Nagoya University
NagoyaUniversity

i4C02

Emission from the Ground Surface in a Japanese Forest

Jun MORIIZUMI, Wei LIUi,ShintaroKAWAI, HiromiYAMAZAWA
and Takao IIDA
Dept.ofEneTgy
lingineeringand Science,
GraduateSchoolofEngineering,
Ndgoya Universi4x
Furo-cho,Chikusa-kuIVdgoya464-8603 JAIMN.
Phone: +81-52-789-5134
Max: +81-52-789-3782.
E-mait:JLmoriizumi@nucl.nagoya-u.ac,ip.

1. Introduction
Forestis oneof the importantinterface
between the atmosphereand the land biosphere,
where

C02 isexchanged through photosyilthesis
and respiration processes.At present, itisthatamounts of produced and absorbed C02 by land biosphere,includingforest,areestimated to be almost balanced,
or the land biosphereplay a role of net sink of atmospheric C02
2001).
This
balanceshouldbe
disturbedbyclimatechanges due to the globalwarming.
(IPCC,
While,the largevariety and non-uniformity of the globalnature make lackof our knowledgeand
uncertainty of predictionsof the change
in the balance.This study aims at quantitatjve
understandingof mechanismof carbon
cycle relating to
respiration,' i.e.,
C02 productions
byrespirationof liveroots and decompositionof organic matter infonsoil. Variationsin effiux andradio- and stable carbon
isotopiccompositionsof C02 emitted
from the ground surface have beenmeasuredin a rnountain forestin Japan.The results was analyzed by using dilferent
depth profilesof carbon
isotopicratios fbrC02 sources
inforestsoil.
atmosphericconsidered`soil

2. Methods
2.1Location and periodof the observation
The observationsite islocatedin a Japaneselarch(Larix
teptolepis)
forestin Inabu,Toyota city,
Aichi Pref.of Japan (30012'N,
137e24'E), shown in Fig.1,where is60 km distantfiromNagoya. It
is in a mountaincoveredwith temperate
deciduous forestsand cool-temperateconiferous
forests,and its elevation is
1010m a.s,1. The larchtrees in the site"`"]
are afforested
about
40 y ago, and standcrVwith 2-3 m intervals.
Their mean heightat the pointof the observation
was 23 m.
In warmseason,the forestfloorwas
coyeredby understory plantswith c.a. 1
m height.
The observation
every
l monthwastaken place from 2004 to 2006
N
exceptforsnow covered seasons.
2.2Measurements
Effluxesof C02 from the ground surface
were
obtainedfrom air samples with c.a.
10 L volume
collected
from a 144L

iillli

acavc

Ocean

Lp-f

eY

Fig.1 The locationof the observation site(Inabu).
iPresentAddress:Shanghai IristitutePhysics,7VteChineseAcademy
ofitipptied
Shanghai,CMNA.

ofSciences,

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itsbottom area of 1.5m × O.2 m, which were closed for 30 min over the
ground surface in the site. Soilgas samples with their volumes of 500 cm3 (in2004) or 100 cm3
2005) were drawn by an air-tight syringe through stainless-steel probes with an inner(afterdiameterof 6 mm, All air samples were stored in aluminum-coatedbags and were broughtplastic
to our laboratory
forsample preparationof isotopic
analysis.
Flux densitiesof C02 from the groundwere
also measuredby small closed chambers (1 L volume)withinfraredC02 gas analyzers
and
LI-840,Li-Cor,Lincoln,USA)NE,
at 5-10 pointsinthe site.At each measured(LI-820
point,anot-disturbed
surfaceandfromsurfaceofmineralsoil,
i.e.,pair of fluxesfrom normal, i.e.,
groundwhere
the litter
layeron itwas removed,weremeasured.
These two surfaces came close within adistanceof 20 cm. For bothof 144 L and 1 L volume chambers, theirbasementshad been set on the
ground of their measilring pointsmore than l month priorto the measurement and sampling.
volumechamberwithSoilsamples (O-1Ocm
depth)and cores with a 5 cm diameter (IO-30
cm depth)were collected tomeasure depthprofiiesof the carbon isotopic
ratios of organic carbon in soil and physicalpropenies(Liuet al., 2006). In thispaper,a soil depthsisexpressed by distancefrom the surface of mineralsoil, i.e.,from the levelwhere the surface litter
layerswere removed. Soilorganic matter wasconverted into
COz by furnace
at 8500C supplied by artificialair,
Each sample

C02 wascryogenically extracted with a vacuum
glasslinefortheirradio- and stable
isotopic ratio measurements
witha Nagoya
UniversityAMS (Tandetron-2,
HVEE, theNetherlands) (Nakamura
et al., 2004) and a stable isotopicratio mass spectrometer, (Finnigan
MPffcarbon252,Thermo FisherScientific,
Waltham, MA, USA), respectiyely,

3. Resultsand Discussions
3.1C02 fluxdensityand
Steep increaseshown
increasing temperaturesoil temperaturein Fig. 2 of C02 fiuxesfrom both normal
in surface

soil wasobservedaround

and

19

OC.

litter-removed
surfaceswith
It would be attributed to'Tr"rmr

O.4

il
T=

.........l･...e...

