Amelioration of Indian urban air pollution phytotoxicity in Beta vulgaris L. by modifying NPK...

8/14/2019 Amelioration of Indian urban air pollution phytotoxicity in Beta vulgaris L. by modifying NPK nutrients

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Amelioration of Indian urban air pollution phytotoxicity

in Beta vulgaris L. by modifying NPK nutrients

Anoop Singha, S.B. Agrawalb,*, Dheeraj Rathorea

aLaboratory of Air Pollution and Global Climatic Change, Department of Botany,

Allahabad Agricultural Institute - Deemed University, Allahabad 211 007, IndiabDepartment of Botany, Banaras Hindu University, Varanasi 221 005, India

Received 28 November 2003; accepted 17 September 2004

Air pollution caused adverse impact on growth and biomass accumulation of Beta vulgaris L. plants

while higher fertility levels showed reduced yield losses.

Abstract

Air pollution levels are increasing at an alarming rate in many developing countries, including India and causing a potential

threat to crop production. Field experiments were conducted to examine the impact of urban air pollutants on biomass (yield) and

some physiological and biochemical parameters of palak (Beta vulgaris L. var. All Green) that grew from germination to maturity at

seven periurban sites of Allahabad city having different concentrations of air pollutants under different levels of nutrients. The 6 h

daily mean NO2, SO2 and O3 concentrations varied from 2.5 to 42.5, 10.6 to 65 and 3.5 to 30.8 mg m3, respectively at different

locations. Levels of air pollution showed significant negative correlations with photosynthetic pigments, protein, ascorbic acid and

starch contents and catalase activity of palak leaves. A significant negative correlation was found for total biomass with SO2

(rZ

0.92), NO2 (rZ

0.85) and O3 (rZ

0.91) concentrations. The increased fertilizer application (N, P and K) over therecommended dose resulted in a positive response by reducing losses in photosynthetic pigments and total biomass. This study

proved that ambient air pollution of Allahabad city is influencing negatively to the growth and yield of palak plants.

2004 Elsevier Ltd. All rights reserved.

Keywords: Air pollution; Nutrients; Beta vulgaris; Biomass; Yield

1. Introduction

The impacts of air pollution have long been recognized

as major cause of losses in crop production in several

developed countries. However, little attention has beenpaid in developing countries, including India, on poten-

tial impacts of air pollution on growth and productivity.

The Indian national ambient quality data indicate that

emissions of a range of air pollutants are generally

increasing (Agrawal, 1998). The annual average of SO2

concentrations ranged from 10.4 to 39.0 mg m3 ppb in

most parts of the country, while NO2 concentrations were

found between 43.2 and 60.1 mg m3 in metropolitan

cities. Pandey et al. (1992) reported elevated concen-

trations of O3 in Varanasi city, an adjoining district ofAllahabad, where significant negative influence of urban

air pollutants was recorded on a variety of plant species

growing in periurban areas (Agrawal et al., 2003).

Urban air pollution has direct impact on periurban

agriculture due to dispersion of pollutants in all

directions along the wind. During transportation

primary pollutants often form secondary pollutants,

causing greater adverse effects on crop production in

periurban areas. Effects of air pollutants have been

* Corresponding author. Tel.: C91 542 2368156; fax: C91 542

2368174.

E-mail address: [email protected] (S.B. Agrawal).

0269-7491/$ - see front matter 2004 Elsevier Ltd. All rights reserved.

doi:10.1016/j.envpol.2004.09.017

Environmental Pollution 134 (2005) 385395

www.elsevier.com/locate/envpol
mailto:[email protected]://www.elsevier.com/locate/envpolhttp://www.elsevier.com/locate/envpolmailto:[email protected]


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described in terms of foliar injury (Jacobson and Hill,

1970), reduction in photosynthetic pigments (Agrawal

et al., 1982), inhibition of physiological processes (Saxe,

1991), alteration in metabolic functions (Malhotra and

Khan, 1984), enzyme activities (Nandi et al., 1986) and

nutrient uptake and suppression of growth and yield of

agricultural crop plants (Lee, 2000; Verma et al., 2000;Ribas and Penuelas, 2003; Singh et al., 2003).

