Pollution Resistance Characteristics of Street Trees

Jingtian Xu

, Simengyu Li

, Xuesong Zhang

and Ruifang Wang

1,2,* d

College of Agriculture and Forestry, Puer University, Puer, Yunnan Province, 665000, China

Xishuangbanna Tropical Botanical Garden, Chinese Academy of Sciences, Mengla, 666303, China

Keywords: Antipollution, Alee-Tree, Pu 'er Avenue.

Abstract: Garden or urban street construction planting plants with high pollution resistance can not only play a remedial

role in the surrounding environment, such as reducing dust and noise, absorbing toxic gases and substances,

but also beautify the environment and play a role in shade and soil preservation, climate regulation, etc. Three

street trees, Cassia nodosa, Cinnamomum camphora and Spathodea campanulata were selected as the objects,

conductivity, chlorophyll content and plant leaf dust retention were used to reflect the pollution resistance

characteristics of these three plants. The results showed that C. Camphor had the strongest anti-pollution

characteristics, followed by Spathodea Campanulata, and Cassia Nodosa was the weakest. This conclusion

provides theoretical guidance for the selection and utilization of street trees.

1 INTRODUCTION

Accelerated urbanization and increased population,as

well as the using of various non-clean energysources

have led to prominent environmental pollution

problems, which seriously affect the humanliving

environment and the sustainable development of the

future economy(Lan 2017). Anti-pollution plants are

plants that can absorb harmful gases, retain dust, kill

bacteria, attenuate noise, and maintain the balance of

oxygen and carbon dioxide in the atmosphere (Xu

2006). In general anti-pollution plants have great

advantages in environmental pollution prevention,

and compared to artificial treatment, plant regulation

is greener and more in line with the development of

ecological balance.

Some trees are significantly resistant to

atmospheric pollution, and most tree species exhibit

greater pollution resistance in areas with suitable

environmental conditions than in other areas, while

the anti-pollution properties of plants are relatively

reduced when planted in areas that are not adapted.

Thus it can be seen that municipal engineer for each

district should select tree species with pollution

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resistance characteristics that are more suitable for the

area according to the natural environmental

conditions of the locality.

The needs and development of society require us

to continue to discover or breed tree species with

better pollution resistance. Some of the ways we can

take include: discovering and introducing new tree

species with pollution resistance characteristics;

obtaining varieties or types with stronger pollution

resistance characteristics through single plant

selection; and breeding new tree species with pollution

resistance characteristics through hybridization,

mutagenesis, and other breeding means.

There are also some related studies in China, in

which the response of Dianthus superbus L., Iris

tectorum Maxim., Zephyranthes candida (Lindl.)

Herb., Reineckea carnea (Andrews) Kunth and

Sedum sarmentosum Bunge, cadmium and lead was

studied in the selection of anti-pollution garden

plants. The results of the study showed that Dianthus

superbus L. had a significant remediation effect on

cadmium-contaminated soils, Reineckea carnea

(Andrews) Kunth had the best remediation effect on

copper-contaminated soils and Sedum sarmentosum

Bunge had the best remediation effect on lead-

Xu, J., Li, S., Zhang, X. and Wang, R.

Pollution Resistance Characteristics of Street Trees.

DOI: 10.5220/0011369700003444

In Proceedings of the 2nd Conference on Artiﬁcial Intelligence and Healthcare (CAIH 2021), pages 343-347

ISBN: 978-989-758-594-4

343

contaminated soils; in heavy metal-contaminated

soils, Dianthus superbus L. had the best remediation

effect, followed by Sedum sarmentosum Bunge,

Reineckea carnea (Andrews) Kunth and Iris tectorum

Maxim., and the worst was Zephyranthes candida

(Lindl.) Herb (Zhang 2004).

