全 文 ：Received 28 Jan. 2003 Accepted 30 Jun. 2003
Supported by the State Key Basic Research and Development Plan of China (G1998040800).
* Author for correspondence.
http://www.chineseplantscience.com
N2O Exchange Within a Soil and Atmosphere Profile in Alpine
Grasslands on the Qinghai-Xizang Plateau
PEI Zhi-Yong, OUYANG Hua*, ZHOU Cai-Ping, XU Xing-Liang
(Institute of Geographical Sciences and Natural Resources Research, The Chinese Academy of Sciences, Beijing 100101, China)
Abstract: Knowledge of nitrous oxide (N2O) exchanges through soils and atmosphere in various eco-
systems has been of great importance in global climate change studies. However, the relative magnitude of
surface and subsurface N2O production sources from the alpine grassland ecosystem is unclear. In the
present study, the N2O concentration profile from 1.5 m in depth in soil to 32 m in height in air was
measured from July 2000 to July 2001 in alpine grassland located in the permafrost area of the Qinghai-
Xizang Plateau, which revealed that N2O concentrations had a distinct variation pattern both in air and in
soil during the study period. Mean N2O concentrations in the atmosphere were significantly lower than
those in the soil, which induced the N2O emission from the alpine steppe soil into the atmosphere. Mean
flux of N2O in this alpine grassland experiment site was 0.05×10-4 mmol·m-2·s-1. But the variation in N2O
emissions did not show any clear trends over the whole-year experiment in our study site. The highest N2O
concentration was found at the depth of 1.5 m in the soil while the lowest N2O concentration occurred at
the height of 8 m in the atmosphere. Mean N2O concentrations in the soil increased significantly with
depth. This was the influence of increasing soil moistures, which induced the increasing denitrification
potential with depth. The mean N2O concentrations at different heights in the air remained a more steady
state because of the atmospheric negotiability. Seasonal variations of N2O concentrations showed
significant correlations between the neighbor layers both in the soil and in the atmosphere. The seasonal
variations of N2O concentrations at all horizons in the soil showed very clear patterns, with the highest
concentrations occurring from the onset of frost to the freeze-thaw period and lowest concentrations
occurring during the spring and the summer. Further analyses showed that the seasonal variations of N2O
concentrations in the soil were hardly explained by soil temperatures at any depth. Temporally,
atmospheric N2O concentrations at all heights exhibited almost the same seasonal pattern with the soil
N2O variations, while soil is believed to be the predominant natural source of atmospheric N2O near the
earth surface in this alpine grassland area. Also, a significant correlation was found between N2O emissions
and soil N2O concentrations at 0.2 m in depth during the study period. This implied the variation of N2O
concentrations in the soil surface horizon was the most direct driving force of N2O exchanges between
the soil and the atmosphere. Soil atmospheric N2O at surface layers is the main source of N2O emissions
from the soil surface to the atmosphere. Soil N2O concentrations at deeper layers were all significantly
higher than those at surface layers, which indicated that N2O was diffused from the deeper layers to the
surface layers in the soil, and finally was emitted to the atmosphere.
Key words: N2O; soil; air; alpine grassland; Qinghai-Xizang Plateau
Global warming has been of great concern, and the ac-
cumulation of greenhouse gases in the atmosphere is as-
sumed to be responsible for the rise in mean global tem-
peratures (Tett et al., 1999; Crowley, 2000). As one of the
most effective greenhouse gases, nitrous oxide (N2O) is a
long lived atmospheric trace gas and responsible for al-
most 5% of anticipated annual global warming undergoing
an atmospheric concentration increasing of 0.25% per year
or more (Rodhe, 1990; Fluckiger et al., 1999). Besides, N2O
is also involved in the depletion of the ozone layer in the
stratosphere which protects the biosphere from the
harmful effects of solar ultra violet radiations (Bange, 2000).
