiosa (chlorophyll and ascorbic acid).

 

Figure 3
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  		Fig. 3. Seasonal variation in leaf pigment content of Ficus benghalensis (chlorophyll and ascorbic acid).

 

Figure 4
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  		Fig. 4. Seasonal variation in leaf pigment content of Mangifera indica (chlorophyll and ascorbic acid).

 

Figure 5
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  		Fig. 5. Seasonal variation in leaf pigment content of Dalbergia sisso (chlorophyll and ascorbic acid).

 

Figure 6
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  		Fig. 6. Seasonal variation in leaf pigment content of Psidium guajava (chlorophyll and ascorbic acid).

 

Figure 7
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  		Fig. 7. Seasonal variation in leaf pigment content of Dendrocalamus strictus (chlorophyll and ascorbic acid).

 
The study showed changes in the levels of pigment (total chlorophyll and ascorbic acid) content in the plants exposed to atmospheric dust fall. Chlorophyll content decreased and ascorbic acid content increased with increased dust deposition on leaves. The Pearson correlation coefficient values of dust deposition with total chlorophyll content (r1) and with ascorbic acid content (r2) in all the six plant species are presented in Table 2 . The table clearly shows highly significant negative correlations between dust load and chlorophyll content and highly significant positive correlations between dust load and ascorbic acid content.


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  		Table 2. Correlation of dust load with total chlorophyll content (r1) and with ascorbic acid content (r2) in different plant species.

 

   Discussion
TOP
 NOTES
 ABSTRACT
 INTRODUCTION
 Experimental
 Results
 Discussion
Conclusions
 REFERENCES
 
Dust Fall
The present study shows that there is significant variation in dust accumulation in different plants and in different seasons. Dust interception and its accumulation in different plant species depends on various factors, such as leaf shape and size, orientation, texture, presence/absence of hairs, length of petioles etc., weather conditions and direction and speed of wind and anthropogenic activities. Higher dust accumulation in Dalbergia sissoo may be due to rough leaf surface and small petioles that reduce movement of leaves in wind, while in the case of Mangifera indica and Psidium guajava it may be due to their waxy coating on leaves with slightly folded margin and rough surface with slightly folded margin, respectively. Lower dust accumulation in F. religiosa may be due to long petioles that help the leaves to flutter during wind, and the vertical position of the leaves which prevents dust retention. Lower dust accumulation for D. strictus may be due to the thin lamina of their leaves and vertical position of the leaf. The influence of leaf characteristics on dust accumulation have also been studied (Vora and Bhatnagar, 1986; Somashekar et al., 1999; Garg et al., 2000). The high dust accumulation in the winter season may be due to wet surfaces of leaves which help in capturing dust, with a gentle breeze and foggy condition preventing particulate dispersion. In the rainy season the least dust accumulation is reported because of washing of leaves and settling of particulates due to rain. Despite a high concentration of dust in summer, high wind speed may be the reason for the relatively lower dust accumulation in the summer than in winter.

Pigment Content
Overall growth and development of plants are functions of various environmental factors such as air, water, and soil (Katiyar and Dubey, 2000). The variation in leaf pigment (chlorophyll and ascorbic acid) content in plants is because of these factors. Dust particles might be the cause of inhibition of chlorophyll synthesis since it has various metals and polycyclic hydrocarbons, thus inhibiting the enzyme necessary for synthesizing chlorophyll particles. Dust deposition affects the light available for photosynthesis and blocks the stomatal pore for diffusion of air and thus put stress on plant metabolism (Eller, 1977; Hope et al., 1991; Keller and Lamprecht, 1995; Anthony, 2001). It is evident from the present investigation that both chlorophyll and ascorbic acid content showed different responses to dust. Decrease in total chlorophyll content in the leaves may be due to the alkaline condition created by dissolution of chemicals present in the dust particulates in cell sap which is responsible for chlorophyll degradation. The ascorbic acid content of leaves increases to cope with these stresses since it retards leaf senescence (Garg and Kapoor, 1972). Total chlorophyll content of polluted leaves is lower than that of control leaves and is reported by several researchers (Somashekar et al., 1999; Mandal and Mukherji, 2000; Samal and Santra, 2002).


   Conclusions
TOP
 NOTES
 ABSTRACT
 INTRODUCTION
 Experimental
 Results
 Discussion
 Conclusions
REFERENCES
 
The dust interception capacity of different leaves depends on leaf structure, phyllotaxy, presence/absence of hairs, presence of wax on leaf surface, size of petioles, and canopy structure. Plants with a waxy coating, rough leaf surfaces, and short petioles tend to accumulate more dust than plants with long petioles and smoother leaf surfaces. Dust particles affect leaf biochemical parameters, bringing about some morphological symptoms. The extent of such effects depends on plant tolerance toward dust particles and on the chemical nature of the dust. Decline in pigments may be because of a drop in pigment synthesis due to the shading effect of dust, the alkaline condition caused by dissolution of dust particles in cell sap that may lead to pigment degradation (due to photo bleaching), and/or the inhibition of enzymes essential for biosynthesis of pigments. All these changes exerts stress on plant physiology.


   ACKNOWLEDGMENTS
 
The authors are thankful to Council of Scientific and Industrial Research, New Delhi for financial assistance.


   NOTES
TOP
 NOTES
ABSTRACT
 INTRODUCTION
 Experimental
 Results
 Discussion
 Conclusions
 REFERENCES
 
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   REFERENCES
TOP
 NOTES
 ABSTRACT
 INTRODUCTION
 Experimental
 Results
 Discussion
 Conclusions
 REFERENCES
 





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