Botanical Studies (2008) 49: 67-72.

*

Corresponding author: Email: shiyi@iae.ac.cn; Tel:

+86-24-83970371; Fax: +86-24-83970436.

INTRODUCTION

In the troposphere, volatile organic compounds (VOCs)

play an important role in a number of chemical processes

including formation/decomposition of ozone and other

oxidants as well as secondary formation of organic aero-

sols and organic acids (Padhy et al., 2005). Emission

sources for these compounds are both anthropogenic and

biogenic. Estimates of the global anthropogenic VOC

emission range is between 56 and 98 Tg C yr

-1

(Holzke et

al., 2006a). In comparison, it is reported that more than

1150 Tg C¡Pyr

-1

of biogenic volatile organic compounds

(BVOCs) has been released into the atmosphere (Simp-

son et al., 1999). The Center of Environment Science of

Peking University has simulated the influence of BVOCs

on ozone and considers that natural sources are more im-

portant than anthropogenic VOCs at present (Yang et al.,

2001). Consequently, study of the emission rate and fac-

tors influencing BVOC emissions in different ecosystems

is important if we are to gauge the effect they have on the

environment.

Methods of sampling and analysis, as well as the source,

distribution, and variations of VOCs have been studied

(Li et al., 2005). Some reports on VOCs have focused on

anthropogenic sources in the urban environment (Holzke

et al., 2006a).

Urban vegetation is often characterized by

the presence of exotic species interspersed with natural

vegetation. The different management (e.g. pruning, fertil-

ization) and the stressful conditions to which urban trees

are subjected (including repeated exposure to soil and air

pollution episodes and the acclimation problems of exotic

species to environmental constraints) may affect BVOC

emission rates (Centritto et al., 2005). Norwak et al. (2000)

investigated the impact of urban trees in Washington, D.C.,

on ozone formation. They found that urban trees reduced

ozone concentrations in cities, but overall ozone concen-

tration in the wider model domain had increased. Thus it

appears that urban tree canopies in some parts of the world

may influence urban ozone chemistry in a significant way.

In addition to their contribution to atmospheric chemistry,

monoterpenes play important ecologic roles as defense

compounds (Fischbach et al., 2000).

The aim of this paper is to study the emission rates,

seasonal variations, patterns, and correlations of volatile

organic compounds from urban Chinese Pine (Pinus tabu-

laeformis Carr.) trees in Shenyang, China.

MATERIALS AND METHODS

The measurements were performed on street trees in

Shenyang (41¢X46¡¦1.29" N, 123¢X26¡¦27.51" E) in northeast-

ern China. Chinese Pine (Pinus tabulaeformis) is a native

dominant conifer species in Shenyang and the surrounding

area. These studied trees were characterized by a canopy

height of 5 m on average, tree age of 30 years, and good

health conditions. Three trees were measured.

Volatile organic compound emissions from urban trees

in Shenyang, China

D.W. LI

1,2

,

Y. SHI

1,

*, X.Y. HE

1

, W. CHEN

1

, and X. CHEN

1

1

Key Laboratory of Terrestrial Ecological Process, Institute of Applied Ecology, Chinese Academy of Sciences, P. O. Box

417, Shenyang 110016, People¡¦s Republic of China

2

Graduate School of the Chinese Academy of Sciences, Beijing 100039, People¡¦s Republic of China

(Received January 26, 2007; Accepted August 8, 2007)

ABSTRACT.