Use of chemical protectants, such as growth regu-

lators, antioxidants and fertilizers is suggested to be

a short-term solution to reduce the risk of air pollution

damage. Researchers have suggested that application of

mineral nutrients promotes growth, and reduce pollut-

ant induced injury to crops (Ormrod et al., 1973).

Rajput and Agrawal (1994) have found that soybean

plants grown at recommended fertility levels were less

injured by SO2 in comparison to unfertilized crop.

In view of the above, the present investigation was

aimed to suggest an economical and ecofriendly solution

to ambient air pollution induced damage, by altering the

level of mineral nutrients in palak (Beta vulgaris var. All

Green) plants grown at different periurban and urban

sites of Allahabad city (Eastern Uttar Pradesh, India).

2. Materials and methods

The study was performed in the periurban and urban

environment of Allahabad city with a population of 0.85

million located in the eastern Gangetic plains of India

between 24 47#N latitude and 82 21#E longitude and

96 m above mean sea level. During the study period

mean minimum and mean maximum temperatures

ranged between 14.924.3 C and 30.834.6 C, respec-

tively (Table 1). The average relative humidity varied

between 59.8 and 68.4% and wind speed 3.56.8 km h1.

Total precipitation was 164.2 mm during September and

77 mm during October (Table 1). Prominent wind was

westerly. The plant species chosen for this study is

a cheap and popular vegetable and consumed mainly as

a source of iron in the diet. Periurban area of Allahabad

provides 85% of the palak crop consumed in the city.

An experiment was conducted from September to

November 2001 at seven selected sites (viz. AllahabadAgriculture Institute (AAI), Civil lines (CL), Mehdeori

(Mh), Jhunsi (Jh), Bahrana (Bh), Arail (Ar) and

Rajrooppur (RRP)) on the periphery and within the

city of Allahabad. The location of sites and a brief

description of their characteristics are given in Fig. 1

and Table 2. The soil was prepared at one place by

mixing garden soil and farmyard manure in 3:1 ratio

following the normal agronomical practices for unifor-

mity of edaphic conditions. Soil used in the experimenthad pH 7.62, organic carbon 1.64%, N 690 mg 100 g1

soil, P 16.4 mg 100 g1 soil and K 136.2 mg 100 g1.

Palak var. All Green seeds were sown in pots (30 cm

diameter) with four treatments of fertilizers, i.e. without

fertilizer (F0), recommended dose (RD) of N, P and K

(F1), one and half times of RD of N, P and K (F2) and

two times of RD of N, P and K (F3) on September 26,

2001. Recommended doses of NPK were 80, 40,

40 kg ha1, respectively. Nitrogen was given in form of

urea, phosphorus as single super phosphate and

potassium as murate of potash. Half dose of nitrogen

and full dose of phosphorus and potassium were given

as basal dressing and another half of nitrogen as top

dressing. After sowing, 32 pots were transferred to each

site. Pots were placed in unshaded open area receiving

uniform light. Micrometeorological variations in tem-

perature were 0.10.2 C, relative humidity 13%

between the sites. Light intensity was identical at all

sites. The pots were uniformly watered throughout the

experiment in order to maintain constant soil moisture.

For analysis, triplicate random samples of plants from

each treatment of each site were taken at 20 days after

sowing (DAS) and then at regular intervals of 15 days.

Final harvest was done on November 16, 2001 at 50

DAS. For total biomass determination, plants were ovendried at 80 C until the constant weight was obtained

and values were expressed as g plant1. The chlorophyll

content was expressed as mg g1 dry leaf and measured

by using the method of Machlachlan and Zalik (1963).

Carotenoid content was calculated by the method of

Duxbury and Yentsch (1956). Protein analysis in fresh

leaves was performed by using the method of Lowry

et al. (1951). Ascorbic acid in fresh leaves was measured

using the 2,6 dichlorophenol indophenol method of

Keller and Schwager (1977). Catalase and peroxidase

enzyme activities were determined using the methods of

Kar and Mishra (1976) and Britton and Mehley (1955),

respectively. Determination of reducing and total soluble

sugars was performed by reference to glucose standards

using the calorimetric copper method of Somogyi (1952)

and for starch extraction, the method ofMcCready et al.

(1950) was followed.

