Environ Geol (2008) 54:1403–1409
DOI 10.1007/s00254-007-0921-5
O R I GI NA L AR T I C L E
Analysis of impact factors on scrubland soil respiration
in the southern Gurbantunggut Desert, central Asia
Hong Zhu Æ Chengyi Zhao Æ Jun Li Æ Yujie Li Æ
Feng Wang
Received: 12 June 2007 / Accepted: 26 June 2007 / Published online: 21 July 2007
Springer-Verlag 2007
Abstract Monitoring soil CO2 respiration with chamber
measurements and identifying controlling factors such as
the diversity of vegetation species, moisture and temperature can help guide desert scrubland management. Soil CO2
respiration and potential controlling factors at four sites in
desert scrubland were examined along the Sangong River
Basin (SRB) in northwesternChina in 2004. Soil CO2 respirationdescended along the SRB as did the diversity of
vegetation species, air temperature and air humidity. The
two sites of the field station (FS) and the north desert (ND)
and the low reaches of the SRB among these locations were
monitored to analyze the effects of pH value, soil organic
carbon (SOC), total nitrogen (TN) and calcium carbonate(CaCO3) on soil CO2 respiration during the growing
season in 2005. The ND site was located at the southern
edge of the Gurbantunggut Desert; the FS site was in the
border area of the SRB Alluvial Fan. One-way ANOVA
was performed. The result showed that air humidity and
CaCO3 content had a strong influence on soil CO2 respiration; SOC content was a limitation to soil CO2 respiration
in the arid-desert zone. Effective management activities
can attenuate soil CO2 respiration and keep carbon balance
trends at a desirabe level in desert scrublands.
H. Zhu (&) C. Zhao J. Li Y. Li F. Wang
Xinjiang Institute of Ecology and Geography,
Chinese Academy of Sciences,
Urumqi 830011, China
e-mail: [email protected]
C. Zhao
e-mail: [email protected]
H. Zhu J. Li Y. Li F. Wang
Graduate School, Chinese Academy of Sciences,
Beijing 100039, China
Keywords
Soil respiration Arid zone CaCO3 content
Introduction
Soil is the major reservoir of carbon in terrestrial ecosystems (Schlesinger and Andrews 2000), containing more
than two-thirds of the total carbon in the terrestrial part of
the biosphere. Soil respiration is one of the main processes of organic carbon (Raich and Potter 1995), which
includes three biological processes (soil microbial respiration, root respiration and soil fauna respiration) and an
abiotic process (oxidation of minerals containing carbon)
(Singh and Gupta 1977). Soil CO2 respiration is controlled by the complex interaction of environmental and
biotic factors. Temperature is well known to be a dominant environmental control on soil CO2 respiration rates
(Raich and Schlesinger 1992; Lloyd and Taylor 1994).
There is a sensitivity of soil respiration with an increasing
temperature to a certain extent. Soil carbon,vegetation
coverage and root biomass affect soil CO2 respiration
sensitivity also. Few studies evaluate the loss of carbon
from arid and semiarid soils compared to other ecosystems (Maestre and Cortina 2003). Arid and semiarid areas
where the distribution of ecological factors and organisms
are markedly patches, including a significant spatial variation in soil CO2 respiration (Maestre and Cortina 2003;
Schlesinger and Pilmanis 1998). Most of the arid and
semiarid areas of West Africa are characterized by long
dry periods and very infertile soils (Duponnois et al.
2005), which become the limitation to soil CO2 respiration. Soil CO2 respiration in the arid ecosystems respond
positively to air humidity. However, air humidity is just
one of many factors controlling soil CO2 respiration. Plant
growth is limited by low soil organic matter (SOM)
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Environ Geol (2008) 54:1403–1409
content, particularly during the early period of the plants’
growth, which produces a lesser amount ofby-products
such as a small amount of litter and exudates and root
biomass. The matter mentioned above influences soil CO2
respiration indirectly.
