Directory UMM :Data Elmu:jurnal:S:Soil Biology And Chemistry:Vol32.Issue6.Jun2000:
Soil Biology & Biochemistry 32 (2000) 769±777
www.elsevier.com/locate/soilbio
Methane oxidation in Japanese forest soils
Shigehiro Ishizuka*, Tadashi Sakata, Kazuhiro Ishizuka
Forest Environment Division, Forestry and Forest Products Research Institute, P.O. Box 16, Tsukuba Norin Kenkyu Danchi-nai, Ibaraki 305-8687,
Japan
Accepted 17 October 1999
Abstract
To evaluate the CH4 uptake rate in Japanese deciduous and coniferous evergreen forest soils, the CH4 ¯ux and CH4
concentration in soil gas were measured at seven sites in central Japan. The CH4 uptake potential was calculated from
incubation of soil cores. The CH4 ¯uxes at all sites were negative (uptake by the soils) at every sampling time. The CH4 uptake
rate was very high (7.6 mg CH4 mÿ2 dÿ1) in one deciduous forest soil. Fluxes were highly correlated to the air temperature
except a coniferous forest site. The most active layer of CH4 uptake in each plot diered with site: subsurface (10±15 cm) at two
coniferous forest sites and topsoil (0±5 cm) at the other ®ve sites. The potential of the subsurface layer to oxidize CH4 made a
substantial contribution to soil CH4 uptake mechanisms, especially when the topsoil had a low ability to oxidize CH4. Methane
uptake rates were nine times higher than those of previous studies. The soil CH4 uptake rate on a global scale may be
underestimated. 7 2000 Elsevier Science Ltd. All rights reserved.
Keywords: Methane ¯ux; Forest soils; Methane oxidation; Global methane uptake rate
1. Introduction
Methane (CH4) is a greenhouse gas with strong
absorption bands in the infrared region, and currently
contributes 15% to global warming (Rohde, 1990).
Methane concentration in the atmosphere is approximately 1.71 ml lÿ1 in 1992 and was increasing at an
annual rate of 0.4% between 1990 and 1992 (Prather
et al., 1995). Methane evolves from rice paddy ®elds
(Seiler et al., 1984b; Holzapfel-Pschorn and Seiler,
1986; Yagi and Minami, 1990), swamps (Harriss et al.,
1982; Bartlett et al., 1988) and marshes (Bartlett, 1985;
Sebacher et al., 1986). The uptake of CH4 by soils was
®rst reported by Harriss et al. (1982) in peat soils in a
relatively dry season. Since then the uptake of CH4
has been measured in forest soils (Seiler et al., 1984a;
* Corresponding author. Present address: Hokkaido Research Center, Forestry and Forest Products Research Institute, 7 Hitsujigaoka,
Sapporo, 062-8516, Japan. Tel.: +81-11-851-4131; fax: +81-11-8514167.
E-mail address: ishiz03@pri-hkd.arc.go.jp (S. Ishizuka).
Keller, 1986; Whalen et al., 1992; Adamsen and King,
1993; Singh et al., 1997), grassland soils (Whalen and
Reeburgh, 1990; Mosier et al., 1993, 1997; Tate and
Striegl, 1993) and deserts (Striegl et al., 1992). Many
studies suggest that soil moisture has an important
role in CH4 uptake (Steudler et al., 1989; Mosier et al.,
1991; Castro et al., 1994; Czepiel et al., 1995). DoÈrr et
al. (1992) mapped the CH4 uptake rate on a global
scale by soil texture class. Their model was based on
the assumption that CH4 uptake rate depends on gas
transport, which was determined by soil texture. They
estimated that global CH4 uptake was in the range of
9.0±55.9 Tg CH4 yrÿ1 (28.7 Tg CH4 yrÿ1 as the best
estimate in the report). They divided soil into eight
textured classes, which were combinations of coarse,
medium and ®ne according to a FAO soil map classi®cation and adopted the uptake rate 1.43 for coarse,
0.42 for medium and 0.19 mg CH4 mÿ2 dÿ1 for ®netextured soils. Koschorreck and Conrad (1993)
obtained ¯ux data comparable with these uptake rates.
Although most studies have been made in the USA
0038-0717/00/$ - see front matter 7 2000 Elsevier Science Ltd. All rights reserved.
PII: S 0 0 3 8 - 0 7 1 7 ( 9 9 ) 0 0 2 0 0 - X
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S. Ishizuka et al. / Soil Biology & Biochemistry 32 (2000) 769±777
and Europe, data from other regions of the world are
needed to more precisely estimate global CH4 uptake.
In Japan, forest soils mostly contain volcanic ash,
and the textures are usually sandy clay loam, clay
loam or loam (®ne or medium according to the FAO
classi®cation). We measured the CH4 concentration in
the soil gas, CH4 ¯uxes and incubated soil cores to
evaluate the CH4 uptake rate by Japanese temperate
deciduous and coniferous forest soils.