Air monitoring of gaseous pollutants (SO2, NO2 and

O3) was done with the help of gas samplers kept at

30 cm height from ground at each site by using wet

chemical methods. SO2, NO2 and O3 were measured by

methods of West and Gaeke (1956), Merryman et al.

(1973) and Byers and Saltzman (1958), respectively. No

continuous advanced gas analyzers were available and

Table 1

Meteorological data during the experimental period

Month and

year

Precipitation

(mm)

Temperature ( C) Relative

humidity

(%)

Wind

speed

(km h1)Max. Min.

September,

2001

164.2 34.6 24.3 68.4 6.8

October, 2001 77.0 33.7 20.7 64.6 4.2

November, 2001 0.0 30.8 14.9 59.8 3.5

386 A. Singh et al. / Environmental Pollution 134 (2005) 385395


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gas samplers using wet chemical methods were the best

possible devices with the available resources. Monitor-

ing of pollutants was conducted for 6 h from 10 A.M. to

4 P.M. at weekly intervals at each site, this was the only

option to ensure the safety of the samplers and because

of frequent failure of electricity at various sites as

samplers have a battery back up of only 6 h.

Data were analyzed through three-way and two-way

ANOVA using SPSS software (SPSS Inc., version 10.0)

for assessing the significance of quantitative changes in

different parameters due to ambient air pollution.

3. Results

Results of air monitoring showed that RRP was the

most polluted sites among all experimental sites, where

SO2, NO2 and O3 were recorded in the range of 38.2

65.0, 30.842.5 and 17.030.8 mg m3, respectively. Min-

imum concentrations of SO2, NO2 and O3 ranged

between 10.618.3, 2.512.5 and 3.515.3 mg m3, re-

spectively at site Ar (Table 3). Since all the pollutants

showed minimum concentrations at Ar, this site was

treated as reference site for comparing the levels of

changes in various parameters recorded at other sites

with relatively elevated levels of pollutants.

Total biomass of palak plants was reduced with

increasing pollution load at all sampling intervals

(Fig. 2) Significant negative correlations were found

between total biomass and SO2 (rZ0.92, p! 0.01),

NO2 (rZ0.85, p! 0.05) and O3 (rZ0.91,

p! 0.01) (Table 4). F2 treatment showed a positive

response against air pollutants by increasing the total

biomass. Maximum total biomass (4.7 g plant1) was

Fig. 1. Map of Allahabad city showing location of experimental sites.

387A. Singh et al. / Environmental Pollution 134 (2005) 385395


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recorded at site Ar in F2 treatment, which was 3.9 g

plant1 at F0 treatment. Total biomass was least at site

RRP (3.3 g plant1) under F0 treatment and it increasedto 4.3 g plant1 due to F2 treatment (Fig. 2). Three-way

ANOVA test showed that the variations in total

biomass were significant (p! 0.001) due to plant age,

site, nutrient treatment and their interactions (Table 5).

Total chlorophyll and carotenoid contents in palak

leaves were lower at sites experiencing higher pollution

load (Fig. 3). Maximum total chlorophyll (0.95 mg g1

dry leaf) and carotenoid contents (0.44 mg g1 dry leaf)

were observed at Ar (reference site) and minimum at

RRP, most polluted site (total chlorophyll 0.65 mg g1

dry leaf; carotenoid 0.3 mg g1 dry leaf) 50 DAS under

F2 treatment. Total chlorophyll and carotenoid contents

showed significant negative correlations with SO2(rZ1.0, p! 0.001 and rZ0.99, p! 0.001, respec-

tively), NO2 (rZ0.96, p! 0.001 and rZ0.98, p!

0.001, respectively) and O3 (rZ0.98, p! 0.001 and

rZ0.99, p! 0.001, respectively) (Table 4). ANOVA

test showed that total chlorophyll and carotenoid

contents varied significantly due to plant age, site,

fertilizer treatment and their interactions except for

plant age! site! fertilizer treatment interactions for

carotenoid (Table 5).

Protein and ascorbic acid contents showed significant

negative correlations with individual air pollutants

(Table 4). Protein content increased with the increase

of plant age, while ascorbic acid decreased. Maximum

protein and ascorbic acid contents were observed at 50

and 35 DAS, respectively under F2 treatment at Ar

(Fig. 4). Variations in for protein and ascorbic acid

Table 2

Brief description of experimental sites

Site code Experimental

site

Character of site Distance (km)

and direction

from city centre

AAI Allahabad

Agricultural

Institute

Near bank of river

Yamuna, and national

highway (NH-27); heavytraffic, frequent congestion,

heavy vehicles, medium

density population.