SRB (30 · 80 km) is between the north slope of the
Tianshan mountains and the south edge of the Gurbantunggut Desert in western China’s Xinjiang Uigur
Autonomous region. It is a typical representative of arid
and semiarid areas, and is thus well suited for studying
soil CO2 respiration. Through a case study of this area,
the project presented in this paper has evaluated the local
spatial variations of soil CO2 respiration in scrublands
along SRB.
The objectives of this research are first to analyze the
variation of soil CO2 respiration along SRB, and second, to
evaluate the effects promoted by small scale spatial variations in vegetation and surface soil features and climate
factors on soil CO2 respiration in arid scrubland.
Materials and methods
Study site description
Fig. 1 Sketch of the study zone (Zhu)
The study sites are located in SRB, a typical inland river
basin with floods in the spring and autumn seasons, on the
southern edge of Gurbantunggut Desert in central Asia
(N43200 37@–44290 53@, E87500 24@–88170 06@). Starting
in the northern uplands of the North Tianshan Mountains,
the elevation along the basin descends from 750 to 450 m
above sea level. Passing by plain oasis landscapes in the
middle, it reaches the southern edge of Gurbantunggut
Desert, a total distance of less than 80 km. The north desert
(ND) site is dominated by Haloxylon ammodendron Bge.,
the flood canal (FC) and field station (FS) sites in the
middleby Tamarix ramosissima Ledeb., and upslope (US)
and downgrade (DG) sites in the upland by Anabasis
elatior (C.A.Mey.) Schischk and A. aphylla L. Thesite
details are shown in Fig. 1. This is a typical zone of the
Central Asian arid lands. It contains most of the vegetation
types and hydrological processes that occur in this arid
area, ranging from natural mountain grasslands to desert
with sparse vegetation, from river outlet to depletion areas.
The soils in the alluvial plain are gray desert soil, including
luvic yermosole and meadow solonchaks. The land surface
is partitioned into bare soil and vegetation-covered components, where plants are spaced further apart. The climate
is arid to semi-arid, with a 1961–2000 mean annual rainfall
and evapotranspiration of 220 and 1,817 mm, respectively.
The mean annual temperature is 6.9C (Luo et al. 2002).
On the south edge of Gurbantunggut Desert, the rainfall is
even less than 115 mm (Zhou 2001). The geomorphy is
dominated by some waving 5–25-m high sand dunes. The
temperature varies by as much as 35C in August to as low
as 37C in January.
Zhang et al. (2002) showed the vegetation species’
composition and structures in these sites. The vegetation was
typically dominated by scrub Tamarix ramosissima Lede.
(typical height 120–300 cm) in the middle and Haloxylon
ammodendron Bge. (typical height 150–400 cm) in the
lower reaches of SRB. Vegetation distribution was in patches, and it had a low coverage atapproximately 30%. The
main vegetation included Reaumuria soongorica Maxim.
(typical height 10–25 cm), Ceratocarpus arenarius L.
(typical height 5–30 cm) and Suaeda physophora Pall.
(typical height 20–50 cm), which accounted for more than
35% of the total coverage of vegetation,besides some
ephemeral herbaceous vegetation. Dispersed grasses, such
as Petrosimonia sibirica Bge, S. nitraria Pall, etc., were also
present. Biological crusts and mosses were common features
of the soil surface at the south edge of Gurbantunggut Desert
(Zhang et al. 2005). But unordered grazing and human
activity have disturbed the soil surface stability. Livestock’s
trampling has destroyed the physical texture of the soil
surface such as biological crusts and mosses. Activities like
gatheringbranches and burrowing by animalsalter the soil
surface condition. All these activities have influenced the
soil CO2 respiration and the balance of soil carbon in the
terrestrial ecosystem.
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Environ Geol (2008) 54:1403–1409
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Vegetation variable
Dugas 2000). In addition, environmental factors such as air
temperature and air humidity were measured.