Biogenic emissions of the volatile organic compounds isoprene and monoterpene (BVOCs)

contribute to tropospheric ozone and secondary particle formation and have indirect effects on global climate

change. However, little research has focused on BVOC emissions from urban trees. In this study, the mono-

terpene emissions of Chinese Pine (Pinus tabulaeformis Carr.) have been measured by GC/MS. The emission

rates of £\-pinene, £]-pinene, camphene and limonene reached their maximum 78.55, 0.67, 0.82 and 0.31 £gg g

-1

dw h

-1

(p<0.05), respectively, in August. For £G3-carene, the highest emission rate, about 0.51 £gg g

-1

dw h

-1

,

was observed in June. The dominant monoterpene emitted was £\-pinene. In August and September, this mono-

terpene accounted for more than 97% of the emissions. Correlation analyses revealed significant correlations

among emission rates of £\-pinene, £]-pinene, camphene, and limonene (p<0.01). This may imply that the bio-

synthesis of £\-pinene, £]-pinene, camphene, and limonene were controlled by some common metabolic routes.

Keywords: GC/MS; Isoprene; Monoterpenes; Pinus tabulaeformis Carr.

ECOLOgy

68

Botanical Studies, Vol. 49, 2008

The measurements in 2006 were performed once every

month around the 20th on a clear day in the months from

May to September. On each date, six replicate samples

were collected between 8:00 and 10:00 am.

Transparent plastic bags were used to cover well-

lighted branches or clumps of foliage, and the base of each

bag was carefully closed. Background BVOC emissions

of empty plastic bags were checked and found negligible.

Care was taken to avoid BVOC release due to rough han-

dling, for damaged or crushed foliage usually increases

BVOC emissions remarkably (Karlik et al., 2002).

The samples were collected from inside of the bags on

adsorbent tubes filled with Tenax-TA using a constant-flow

type pump. The flow rates were 100 ml/min,

and the sam-

pling time was 10 min.

After emission sampling, the leaves enclosed in the

bags were removed from the trees, and placed in a drying

oven at 60¢XC for 48 h. The dry weights were used for nor-

malization of BVOC emission rates to unit leaf mass.

Ambient air temperature and illuminance were recorded

inside and outside the branch enclosure while emission

samples were taken during sampling. Temperature was

measured with a digital thermometer (TES-1364, Taiwan).

Illuminance was measured with a digital luminometer

(TES-1330A, Taiwan).

The sampling tubes were thermally desorbed by an

Aero trap desorber (Tekmar 6000, Dohrmann, USA) at

a temperature of 225¢XC for 20 min, and the desorbed

BVOCs were carried by ultra-pure helium gas (99.9999 %)

to a charcoal trap cooled with liquid nitrogen to -165¢XC.

The trap was then thermally desorbed at 240¢XC for 4 min

and BVOCs were transferred to the CryoFocus Module

(CM) at -150¢XC. Finally, the CM was heated rapidly to

225¢XC for sample injection to GC/MSD (HP 5890 with HP

5972 mass selective detector, Hewlett-Packard, Palo Alto,

USA) for detection.

GC-MS analysis of the samples was performed on a

Hewlett Packard 5890 gas chromatograph (carrier gas: He

at 1 ml/min; splitless injection temperature 240¢XC) with

the PONA (50 m ¡Ñ 0.2 mm ¡Ñ 0.5 £gm) column temperature

programmed from 0¢XC for 1 min, followed by a rise of

10¢XC/min until 100¢XC for 1 min, which was then increased

to 150¢XC at a rate of 5¢XC/min, and at last increased to

280¢XC by 12¢XC/min, connected to a 5972 quadrupole-type

mass selective detector with a transfer line temperature of

220¢XC, a source temperature of 180¢XC, a multiplier voltage

of 2.24 Kv, and a scan range of 40-250 amu. The lowest

limit was 7

-12

~40

-12

V/V, the recovery was 88-111%, with

an average of 100.8¡Ó5.6%; and the bias error of precision

was 2-14%, with an average of 6.6%. The blank values

were measured and subtracted.

The mass spectrometer with an electron impact ioniza-

tion source was operated on a selective-ion monitoring

mode. Monitoring ions of m/z 67 were used for quantifica-

tion of isoprene and m/z 93 and 136 for monoterpenes. A

standard VOC mixture (TO-14) containing 37 hydrocarbon

species of 100 ppbv was analyzed once a day for calibra-

tion before the atmospheric samples were processed.