2. Materials and methods
2.1. Sampling sites
Four sampling sites (seven sampling plots) were
selected for ®eld measurement. Ogawa Forest Reserve
(6856'N, 140835'E, altitude 620±670 m) was in Kitaibaraki City, Ibaraki Prefecture, about 150 km NNE
from Tokyo. The mean annual temperature is 12.48C;
and the annual precipitation is about 1200 mm.
Masaki et al. (1992) describe other details for this site.
At this site we established three plots, one at the valley
head (OFD1) and one on the upper part of a slope
(OFD2). The vegetation of these plots was an oldgrowth deciduous forest dominated by oak (Quercus
serrata ) and beech trees (Fagus japonica and Fagus
crenata ). The third plot (OFC) was in Japanese cedar
forest (Cryptomeria japonica, 44 yr old) 2 km west
from OFD1 and OFD2. The second sampling site was
at Hitachi Ohta Experimental Site (36834'N, 140835 'E,
altitude 280±340 m) in Hitachi Ohta City, Ibaraki Prefecture, about 120 km NNE from Tokyo. The mean
annual temperature is 13.78C and the annual precipitation is about 1500 mm. Tsuboyama et al. (1994)
describe details of this site. Two plots were established
in this site: one (HEC) was planted with cypress (Chamaecyparis obtusa ) and Japanese cedar and the other
(HED) was deciduous forest dominated by oak trees
(Q. serrata ). The third sampling site was at Tsukuba
Research Site (TRC, 36820'N, 140818 'E, altitude 300±
360 m), in Ibaraki Prefecture, about 70 km NNE from
Tokyo, planted with Japanese cedar. The mean annual
temperature is 14.18C and the annual precipitation is
about 1400 mm (Ohnuki and Yoshinaga, 1995). The
fourth sampling site was at Kaba Research Site
(KRD, 36820'N, 140818'E, altitude 470 m), which was
deciduous forest located near TRC. In summary the
vegetation at OFC, TRC and HEC was coniferous forest, and at OFD1, OFD2, HED and KRD, deciduous
forest.
Table 1 shows the general soil properties of these
plots. All soils contain volcanic ash, so bulk densities
were relatively low (range: 0.30±0.58 Mg mÿ3). The
soils at OFD1, OFC, TRC and KRD were strongly
aected by volcanic ash, with high carbon contents
(125±230 mg gÿ1 soil) and weak or strong andic soil
properties. The soil pH ranged from 4.2 to 5.0. The
soils of OFD1 and TRC were wet and had a high
water-holding capacity. The ratio of air volume of
OFD1 and HEC was >0.1 m3 mÿ3 soil volume and
was lower than those of the other sites.
Table 1
General properties of surface soilsa
Soil type
Vegetation
pH (H2O)
Water content (g gÿ1)
Bulk density (Mg mÿ3)
Air volume (m3 mÿ3)
0±5 cm
10±15 cm
20±25 cm
Total carbon (mg gÿ1)
Total nitrogen (mg gÿ1)
C/N
Inorganic NH4 (mg N gÿ1)
0±10 cm
10±20 cm
20±30 cm
Inorganic NO3 (mg N gÿ1)
0±10 cm
10±20 cm
20±30 cm
a
N.D.=not determined.
OFD1
OFD2
OFC
HEC
HED
TRC
KRD
Andisol
deciduous
4.8
1.69
0.33
Inceptisol
deciduous
5.0
0.75
0.51
Andisol
coniferous
4.5
1.04
0.35
Inceptisol
coniferous
4.2
0.98
0.58
Inceptisol
deciduous
4.5
0.50
0.63
Inceptisol
coniferous
4.4
1.47
0.30
Inceptisol
deciduous
4.6
0.94
0.34
0.27
0.21
0.14
230
13
18
0.42
0.39
0.31
85
4.8
18
0.51
0.35
0.33
162
10
16
0.29
0.28
0.24
88
4.5
20
0.40
0.30
0.22
48
3.1
15
0.40
0.33
0.25
163
11
15
0.57
0.46
0.38
125
10
12
18.4
14.2
12.7
10.7
8.6
9.3
9.3
9.9
11.5
9.8
7.2
N.D.
13.5
7.7
7.9
14.0
10.8
8.9
11.1
15.3
13.0
20.4
7.0
6.7
0.9
4.4
4.6
17.3
7.5
6.5
3.8
1.6
N.D.
18.5
9.8
6.1
51.6
16.7
13.0
11.4
7.1
6.5
S. Ishizuka et al. / Soil Biology & Biochemistry 32 (2000) 769±777
2.2. Soil sampling and chemical analysis
Soil for chemical analysis was sampled from 0±5,
10±15 and 20±25 cm depth and fresh soils were sieved
(2 mm) in the laboratory. The concentrations of NH+
4 N and NOÿ
3 -N in the surface soils were determined on
soil extracts by steam-distillation methods (Mulvaney,
ÿ
1996). After NH+
4 -N and NO3 -N determination, the
soil was stored at 58C in a refrigerator until analyzed.