The gradient changes of the vegetation community structure
were studied. Vegetation diversity was registered in four
plots of 10 · 10 m. Four subplots of 1 · 1 m were investigated witha relative abundance in each plot mentioned
above at the upland. Then an average value was found,
which presented the vegetation diversity of each plot of
10 · 10 m. Finally, a mean was derived from the four
averages. The mean reflected the vegetation diversity at the
upland. The same investigation was carried out at the middle
and the south edge of the Gurbantunggut Desert along the
SRB. Theherbaceous and scrub plants were counted in order
to analyze the species diversity, which is an important index
regarded by ecologists. The index displayed the condition of
vegetation community development, as did the evenness
index. The statistical indices of integrate species diversity
and evenness were calculated in the following formula.
The diversity of vegetation species was calculated with
the Shannon index H (Hv) (Shannon 1948):
n
X
Hv ¼ pi ln pi
ð1Þ
i¼1
where pi is the relative abundance of each plant in the plot
and n is the number of detected vegetation. The equitability
of the vegetation was calculated with Shannon’s evenness
E (Ev) (Shannon 1948):
Ev ¼ H= ln ðSÞ
ð2Þ
where S is the total number of vegetation measured in the
plot.
Soil CO2 respiration measurements
Soil CO2 respiration was measured in situ using an infrared
gas analyzer system (model CIRAS-1, PP Systems,
Hitchin, UK) equipped with a flow-through closed chamber. At the time of the measurements, the chamber, which
had an area of 78 cm2 and a volume of 1,170 cm3, was
inserted 3 cm into the surface soil. Measurements at each
sampling point took 120 s, a sampling interval long enough
to get reliable estimates of soil CO2 respiration with the
equipment. Measurements were performed at four sites
along the SRB on 23 July 2004, and the upland of the front
Tianshan Mountains was measured at the US and DG sites,
respectively. In 2005, the measurements were performed
monthly at two sites, FS and ND, from March to November. Every time, the measurements were performed between 12:00 and 16:30 h, because it showed midday values
of soil CO2 respiration. The midday values were representative of daily averages in scrublands (Mielnick and
Soil sampling
A field sampling survey was carried out on 23 July 2004,
and soil CO2 respiration measurement along the SRB. The
topsoil (0–20 cm) under the canopies of different vegetation species was analyzed for physical–chemical characteristics in each sampled area. Soil samples were collected
in the following three sites: FC in the middle area, FS in
ecotone of oasis and desert and ND on the south edge of
Gurbantunggut Desert. No scrubs were in the upland, and
the soil characteristics analyses of the US and DG sites were
ignored. The soil samples under the canopies of different
species of vegetation were collected and then mixedtogether to obtain a composite sample at each of the three
sites. A subsample was air-dried and sieved (<2 mm) for
physical–chemical characteristics analysis. Measurements
were carried out in replication using the methods outlined
by the Nanjing Agriculture University (1966). In addition,
the physical–chemical characteristics of soil at theFS and
ND sites were analyzed from March to November 2005.
The soil pH value was measured in a 1:5 (v/v) aqueous
solution. The soil’s organic carbon (SOC) content was
determined by the Walkley–Black method (Editorial Committee 1996), and the wet dichromate digestion method. TN
concentration was determined by the Kjeldahl procedure.
CaCO3 content was calculated by CO2 produced from the
reaction of soil and HCl solution (Institute of Soil Science,
CAS 1978). The soil particle sizes were determined by
Mastersizer2000 (Malvern Instruments Ltd., Malvern, UK)
and classified by the Udden–Wentworth scale standard.
Statistical analyses
All soil parameters were analyzed for variance using the
SPSS 13.0 package (SPSS, Chicago, IL). The vegetation
data were analyzed for the correlation with soil CO2 respiration according to diversity indices and evenness indices. The relationships were analyzed among selected soil
CO2 respiration and environmental factors (air humidity,
air temperature)and soil characteristics (pH value, CaCO3,
SOC and TN). The significance level of these relationships
was tested using the least significant differences (LSD) test.