All data were subjected to one-way analysis of variance

(ANOVA) and correlation analysis in the SPSS statistical

package.

RESULTS

Seasonal variations in emission rates

The emission rates of £\-pinene, £]-pinene, camphene,

and limonene reached their maximum 78.55 (df=4 and 25,

F=2.949, p<0.05), 0.67 (df=4 and 25, F=2.165, p<0.05),

0.82 (df=4 and 25, F=3.738, p<0.05), and 0.31 £gg g

-1

dw

h

-1

(df=4 and 25, F=5.167, p<0.05), respectively, in August

(Figure 1). However, for £G3-carene, the highest emis-

sion rate, about 0.51 £gg g

-1

dw h

-1

(df=4 and 25, F=2.269,

p<0.05), was observed in June. Moreover, our study shows

that the isoprene emission rate ranged from 0.01 to 0.39 £gg

g

-1

dw h

-1

(from May to July), and this result approximated

that of Chinese pine in Beijing (Li et al., 1994).

Table 1. The relative abundance (%) of the terpenoid

compounds.

May June July Aug. Sep.

Camphene 1.30 2.67 1.42 1.01 0.41

£G3-carene 1.88 21.14 1.51 0.07 0.37

£]-pinene

6.49 9.96 3.83 0.84 0.94

Isoprene

0.94 2.02 14.50 0.08 0.56

£\-pinene

89.21 62.25 77.89 97.61 97.31

Limonene 0.18 1.96 0.85 0.38 0.42

Table 2. Correlation coefficient (r) among the emission rates of six terpenoid compounds.

£\-Pinene £]-Pinene

£G3-Carene

Camphene

Limonene

Isoprene

£\-Pinene

1

0.952**

0.434

0.997**

0.992**

0.496

£]-Pinene

1

0.675

0.961**

0.981**

0.635

£G3-Carene

1

0.471

0.542

0.522

Camphene

1

0.994**

0.507

Limonene

1

0.557

Isoprene

1

**Is significant at p < 0.01 in ANOVA analysis.

LI et al. ¡X VOC emissions from urban trees

69

BVOC emission pattern

Due to their different sources, the relative abundance

of the monoterpenes and isoprenes vary throughout the

growing season. Table 1 showed that £\-pinene was the

most abundant compound throughout the season,

the

other important terpenoid compounds being £]-pinene,

£G3-carene, limonene, camphene, and isoprene. In August

and September, more than 97% of the compounds were

£\-pinene. However, in June, £G3-carene accounted for

21% of the total terpenoid, and in July isoprene accounted

for near 15% of the total. The other monoterpenes were

emitted in lesser quantities.

Correlation analysis

Correlation analyses of terpenoid compounds (Table 2)

showed that there were significant correlations of £\-pinene

with £]-pinene, camphene, and limonene, and of £]-pinene

with camphene and limonene (p<0.01), respectively.

DISCUSSION

Seasonal variations

in emission rates

The rates of monoterpenes and isoprene emission from

Chinese Pine showed evident seasonal variations, which

were similar to the seasonal dynamics of emission rates

of monoterpenes from Scots pine previously observed in

Sweden (Janson et al., 1999). Hakola et al. (1998) reported

the seasonal variation of emissions from tea-leafed willow

(Salix phylicifolia), aspen (Populus tremula), and silver

birch (Betula pendula). The emissions of willow and aspen

reached the highest values in May and then decreased. The

emission rates in Birch were highest in August and lowest

in June and September. A similar observation was made

on ambient air above a boreal coniferous forest in Finland

(Hakola et al., 2003). However, Kim et al. (2005) reported

that the emission rates from Pinus koraiensis were not sig-

nificantly different in the spring and summer. The isoprene

and monoterpene emissions are mainly correlated to the

air temperature and solar radiation (Simon et al., 2005).