There are many sources of N2O, but the most important
natural source of atmospheric N2O is assumed to be micro-
bial activities in environments like soil, sediments, and waste-
water treatment plants (Andersen et al., 2001). According to
the previous studies, soils are believed to be the predomi-
nant source, contributing about 70% of the total N2O emit-
ted from the biosphere into the atmosphere (Fluckiger et al.,
1999). N2O is produced in soils primarily by two dissimilar
energy producing microbial processes, biological nitrifi-
cation and denitrification (Mummey, 1998). Nitrogen-
Acta Botanica Sinica
植 物 学 报 2004, 46 (1): 20-28
21PEI Zhi-Yong et al.: N2O Exchange Within a Soil and Atmosphere Profile in Alpine Grassland on the Qinghai-Xizang Plateau
containing organic compounds are degraded into ammonia,
which is then converted to nitrate by ammonia- and nitrite-
oxidizing nitrifiers. Nitrate (NO3-), the final product of
nitrification, is gasified to N2 in an anoxic condition by the
metabolism of several nitrate-, nitrite- and nitrous oxide-
reducing denitrifiers. During these two biological processes,
formation of N2O as a byproduct from nitrification, or as an
intermediate in denitrification occurs (Hwang and Hanaki,
2000). N2O production by the both processes is regulated
by complex interactions between ammonium (NH4+), NO3-,
nitrite (NO2-), soil moisture, oxygen status, soil types,
textures, pH, organic carbon contents, and land-use
changes (Mosier et al., 1991; Bouwman, 1998; Kondo et
al., 2000). N2O studies have been performed in many
ecosystems, including those of forests (Kester et al., 1997),
grasslands (Kammann et al., 1998), and agriculture soils
(Sitaula et al., 2000) and tropical peatlands (Hadi et al.,
2000) in plain areas. As far as alpine grassland is concerned,
it is unclear that where or when N2O concentrations both in
soils and in atmospheres accumulate under the influence
of environmental factors. The above studies were all lim-
ited the N2O production of consumption in soils. Few works
have been done about the N2O exchanges within the soil-
biosphere-atmosphere profile in one unique site point. It is
of great importance to improve the general understanding
of N2O exchanges in an integrated ecosystem.
The Qinghai-Xizang Plateau, “the third pole” of the earth,
is an only active continental collision area in the world.
The mean altitude of the plateau is more than 4 000 m
above sea level with an area about 2 500 000 km2. Great
uplift of the plateau since Late Cenozoic has been strongly
affecting the physical environment of the plateau itself and
its neighboring regions. Meanwhile, the plateau is also a
sensitive trigger of climate change in Asian monsoon region,
which is closely related to the global change (Zheng and
Zhu, 2000). Due to the topographic features and the char-
acteristics of the atmospheric circulation, typical alpine
zones of forests, meadows, grasslands and deserts appear
in succession from southeast to northwest in the plateau
(Zheng et al., 1979). Alpine grassland is one of the most
important ecosystems on the Qinghai-Xizang Plateau be-
cause of its large area. Besides, the area is special for its
lacking of human activities. It provides an ideal scientific
field for understanding on N2O exchanges in a soil-plant-
atmosphere profile.
The objects of this work were: (1) to measure N2O con-
centrations within an atmosphere and soil profile to deter-
mine when and where N2O accumulated in the alpine grass-
land ecosystem on the Qinghai-Xizang Plateau; (2) to
understand the N2O exchange features between soils and
atmospheres; and (3) to analyse the relationships between
N2O concentrations, fluxes and environmental factors.
1 Materials and Methods
1.1 Study site
The study was carried out on the top of the hill in
Wudaoliang, Qinghai Province, China (35.13° N, 93.05° E).
The altitude is 4 767 m above sea level. The climate in this
area is semi-arid. The average monthly air temperatures were
all below 0 ℃ except the growing seasons (from June to
September), and the mean annual temperature was –5.6 ℃
(Sun and Zheng, 1997). The mean annual rainfall ranged
from 200 mm to 400 mm, with 84% of the annual precipita-
tions occurring during growing seasons. There was perma-
frost soil and the soil was alpine steppe soil, which was not
well developed. The ecosystem was classified as an alpine
grassland ecosystem, and the majority of the vegetation
was covered with Stipa lawn community dominated by
Stipa purpurea (Zheng et al., 1979).
1.2 Experimental design
A 32-meter-iron-tower was built in 1993 by the Cold and
Arid Regional Environment and Engineering Research
Institute, The Chinese Academy of Sciences (former Lanzhou
Institute of Plateau Atmospheric Physics, The Chinese
Academy of Sciences). It is convenient for us to gather the
gas samples from the upper layers in atmosphere. Four poly-
vinyl chloride (PVC) pipes (4 mm in diameter) were fixed
from the heights of 4, 8, 16 and 32 m to the ground,
respectively.
N2O concentrations at different layers both in the soil
and in the air were examined from July 2000 to July 2001.
N2O concentrations were measured once (1 d) a month dur-
ing non-growing seasons, and once semimonthly during
growing seasons (from June to September). In each sam-
pling day, N2O concentrations were measured three times
between 10:00 and 16:00 during growing seasons, and two
times between 11:00 and 15:00 during non-growing seasons.