The total soil carbon and nitrogen contents were
measured with a CN analyzer (Yanaco, MT-600). Soil
water content was measured by drying the soil samples
at 1058C for 24 h.
2.3. Methane ¯ux
The CH4 ¯ux was measured by the closed chamber
method. Cylindrical stainless steel chambers (40 cm dia
and 15 cm height) were inserted into the soil to a
depth of approximately 5 cm and were left throughout
the study. Measurement began at least 7 d later after
setting the chambers in order to eliminate the disturbance of soil. When sampling, the static chamber was
covered with stainless steel lids with sampling ports
and air bags to equilibrate air pressure in the chamber.
A 30-ml headspace of air was sampled at 0, 15 and 30
min using syringes equipped with three-way cocks and
silicon rubber septa. The leakage of these sampling
syringes was negligible ( OFD1
> HEC > TRC, which was comparable with the order
for CH4 ¯ux data.
4. Discussion
4.1. Methane ¯ux estimation
In this study, the rate of soil CH4 consumption ranged from 1.8 to 7.6 mg CH4 mÿ2 dÿ1 and the mean
CH4 uptake rate was 3.8 mg CH4 mÿ2 dÿ1. These
¯uxes were comparable to some reports (Steudler et
al., 1989; Adamsen and King, 1993; Castro et al.,
1995; Goldman et al., 1995) where relatively high
values had been demonstrated (Table 2). According to
the soil texture class of the FAO classi®cation, all soils
in our study were medium texture. The soil CH4 ¯ux
was ninefold larger than the uptake rates (0.42 mg
CH4 mÿ2 dÿ1) of the medium soils estimated by DoÈrr
et al. (1992). Our results suggest that DoÈrr et al. (1992)
may have underestimated the global CH4 uptake rate,
and that more information is needed on the global
scale variations of CH4 uptake.
At KRD, the average ¯ux was 7.6 mg CH4 mÿ2 dÿ1
and the highest uptake rate was 10.7 mg CH4 mÿ2 dÿ1
in August 1997. This was one of the highest ever
reported for forest soils. This soil had a high porosity
(the air volume was 57% of the whole soil volume)
and the plot had good drainage properties because it
was in the middle of a long slope (318). These soil
properties minimized diusion limitation of CH4 from
the air into the soil and maintained good aeration
properties. In addition to good aeration, other factors
may have contributed to the unusually large ¯ux,
because the ¯ux was much larger than DoÈrr et al.
(1992) estimated for coarse-textured soils. The factors
aecting CH4 uptake rate in the ®eld have been widely
reported, including inorganic nitrogen (Steudler et al.,
1989; Adamsen and King, 1993) and soil temperature
(Prieme and Christensen, 1997). Little attention has
been given to site-to-site dierences. The ¯uxes
reported by Singh et al. (1997) were very high. They
discussed the relationship between ¯ux and water content, but did not explain why the uptake rates were
higher than those reported elsewhere. The population
of methanotrophs is likely to be an important factor
aecting CH4 uptake rate, but little information on
this exists. Further research is needed to clarify the relationship between ¯ux and the population of methanotrophs.
4.2. Depth distribution of methane consumption
Fig. 4. Depth pro®le of methane uptake rate of three soils (only
shows the results by Fick's equation). The vertical lines indicate 1
S.D. not determined.
The CH4 concentration in the soil was lower than
that in ambient air and it decreased with depth,
suggesting that CH4 was absorbed at every layer and
that CH4 production was negligible in these forest
soils. Many studies have reported dierences in soil
depth pro®les of CH4 consumption. Some showed
maximum uptake rates occurred in topsoils (Whalen
and Reeburgh, 1990; Koschorreck and Conrad, 1993),
whilst others indicated that uptake rates are highest in
subsurface soils, including 10±20 cm (Whalen et al.,
1992), 6±10 cm (Adamsen and King, 1993; Prieme and
Christensen, 1997 (the interface of organic and mineral
soils)), and 3±6 cm depth (Czepiel et al., 1995). Our incubation experiment and the calculation from soil gas
concentrations in the ®eld, suggest that the layer consuming the most CH4 diered among the sites. Our
results at HEC and TRC showed that the maximum
775
S. Ishizuka et al. / Soil Biology & Biochemistry 32 (2000) 769±777
CH4 uptake rate was in subsurface soil (10±15 cm
depth), while the maximum CH4 uptake rate was
observed in the topsoils at OFD1, OFD2, OFC, HED
and KRD. Adamsen and King (1993) suggested that
the subsurface maximum uptake is associated with the
mineral soil horizon, but our results do not agree with
theirs. Schnell and King (1994) and Prieme and Christensen (1997) suggested that inorganic N possibly inhibits the CH4 uptake rate. The inorganic N content of
the soil we used was higher than that of the soils they
used, and the CH4 uptake rate was not related to the
inorganic N contents. It is possible that the depth
properties of CH4 uptake depend on other soil characteristics that aect the activity of methanotrophs.