3 km south

Ar Arail Near bank of river

Yamuna, open, small

population

3 km south east

Bh Bahrana City centre, near national

highway (NH-2), heavy

and light motor vehicles,

frequent traffic jams, high

density population.

0 km

Jh Jhunsi Near national highway

(NH-2) periurban area

5 km east south

Mh Mehdeori Near bank of river

Ganga, light vehicles,

periurban area.

5.5 km north

CL Civil lines Commercial area, near

railway station, urban

area

2.5 km

north west

RRP Rajrooppur Near national highway

(NH-2), industries,

railway track, heavy

traffic, high density

population, urban area

6.5 km west

Table 3

Levels of SO2, NO2 and O3 at different sites during experiment

(mg m3)

Gaseous

pollutants

Experimental sites

CL Ar RRP Mh Jh Bh AAI

Sep., 2001

SO2 16.4 10.6 38.2 14.2 16.1 35.4 25.4

NO2 18.6 2.5 30.8 7.5 12.5 27.5 22.2

O3 10.2 3.5 17.0 6.5 8.4 16.4 12.5

Oct., 2001

SO2 40.0 15.3 55.7 23.5 30.2 51.2 44.6

NO2 24.4 8.0 36.6 14.6 20.5 31.9 26.5

O3 14.3 10.3 27.6 10.0 11.7 22.5 18.6

Nov., 2001

SO2 45.7 18.3 65.0 32.5 38.6 60.3 50.4

NO2 27.5 12.5 42.5 18.7 23.6 37.5 31.6

O3 20.4 15.3 30.8 15.9 16.9 26.4 24.0

Totalb

iomass(gplant-1)

Totalbiomass(gplant-1)

Totalbiomass(gplant-1)

0.0

0.1

0.2

0.3

0.4

0.5

0.6

1.0

1.5

2.0

2.5

3.0

3.5

4.0

Experimental sites

AAI CL Mh Jh Bh Ar RRP2.5

3.0

3.5

4.0

4.5

F0 F1 F2 F3 20 DAS

35 DAS

50 DAS

Fig. 2. Effect of air pollution on total biomass of palak plants grown at

different experimental sites with varying fertility levels.



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contents were significant due to plant age, site, fertilizer

treatments (Table 5).

Catalase activity decreased with increasing levels of

air pollutants, while peroxidase activity increased

(Fig. 5). Catalase activity showed significant negative

correlations with SO2 (rZ0.97, p! 0.001), NO2 (rZ

0.95, p! 0.001) and O3 (rZ

0.95, p! 0.001), whileperoxidase activity showed highly significant positive

correlation with SO2 (rZ 0.99, p! 0.001), NO2 (rZ

0.95, p! 0.001) and O3 (rZ 0.98, p! 0.001) (Table 4).

Three-way ANOVA test showed significant variations in

enzyme activities due to plant age, site and fertilizer

treatment and their interactions except for plant

age! site, site! treatment and plant age! site!

treatment interactions for catalase activity (Table 5).

Starch and reducing sugar contents also decreased

with increasing levels of air pollutants while soluble

sugars increased (Fig. 6). Correlation matrix showed

a significant negative correlation between individual

pollutants and starch and reducing sugars and positive

correlation between soluble sugars and pollutants (Table

4). Starch, reducing sugars and soluble sugars varied

significantly due to plant age, site, fertilizer treatment

and their interactions except for plant age! site,

site! treatment and plant age! site! treatment for

starch and soluble sugars (Table 5).

4. Discussion

In many cities of developing countries, the levels of

air pollutants often exceed toxic limits and adverselyaffect human health, vegetation and built cultural

heritage. In urban areas of Allahabad city, high levels

of automobile emissions have elevated the levels of

pollutants to an extent that inhibited the plant growth

and reduced the yield of palak grown in urban and

periurban areas. Urban air quality of Varanasi, an

adjoining city of Allahabad has also been shown to

cause deleterious effects on woody transplants grown in

urban areas (Pandey and Agrawal, 1994) and yield

losses in crop plants grown in periurban areas (Agrawal

et al., 2003).