We bumped out all remain gas from the pipes before
each sampling time in order to get the actual gas concentra-
tion at each height in atmosphere. All gas samples were
taken with 100 mL polypropylene syringes equipped with
three-way stopcocks into polyethylene-coated aluminum
bags for further N2O concentration analyses (Maljanen et
al., 2001). Unfortunately, the N2O concentrations at the
heights of 16 and 32 m in atmosphere on December 14, 2000
were missed because the PVC pipes were damaged by a
snowstorm.
We gathered the soil gas samples at the depths of 0.2,
Acta Botanica Sinica 植物学报 Vol.46 No.1 200422
0.5, 1.0 and 1.5 m from the soil surface. The below-ground
gas samples were gathered through soil gas samplers, which
were similar with Burton’s facilities (Burton and Beauchamp,
1994). Our gas samplers were made of stainless steel tubes.
The outside tube has a diameter of 10 cm, and the diameter
of the inside pipes was 8 mm. The top of the inside pipes
were tightened by three-way stopcocks, thereby dividing
the inner soil gas from the outer atmosphere without a di-
rect contact (Fig.1). Three sampling plots were selected on
different surfaces representing vegetation biomass of the
study area, and three example wells were dug on July 20,
2000. Samplers were put in each well osculated to the soil
profile in order to get the exact N2O concentrations at dif-
ferent soil layers. Gas samples were gathered from each air-
tightened pipes with polypropylene syringes into polyeth-
ylene-coated aluminum bags. Further more, the soil surface
N2O fluxes were also measured using static chamber
technique. Above-ground biomass (including live, stand-
ing dead and litter) in each plot was harvested before put-
ting a stainless steel collar (0.5 m×0.5 m, height 0.04 m)
into the soil. In the next day, a non-transparence acrylic
chamber (0.5 m×0.5 m, 0.3 m in height, equipped with a
thermometer and two fans inside the top) was placed over
the collars, which had water filled grooves in the upper end
to ensure gas tightness. Gas samples were taken with 100
mL polypropylene syringes equipped with three-way stop-
cocks into polyethylene-coated aluminum bags for further
concentration analysis (Maljanen et al., 2001). Gas samples
were collected at 0, 10, 20, 40 min after the chambers installed.
At the same time of gas sampling, soil temperatures at depth
of 0.05, 0.10, 0.15, 0.20, 0.50, 1.00 and 1.50 m were measured
in order to relate the soil gas concentrations to major envi-
ronmental factors (Tuittila et al., 2000). Soil temperatures at
0.5, 1.0 and 1.5 m in depth were measured all the experimen-
tal time, and others were measured only during the growing
seasons. Soil samples (3.2 cm in diameter core) from sur-
face to the depth of 1.5 m were taken at the end of the
experiment.
1.3 Sample analyses
The plant samples (both above- and below-ground) were
all dried at 60 ℃ over 48 h. After estimating the amount of
biomass, the samples were used to measure organic carbon
by digestion with potassium dichromate and back-titrating
with 0.025 mol/L ferrous ammonium sulphate (Kalembasa
et al., 1973) and total N by Kjeldahl (Bremner, 1965). The
soil moisture was determined by oven dry method at 60 ℃
for 48 h. Soil pH was measured using a glass electrode by a
1:2 soil-to-water ratio (Xu et al., 2003). Soil organic carbon
and total N were measured using the same method with the
plant samples.
The N2O concentrations were analyzed within 10 d by a
gas chromatography (GC) (Type: Hewlett-Packard 5890 ?),
which was equipped with a flame-ionization detector (FID)
and an electron capture detector (ECD). The GC had a
backflush system with stainless steel precolumn (3.2 mm in
diameter and 1.84 m in length) and analytical column (3.2
mm in diameter and 3.68 m in length) packed PORAPAK Q
with 80-100 mesh for both, and the oven temperature was
held at 90 ℃. The ECD temperature was maintained at 330
℃. The carrier gas (5% CH4 in Ar) flow was adjusted to 26
mL/min through the analytical column, and the backflush
gas to 40 mL/min through the precolumn (Dong et al., 2001).