Because of the higher temperature (31¢XC) and strong in-

cident solar radiation in August in Shenyang (>20000 lx),

the emission rates of monoterpenes were higher than those

of other months. Moreover, previous studies observed an

emission reduction in summer and fall that was correlated

to the lower activity of some terpene synthases (Lehning

et al., 1999). This indicates that the emissions are not only

dependent on exogenous but also on endogenous param-

eters such as the developmental state of the investigated

branches (Holzke et al., 2006a). This may explain the

results reported here concerning seasonal changes in iso-

prene and monoterpene emission rates.

¡ö

Figure 1. Emis sion rates of isoprene and monoterpene from

pine (Pinus tabulaeformis Carr.). Data shown are the means and

standard deviation of six replicates (£gg g

-1

dw h

-1

).

70

Botanical Studies, Vol. 49, 2008

BVOC emission pattern

A number of Pinus nigra populations have been re-

ported to emit primarily monoterepenes (Bojovic et al.,

2005). The pattern of volatiles reported here is similar to

that found in other studies, where £\-pinene was also found

to be the main constituent of pine needle volatiles (Bai et

al., 1994; Wang et al., 2003). Gao et al. (2005) quantified

monoterpene species emitted from the pine needles by

GC-MS and found that the composition ratios for mono-

terpenes differed significantly among tree species like P.

tabulaeformis, P. bungeana, S. chinensis, and S. japonica,

over the observation period. Our results are also in agree-

ment with observations by Holzke et al. (2006b) on Scots

pine in field studies. Janson and De Serves (2001) reported

that £\-pinene and £G3-carene were the most abundant com-

pounds in the emissions of P. sylvestris. These results are

different from VOC flux measurements carried out above

a boreal coniferous forest in June 1996. The most abun-

dant compounds found above this canopy were isoprene

and £\-pinene (Hakola et al., 2003). Staudt et al. (2000)

revealed large seasonal changes in both the quantity and

quality of the monoterpene emissions from Pinus pinea,

and significant monoterpene emissions had been reported

from Salix phylicifolia and Populus tremula soon after

bud-break and prior to the beginning of the isoprene emis-

sions (Hakola et al., 1998).

Correlation analysis

Plants have an enormous capacity to synthesize huge

amounts of diverse isoprenoids, particularly via the com-

bination of the isoprenoid biosynthetic route and other

secondary metabolic pathways. Zeng and Hu (1992) indi-

cated that the synthesis of monoterpenes was controlled

by different genes, so the correlations were not always

significant among various monoterpenes. However, the

good correlations in our work suggested that the synthe-

sis of £\-pinene, £]-pinene, camphene and limonene were

controlled by some common gene. The positive correla-

tion (r=0.95) found between £\-pinene and £]-pinene was

in agreement with the result reported by Hiltunen and

Laakso (1995). It has been shown with Pinus contorta that

£\-pinene can actually be produced by several enzymes

(Savage et al., 1995). If in a group of tree species, sev-

eral enzymes were to produce the same constituent, one

would probably find complex correlations for £\-pinene,

£]-pinene, camphene, and limonene. The strong correla-

tion of £\-pinene and camphene was not specific for Pinus

tabulaeformis Carr., as this has also been found in Norway

spruce (Sjodin et al., 2000). The significant correlation

between £\-pinene and camphene might imply a common

precursor to camphene and £\-pinene. Such a precursor has

been suggested by Wise and Croteau (1999) although Hil-

tunen and Laakso (1995) found no significant relationship

between £\-pinene and camphene emissions. More complex

relations were found among monoterpene species since the

correlation coefficients among pine species showed great

variation (Faldt et al., 2001).

To sum up, the dominant monoterpene emitted was

£\-pinene, and its emission rates reached a maximum of

78.55 £gg g

-1

dw h

-1

(p<0.05) in August. BVOC can en-

hance O

3

and other oxidant levels, especially in locations

rich in nitrogen oxides. VOC is held in air for several

hours, but the influence on urban ozone chemistry should

not be neglected.