Results
Vegetation variations
Along SRB, the successional vegetation indices gradient,
maximal Shannon’s diversity index (1.655) and evenness
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Environ Geol (2008) 54:1403–1409
Table 2 The texture of soils
Sites
Clay (%)
Silt (%)
Sand (%)
FC
FS
ND
8.32
4.38
10.29
74.09
66.73
72.48
17.58
28.89
17.23
Soil characteristics
Fig. 2 Changing trend of the diversity index and evenness index in
vegetation along the Sangong River Basin; the sites of US and DG
were located in the upland of the front Tianshan Mountains (Zhu)
index (0.36) were found in the uplands of the front Tianshan Mountains and minimal values (0.25 and 0.034) in the
ecotone of the oasis and desert. The indicesdeclined along
the SRB (Fig. 2); the indices variations were also similar to
the values of soil CO2 respiration.
Environmental factors
The trends of the changes for air temperature and air
humidity varied in difference (Table 1).
The air temperature was highest at the ND site and
lowest at the FS site. The FS site was situated in the ecotone of the oasis and desert, where human activities like
grazing animals and gathering branches for human use
were very frequent. The oasis was in the arid zone where
the ‘‘cool island’’ (Luo et al. 2002) effect has occurred
easily. The air humidity at the BS site was higher than at
other sites and was lowest at the ND site. The one-way
ANOVA test was performed for the differences in air
humidity, air temperature and soil CO2 respiration at the
five sites; F values showed a significant difference.
Table 1 Variance of environmental factors and soil CO2 respiration
along the Sangong River Basin
Sites
n
Air
humidity
(%)
US
6 31.95 (4.04)
DG
6 35.1 (1.83)
FC
10 25.66 (0.78)
FS
6 19.6 (0.77)
ND
9 13.46 (0.3)
F-value
27.78***
Air
Concentration Soil CO2
respiration
temperature for carbon
(C)
dioxide (ppm) (g m2 h1)
32.48 (0.30)
32.48 (0.30)
33.34 (0.20)
29.35 (0.33)
36.78 (0.17)
116.8***
432.32 (12.11)
437.18 (2.63)
488.97 (28.09)
404.1 (3.92)
405.03 (5.2)
4.65**
0.69 (0.10)
0.98 (0.09)
0.46 (0.10)
0.14 (0.03)
0.08 (0.04)
7.73*
US upslope, DG downgrade, FC flood canal, FS field station in
Fukang, CAS, ND north desert (same to follow). Values are means
(standard errors of means in brackets), ***P < 0.001; **P < 0.01;
*P < 0.05
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Soil texture (0–20 cm depth) was silty (Table 2), with
higher sand content. The content of silts was highest
(>65%), and the content of clays was lowest (<11%) for the
soil under the canopies of scrubs. Some of the main physical–chemical characteristics of soil are shown in Table 3.
The soil characteristics were significantly different in the
two sites, FS and ND.
The soil samples had a slightly alkaline pH, which was
highest at the ND site and lowest at the FS site. The contents
of TN and SOC were highest at the FS site, and they bothcorrelated significantly (r = 0.96, n = 9). The CaCO3 content was highest at the upland and lowest at the ND site, and
declined along the SRB. At the two sites, FS and ND, the
difference of CaCO3 content was significant (F = 173.524,
P < 0.01) (Table 3); it was lower at the ND site than the FS
site in CaCO3 content that was gained in the growing season
in 2005 (Fig. 3).
Spatial variation of soil CO2 respiration
Soil CO2 respiration rates decreased with decreasingair
humidity along the SRB. There were marked changes in
response curves of soil CO2 respiration during 2004. Soil
CO2 respiration rates were significantly different at the sites
of US, DG, FC, FS and ND (Fv = 7.73, P < 0.05, Table 1)
along the SRB. Soil CO2 respiration rates decreased along
the SRB, and ranged from 0.98 to 0.08 g m2 h2 at the DG
and ND sites. Soil CO2 respiration rates were significantly
different (F = 5.74, P < 0.05) at the two sites of FS and ND
in the growing season in 2005, and it was higher at the FS
site than the ND site. The soil CO2 respiration rate was
higher at the ND site than the FS site in spring originally(April–May) and was similar after October (Fig. 4).