Nowadays, there are a lot of harmful gases, dust

and other pollutants in the atmosphere, and it is urgent

to protect the environment. For different sources of

pollution, choosing suitable anti-pollution tree

species can improve the ecological environment more

effectively (Yang 1983). Anti-pollution plants can

absorb harmful substances in the soil and also purify

the air, which can improve the environment. This

paper investigates and analyses data on the anti-

pollution characteristics of street trees in the urban

area, ranks the anti-pollution ability of anti-pollution

tree species in the area, and advocates planting more

of such anti-pollution plants.

The development of pollution-resistant plants will

not only reduce the burden on the city but also bring

efficient returns to the urban environment. Through

this study, we compare the pollution resistance of

street trees in the urban area of Pu'er City, Yunan

Province, and offer constructive suggestions for

urban garden plant configuration and even garden

development.

2 MATERIALS AND METHODS

2.1 Materials

Three main street trees, Cassia nodosa, Cinnamomum

camphora and Spathodea campanulata, were

selected for the study on Pu'er Avenue in Pu'er City.

2.2 Method

2.2.1 Selection of Survey Sites

One representative trunk road was selected based on

the distribution of trunk roads: Pu'er Avenue.

2.2.2 Sample Collection

On the main road of Pu'er Avenue, three plants with

similar growth and condition, namely C. nodosa, C.

camphora and S. campanulata, were selected. Three

plants of each species were selected and spaced at a

certain distance (4-5m) from each other. Plants of

similar growth, height and tendency were selected

and then fresh leaves of the current year were taken

from the middle of the tree canopy. A sample of 10

leaves was taken from each plant. Samples were

collected in the morning and taken back to the

laboratory in self-sealing bags, well marked.

2.2.3 Relative Conductivity

Leaves were selected from the same parts of each

plant, wiped clean with distilled water on the front

and back of the leaves, the midrib was removed with

scissors and the remaining parts were cut to 5 mm ×

5 mm. 0.2 g was placed in a conical flask and 30 ml

of distilled water was added, placed on a HY-5 dual

purpose shaker and shaken in a rotary mode for 4-5

hours, after which the conductivity L1 was measured

promptly. The conical flask was then corked again,

boiled for 20 min, removed and cooled to room

temperature, after which the conductivity L2 was

measured and repeated 3 times. The conductivity was

measured using a DDS-6700 conductivity meter. The

formula was calculated as follows:

Relative conductivity (%) = (L1/L2)*100%(Gao

2003)

2.2.4 Chlorophyll Content using Acetone

Extraction

The fresh leaves were cut into pieces, weighed 0.5 g

and put into a mortar with 3 ml of pure acetone, a little

calcium carbonate and quartz sand, and ground into a

homogenate, then added with 5 ml of 80% acetone

(v/v), the homogenate was transferred into a

centrifuge tube, centrifuged at 4 000 r/min for 10 min

and the precipitate was discarded, the supernatant was

fixed to 10 ml with 80% acetone. 0.5 ml of the above

pigment extract was taken, diluted with 4 ml of 80%

acetone and transferred into a colorimetric cup. The

absorbance values at 663 nm and 645 nm were

measured using 80% acetone as control. Finally, the

concentrations of chlorophyll a, chlorophyll b and

chlorophyll a+b in the pigment extracts were

calculated separately, and then the content of pigment

per gram of fresh weight leaf was calculated according

to the dilution times respectively (Gao 2003).

2.2.5 Dust Retention

There is no unified standard on the method of

determining the amount of stagnant dust. Jiang

Shengli found that the water washing and filtration

method is more accurate than the wiping method in

his research, and the reference in this paper is the

water washing and filtration method. The specific

operation is as follows.

First, the petiole is removed from the sample

leaves, after which the leaves are soaked in distilled

CAIH 2021 - Conference on Artiﬁcial Intelligence and Healthcare

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water for 2 to 3 hours, while the self-sealing bags are

washed 2 to 3 times, stirring intermittently with a

glass rod during the soaking process and brushing the

leaves lightly with a soft brush.

The leaves were taken out with tweezers to dry

and the beaker of the dip was filtered, the inside of the

flask was washed with distilled water using a dropper

during the extraction process, the filter paper used had

been dried and weighed and was padded with 2 layers

to prevent the dip from penetrating the filter paper.