Air monitoring conducted in Varanasi has shown

that SO2 concentration varied from 14 to 43 mg m3,

NO2 from 16 to 34 mg m3 and O3 from 12 to 42 mg m

3

during the rainy season (JulyOctober) in urban areas

(Pandey et al., 1992). The levels of SO2 and NO2observed in the present study are similar to that of

Pandey et al. (1992), but O3 levels are low. From the

meteorological data it is clear that rains were frequent in

September and October, and hence all the pollutants

including O3 showed lower values during these months.

In November, however, O3 formation increased with

a longer sunshine period. The permissible annual safe

limits set by CPCB, India for 8 hourly SO2 and NO2Table4

Correlationmatrixofgaseouspollutants

andtotalbiomassanddifferentphysiologic

alandbiochemicalcharacteristicsofpalak

plants

Totalbiomass

Totalchlorophyll

Carotenoid

Protein

Ascorbicacid

Catalaseactivity

Peroxidaseactivity

Starch

Solublesugars

Reducingsugars

SO2

0.9

2**

0.9

9***

0.9

9***

0.9

6***

0.9

1**

0.9

7***

0.

99***

0.9

6***

0.9

5***

0.9

9***

NO2

0.8

5*

0.9

6***

0.9

8***

0.8

9**

0.9

5***

0.9

5***

0.

95***

0.9

4**

0.8

2*

0.9

7***

O3

0.9

1**

0.9

8***

0.9

9***

0.9

2**

0.9

5***

0.9

5***

0.

98***

0.9

6***

0.8

7**

0.9

9***

Totalbiomass

1.0

0

0.8

8**

0.8

9**

0.8

5*

0.8

5*

0.8

1*

0.

93**

0.8

5**

0.8

8**

0.9

0**

Totalchlorophyll

1.0

0

0.9

9***

0.9

8***

0.9

4**

0.9

8***

0.

99***

0.9

8***

0.9

3**

0.9

9***

Carotenoid

1.0

0

0.9

4**

0.9

4**

0.9

8***

0.

98***

0.9

6***

0.9

0**

0.9

9***

Protein

1.0

0

0.9

1**

0.9

4**

0.

96***

0.9

7***

0.9

5***

0.9

6***

Ascorbicacid

1.0

0

0.8

8**

0.

95***

0.9

7***

0.8

0*

0.9

4*

Catalaseactivity

1.0

0

0.

94***

0.9

4*

0.9

0**

0.9

8***

Peroxidaseactivity

1.

00

0.9

8***

0.9

4**

0.9

9***

Starch

1.0

0

0.9

0**

0.9

7***

Solublesugars

1.0

0

0.9

1**

Reducingsugars

1.0

0

*p

!

0.0

5,

**p

!

0.0

1,

***p

!

0.0

01and

NSZ

notsignificant.



6/11

concentrations in urban areas are 60mg m3. SO2concentration crossed this limit at two sites (RRP and

Bh) during September. NO2 concentration remained

always below the permissible limit. There is no

permissible safe limit set for O3 in India. Since the

monitoring of pollutants was conducted on 6 hourly

sample collections, the measurement of peak concen-

trations in between cannot be provided. In Varanasi, 2 h

Table 5

Variance ratio for total biomass, photosynthetic pigments, protein, ascorbic acid, enzyme activities and carbohydrate content of palak plants grown

with different fertility levels at various experimental sites

Parameter Plant age (A) Site (B) Treatment (C) A!B A!C B!C A!B!C

Total biomass *** *** *** *** *** *** ***

Total chlorophyll *** *** *** *** *** *** ***

Carotenoid *** *** *** *** *** *** NS

Protein *** *** *** NS *** NS NSAscorbic acid *** *** *** NS *** NS NS

Catalase activity *** *** *** NS *** NS NS

Peroxidase activity *** *** *** * *** ** **

Starch *** *** *** NS *** NS NS

Soluble sugars *** *** *** NS *** NS NS

Reducing sugars *** *** *** ** *** *** ***

*p! 0.05, **p! 0.01, ***p! 0.001 and NSZ not significant.