Relationships among vegetation, environmental factors,
soil characteristics and soil CO2 respiration
The correlations in vegetation, environmental factors and
soil CO2 respiration were analyzed. The relationship
between the vegetation diversity index and soil CO2 respiration was 0.94. Soil CO2 respiration was in high correlation
with air humidity (r = 0.97, n = 15). The relationship
between the soil texture and soil CO2 respiration was not
Environ Geol (2008) 54:1403–1409
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Table 3 The difference of soil characteristics and soil respiration in two sites of FS and ND in the growing season in 2005
Sites
pH
SOC (%)
TN
CaCO3 (%)
SR (g m2 h1)
FS
ND
F-value
8.98 (0.20)
9.02 (0.22)
0.91
1.54 (0.77)
0.12 (0.02)
13.575*
0.14 (0.05)
0.02 (0.01)
19.549*
4.45 (0.44)
1.19 (0.23)
173.524**
0.16 (0.10)
0.05 (0.01)
5.74*
Standard deviation given in parentheses
* P < 0.05; ** P < 0.01
good (data not shown), nor was pH. The SOC and N element were two important factors for soil CO2 respiration.
SOC content was in the lower range from 2.22% at the FS
site to 0.64% at the FC site. The soil was infertile in the
SRB. The ratio of carbon to nitrogen was quite low, ranging
from 14.5–4.0. The changes in soil CO2 respiration were in
high correlation with that of the content of CaCO3
(r = 0.93, n = 12).
Fig. 3 Change of CaCO3 content in the growing season in two
sites,FS and ND, in 2005 (Zhu)
Fig. 4 Change of soil CO2 respiration in two sites of FS and ND in
2005 (Zhu)
Discussion
The vegetation diversity and evenness were in favor of soil
CO2 respiration. Rutigliano et al. (2004) showed that
vegetation cover influenced soil characteristics and
microbial properties, as indicated by the existence of fertile
islands (Collins and Cavigelli 2003). Therefore, the estimation of the influence of vegetation on soil CO2 respiration was an equivalently significant response to vegetation
diversity and evenness. Additionally, human activities such
as grazing animals, gathering branches, over-excavation
and mismanagement of water resources have disturbed the
ecosystem stability and broken the natural circle balance of
carbon in this arid zone.
Soil CO2 respiration was generally directly related to
temperature; the response was ameliorated with a decrease
in soil moisture in the arid zone (Conant et al. 2004).
However, large diurnal variation occurred during times of
adequate soil moisture in total ecosystem respiration,
which was primarily controlled by changes in temperature
(Flanagan and Johnson 2005). The soil CO2 respiration in
SRB showed no correlation with the temperature, but a
good correlation occurred with the air humidity that
reflected the soil moisture. Thus, the air humidity was the
limitation factor on soil CO2 respiration rather than temperature in the arid zone. Moisture became the dominant
environmental factor in the arid zone. When temperature
effects were held constant, moisture had an influence on
soil CO2 respiration in semi-arid grasslands during the
growing season (Flanagan and Johnson 2005). Soil texture
influenced the soil’s CO2 respiration response to soil
moisture at the sites. Soil CO2 respiration was suppressed
in the ND sitein 2005 during the growing season (April–
September). Sand played an important role in the surface
soil because of the great porosity for soil water evaporation. However, silt and clay can increase the soil’s waterholding capacity, giving an advantage to soil CO2
respiration, so there were no significant relationships between soil texture and soil CO2 respiration. Dilustro et al.
(2005) observed that clay may buffer soil moisture effects
on soil CO2 respiration. However, in the original spring
thawing snow water was enough to increase moisture to
promote soil CO2 respiration and air humidity indirectly.