Acknowledgments. This research was financially sup-

ported by the National Natural Science Foundation of Chi-

na (Key Program

90411019). The authors wish to express

their appreciation to Prof. Dali Tao, Institute of Applied

Ecology, Chinese Academy of Sciences, Shenyang, China,

for his helpful suggestions and constructive review of this

manuscript.

LITERATURE CITED

Bai, Y.H., J.L. Li, and B.X. Zhang. 1994. The qualitative deter-

mination of hydrocarbon emitted from woods and vegeta-

tions over Beijing area. Res. Environ. Sci. 7(2): 49-54.

Bojovic, S., M. Jurc, D. Drazic, P. Pavlovic, M. Mitrovic, L.

Djurdjevic, R.S. Dodd, Z. Afzal-Rafii, and M. Barbero.

2005. Origin identification of Pinus nigra populations in

southwestern Europe using terpene composition variations.

Trees-Struct. Func. 19: 531-538.

Centritto, M., S.R. Liu, and F. Loreto. 2005. Biogenic emission

of volatile organic compounds by urban forests. Chin. Fore.

Sci. Tech. 4: 20-26.

Faldt, J., K. Sjodin, M. Persson, I. Valterova, and A.-K. Borg-

Karlson. 2001. Correlations between selected monoterpene

hydrocarbons in the xylem of six Pinus (Pinaceae) species.

Chemoecol. 11: 97-106.

Fischbach, R.J., I. Zimmer, R. Steinbrecher, A. Pfichner, and J.P.

Schnitzler. 2000. Monoterpene synthase activities in leaves

of Picea abies (L.) Karst. and Quercus ilex L. Phytochemis-

try 54: 257-265.

Gao, Y., Y.J. Jin, H.D. Li, and H.J. Chen. 2005. Volatile Organic

Compounds and their Roles in Bacteriostasis in Five Coni-

fer Species. J. Integrat. Plant Biol. 47: 499-507.

Hakola, H., J. Rinne, and T. Laurila. 1998. The hydrocarbon

emission rates of tea-leafed willow (Salix phylicifolia), sil-

ver Birch (Betula pendula) and European aspen (Populus

tremula). Atmos. Environ. 32(10): 1825-1833.

Hakola, H., V. Tarvainen, T. Laurila, V. Hiltunen, H. Hellen, and

P. Keronen. 2003. Seasonal variation of VOC concentra-

tions above a boreal coniferous forest. Atm os. Environ.

37(12): 1623-1634.

Hiltunen, R. and I. Laakso. 1995. Gas chromatographic analysis

and biogenic relationships of monoterpene enantiomers

in Scots pine and juniper needle oils. Flavour Fragr J. 10:

203-210.

Holzke, C., T. Hoffmann, L. Jaeger, R. Koppmann, and W. Zim-

mer. 2006a. Diurnal and seasonal variation of monoterpene

and sesquiterpene emissions from Scots pine (Pinus sylves-

LI et al. ¡X VOC emissions from urban trees

71

tris L.). Atmos. Environ. 40: 3174-3185.

Holzke, C., T. Dindorf, J. Kesselmeier, U. Kuhn, and R.

Koppmann. 2006b. Terpene emissions from European beech

(Fagus sylvatica L.): Pattern and emission behaviour within

two vegetation periods. J. Atmos. Chem. 55: 81-102.

Janson, R.W., C. De Serves, and R. Romero. 1999. Emission of

isoprene and carbonyl compounds from a boreal forest and

wetland in Sweden. Agric. For. Meteorol. 98-99: 671-681.

Janson, R. and C. De Serves. 2001. Acetone and monoterpene

emissions

.

from the boreal forest in northern Europe. At-

mos. Environ. 35: 4629-4637.

Karlik, J.F., A.H. Mckay, J.M. Welch, and A.M. Winer. 2002. A

survey of California plant species with a portable VOC ana-

lyzer for biogenic emission inventory development. Atmos.