O,3

I"

nyEo
1@

O.2
lei

×

=e
cuO

o

O.1

i'e

st!Sz

li
,p

e$.i･

[Rl･'

o

O

5

10

15
20
25
SoilTemperatureat 5cm depth10C

Fig.2 The relationship between C02 fluxdensitiesfrom two types of the groundsurfaces and soil
temperature at a depth of 5 cm observedin 2004 and 2005. The solid circle symbols arethose from normal (notdisturbed)surfaces, and the open squares are those from thesurtaces of mineral so", i.e.,
wherethe litter
Iayerson mineral soil were removed.

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C02 Conc./%2
O
-20

l

'cTr)

'i'T.i
Trm-TMT'-'H(a15-"'r l(b)IioERv

2os･"c-i

i

A

L
rF

L.O

4oL

:=1Olco

60
8%

l
2'4

'

68

...1
-30 -25 -20 -15 -10

SoilOrganicCarbon
ContentAtv%..,L-5 -200 -100

a13C1%.

Fig.3 The depthprofilesof content,

concentrations

O

l.

1.LL]

100 200

6i4C/%ostable carbon(a),isotopicratios<b)andradiocarbon isotopicratjos (c)of soil organic carbon
squares),
C02 in soil ajr (soil(solidcircles for 8 Nov, 2004 and open circ]es for 5 Aug. 2005), livingroots (opensquares)
and[ittertr]angle).
(solidactivation of decompositionof organic carbon

in the litter
layerand surface soil. This sensitivity to
C02 fluxfrom forestfloorheatedby patchy solar
radiation shaded by leavesand branchesof forestplants.
The fluxesfrom normal surfaces werelikelyto be largerthan those from litter-remoyedsurfaces.
This discrepancywould
be considered
the contributionof decompositionof the litter
layerto C02 ecaux from the ground surface.
temperature would

result in non-uniformity

3.2Depth profilesof isotopic
ratiosofof soil organiccarbonand soil C02

Forest soil at the observationsite contains
litterlayer(surfaceorganic
layer)with c.a. 7 cm
thicknessfrom the ground surface and mineral soil under it,In the mineral soil, microorganisms,
whichdecompose soil organic matter as nutritive substances,andliveroots of the plantsare
considered to produce C02 by theirrespiration. As shown in Fig.3(a),the content
of soil organiccarbon decreasedsteeply with increasein the depth,in contrast, C02 concentrations
increased.
SeasonallyincreasedC02 concentrations inAug, 2005 would result from activated C02 production
by both of organic decompositionand root respiration under highertemperatures.
As shown in Fig.3(b),the 6i3Cof soil organic carbon slightly increasedwith increaseinthe depth,
in contrast, thatof Iiveroots decrease,
The 6i3Cof C02 in soil air were largerthan both soil organiccarbon and roots, This profile
would
be caused by difference
in diffusion
coefficientsof i2C02
andr3C02, i.e.,
i3C02
theirisotopic
fractionation.
Slowerwould be likely
to remain in deepersoil. This
result suggests that evaluation of contributions of C02 sources in soil to C02 effiux with 6i3C
values needs precise
analysis of transportof two isotopic
gasesin soil.
Soildepthprofile
of radiocarbon
ratio in soil organiccarbonillustrated
inFig.3(c)decreasedwith
soil depth,and showeda spike maximum
at a depth of O-4 cm under the bottom of the organic
layer.This maximum
is attributed to enriched i4C by nuclear weapon
testingin 1950s-60s.The
range of variation in6i4Cof soil organic carbon with the depthwere significantly larger
than that in
6i3C.In contrast, the profile6i4C of soil C02 was nearly constant or rather increaseslightly indeeper layer.It is suggested
that ether soil organiccarbonin shallow layer (including
Iitter)or liveroot in deeperlayer,
or both of them, would
result in this 6i4C profile
of soil C02, since they have
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6i4Cvalues"modern"

are largerthan O %e. Large discrepancyof 6i4Cvalues

which

in soil comparing
to that of 6i3Camong
contributionsof C02 sources
insoil to C02 efflux

the sources suggests

sources

with

among

C02

feasibilityof estimationof

6i4Cvalues.