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The correlation of C and N was higher, but the ratio of
C to N was lower (4.0–14.5) in the SRB. Gallardo and
Schlesinger (1992) demonstrated that the low ratio of C to
N limited microbial biomass by C in Chihuahuan desert
soil. Maestre and Cortina (2003) showed that the soil CO2
respiration was in a positive relationship with SOC content
in a Mediterranean semiarid steppe. The lower soil C
content limited the microbial activities and microbial biomass, thereby influencing soil CO2 respiration indirectly in
the SRB. Conant et al. (2004) showed the soil CO2 respiration responses to temperature may have been limited by
soil C content in semiarid soils. Ritz et al. (2004) showed
that total C and N were highly correlated in upland
grassland in the Scottish Borders.
The changing trend of soil CaCO3 content was similar to
that of soil CO2 respiration in this zone. The results showed
that CaCO3 may have a significantly positive effect on soil
CO2 respiration in scrublands in SRB. CaCO3 was ubiquitous, and formed the calcium stratum easily in the arid
zone (Duan et al. 1999). It influenced soil CO2 respiration
by controlling soil water movement, which impacted the
soil moisture. CaCO3 existed in states of liquid or solid, in
general, which would change from solid to liquid state or
vice versa when the pH changed. The reverse reaction of
dissolution and re-precipitation processes would occur
between CaCO3 and Ca(HCO3)2 (Pan 1999). The occurrence changed the motion state of CO2 gas in soil and
influenced soil CO2 respiration. Microbial metabolic processes produced organic acids (fermentation) or inorganic
acids (nitrification or sulfur oxidation), which contributed
to the dissolution and mobilization of carbonates (Rietz and
Hayes 2003). Thus, CaCO3 may release or absorb CO2 in
response to the magnitude of soil CO2 respiration. In the
arid zone, CaCO3 was an important factorworking on soil
CO2 respiration. Fuentes et al. (2006) showed the result
that soil CO2 respiration increased markedly after CaCO3
was added to acid soil.
Some action must be taken to keep the balance of the
carbonic circle. It would be helpful to preventanimal grazingandgathering branches, over-excavation and mismanagement of water resources for cropland irrigation, which
have disturbed the ecosystem stability. Positive actions
would be to increase the vegetation diversity and coverage
degree in order to reduce the event of alternating dry and
wet periods in the soil and promote the stability of CaCO3
content, which decreases the loss of soil carbon.
Conclusions
Arid and semiarid ecosystems occupy over two-fifths of
Earth’s total surface (Reynolds 2001). In arid zones, the
vegetation diversity and evenness have markedly affected
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Environ Geol (2008) 54:1403–1409
thesoil’s CO2 respiration. Air humidity and the response to
moisture are an important limitation factor on soil CO2
respiration in the arid zone. The soil CO2 respiration was
controlled by the SOC, but not N. CaCO3, the important
factor in soil CO2 respiration, can absorb or release CO2 and
alter soil CO2 respiration in the ecosystems. Understanding
variations in soil CO2 respiration and its components, and
their relation to environmental factors, can help guide forest
management. Increasing the vegetation diversity and coverage degree holds soil moisture in a state of low variation
in order to reduce the event of alternating dry and wet
periods of the soil, improves the magnitude of soil CO2
respiration and promotes the SOC content and the stability
of the CaCO3 content. The maintenance will strengthen the
ecosystem stability in the arid zone. The sustainable
development of ecology and society would benefit the region. The above-mentionedmeasure can depress soil CO2
respiration along the SRB and weaken the loss of carbon.
It is possible that spatial properties may also show a
strong temporal dynamic on soil CO2 respiration, which
would also warrant further study (Ritz et al. 2004).
Acknowledgments This study was funded by the National 863
project (2006AA10Z226), the Innovation Project of CAS (KZCX2YW-127) and the National Natural Science Foundation (40571011) of
China. The authors would like to thank to Mrs. Yue H. X. for the
laboratory assistance.
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