The gas flux was calculated from the concentration
change over the sampling period using the following
expression:
F=D×V×
DC
×
1
=×H×
DC
Dt A Dt
where F means gas flux; D is gas density inside the
chamber (D=P/RT, P is air pressure at the sampling site, R
refers to the gas constant, and T is temperature inside the
chamber); DC/Dt is the linear slope of concentration change
during sampling period; V is volume of the chamber; A is
area of the sampling soil surface, and H is the height of
chamber. So the positive value of F means the gas emis-
sion into the atmosphere from soil and the negative value
represents the gas flow from atmosphere to soil or soil ab-
sorption of this kind of gas from the atmosphere (Dong et
al., 2000; Huang et al., 2001). Mean values, standardFig.1. The diagram of the gas sampler used in the soil.
23PEI Zhi-Yong et al.: N2O Exchange Within a Soil and Atmosphere Profile in Alpine Grassland on the Qinghai-Xizang Plateau
deviations, significance and correlations coefficients were
estimated using SPSS (SPSS for Windows 10.0.1, SPSS Inc)
and Excel spreadsheet (Microsoft Corp., USA).
2 Results and Discussion
2.1 Soil and vegetation characteristics
The alpine steppe soil in this site was sandy loam with
the permanent frozen layer, and other characteristics of the
surface soil are shown in Table 1. The organic carbon and
total N in the soil were 0.19% and 0.05%, respectively.
Higher C and N storage was found in the 0.2-0.5 m depth
of this sandy loam soil. Soil moisture increased gradually
with depth from values of about 3.61% at the surface to
13.75% at 1.5 m in depth. The deeper soil temperatures indi-
cated that the permanent frozen soil located at the depth of
1.5 m. The biomass in this area was a bit lower than other
grasslands in the plain area (Table 2). The ratio of biomass
between below-ground and above-ground was almost
16:1, which was a bit higher than other plain areas (Cheng
and Wang, 2000). The root system here was stronger than
the plain area due to the frigid climate.
2.2 N2O fluxes
The fluxes of N2O in alpine grassland ranged from –0.10
× 10-4 to 0.18× 10-4 mmol·m-2·s-1(Fig.2). Mean flux of
N2O was 0.05×10-4 mmol·m-2·s-1. The positive mean flux
of N2O implied that the alpine grassland soil released N2O
into the atmosphere. Other research also showed that the
grasslands in plain areas contributed to be a N2O source
(Williams, 1999). Release of N2O occurs in soils during both
biological nitrification and denitrification, and during chemi-
cal denitrification (Bouwman, 1998). Biological denitrifica-
tion is the reduction of NO3- or NO2- to gaseous in N
oxides and molecular N (N2) by essentially anaerobic
bacteria. The N2O can be produced and consumed by NO2,
which is then readily absorbed onto leaf surfaces if a tree or
shrub canopy is present. Therefore this process can re-
duce the amount of NO2 escaping from the soil-plant sys-
tem into the atmosphere. However this reabsorption pro-
cess is less important in grasslands than in dense forest
canopies (Bouwman, 1998). The variations in N2O emis-
sions did not show any clear trends over the one-year-
experiment of this study.
2.3 N2O concentration profile
N2O concentrations showed widely variations both in
the air and in the soil during the study period. The highest
N2O concentration was found at the depth of 1.5 m in the
soil, and the lowest N2O concentration occurred at the
height of 8 m in the atmosphere. In general, the mean con-
centrations in the atmosphere were all much lower than the
N2O concentrations in the soil, which introduced a N2O
emission from the alpine steppe soil to the atmosphere in
our study area. From the mean concentration columns in
Fig.3, variation of N2O concentrations showed a very sig-
nificant pattern with depth in soil. Soil N2O concentrations
increased gradually with depth, which is similar to the re-
searches at the Agriculture Canada Research Station, Delhi,
Ontario (Burton and Beauchamp, 1994). Further more, the
standard deviations of N2O concentrations in the atmo-
sphere were all much lower than those in the soil.
Soil moisture has been described as the dominant inde-
pendent variable determining N2O emission rates. It has
been clearly demonstrated that N2O in soils was produced
by nitrification and denitrification processes (Kester et al.,
1997; Koops et al., 1997; Russow, 2000; Wolf and Russow,
2000). But things are more complex than this because the
amount of N2O produced by either nitrification or denitrifi-
cation depends on the prevailing oxygen conditions —
maximum yields of the gas occur only in a narrow range of
low oxygen concentrations (Bange, 2000). Some previous
studies suggested that higher N2O concentrations were
Table 1 Soil characteristics in the study site
Depth Moisture
pH
Organic C Total N
(cm) (%) (%) (%)
0-10 3.61 9.02 0.15 0.04
10-20 5.05 9.03 0.15 0.04
20-30 7.28 8.90 0.32 0.07
30-40 7.49 8.90 0.26 0.06
40-50 8.17 8.78 0.25 0.06
50-70 8.36 8.96 0.15 0.05
70-100 9.47 8.96 0.17 0.05
100-120 10.67 8.87 0.17 0.05
120-150 13.75 9.00 0.11 0.04
Table 2 Vegetation characteristics in the study site
Biomass (g/m2) Total C (%) Total N (%)
Fresh 50.52 39.39 1.51
Litter 4.85 35.69 0.82
Root 871.18 25.04 0.93
Fig.2. N2O emissions from the soil to the atmosphere.