3.3Contributionof Soil
C02 Sourcesto C02 Flux
By adoptionof

Ai4C values,

6i4Cyalues by the 6i3Cvalues

isnormalized

which

correspondingtoto 6i3C = -25 %o, influenceof unknown

isotopicfractionation
in C02from deep soil to surface can be canceled (Stuiyer
productionfrom itssubstances and C02 diffusion
and Polach,1977).By using
the differencein C02 fluxesmentioned
above
and the differenceinradiocarbon
isotopicratio of substances used for respiration of liveroots and microorganisms,
thecontribution ratios of three C02 sources, i.e.,the decompositionof litter
that
of
soil
organic(R]itter),carbon (Rorg)by microorganisms
and respiration of liyeroots (RToot)
to total C02 efflux were
estimated by mass balanceof i2C02 and i4C02 as following
equation:
the same

subjectmaterials

A14Cres RrootA14Croot+ RorgA14Corg+ Rlitter
A14Clitter,
=

where

A]4Cresisof obseryedRs, assuming

for C02 efflux. The other subscripts of Ai4C correspondto the same as
Rroot+Rorg+Rlitter=1
were(noother C02 sources and sinks exist). The values of Riitter

O,20'''''.','t'}t1',i1`1'I11.-1--:

O,15

DLitter[]LivingRoots
eeOrganic
Carbon27 ±9O/otttttletttt-tttttttt-ttt-ttttttttttpt-tt-tt-tttpn..,,.",-.,,.,..."".""""".u-･'"V{""""""'"'

T=cyEob..'.'''''..''-t-ttt---t---t---t------t--x1-11:1:,t-11･･--･rv"'1'..i..

24 ± 7O/oo.lo

25±-18Ofo
ttttt-ttt'-t-------tt-tttttt-ttttt.tt-tttt...ttttttt>3esoO.05--1tlr-Et'l-t---td----t---L-----;fp--t------t-s---1:."----111--Jb-P--t-li---･-･･-･5oA

ttttttttt± a･6--P/.--････--･･
iS.--------rlr177

t-'--tftt

24Ofo

±

o.oo
23 Jun, 2004

16:OO

9 Sep. 2004

15:OO
Date and Time (Local
Time)

9Nov. 2004

1O:30

Fig,4 The contributions of three C02 sources [n soil to C02 efflux from the ground $urface
estimatedby using Ai4C of C02 efflux and three source$, The value in each column iscorresponding
ratio of the contribution to the total
fluxwith itserror (1a).

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from the meandifferenceof fluxesbetween the 5-10 pairsof the normal and litterin Section3.1,The values of Ai4Cswere giyenfrom observations;
83,2 %o for Ai4Croot(sampled
in O-15 cm depth),85.1 for Ai4Ciitter.
The value of 131.2 %o for
Ai4Corgwas obtained from a laboratory
measurement
fbrC02 emitted from soil at 10 cm depthand
150C.
calculated

removedsurfaces mentioned

The results of the estimation isshowed inFig.4,The contribution of decompositionof soil organiccarbonseems
to depend on the variation in temperature, The air temperature varied 21.0, 24.0 and
10,O and the soil temperature at 5 cm depth varied 19.6, 22.7 and 9.2
at the times of theobservation
on 23 Jun.2004,9 Sep.2004 and 9 Nov. 2004, respectively,
The livingroots producesmorethan halfof C02 fluxin early summer,while
its contribution
decreasesin summer. Thissuggeststhat C02 productionby root respiration showed correlation with seasonal activity of trees'in summer, whengrowthrather than soil temperature. The C02 fromthe organic carbon increase
the soil temperature has maximum.
The litterhas littlecontributions
in winter, when surface
temperature becomes low.These are consistent with meteorological seasonality,
OC

OC

3.4Diurnal variation
Not only seasonalfor 6i4C of C02

in ai4C of C02 efflux

but also wide and complicate diurnalvariations, shown in Fig,5, were observed
form the ground surface. They seem to have positive correlation withtemperature inthe surface soil. Especiallyin November, the largestamplitude
wasobserved,
andthe highest6i4C values were obseryed in daytime.This would be caused by characteristic depthof 6i4Cof soil organic matter, whichshowed a maximum
inshallow soil shown inFig.3(c),profileand that of soil temperature, which typicallyhas the largest
amplitude of temporal variation at thesurface, The temporal yariation in soil temperature isgenerallytransferedto deeperlayerwith delayof itsphaseand decreaseof itsamplitude. In case thatjust
surface soil becomes highertemperatureemitted

14:OO

140
em20042005

120

oas

80e.O

.i i4:oo

15:OO

10:30

4:30

.;..3..P

i6
iSE

i

S

a

9 3o

14: oo1OO+lli-""""""':oo14:OO!

i

O:30

5:30
c-:--oo""e,,o6'i'.m.."....................
'i.........12.:.O.O.......................................................
...........7..:.30..
60ro40:30......14.;.O.Q.."..."................................-..