The filtered filter paper was put into an oven at 65

°C for 24 hours, after which the dried filter paper was

weighed on a balance and the difference between the

two filter papers before and after was the total dust

retention.

3 RESULTS AND ANALYSIS

3.1 Conductivity Analysis

Numerous studies have proven that the first thing

affected in plants subjected to environmental

pollution is the cell membrane, and that the disruption

of the permeability of the cell membrane leads to the

extravasation of electrolytes, mainly potassium ions

in large quantities, thus causing the conductivity of

the leaf extravasate to increase in varying degrees

with the degree of pollution. The greater the degree

of injury to the cell membrane, the more serious the

contamination of the area (Fig.1).

The relative conductivity of C. nodosa is

significantly higher than that of S. campanulata and

C. camphora. The Cassia Nodosa is in a more

polluted environment, and the fact that it has the

largest relative conductivity value means that it is less

resistant to pollution. Conversely, the smallest

relative conductivity of the three plants was that of C.

camphora, reflecting its relatively greater resistance

to pollution than that of C. nodosa, and more than that

of S. campanulata.

3.2 Chlorophyll Content

It has been shown that both chlorophyll a and

chlorophyll b are damaged in the presence of

atmospheric pollution (Gao 2003, Du 2007).

Chlorophyll b plays an auxiliary and protective role,

because chlorophyll b tends to break down when

exposed to environmental pollution, so that in both

types of plants in heavily polluted and less polluted

locations, the more polluted plants will have greater

chlorophyll a/b values (Yang 1983). The combined

results chlorophyll content depends on the pollution

the plants are subjected to. As can be seen from Fig.2

below, there is no significant difference between the

chlorophyll a/b content and the total content of the

three plants selected here (P>0.05) (Fig.2-3).

3.3 Dust Retention

Although there is no significant difference in the

amount of dust retained on the three plants, S.

campanulata has a higher dust retention capacity

(0.12 g/cm2>P>0.10 g/cm2). Possibly on the one

hand, the plant itself, which has sunken veins like S.

campanulata, and a fine-tomentose leaf surface, a

structure that tends to trap dust, and the relatively

smooth, leathery leaf surface of C. camphora, which

has no tufts, and therefore does not tend to trap dust

(Fig.4).

The canopy of plants has the effect of reducing

wind speed, the large particles of dust carried in the

wind will sink and fall onto the leaves of the trees or

the ground, which produces a stagnant dust effect.

Some garden plants have more fluff on the leaf

surface, and some plant leaves also secrete sticky

grease and sap, etc., so that they can absorb large

amounts of dustfall. The dust retention capacity of

tree species varies, with the strongest trees being S.

campanulata, Ficus religiosa L. and Ficus altissima

Blume, and studies have shown that after 12 d of

accumulated dust retention in street trees, S.

campanulata and Ficus religiosa L. have the best dust

retention capacity per unit leaf area, while Terminalia

neotaliala Capuron and Khaya senegalensis (Desr.)

A. Juss. have the worst. The difference in the dust

retention capacity of different species of street trees

was related to the structure of the leaves. The dorsal

and ventral surfaces of the leaves of S. campanulata

and Ficus religiosa L. were densely packed with

hairs, which had a high dust retention capacity,

whereas the leaf surfaces of Terminalia neotaliala

Capuron, Khaya senegalensis (Desr.) A. Juss. and C.

camphora were waxy, and the leaf surfaces were not

deeply veined, had few folds and were smooth, which

had a poor dust retention capacity. In another study,

similar conclusions were made for S. campanulata,

what can be used as a green belt and barrier for

highways, railways, embankments and river slopes as

well as a fast mulching plant for slope protection and

sand sealing due to its advantages of dust retention

and noise reduction, resistance to rough management

and strong soil fixation to improve the environment

efficiently. The difference in dust retention between

the three plants in this study was not significant.

Pollution Resistance Characteristics of Street Trees

345

Figure 1: Relative conductivity (μS/cm).