0.1

0.2

0.3

0.4

0.5

0.6

0.7

Totalchlorophyll(mgg-1dryleaf)

0.2

0.3

0.4

0.5

0.6

0.7

0.8

AAI CL Mh Jh Bh Ar RRP

0.2

0.4

0.6

0.8

1.0

0.0

0.5

0.1

0.2

0.3

0.4

Carotenoid(mgg-1dryleaf)

0.0

0.1

0.2

0.3

0.4

Experimental sites Experimental sites


0.0

0.1

0.2

0.3

0.4

0.5

F0 F1

F2F3

F0F1

F2F3

50 DAS 50 DAS

35 DAS 35 DAS

20 DAS20 DAS

Fig. 3. Effect of air pollution on total chlorophyll and carotenoid contents in leaves of palak plants grown at different experimental sites with varying

fertility levels.



7/11

peak concentrations of SO2 varied from 25 to 95 mg m3,

NO2 from 27 to 61 mg m3 and O3 from 21 to 102 mg m

3

in periurban and urban areas (Pandey et al., 1992). Peak

concentration affects vegetation more adversely than

prolonged exposure to low concentrations (Lefohn and

Jones, 1986). The lower O3 concentration recorded

during the present study may also be ascribed to the

presence of monitoring sites near roads, where O3 is

quickly scavenged.

The adverse effects of urban air pollutants are clearly

evident on physiological and biochemical processes of

palak plants during the present investigation. Photo-

synthetic pigments are fairly sensitive to air pollutants

and their sensitivity may determine the responses of

plants to pollutants. Significant negative correlations

were obtained between air pollutants and total chloro-

phyll and carotenoid contents. Khan and Khan (1994)

reported that combined treatments of O3 and SO2 at all

concentrations had a significant negative effect on the

leaf pigments. Exposure to SO2 causes more reduction in

chlorophyll than carotenoids in wheat plants (Verma

and Agrawal, 2001). El-Khatib (2003) also reported

reductions in chlorophyll and carotenoid contents

35 DAS50 DAS

Experimental sites

AAICL Mh Jh Bh Ar RRP

0.45

0.60

0.75

0.90

Experimental sites

AAICL Mh Jh Bh Ar RRP

Ascorbicacid(mgg-1freshleaf)

0.8

1.2

1.6

50 DAS35 DAS

10

11

12

13

14

15

Protein(mgg-1freshleaf)

Ascorbicacid(mgg-1freshleaf)

Protein(mgg-1freshleaf)

6

7

8

9

10

11

12

13

14

F0 F1F2 F3

Fig. 4. Effect of air pollution on protein and ascorbic acid contents in

leaves of palak plants with varying fertility levels at different

experimental sites.

20

30

40

50

60

70

80

90

Experimental sites


Perox

idaseactiv

ity

(mM

purpuroga

llinformedm

in-1

g-1

fresh

lea

f)

Ca

talaseact

ivity

(mM

H2

O2

decompose

dm

in-1g-1

fresh

lea

f)

0

1

2

3

4

5

F0 F1

F2 F3

Fig. 5. Effect of air pollution on catalase and peroxidase activity in

leaves of palak plants at 50 DAS with varying fertility levels at

different experimental sites.

300

325

350

375

400

175

200

225

250

275

300

Experimental sites


Reducingsugars(mgg-1dryleaf)

Solublesugars(mgg-1dryleaf)

Starc

h(mgg-1dryleaf)

150

200

250

F0 F1 F2 F3

Fig. 6. Effect of air pollution on starch, soluble and reducing sugar

contents in leaves of palak plant at 50 DAS sites with varying fertility

levels at different experimental.



8/11

caused by elevated levels of O3 in five common Egyptian

plant species. Nutrient amendment in various combina-

tions significantly lowered the magnitude of reduction in

chlorophyll as compared to unamended plants (F0treatment). Verma et al. (2000) also reported that

nutrient amendment lowered the magnitude of reduc-

tion in chlorophyll content as compared to unamendedones, confirming the results of the present investigation.

Nitrogen supply is reported to increase the leaf

photosynthesis via the amount of N-containing compo-

nents such as ribulose-1,5 bisphosphate carboxylase/

oxygenase activity (Sivasankar et al., 1993) and also by

chlorophyll formation (Agrawal and Verma, 1997).