20o-.1.....-"nv

Apl.MayJun.

Jul. Aug.
Month

Sep.

oct.Nov,

Fig,5 The seasonal and diurnal
variation in 6i4Cof C02 eff]uxfrom the ground surface. The solid
circiesymbols were measured in 2004 and open squares were in 2005. The time notatedc[ose to each symbolin the figure is time of itsobservationtime),and the error bar of(Iocaleach $ymbol corresponds
to 1 a.

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by sunlight but deeper soil remains cold, such as in daytime in winter,productionby surface soil with the highest6i4Cwould be the largest.
The

diurnalvariation

6i4C of efflux

the contribution

C02 means
both dicacultyof
representativeness of the estimation mentioned
in Section3.3 and usefulness for analysis
characteristics of C02 production
in shallow soil, at which soil organic carbon isabundant.
wide

of

of

of C02

seasonalofdetail

4. Conclusion
The observations

in a Japanese Larch fbrestin a mountainof central
Japan showedsomefiux and radiocarbon
isotopic compositionof C02 released from the forest
floor,Steep increase of C02 fiux with increasing
temperature was obtained around 19 eC, and it
suggest the sensitivity of COz productionto temperature of surface soil. The depth profile
of i4Ccharacteristics

about

in soil organic carbon decreasedwith soil depth.Itsspike
O-4 cm under thebottom of the litter
layer,
attributed
to nuclear
ratio

maximum
weapondepthoftestingin l950s-60s.
wasobtainedat a

By using Ai4C values of source substances of C02 in soil, the seasonal contributions of soil organiccarbon,litterandlivingroot respiration to C02 effiux were estimated. The decompositionof
organic
carbonincludinglittershowed
their correlationwithtemperature.While, the root
respiration
seems
to be correlated with plantactivity rather than temperature.
The complicate%o, and they

diurnalvariations in 6i4C of C02 effiux were also found with their ranges of 20-70
seems
to be related to the variationin depth profileof soil temperature.
It isconsideredthat i4C isusefu1 to analyze detailmechanismof soil respiration
rather than simple COz
fluxmeasurement,
especiallyin shallow soil with rich organic carbon.
Acknowtedgment - We would liketo thank Prof.Toshio NAKAMURA,
Ms. Akiko IKEDA and
Ms. Tomoko OTA of Nagoya University
CenterforChronologicalResearchfortheircooperationinthe measurementof the radiocarbon
and stable carbon
isotopicratios, and Prof.Ei-ichi
SHIBidffIA,
Mr. Yasoji IMAIZUMI and Mr. Norio YAMAGUCHIof Nagoya UniversityForestfor theircooperationin operating the observationsite. This study was
supportedby the 21stCentury COE
Science and Engineeringfi;om Basics to Applications"'from Ministry of
program
Education,Culture,Sports,Scienceand Technology, Japan,"Isotope

REIlerences
IPCC (Intergovernmental
Panel on Climate Change) (2eOl)Ctimate Change 2001 7]Fie7Vzird
Assessment Report: Vllorking
Group I; 71heScientijic
Basis, pp. 185-218, Cambridge
University
Press,Cambridge,New York.
Liu,W., Moriizumi,J.,Yamazawa, H. and Iida,T.,(2006)
Depth profilesof radiocarbon
and carbon
isotopic
compositionsof organic matter and C02 in a forestsoil. JournalofEnvironmentag
R(idioactivitly
90,210-223,
Nakamura, T.,Niu, E, Oda, H., Ikeda,A., Minami, M. Ota,T. and Oda, T. (2004)
High precision
i4C measurementswith the HVEE TandetronAMS system
at Nagoya University.
Nuct. instn
and Meth. inPhys,Res.B223-224, 124-129,
Stuiver,
M. and Polach,H, A. (1977)
Reportingof i4C data,Radiocarbon 19,355-363.