Figure 2: Chlorophyll a/b content (mg/L).

Figure 3: Total chlorophyll content (mg/L).

Figure 4: Dust retention (g/cm

CN: Cassia nodosa CC: Cinnamomum camphora

SC: Spathodea campanulata

4 DISCUSSION AND

CONCIUSIONS

4.1 Discussion

Plant photosynthesis can be used to judge the degree

of plant growth, and chlorophyll content is an

important indicator of plant photosynthesis, so the

amount of chlorophyll content can be used to measure

the growth of plants, and can even be used as an

important indicator of plant resilience. The

chlorophyll content of plants is used here as an

indicator of their resistance to pollution, with those

with more chlorophyll being more resistant to

pollution. The chlorophyll content of the three plants

in this study was not significantly different.

When plant tissues are exposed to various

unfavourable environmental conditions (e.g. low

temperature, high temperature, salinity and air

pollution), the structure and function of cell

membranes are firstly damaged and the permeability

of cell membranes is increased, mainly by potassium

ion extravasation, resulting in different degrees of

increase in the conductivity of leaf exudates with the

increase in the degree of contamination. At this point,

measuring the conductivity of plant tissue extracts or

exudates and observing changes in cell membrane

permeability can reflect the degree of plant resistance

and injury, where the magnitude of plant conductivity

is chosen to reflect the degree of plant resistance to

contamination. In the conductivity measurements, the

relative conductivity of C. nodosa was greater than

that of S. campanulata than C. camphora. In the

effect of environmental pollution on the physiological

characteristics of plants in Nanyang City, the same

relative conductivity was chosen to reflect plant

resistance to pollution (PANG 2012). After the

environment is polluted the permeability of the cell

membrane is changed and electrolytes are

extravasated, so the greater the relative conductivity

of that plant. The greater the relative conductivity, the

weaker the plant's resistance to pollution, and the

results show that for relative conductivity, C.

camphora is more resistant to pollution than S.

campanulata and C. nodosa.

4.2 Conclusion

C.camphora is more resistant to environmental

pollution, followed by S. campanulata and finally C.

nodosa. C. camphora is suitable for planting in

polluted areas and can also be used to prevent

environmental pollution, while C. nodosa and S.

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346

campanulata can be used as indicators to detect the

level of pollution. This study provides a partial basis

for the planting configuration of urban greenery.

More physiological and ecological characters are

needed in further related researches for analysing the

resistant of steet trees.

ACKNOWLEDGEMENTS

This work was supported by the Outstanding Young

Teacher program (2020GGJS006).

REFERENCES

Du Minhua, Zhang Naiqun, Li Yuying, et al. Effect of

atmospheric pollution on chlorophyll content of urban

greenery[J]. China Environmental Monitoring, 2007,

23(2) : 86- 88.

Gao Houqiang, Zhang Xiaoling. Effect of atmospheric

pollution on the chlorophyll (a/b content ratio of plants

in Hefei[J]. Anhui Agricultural Science, 2003, 31(3):

367- 368.

Lan ZF. Current status and analysis of anti-pollution plant

applications in greening in Zhangzhou City[J]. Flora,

2017, (6) : 68- 70.

PANG Fa-Hu, YANG Jian-Wei, WANG Zheng-De, JI

Rou-Feng. Effects of environmental pollution on the

physiological characteristics of plants in Nanyang

City[J]. Henan Agricultural Science, 2012, 41(10) : 79-

82.

Xu Guifang, Wu Tie Ming, Zhang Chaoyang. Application

of anti-pollution plants in landscaping [J]. Forestry

Survey and Planning, 2006, (02):146- 149.

Yang, Shan-Yuan. On the determination of chlorophyll

content and a:b values and some other issues Plant

Physiology Letters [J]. 1983, (4): 61- 62

Zhang B, Lian FQ, Zhu MY, Xiong ML. Selection of

pollution-resistant garden plants [J]. Journal of Jiangxi

Agricultural University, 2004, (06): 941- 943.

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