Acta Botanica Sinica 植物学报 Vol.46 No.1 200424
caused by increased N2O production from denitrification,
rather than by increased production from nitrification in
soils (Thornton et al., 1998; Dowrick, 1999). Denitrification
is the pathway in which ammonia (NH3) is oxidized to NO2-
followed by the reduction of NO2- to nitric oxide (NO), and
N2O and N2 (Wrage et al., 2001). Denitrification can be
regarded as the last, a crucial step in the N-cycle, whereby
fixed N is returned to the atmospheric N pool (Simek, 2000).
A positive correlation between soil moistures and denitrifi-
cation potentials has been reported (Chao and Young, 1994;
Borjesson et al., 1998; Clemens and Huschka, 2001). The
soil surface moistures in our study site were all lower than
10% and the moistures increased gradually with depth due
to the high evaporation in this dry area (Cao and Li, 1995).
The increasing soil moistures resulted in a higher N2O pro-
duction rate. The reason of N2O concentrations in this al-
pine steppe soil increased with depth might be caused by
the increasing soil moistures, which agrees well with
Hwang’s study in 2000 (Hwang and Hanaki, 2000).
2.4 Temporal variations of N2O concentrations
Soil atmosphere N2O concentration profiles varied sig-
nificantly during the study period, both temporally and with
depth. Seasonal variation of N2O concentrations in the soil
profile during the sampling period were the greatest at
deeper depths (Fig.4). This was quite different and pro-
vided an interesting contrast to some previous studies
(Mosier and Hutchinson, 1981; Cates and Keeney, 1987;
Bouton and Beauchamp, 1994). Their experiments were car-
ried out in the areas with strongly human impacts.
Production of N2O at lower soil depth during denitrifica-
tion and nitrification changed widely with human activities
including N fertilizer application, farming and land-use
changes (Hadi et al., 2000; Pathak and Nedwell, 2001). But
our study site was located at a remote plateau with few
human activities. N2O concentrations in the surface layers
kept more stable state than those in the deeper layers, where
as the diffusion of N2O in deeper layers were lacking of
efficient pathways. The seasonal variation of N2O concen-
trations in soil showed a very clear pattern, with the higher
N2O concentration occurring from the early autumn to the
mid-winter and the lower concentrations during spring and
summer. Further analyses demonstrated that the correla-
tions between N2O concentrations and soil temperatures
at different layers were not significant, so the seasonal pat-
tern of N2O concentration variations were hardly explained
by soil temperatures. The high N2O concentrations from
the onset of frost to the freeze-thaw period have been ob-
served (Burton and Beauchamp, 1994; Kammann et al.,
1998; Teepe et al., 2000; Teepe et al., 2001). It is know that
the terrestrial N cycles are driven by the activities of
microorganisms. Some of them can obtain their energy by
transforming various forms of nutrients such as NO3-, NO2-
and NH4+ (Bange, 2000). According to Teepe’s study (Teepe
et al., 2000; 2001), these high N2O concentrations were
produced during continuous soil freezing in an unfrozen
water film on the soil matrix by the microorganisms which
were still active in this cold period. The frozen water in form
of an ice layer represents a diffusion barrier which reduces
O2 supply to the microorganisms and partly prevents the
release of the N2O.
Variations of atmospheric N2O concentrations in air
showed almost the same range at all heights (Fig.5), and
this same variation range of N2O concentrations may be
caused by the atmospheric negotiability. During the ex-
perimental period, the variation of atmospheric N2O
Fig.3. N2O concentration profile at different layers from the soil
to the atmosphere.
Fig.4. Variations of mean N2O concentrations at different depths
in the soil.