Environ. 36: 5221-5230.

Kim, J.C., K.J. Kim, D.S. Kim, and J.S. Han. 2005. Seasonal

variations of monoterpene emissions from coniferous trees

of different ages in Korea. Chemosphere 59: 1685-96.

Lehning, A., I. Zimmer, R. Steinbrecher, N. Bruggemann, and

J.P. Schnitzler. 1999. Isoprene synthase activity and its rela-

tion to isoprene emission in Quercus robur L. leaves. Plant

Cell Environ. 22: 495-504.

Li, J.L., Y.H. Bai, and J.X. Hu. 1994. Diurnal variation in the

conce ntration of terpe ne s a nd i t¡¦s e mis si on ra te me a-

surements from Chinese pine. Chin Environ S ci. 14(3):

165-169.

Li, D.W., Y. Shi, and X.Y. He. 2005. Research advances in the

effects of elevated atmospheric carbon dioxide and ozone

on biogenic VOCs emission. Chin J. Appl. Ecol. 16(12):

2454-2458.

Norwak, D.J., K.L. Civerolo, S.T. Rao, G. Sistla, C.J. Luley, and

D.E. Crane. 2000. A modeling study of the impact of urban

trees on ozone. Atmos. Environ. 34: 1601-1613.

Padhy, P.K. and C.K. Varshney. 2005. Emission of volatile or-

ganic compounds (VOC) from tropical plant species in In-

dia. Chemosphere 59(11): 1643-1653.

Savage, T.J., H. Ichii, S.D. Hume, D.B. Little, and R. Croteau.

1995. Monoterpene synthases from gymnosperms and an-

giosperms: stereospecificity and inactivation by cysteinyl-

and arginyl-directed modifying reagents . Arch Biochem

Biophys. 320: 257-265.

Simon, V., L. Dumergues, P. Bouchou, L. Torres, and A. Lopez.

2005. Isoprene emission rates and fluxes measured above a

Mediterranean oak (Quercus pubescens) forest. Atmos. Res.

74: 49-63.

Simpson, D., W. Winiwarter, and G. Borjesson. 1999. Inventory-

ing emissions from nature in Europe. J. Geoph Res. 104:

8113-8152.

Sjodin, K., M. P erss on, J. F aldt, I. Ekberg, and A.K. Borg-

Karlson. 2000. Occurrence and correlations of monoterpene

hydrocarbon enantiomers in Pinus sylvestris and Picea ab-

ies. J. Chem. Ecol. 26: 1701-1720.

Staudt, M., N. Bertin, B. Frenzel, and G. Seufert. 2000. Seasonal

variations in amount and com position of monoterpenes

emitted by young Pinus pinea trees - implications for emis-

sion modeling. J. Atmos. Chem. 35: 77-99.

Wang, Z.H., Y.H. Bai, and S.Y. Zhang. 2003. A biogenic volatile

organic compounds emission inventory for Beijing. Atmos.

Environ. 37: 3771-3782.

Wise, M.L. and R. Croteau. 1999. Monoterpene biosynthesis [C].

In J. Faldt, K. Sjodin, M. Persson, I. Valterova, and A.-K.

Borg-Karlson. 2001. Correlations between selected mono-

terpene hydrocarbons in the xylem of six Pinus (Pinaceae)

species. Chemoecol. 11: 97-106.

Yang, D.Q., Y.H. Bai, J.L. Li, N.M. Pan, K.H. Yu, L. Tang, L.X.

Peng, and H. Su. 2001. A study on hydrocarbon compounds

emitted from natural forest sources in Pearl River Delta.

Guangzhou Environ. Sci. 16(3): 34-38.

Zeng, Y.H. and X.J. Hu. 1992. Geographic variation in compo-

nents of monoterpene and sesquiterpene in Pinus armandi.

Sci. Silvae Sin. 28: 161-166.

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