On several occasions the CH4 concentration at 20
cm depth was higher than 0.5 ml lÿ1. At these times
the CH4 uptake rate of the soil between 0 and 20 cm
depth was smaller than usual. If the soil below 20 cm
had a low ability to absorb CH4, the CH4 concentration at 40 cm was higher than usual, for example,
0.7 ml lÿ1 at 40 cm at LU in HED. The gradient of
CH4 concentration between the air and surface soil gas
aected the ¯ux of CH4, and the CH4 concentration of
surface soil gas was aected by the capacity of the subsurface soil to oxidize CH4, especially when the uptake
rate of surface soil was low. This suggested that the
potential of the subsurface layer to oxidize CH4 made
a substantial contribution to soil CH4 uptake mechanisms, especially when the uptake rate of the surface
soil was unusually small, as in winter and at dawn.
4.3. Comparison between coniferous and deciduous
forest
The mean ¯uxes of deciduous forests were lower
than for coniferous forests. Many studies have
obtained similar results, which indicate that soils in
deciduous forests absorb more CH4 than soils in coniferous forests (Steudler et al., 1989; Born et al., 1990;
Castro et al., 1995; Dobbie et al., 1996a). Heyer (1977)
provided a clue to this mechanism, suggesting that
methanotroph isolates from acid soils of coniferous
woods and heath were rare. Further research is needed
to con®rm this suggestion.
Table 2
CH4 uptake rate of the forest soils in the world (by chamber method)
Region
North America
Country
USA
USA
USA
Canada
USA
USA
USA
Central America
Europe
USA
Costa Rica
Germany
Middle Asia
East Asia
Scotland
Denmark
Poland
UK
Denmark
India
Japan
a
Value read from graphs.
Recalculated.
c
Value measured only once.
b
Vegetation
Pinus
Quercus, Acer
Tsuga, Pinus, Prunus etc.
Populus
Betula
Picea
Picea, Ledum, Betula
Pinus, Quercus
spruce and ®r
Pinus
Pinus
hardwood
Quercus
Laetia, Pentaclethra
?
deciduous forest
spruce forest
Acer, Fraxinus
Fagus, Picea etc
birch, alder, oak, pine, etc.
Acer, Fraxinus, Fagus
Picea, Quercus
Ziziphus, Shorea, Acacia
Cryptomeria
Chamaecyparis
Quercus, Fagus, Acer
Uptake rate (mg CH4 mÿ2 dÿ1
range (seasonal)
average (annual)
3.2±4.2a
3.5±5.3a
0±2.8
0.55c
0.22c
0.62 and 0.55c
ND
ND
0.64±2.6b
3.2±7.0b
0±7.4
0.8±6.4
2.1±7a
0.3±2.3a
0±1.8b
0±5.9a,b
ND
0.19±3.30
0.27±1.06
0.84±1.23c
2.19±2.97
ND
6.2±17.0
0.81±5.59
1.62±1.93
0.69±10.7
3.5b
4.2b
1.65
ND
ND
ND
0.27±1.57
2.7
0.64±1.7b
ND
2.9
4.5
3.8±5.4
1.20±1.26
0.49b
2.2b
0.25b
1.4
0.7
1.0
ND
0.64±1.7b
8.6±13.7
1.8, 4.9
1.8
2.5±7.6
Reference
Steudler et al., 1989
Steudler et al., 1989
Crill, 1991
Whalen et al., 1992
Whalen et al., 1992
Whalen et al., 1992
Adamsen and King, 1993
Adamsen and King, 1993
Castro et al., 1993
Castro et al., 1994
Castro et al., 1995
Castro et al., 1995
Goldman et al., 1995
Keller and Reiners, 1994
Koschorreck and Conrad, 1993
Born et al., 1990
Born et al., 1990
Dobbie et al., 1996a
Dobbie et al., 1996a
Dobbie et al., 1996a
Dobbie and Smith, 1996b
Prieme and Christensen, 1997
Singh et al., 1997
this study
this study
this study
776
S. Ishizuka et al. / Soil Biology & Biochemistry 32 (2000) 769±777
5. Conclusion
The CH4 uptake rates at seven sites in Japanese
deciduous and coniferous evergreen forest soils were
highly correlated with air temperature except at one
site (HEC). The CH4 uptake rate was higher than that
of previous studies. In one deciduous forest soil
(KRD), the CH4 uptake rate (7.6 mg CH4 mÿ2 dÿ1)
was one of the highest ever reported for forest soils.
We conclude that CH4 uptake rates by soil on a global
scale may be underestimated.