However, N and P deficiency reduces the chlorophyll

concentration (Rousseau and Reid, 1990).

Air pollutants are known to induce the degradation of

biologically important molecules such as proteins with

the consequent release of malondialdehyde (Mudd,

1982). Protein content showed significant negative cor-

relations with air pollutants and significant increase in

protein content was observed due to application of

mineral nutrients at all sites. The protein content

depends upon N uptake and plants receiving a higher

dose assimilate more N as compared to the unamended

plants. Plants grown with higher N-supply invest

a greater proportion of carbon in protein (Makino et al.,

1984). Verma and Agrawal (1996) also noticed that N, P

and K amendment in soybean plants significantly

reduced the levels of decrease in protein content of SO2exposed plants.

Ascorbate is a ubiquitous soluble antioxidant in

photosynthetic organisms and the most importantreducing substrate for H2O2 detoxification. It has been

suggested that pollutants produce oxyradicals in plants

(Shimazaki et al., 1980; Sakaki et al., 1983). These

radicals cause widespread damage to membranes and

associated molecules including the chlorophyll pigments

(Sakaki et al., 1983). Several authors have reported that

ascorbic acid can serve as a free radical scavenger

against O3 (van Hove et al., 2001; El-Khatib, 2003). The

reduction in ascorbic acid concentration may be

ascribed to its consumption during removal of cytotoxic

free radicals generated in chain reactions after the

penetration of oxidative pollutants into leaf tissues.

Agrawal and Verma (1997) also observed higher

ascorbic acid content in SO2 exposed plants amended

with fertilizers.

Peroxidase activity showed an increasing trend with

increasing pollution levels at various sites, while catalase

activity decreased. Singh (1998) also found that wheat

plants exposed to O3 showed increase in peroxidase

activity without any specific symptoms of O3 on foliage.

Tingey et al. (1975) stated that stimulation of peroxidase

activity in pollutant-exposed plants might be due to

increased oxidative processes under pollutant stress.

Present observations are in conformity with the earlier

findings of Ranieri et al. (1997), who showed that

catalase activity decreased with increase in SO2 levels

while peroxidase activity increased.

Starch content showed significant negative correla-

tion with individual pollutants. Rennenberg et al. (1996)

suggested that O3 probably interacts with carbon

allocation by inhibiting sucrose export. This causes anaccumulation of starch in leaves, which results in

reduction of photosynthesis and consequently reduces

the level of starch in plants. Nutrient amendment in

different combinations has significantly elevated the

levels of starch in plants. Agrawal and Verma (1997)

also reported reduction in foliar starch content of two

cultivars of wheat treated with SO2 compared with

untreated plants and also found significant increase after

nutrients application.

An increase in total soluble sugars was recorded

with increasing pollution levels while reducing sugars

reduced. The adverse effects of air pollutants are evident

in the form of changes in pool volume of free carbo-

hydrates in palak grown at different sites with various

fertility levels. Katase et al. (1983) reported that SO2-

induced inhibition of photosynthesis in rice reduced the

level of starch in the plants. An increase in concentration

of sugar was associated with reduced starch content,

suggesting increased hydrolysis of polysaccharides into

monosaccharides due to gaseous pollution (Koziol and

Jorden, 1978). Nutrient amendment has significantly

reduced the level of decrease in starch and reducing sugar

contents at various sites, which might be due to increased

photosynthetic rate led by nutrient amendment. Meyer

et al. (2000) reported that O3 caused inhibition ofphotosynthesis, and consequently decline in assimilate

production. Agrawal et al. (2003) have also reported

significant reductions in photosynthetic rate of a number

plant species growing in a periurban area of Varanasi

experiencing higher level of pollutants.

Total biomass accumulation reduced in palak with

increasing pollution load at various sites. This suggests

that air pollutants directly interfere with various

fundamental processes of plants, resulting in lower

biomass accumulation. Ashmore et al. (1987) have also

reported a decline in biomass accumulation in different

plant parts along a gradient of air pollution around

London. Agrawal et al. (2003) have also reported a

negative correlation between ambient air pollutant levels

and biomass accumulation in plants grown in the out-

skirts of Varanasi city experiencing similar climatic

conditions. Verma et al. (2000) reported that 390 mg m3

SO2 treatment for 4 h daily for 5 days week1 for 8

weeks resulted in a significant reduction in biomass

accumulation and productivity in wheat plants were due

to the integrated result of effects on a range of bio-

chemical, physiological and metabolic activities in

plants. The joint action of O3 and SO2 caused significant

suppression in dry matter of tomato shoot and root at



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all concentrations (Khan and Khan, 1994). McKee et al.