25PEI Zhi-Yong et al.: N2O Exchange Within a Soil and Atmosphere Profile in Alpine Grassland on the Qinghai-Xizang Plateau
concentrations also showed a clear pattern. The highest
N2O concentrations occurred during the frost period and
microbial activities. That is the reason why the correlation
between N2O concentration variations at deeper layers was
more significant than that at surface layers. The N2O con-
centrations in atmosphere exhibited synchronous variations
during the study period (Fig.5), so the variations of N2O
concentration also showed significant correlations (R2 =
0.51, P＜ 0.01) between the neighbor layers in the
atmosphere. A significant correlation (R2 = 0.61,P＜0.01)
was also found between N2O at soil surface fluxes and soil
N2O concentrations at 0.2 m in depth during the study pe-
riod (Fig.7). This implied the variation of N2O concentra-
tions in the surface horizon was the most direct driving
force of N2O emissions from the soil to the atmosphere.
Soil atmospheric N2O at surface layers is the main source
of N2O emissions from soil surface to the atmosphere. N2O
concentrations at deeper layers were all significantly higher
than those at surface layers, which indicated that N2O was
diffused from deeper layers to the surface layers in soil,
Fig.6. Correlations between N2O concentrations at different depths in the
soil.
the freeze-thaw period, which was almost the same
with the N2O concentration variation in soil. It is
well known that gas emission into the atmosphere
from soil was the direct source of atmospheric N2O
near the earth surface, so the N2O concentrations
both in soil and in atmosphere showed the same
seasonal pattern during the study period.
2.5 N2O concentrations and fluxes
Although mean N2O concentrations varied
widely with depth in the soil, the seasonal varia-
tions of N2O concentrations showed significant
correlation between different layers in soil (Fig. 6).
The most interesting result is the correlations be-
tween N2O concentrations at different layers in-
creased with depth, and the most significant cor-
relation was found at deeper layers where the great-
est variation of N2O concentrations were
measured. The natural factors which have effect
on the N2O production and consumption proce-
dures were easily disturbed by the outside envi-
ronment at soil surface, on the contrary, the envi-
ronmental factors showed more stable state at
deeper layers relatively because of obstruction.
Furthermore, the vegetation root systems and the
microorganisms have the influences on N2O pro-
duction and consumption processes at the soil
surface layers, but we can hardly find the grass
roots deeper than 0.6 m depth in the soil. The situ-
ation in the deeper layers in soil are relatively
simple than the soil surface layers, so the N2O
procedures here were only dominated by the
Fig.5. Variations of mean N2O concentrations at different layers
in air. Illustration: PVC pipes accessing to 16 m and 32 m in
height were damaged by a snowstorm before December 14, 2000,
so we lost the N2O concentrations of those heights during the
experiment on Dec. 14.
Acta Botanica Sinica 植物学报 Vol.46 No.1 200426
and finally was emitted to the atmosphere. As the most
important N2O produced processes, nitrification and deni-
trification are significantly controlled by the environmental
factors, so the environmental conditions also have great
influence on the N2O exchanges between the soil and the
atmosphere.
3 Conclusion
Through the measurement of the N2O concentration
profile in an alpine grassland ecosystem on Qinghai-Xizang
Plateau, the following conclusion remarks were obtained:
(1) Mean concentrations in the atmosphere were all
much lower than the N2O concentrations in the soil, which
introduced a N2O emission from the alpine steppe soil to
the atmosphere in the study area. During the experiment
period, the highest N2O concentration was found at the
depth of 1.5 m in the soil, and the lowest N2O concentration
occurred in the atmosphere.
(2) Mean N2O concentrations in soil increased gradu-
ally with depth, which was caused by the increasing soil
moisture. The mean N2O concentrations at different layers
in the atmosphere showed more stable state than N2O con-
centrations below-ground.
(3) The seasonal variation of N2O concentrations in
soil showed very clear pattern, with the highest N2O con-
centrations being measured from the onset of frost to the
freeze-thaw period and the lowest concentrations during
spring and summer. The atmospheric N2O concentrations
also showed the same seasonal variation pattern with N2O
concentrations in soil.
(4) Seasonal variations of N2O concentrations showed
significant correlations between the neighbor layers both
in soil and in atmosphere. Furthermore, the significant cor-
relation between N2O soil surface fluxes and N2O concen-
trations near the soil surface implied that the N2O concen-
trations difference was the most direct driving force of N2O
emissions from soil to the atmosphere.
Acknowledgements: We would like to thank LIU Yun-
Fen, MA Zhi-Xue and SHI Bu-Hong for their assistance in
field sampling, and we are grateful to QI Yu-Chun for his
help in laboratory. Thanks also should be given to NIU
Hai-Shan for his suggestions during the data analyses.
References:
Andersen K, Kjar T, Revsbech N P. 2001. An oxygen insensitive
microsensor for nitrous oxide. Sensor Actuat B-Chem, 81:42-
48.