Acknowledgements
We thank Dr. Masamichi Takahashi for giving important advice about this paper.
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www.elsevier.com/locate/soilbio
Methane oxidation in Japanese forest soils
Shigehiro Ishizuka*, Tadashi Sakata, Kazuhiro Ishizuka
Forest Environment Division, Forestry and Forest Products Research Institute, P.O. Box 16, Tsukuba Norin Kenkyu Danchi-nai, Ibaraki 305-8687,
Japan
Accepted 17 October 1999
Abstract
To evaluate the CH4 uptake rate in Japanese deciduous and coniferous evergreen forest soils, the CH4 ¯ux and CH4
concentration in soil gas were measured at seven sites in central Japan. The CH4 uptake potential was calculated from
incubation of soil cores. The CH4 ¯uxes at all sites were negative (uptake by the soils) at every sampling time. The CH4 uptake
rate was very high (7.6 mg CH4 mÿ2 dÿ1) in one deciduous forest soil. Fluxes were highly correlated to the air temperature
except a coniferous forest site. The most active layer of CH4 uptake in each plot diered with site: subsurface (10±15 cm) at two
coniferous forest sites and topsoil (0±5 cm) at the other ®ve sites. The potential of the subsurface layer to oxidize CH4 made a
substantial contribution to soil CH4 uptake mechanisms, especially when the topsoil had a low ability to oxidize CH4. Methane
uptake rates were nine times higher than those of previous studies. The soil CH4 uptake rate on a global scale may be
underestimated. 7 2000 Elsevier Science Ltd. All rights reserved.
Keywords: Methane ¯ux; Forest soils; Methane oxidation; Global methane uptake rate
1. Introduction
Methane (CH4) is a greenhouse gas with strong
absorption bands in the infrared region, and currently
contributes 15% to global warming (Rohde, 1990).
Methane concentration in the atmosphere is approximately 1.71 ml lÿ1 in 1992 and was increasing at an
annual rate of 0.4% between 1990 and 1992 (Prather
et al., 1995). Methane evolves from rice paddy ®elds
(Seiler et al., 1984b; Holzapfel-Pschorn and Seiler,
1986; Yagi and Minami, 1990), swamps (Harriss et al.,
1982; Bartlett et al., 1988) and marshes (Bartlett, 1985;
Sebacher et al., 1986). The uptake of CH4 by soils was
®rst reported by Harriss et al. (1982) in peat soils in a
relatively dry season. Since then the uptake of CH4
has been measured in forest soils (Seiler et al., 1984a;
* Corresponding author. Present address: Hokkaido Research Center, Forestry and Forest Products Research Institute, 7 Hitsujigaoka,
Sapporo, 062-8516, Japan. Tel.: +81-11-851-4131; fax: +81-11-8514167.
E-mail address: ishiz03@pri-hkd.arc.go.jp (S. Ishizuka).
Keller, 1986; Whalen et al., 1992; Adamsen and King,
1993; Singh et al., 1997), grassland soils (Whalen and
Reeburgh, 1990; Mosier et al., 1993, 1997; Tate and
Striegl, 1993) and deserts (Striegl et al., 1992). Many
studies suggest that soil moisture has an important
role in CH4 uptake (Steudler et al., 1989; Mosier et al.,
1991; Castro et al., 1994; Czepiel et al., 1995). DoÈrr et
al. (1992) mapped the CH4 uptake rate on a global
scale by soil texture class. Their model was based on
the assumption that CH4 uptake rate depends on gas
transport, which was determined by soil texture. They
estimated that global CH4 uptake was in the range of
9.0±55.9 Tg CH4 yrÿ1 (28.7 Tg CH4 yrÿ1 as the best
estimate in the report). They divided soil into eight
textured classes, which were combinations of coarse,
medium and ®ne according to a FAO soil map classi®cation and adopted the uptake rate 1.43 for coarse,
0.42 for medium and 0.19 mg CH4 mÿ2 dÿ1 for ®netextured soils. Koschorreck and Conrad (1993)
obtained ¯ux data comparable with these uptake rates.
Although most studies have been made in the USA
0038-0717/00/$ - see front matter 7 2000 Elsevier Science Ltd. All rights reserved.
PII: S 0 0 3 8 - 0 7 1 7 ( 9 9 ) 0 0 2 0 0 - X
770
S. Ishizuka et al. / Soil Biology & Biochemistry 32 (2000) 769±777
and Europe, data from other regions of the world are
needed to more precisely estimate global CH4 uptake.
In Japan, forest soils mostly contain volcanic ash,
and the textures are usually sandy clay loam, clay
loam or loam (®ne or medium according to the FAO
classi®cation). We measured the CH4 concentration in
the soil gas, CH4 ¯uxes and incubated soil cores to
evaluate the CH4 uptake rate by Japanese temperate
deciduous and coniferous forest soils.