(1997) also reported that elevated O3 caused a 15%

decline in total biomass accumulation in wheat plants.

Fertilizer amendment has a significant effect on plant

response to air pollutants. Agrawal and Verma (1997)

reported that plant height and total biomass reduced

significantly in SO2 treated plants, except those grownusing recommended and twice recommended N, P and

K applications. In the present investigation, F2 treat-

ment showed the most positive impact on biomass

accumulation and photosynthetic pigments by decreas-

ing the negative impact of air pollutants. The percent

reduction in total biomass at 50 DAS was 15.5 and

9.5%, respectively at RRP site in nutrient unamended

and amended plants as compared to the same growing at

Ar site experiencing lowest levels of air pollutants. The

double recommended dose of nutrients showed maxi-

mum percent reduction in total biomass (29% at RRP

site compared to Ar site) suggesting that this dose is

supra optimal and caused negative influence on the

plants. Application of nutrients higher than the demand

has been shown to reduce the positive effects of

fertilizers (Agrawal and Verma, 1997; Verma et al.,

2000). Recently, Singh et al. (2003) also revealed that air

pollutants suppressed the growth and yield of wheat

plants grown at various urban and periurban sites of

Allahabad but fertilizer amendment higher than the

recommended dose resulted in a positive response by

increasing the total biomass, weight of 1000 seeds and

yield.

The supply of macro nutrients N, P and K increased

the total biomass in palak by increasing the levels ofphotosynthetic pigments, antioxidative property and

metabolites in foliar tissue, which have further reduced

the magnitude of reduction in biomass due to air

pollutants compared to unfertilized plants. Coleman

et al. (1989) have suggested that plants growing in

nutrient poor conditions may be more sensitive to air

pollution with respect to changes in carbon gain. N

limitation has been shown to decrease chlorophyll and

protein contents, RuBP carboxylase activity and in-

crease the mesophyll resistance, which all limit CO2fixation (Osman and Milthorpe, 1971). High P avail-

ability is found to increase the rate of photosynthesis

(Rousseau and Reid, 1990). K fertilization is also

beneficial due to its role in stomatal opening, photosyn-

thesis, protein synthesis and osmotic and pH regulation

(Wyn Jones and Pollard, 1983).

5. Conclusions

The data obtained in the present investigation suggest

that both air pollutants and nutrient deficiency have

caused adverse impact on various physiological and

biochemical processes and total biomass accumulation

of palak plants grown at sites experiencing elevated

pollutant concentrations. Increasing pollution load also

deteriorated the nutritive quality of palak plants, as

protein and carbohydrate contents were decreased. One

and half times of recommended dose of NPK was most

efficient in reducing the adverse effects of air pollutants

on palak plants. The present investigation also suggeststhat urban air quality of Allahabad city is unfavourable

for vegetable production in urban and periurban areas.

Though the concentrations of individual pollutants were

not very high except SO2, the levels of reductions were

fairly significant. This clearly shows that pollutants in

combination may have acted synergistically in causing

greater adverse impact. Low concentrations of pollu-

tants have been shown to increase the stomatal

conductance thus facilitating the pollutant uptake and

consequently greater negative response. Palak plants

seem to be fairly sensitive to air pollutants under

ambient conditions. More large-scale studies are,

however, required to ascertain the potential for use of

this plant as a biomonitor of air pollution.

Acknowledgements

Authors wish to express sincere thanks to Prof. R.B.

Lal, Vice Chancellor, Allahabad Agricultural Institute -

DU and Prof. P.W. Ramteke, Director (Research) for

providing laboratory facilities and encouragements and

to C.S.I.R. (New Delhi) for providing financial support.

Authors are also grateful to Professor Madhoolika

Agrawal (B.H.U.) and to anonymous reviewers forcomments and fruitful suggestions.

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