Bange G W. 2000. It’s not a gas. Nature, 408:301-302.
Borjesson G, Sundh I, Tunlid A, Frostegard A, Svensson B H.
1998. Microbial oxidation of CH4 at high partial pressures in
an organic landfill cover soil under different moisture regimes.
Fems Microbiol Ecol, 26:207-217.
Bouwman A F. 1998. Nitrogen oxides and tropical agriculture.
Nature, 392:866-867.
Bremner J M. 1965. Inorganic forms of nitrogen. Black C A.
Methods of Soil Analysis. Vol. 2. Madison: American Soci-
ety of Agronomy. 1179-1237.
Burton D L, Beauchamp E G. 1994. Profile nitrous oxide and
carbon dioxide concentrations in a soil subject to freezing. Soil
Sci Soc Am J, 58:115-122.
Cates R L, Keeney D R. 1987. Nitrous oxide production through-
out the year from fertilized and manure maize fields. J Environ
Qual, 16:443-447.
Chao C C, Young C C. 1994. Enhancement of denitrification by
green manure. Lal R, Kimble J M, Levine E. Soil Processes
and Greenhouse Effect. Linconln NE: USDA, Soil Conserva-
tion Service, National Soil Survey Center. 145-155.
Chen Z-Z, Wang S-P. 2000. The Typical Grassland Ecosystems
in China. Beijing: Science Press. (in Chinese)
Clemens J, Huschka A. 2001. The effect of biological oxygen
demand of cattle slurry and soil moisture on nitrous oxide
emissions. Nutr Cycl Agroecosys, 59:193-198.
Crowley T J. 2000. Causes of climate change over the past 1000
years. Science, 298:270-277.
Dong Y, Scharffe D, Qi Y, Peng G B. 2001. Nitrous oxide emis-
sions from cultivated soils in the North China Plain. Tellus B,
53:1-9.
Dong Y-S , Zhang S , Qi Y-C , Chen Z-Z, Geng Y-B. 2000. Fluxes
of CO2, N2O and CH4 from typical temperate grassland in
Inner Mongolia and its daily variation. Chin Sci Bull , 45:
1590-1594.
Dowrick D J, Hughes S, Freeman C, Lock M A, Reyonlds B,
Hudson J A. 1999. Nitrous oxide emissions from a gully mire
in mid-wales, UK, under simulated summer drought.
Biogeochemistry, 44:151-162.
Fig.7. Correlations between N2O fluxes and concentrations at
0.2 m depth in the soil.
27PEI Zhi-Yong et al.: N2O Exchange Within a Soil and Atmosphere Profile in Alpine Grassland on the Qinghai-Xizang Plateau
Fluckiger J, Dallenbach A, Blunier T, Stauffer B, Stocker T F,
Raynaud D, Barnola J M. 1999. Variations in atmospheric
N2O concentration during abrupt climate changes. Science,
285:227-230.
Gao Y-X, Li M-S. 1995. Soil regionalization of the Qinghai-Xizang
Plateau. Mt Res, 13:203-211. (in Chinese)
Hadi A, Inubushi K, Purnomo E, Razie F, Yamakawa K, Tsuruta
H. 2000. Effect of land-use changes on nitrous oxide (N2O)
emission from tropical peatlands. Chemosphere-Global
Change Sci, 2:347-358.
Huang G-H, Xiao D-N, Li Y-X, Chen G-X, Yang Y-C, Zhao C-W.
2001. CH4 emissions from the reed wetland. Acta Ecol Sin ,
21:1494-1497. (in Chinese)
Hwang S, Hanaki K. 2000. Effects of oxygen concentration and
moisture content of refuse on nitrification, denitrification and
nitrous oxide production. Biores Technol, 71:159-165.
Kalembasa S J, Jenkinson D S. 1973. A comparative study of
titrimetric and gravimetric methods for determination of or-
ganic carbon in soil. J Sci Food Agr, 24:1085-1090.
Kammann C, Grunhage L, Muller C, Jacobi S, Jager H J. 1998.
Seasonal variability and mitigation options for N2O emissions
from differently managed grasslands. Environ Pollut, 102(S1):
179-186.
Kester R A, Meijer M E, Libochant J A, Boer W D, Laanbroek H
J. 1997. Contribution of nitrification and denitrification to the
NO and N2O emissions of an acid forest soil, a river sediment
and a fertilized grassland soil. Soil Biol Biochem, 29:1655-
1664.