2. Materials and methods
2.1. Sampling sites
Four sampling sites (seven sampling plots) were
selected for ®eld measurement. Ogawa Forest Reserve
(6856'N, 140835'E, altitude 620±670 m) was in Kitaibaraki City, Ibaraki Prefecture, about 150 km NNE
from Tokyo. The mean annual temperature is 12.48C;
and the annual precipitation is about 1200 mm.
Masaki et al. (1992) describe other details for this site.
At this site we established three plots, one at the valley
head (OFD1) and one on the upper part of a slope
(OFD2). The vegetation of these plots was an oldgrowth deciduous forest dominated by oak (Quercus
serrata ) and beech trees (Fagus japonica and Fagus
crenata ). The third plot (OFC) was in Japanese cedar
forest (Cryptomeria japonica, 44 yr old) 2 km west
from OFD1 and OFD2. The second sampling site was
at Hitachi Ohta Experimental Site (36834'N, 140835 'E,
altitude 280±340 m) in Hitachi Ohta City, Ibaraki Prefecture, about 120 km NNE from Tokyo. The mean
annual temperature is 13.78C and the annual precipitation is about 1500 mm. Tsuboyama et al. (1994)
describe details of this site. Two plots were established
in this site: one (HEC) was planted with cypress (Chamaecyparis obtusa ) and Japanese cedar and the other
(HED) was deciduous forest dominated by oak trees
(Q. serrata ). The third sampling site was at Tsukuba
Research Site (TRC, 36820'N, 140818 'E, altitude 300±
360 m), in Ibaraki Prefecture, about 70 km NNE from
Tokyo, planted with Japanese cedar. The mean annual
temperature is 14.18C and the annual precipitation is
about 1400 mm (Ohnuki and Yoshinaga, 1995). The
fourth sampling site was at Kaba Research Site
(KRD, 36820'N, 140818'E, altitude 470 m), which was
deciduous forest located near TRC. In summary the
vegetation at OFC, TRC and HEC was coniferous forest, and at OFD1, OFD2, HED and KRD, deciduous
forest.
Table 1 shows the general soil properties of these
plots. All soils contain volcanic ash, so bulk densities
were relatively low (range: 0.30±0.58 Mg mÿ3). The
soils at OFD1, OFC, TRC and KRD were strongly
aected by volcanic ash, with high carbon contents
(125±230 mg gÿ1 soil) and weak or strong andic soil
properties. The soil pH ranged from 4.2 to 5.0. The
soils of OFD1 and TRC were wet and had a high
water-holding capacity. The ratio of air volume of
OFD1 and HEC was >0.1 m3 mÿ3 soil volume and
was lower than those of the other sites.
Table 1
General properties of surface soilsa
Soil type
Vegetation
pH (H2O)
Water content (g gÿ1)
Bulk density (Mg mÿ3)
Air volume (m3 mÿ3)
0±5 cm
10±15 cm
20±25 cm
Total carbon (mg gÿ1)
Total nitrogen (mg gÿ1)
C/N
Inorganic NH4 (mg N gÿ1)
0±10 cm
10±20 cm
20±30 cm
Inorganic NO3 (mg N gÿ1)
0±10 cm
10±20 cm
20±30 cm
a
N.D.=not determined.
OFD1
OFD2
OFC
HEC
HED
TRC
KRD
Andisol
deciduous
4.8
1.69
0.33
Inceptisol
deciduous
5.0
0.75
0.51
Andisol
coniferous
4.5
1.04
0.35
Inceptisol
coniferous
4.2
0.98
0.58
Inceptisol
deciduous
4.5
0.50
0.63
Inceptisol
coniferous
4.4
1.47
0.30
Inceptisol
deciduous
4.6
0.94
0.34
0.27
0.21
0.14
230
13
18
0.42
0.39
0.31
85
4.8
18
0.51
0.35
0.33
162
10
16
0.29
0.28
0.24
88
4.5
20
0.40
0.30
0.22
48
3.1
15
0.40
0.33
0.25
163
11
15
0.57
0.46
0.38
125
10
12
18.4
14.2
12.7
10.7
8.6
9.3
9.3
9.9
11.5
9.8
7.2
N.D.
13.5
7.7
7.9
14.0
10.8
8.9
11.1
15.3
13.0
20.4
7.0
6.7
0.9
4.4
4.6
17.3
7.5
6.5
3.8
1.6
N.D.
18.5
9.8
6.1
51.6
16.7
13.0
11.4
7.1
6.5
S. Ishizuka et al. / Soil Biology & Biochemistry 32 (2000) 769±777
2.2. Soil sampling and chemical analysis
Soil for chemical analysis was sampled from 0±5,
10±15 and 20±25 cm depth and fresh soils were sieved
(2 mm) in the laboratory. The concentrations of NH+
4 N and NOÿ
3 -N in the surface soils were determined on
soil extracts by steam-distillation methods (Mulvaney,
ÿ
1996). After NH+
4 -N and NO3 -N determination, the
soil was stored at 58C in a refrigerator until analyzed.