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NagoyaUniversity○平成 18 年度 セ ン タ ー 利 用 卒業論文
伊藤 恒 太 1炭 素同位体比 を 用 い た 森林 大 気 中CO2 輸送量定量評価 法 の 開 発 」
工 学科 量 子 エ ネ ル ギ ー 工 学 コ ー ス

工 学部 物理（）○平成 18 年度 セ ン タ ー 利 用 学 術 論文

Liu W ．Moriizumi J ．Yamazawa H ．and IidaT ．（2006）Depth pro創 es of radiocarbon and carbon
isotopiccompositionsof organic matter and CO2 hl a fbrestsoi1 ，Journalof Environmentat＿
Radioacti
り’
90
210
223
．
，
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，

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○ 平 成 18 年 度 セ ン タ ー 利用 学会 発表

醴J ．Moriizumi ，W

Liu H ．Kobayashi S ．Kawai H ．Yamazawa
and
T Iida， Radiocarbon
StableCarbon IsotopicAnalysisf（）r Carbon Cycle Estimation in Forest Canopy andSoilof a Japanese Larch Forest．Joint CACGP ／IGAC 〆WMO Symposium Atmospheric
Chemistry at the Interfaces2006 17 ・23 September 2006 Cape Town South Alieica．
，

，

，

and

，

，

，

W ．Liu，J．Moriizumi H Yamazawa and T Iida Estimating Contributionof Sources of
So 且 CO2 at the Shalower Layer in a Japanese Larch ForestArea ． 7th International
Symposium on Environmental Geochemistry ，24−27 September 2006 Beijing，China ．
，，，

J ．Moriizumi W ．Liu S ．Kawai H ，Yamazawa and T ．Iida 14CO2 Emission from the GroundSu face in a JapaneseForest，InternationalSymposium on RadiometricDatingStudies− Frontier
l4C Dating Methods −of Technical development and Applicationof CHIME
and AMS15− 17January2007 ，Nagoya UniversityJapan．
，

，

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国内
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森 林 土 壌 二 酸 化 炭 素 の 濃度 及 び 同 位 体比 の 時空 間 分 布 ，第 4 回 同 位 体 科 学 研 究 会 ，

2006 ，
3．
8

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名古 屋 大 学

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純 ， 山 澤 弘 実 ， 飯 田 孝 夫 ，森林 土 壌 中 の 有機物 及 び CO2 の 炭 素 同位体 比 によ っ て 土壌炭素 循 環 に つ い て 研 究 ，第 4 回 同 位体科学 研 究会， 2006 ．
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9， 名 古屋 大 学

劉衛 森 林 土 壌 に お け る 微 粒有 機体炭素 （POC ） と 非微 粒 有機 体 炭 素 の 測 定 お よ び 同位体，の 測定に お ける土壌炭 素 の 時空 間分 布 につ い て の 研 究，

第 4 回 同位 体 科 学 研 究 会 ，

2006 ．
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9， 名 古 屋 大 学
飯 田 孝夫 森 林 土 壌 CO2 フ ラ ッ ク スに 対 す る 地 温 の 影 響 日本 原 子 力 学 会 2006 年春 の 年会， 2006 ．
3．
25 −27 ， 茨城

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劉衛 ， 森泉純

山 澤 弘 実 ，飯 田 孝 夫 ，森林 土 壌 二 酸化 炭 素 お よ び 有 機物 の 14C 比放 射能 と炭 素同位 体比 を 用 い た 土 壌 二 酸化炭 素 の 起源 に つ い て の 研究 ，日 本保健 物理 学会第 40 回 研 究
6．
8 −9 ，広 島
発 表会， 2006 ．
森泉

純

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山 澤 弘 実，小林均，河 合伸太 郎 ， 飯 田 孝夫 ，安 定 お よ び 放 射 性 炭 素 同位 体 を 用 い た山林 土壌 中お よ び キ ャ ノ ピー 内 の CO2 生 成 ・吸 収 ・輸 送 成 分 の 定 量 評価 ，大 気
6．
14 −16 ， 山 形
学 会研 究 会 第 12 回 大 気 化 学 討 論 会 ， 2006 ．
河 合 伸太郎， 山澤 弘実， 劉CO2 の 評 価 ， 日 本 原 子 力 学 会衛，森 泉

飯 田 孝夫， 炭素 同 位対比 を 用 い た 森林土壌 呼 吸2006 年秋 の 大 会 2006 ．
9．
27 −29 ， 北 海 道純

以上

名古 屋 大 学 大 学院 工 学研 究 科 エ ネ ル ギ ー 理 工 学 専攻
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