Kondo T, Mitsui T, Kitagawa M, Nakae Y. 2000. Association of
fasting breath nitrous oxide concentration with gastric juice
nitrate and nitrite concentrations and helicobacter pylori
infection. Digest Dis Sci, 45:2054-2057.
Koops J G, van Beusichem M L, Oenema O. 1997. Nitrogen loss
from grassland on peat soils through nitrous oxide production.
Plant Soil, 188:119-130.
Maljanen M, Hytönen J, Martikainen P J. 2001. Fluxes of N2O,
CH4 and CO2 on afforested boreal agricultural soils. Plant
Soil, 231:113-121.
Mosier A, Schimel D, Valentime D, Broson K, Parton W. 1991.
Methane and nitrous oxide fluxes in native, fertilized and cul-
tivated grasslands. Nature, 350:330-332.
Mosier A R, Hutchinson G L. 1981. Nitrous oxide emissions
from cropped fields. J Environ Qual, 10:169-173.
Mummey D L, Smith J L, Bluhm G. 1998. Assessment of alterna-
tive soil management practices on N2O emissions from US
agriculture. Agr Ecosyst Environ, 70:79-87.
Pathak H, Nedwell D B. 2001. Nitrous oxide emission from soil
with different fertilizers, water levels and nitrification inhibitors.
Water Air Soil Poll, 129:217-228.
Rodhe H. 1990. A comparison of the contribution of various
gases to the greenhouse effect. Science, 248:1217-1219.
Russow R, Sich I, Neue H U. 2000. The formation of the trace
gases NO and N2O in soils by the coupled processes of nitri-
fication and denitrification: results of kinetic 15N tracer
investigations. Chemosphere - Global Change Sci, 2:359-
366.
Simek M, Cooper J E, Picek T, Santruckova H. 2000. Denitrifica-
tion in arable soils in relation to their physico-chemical prop-
erties and fertilization practice. Soil Biol Biochem, 32:101-
110.
Sitaula B K, Hansen S, Sitaula J I B, Bakken L R. 2000. Effects of
soil compaction on N2O emission in agricultural soil. Chemo-
sphere - Glob Chan Sci, 2:367-371.
Sun H-L, Zheng D. 1997. Formation, evolution of Qinghai-Xizang
Plateau. Shanghai Science and Technology. Guangzhou:
Guangdong Press. (in Chinese)
Teepe R, Brumme R, Beese F. 2000. Nitrous oxide emissions
from frozen soils under agricultural, fallow and forest land.
Soil Biol Biochem, 32:1807-1810.
Teepe R, Brumme R, Beese F. 2001. Nitrous oxide emissions
from soil during freezing and thawing periods. Soil Biol
Biochem, 33:1269-1275.
Tett S F B, Stott P A, Allen M R, Ingram W J, Mitchell J F B.
1999. Causes of twentieth-century temperature change near
the Earth’s surface. Nature, 399:569-572
Thornton F C, Shurpali N J, Bock B R, Reddy K C. 1998. N2O
and NO emissions from poultry litter and urea applications to
bermuda grass. Atmos Environ, 32:1623-1630.
Tuittila E S, Komulainen V M, Vasander H, Nykänen H,
Martikainen P J, Laine J. 2000. Methane dynamics of a re-
stored cut-away peatland. Glob Chan Biol, 6:569-581.
Williams D L, Ineson P, Coward P A. 1999. Temporal variations
in nitrous oxide fluxes from urine-affected grassland. Soil Biol
Biochem, 31: 779-788.
Wolf I, Russow R. 2000. Different pathways of formation of
N2O, N2 and NO in black earth soil. Soil Biol Biochem, 32:
229-239.
Wrage N, Velthof G L, van Beusichem M L, Oenema O. 2001.
Role of nitrifier denitrification in the production of nitrous
oxide. Soil Biol Biochem, 33:1723-1732.
Xu X-L, Ouyang H , Pei Z-Y, Zhou C-P . 2003. Fate of 15N
labeled nitrate and Ammonium salts added to an alpine meadow
in the Qinghai-Xizang Plateau, China. Acta Bot Sin , 45:276-
281.
Zheng D, Zhu L. 2000. Formation and Evolution, Environmental
Changes and Sustainable Development on the Tibetan Plateau.
Beijing: Academy Press.
Zheng D, Zhang R-Z, Yang Q-Y. 1979. The natural zonation in
Acta Botanica Sinica 植物学报 Vol.46 No.1 200428
the Qinghai-Xizang Plateau. Acta Geogr Sin , 34:1-11. (in
Chinese)
(Managing editor: HAN Ya-Qin)