The total soil carbon and nitrogen contents were
measured with a CN analyzer (Yanaco, MT-600). Soil
water content was measured by drying the soil samples
at 1058C for 24 h.
2.3. Methane ¯ux
The CH4 ¯ux was measured by the closed chamber
method. Cylindrical stainless steel chambers (40 cm dia
and 15 cm height) were inserted into the soil to a
depth of approximately 5 cm and were left throughout
the study. Measurement began at least 7 d later after
setting the chambers in order to eliminate the disturbance of soil. When sampling, the static chamber was
covered with stainless steel lids with sampling ports
and air bags to equilibrate air pressure in the chamber.
A 30-ml headspace of air was sampled at 0, 15 and 30
min using syringes equipped with three-way cocks and
silicon rubber septa. The leakage of these sampling
syringes was negligible ( OFD1
> HEC > TRC, which was comparable with the order
for CH4 ¯ux data.
4. Discussion
4.1. Methane ¯ux estimation
In this study, the rate of soil CH4 consumption ranged from 1.8 to 7.6 mg CH4 mÿ2 dÿ1 and the mean
CH4 uptake rate was 3.8 mg CH4 mÿ2 dÿ1. These
¯uxes were comparable to some reports (Steudler et
al., 1989; Adamsen and King, 1993; Castro et al.,
1995; Goldman et al., 1995) where relatively high
values had been demonstrated (Table 2). According to
the soil texture class of the FAO classi®cation, all soils
in our study were medium texture. The soil CH4 ¯ux
was ninefold larger than the uptake rates (0.42 mg
CH4 mÿ2 dÿ1) of the medium soils estimated by DoÈrr
et al. (1992). Our results suggest that DoÈrr et al. (1992)
may have underestimated the global CH4 uptake rate,
and that more information is needed on the global
scale variations of CH4 uptake.
At KRD, the average ¯ux was 7.6 mg CH4 mÿ2 dÿ1
and the highest uptake rate was 10.7 mg CH4 mÿ2 dÿ1
in August 1997. This was one of the highest ever
reported for forest soils. This soil had a high porosity
(the air volume was 57% of the whole soil volume)
and the plot had good drainage properties because it
was in the middle of a long slope (318). These soil
properties minimized diusion limitation of CH4 from
the air into the soil and maintained good aeration
properties. In addition to good aeration, other factors
may have contributed to the unusually large ¯ux,
because the ¯ux was much larger than DoÈrr et al.
(1992) estimated for coarse-textured soils. The factors
aecting CH4 uptake rate in the ®eld have been widely
reported, including inorganic nitrogen (Steudler et al.,
1989; Adamsen and King, 1993) and soil temperature
(Prieme and Christensen, 1997). Little attention has
been given to site-to-site dierences. The ¯uxes
reported by Singh et al. (1997) were very high. They
discussed the relationship between ¯ux and water content, but did not explain why the uptake rates were
higher than those reported elsewhere. The population
of methanotrophs is likely to be an important factor
aecting CH4 uptake rate, but little information on
this exists. Further research is needed to clarify the relationship between ¯ux and the population of methanotrophs.
4.2. Depth distribution of methane consumption
Fig. 4. Depth pro®le of methane uptake rate of three soils (only
shows the results by Fick's equation). The vertical lines indicate 1
S.D. not determined.
The CH4 concentration in the soil was lower than
that in ambient air and it decreased with depth,
suggesting that CH4 was absorbed at every layer and
that CH4 production was negligible in these forest
soils. Many studies have reported dierences in soil
depth pro®les of CH4 consumption. Some showed
maximum uptake rates occurred in topsoils (Whalen
and Reeburgh, 1990; Koschorreck and Conrad, 1993),
whilst others indicated that uptake rates are highest in
subsurface soils, including 10±20 cm (Whalen et al.,
1992), 6±10 cm (Adamsen and King, 1993; Prieme and
Christensen, 1997 (the interface of organic and mineral
soils)), and 3±6 cm depth (Czepiel et al., 1995). Our incubation experiment and the calculation from soil gas
concentrations in the ®eld, suggest that the layer consuming the most CH4 diered among the sites. Our
results at HEC and TRC showed that the maximum
775
S. Ishizuka et al. / Soil Biology & Biochemistry 32 (2000) 769±777
CH4 uptake rate was in subsurface soil (10±15 cm
depth), while the maximum CH4 uptake rate was
observed in the topsoils at OFD1, OFD2, OFC, HED
and KRD. Adamsen and King (1993) suggested that
the subsurface maximum uptake is associated with the
mineral soil horizon, but our results do not agree with
theirs. Schnell and King (1994) and Prieme and Christensen (1997) suggested that inorganic N possibly inhibits the CH4 uptake rate. The inorganic N content of
the soil we used was higher than that of the soils they
used, and the CH4 uptake rate was not related to the
inorganic N contents. It is possible that the depth
properties of CH4 uptake depend on other soil characteristics that aect the activity of methanotrophs.
On several occasions the CH4 concentration at 20
cm depth was higher than 0.5 ml lÿ1. At these times
the CH4 uptake rate of the soil between 0 and 20 cm
depth was smaller than usual. If the soil below 20 cm
had a low ability to absorb CH4, the CH4 concentration at 40 cm was higher than usual, for example,
0.7 ml lÿ1 at 40 cm at LU in HED. The gradient of
CH4 concentration between the air and surface soil gas
aected the ¯ux of CH4, and the CH4 concentration of
surface soil gas was aected by the capacity of the subsurface soil to oxidize CH4, especially when the uptake
rate of surface soil was low. This suggested that the
potential of the subsurface layer to oxidize CH4 made
a substantial contribution to soil CH4 uptake mechanisms, especially when the uptake rate of the surface
soil was unusually small, as in winter and at dawn.
4.3. Comparison between coniferous and deciduous
forest
The mean ¯uxes of deciduous forests were lower
than for coniferous forests. Many studies have
obtained similar results, which indicate that soils in
deciduous forests absorb more CH4 than soils in coniferous forests (Steudler et al., 1989; Born et al., 1990;
Castro et al., 1995; Dobbie et al., 1996a). Heyer (1977)
provided a clue to this mechanism, suggesting that
methanotroph isolates from acid soils of coniferous
woods and heath were rare. Further research is needed
to con®rm this suggestion.
Table 2
CH4 uptake rate of the forest soils in the world (by chamber method)
Region
North America
Country
USA
USA
USA
Canada
USA
USA
USA
Central America
Europe
USA
Costa Rica
Germany
Middle Asia
East Asia
Scotland
Denmark
Poland
UK
Denmark
India
Japan
a
Value read from graphs.
Recalculated.
c
Value measured only once.
b
Vegetation
Pinus
Quercus, Acer
Tsuga, Pinus, Prunus etc.
Populus
Betula
Picea
Picea, Ledum, Betula
Pinus, Quercus
spruce and ®r
Pinus
Pinus
hardwood
Quercus
Laetia, Pentaclethra
?
deciduous forest
spruce forest
Acer, Fraxinus
Fagus, Picea etc
birch, alder, oak, pine, etc.
Acer, Fraxinus, Fagus
Picea, Quercus
Ziziphus, Shorea, Acacia
Cryptomeria
Chamaecyparis
Quercus, Fagus, Acer
Uptake rate (mg CH4 mÿ2 dÿ1
range (seasonal)
average (annual)
3.2±4.2a
3.5±5.3a
0±2.8
0.55c
0.22c
0.62 and 0.55c
ND
ND
0.64±2.6b
3.2±7.0b
0±7.4
0.8±6.4
2.1±7a
0.3±2.3a
0±1.8b
0±5.9a,b
ND
0.19±3.30
0.27±1.06
0.84±1.23c
2.19±2.97
ND
6.2±17.0
0.81±5.59
1.62±1.93
0.69±10.7
3.5b
4.2b
1.65
ND
ND
ND
0.27±1.57
2.7
0.64±1.7b
ND
2.9
4.5
3.8±5.4
1.20±1.26
0.49b
2.2b
0.25b
1.4
0.7
1.0
ND
0.64±1.7b
8.6±13.7
1.8, 4.9
1.8
2.5±7.6
Reference
Steudler et al., 1989
Steudler et al., 1989
Crill, 1991
Whalen et al., 1992
Whalen et al., 1992
Whalen et al., 1992
Adamsen and King, 1993
Adamsen and King, 1993
Castro et al., 1993
Castro et al., 1994
Castro et al., 1995
Castro et al., 1995
Goldman et al., 1995
Keller and Reiners, 1994
Koschorreck and Conrad, 1993
Born et al., 1990
Born et al., 1990
Dobbie et al., 1996a
Dobbie et al., 1996a
Dobbie et al., 1996a
Dobbie and Smith, 1996b
Prieme and Christensen, 1997
Singh et al., 1997
this study
this study
this study
776
S. Ishizuka et al. / Soil Biology & Biochemistry 32 (2000) 769±777
5. Conclusion
The CH4 uptake rates at seven sites in Japanese
deciduous and coniferous evergreen forest soils were
highly correlated with air temperature except at one
site (HEC). The CH4 uptake rate was higher than that
of previous studies. In one deciduous forest soil
(KRD), the CH4 uptake rate (7.6 mg CH4 mÿ2 dÿ1)
was one of the highest ever reported for forest soils.
We conclude that CH4 uptake rates by soil on a global
scale may be underestimated.
Acknowledgements
We thank Dr. Masamichi Takahashi for giving important advice about this paper.
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