沙漠研究 22-1, 37 -40 (2012 )"ICAL 1 / DT X"

Journal of Arid Land Studies－Refereed Paper－Soil CO2 Flux from Desert Ecosystems in Western China
Masaaki NARAMOTO*1) and Quan WANG 1)
Abstract: Soil CO2 fluxes were measured in July 2010 at two sites in a desert ecosystem, southern Dzungaria Basin of Xinjiang,
China. One site was located in irrigation fields, although seldom irrigated directly compared with neighboring fields. Tamarix
ramosissima dominates in this site with fragment patchy distributions of salt accumulation. Soil CO2 fluxes at bare soils,
salt-accumulated and litter-covered areas were measured with a closed system, which was constructed from CO2 gas analyzer,
chamber and air pump. The other site was located 20 km away from the first site, which was covered by algae-lichen in a patchy
fashion with the dominant shrub species of Haloxylon ammodendron. Soil CO2 fluxes were measured at algae-lichen andlitter-covered areas in this site. The results indicated that soil CO2 flux ranged from -0.8 to 1.4 µmol m-2 s-1 with higher soil CO2
release at litter-covered areas under canopies in both sites. Soil CO2 release at the litter-covered area in the first site was higher thanthat of the desert site. Soil CO2 flux was found to be negative at bare soil and salt-accumulated area. Increase in soil CO2 releasewith the increase in soil temperature was not identified from our results. On the contrary soil CO2 release often decreased with theincrease of soil temperature, suggesting the importance of water content at soil surface on soil CO2 flux in desert ecosystems.
Key Words: Algae-lichen, Litter, Salt accumulation, Soil CO2 flux

1. Introduction
Soil CO2 emission constitutes one of the main sources ofCO2 emissions to the atmosphere, accounting for about
25-35% of global annual emission (Bouwmann and German,1998; Schlesinger and Andrews, 2000). Global soil carbon
pool has been estimated at 2500 gigatons (Gt), which includes
1550 Gt of soil organic carbon, and this is 3.3 times the size ofthe atmospheric pool (760 Gt) (Lal, 2004). Generally, soil
CO2 emission and soil respiration increases with the increase intemperature (Epron et al., 1999; Conant et al., 2004).
Therefore, response of soil CO2 flux to warming is importantfor global carbon balance. On the other hand, some studies
have described the soil surface absorbed CO2 in arid andsemiarid ecosystems (Wohlfahrt et al., 2008; Xie et al., 2009),
although it is difficult to determine whether these results arerepresentative or anomalous. Since arid and semiarid
ecosystems covers more than 30% of the Earth’s land surface,the effect of soil CO2 flux in these ecosystems could be of greatsignificance for evaluation of global carbon cycle.
The mechanism of soil CO2 flux has many processes of
CO2 emissions and absorptions. Soil CO2 emission andrespiration is composed of an autotrophic component by roots,associated rhizosphere and a heterotrophic component by soil
micro-organisms that decompose organic materials.
Generally, temperature is a major environmental factor on soil
respiration (Epron et al., 1999; Conant et al., 2004; Sponseller,* Corresponding Author: amnaram@ipc.shizuoka.ac.jp
836 Ohya, Suruga-ku, Shizuoka city 422-8529, Japan1) Department of Environment and Forest Resources Science, Faculty of Agriculture, Shizuoka University2007). However, soil water content can also be an importantfactor particularly during dry season in arid and semiarid lands(Conant et al., 2004). Soil CO2 absorption has a biologicalprocess via photosynthesis by soil crust and non-biologicalprocess at alkaline soils. Soil crust communities such as
cyanobacteria, algae, mosses and lichens have considerable
photosynthetic potential, although this is limited by thehydration status (Lange et al., 1992; Lange et al., 1998; Jia etal., 2008). Xie et al., (2009) has shown that alkaline soils
absorbs CO2 with a non-biological and inorganic process, andthe rate of CO2 absorption depends on the salinity, alkalinity,temperature and water content of the soil.
Despite existence of numerous studies on soil CO2 flux
(Wohlfahrt et al., 2008; Xie et al., 2009; Conant et al., 2004),
available data is not sufficient to evaluate whether the results ofthese studies are a representative of arid and semiaridecosystems. Soil CO2 flux differs among surface type
(Maestre and Cortina, 2003; Zhang et al., 2007). Spatial
variation in soil CO2 flux is especially important for theestimation of CO2 flux in ecosystems because resource
distribution, conditions and organisms are markedly patchy insemiarid ecosystems (Schlesinger and Pilmanis, 1998; Maestreand Cortina, 2002). The main objective of this study was tocompare soil CO2 flux among soil surface types in the southern
Dzungaria Basin. The results of this study can provide more
information on evaluation of carbon cycle in arid and semiarid
ecosystems.

2

2-1

1-1

Tiµe

21:00

18:00

15:00

12:00

9:00

0
6:00

21:00

18:00

15:00

12:009:00

0

Fc (µµol µ-2 s -1)

30 July, 2010

1

6:00

Fc (µµol µ-2 s -1)

28 July, 2010

Tiµe

Fig. 2. Diurnal course of soil CO2 flux in irrigation field site (left) anddesert site (right). Closed circles (●): litter-covered area, closedtriangles (▲): bare soil, open triangles (▲): salt-accumulated area,open circles (○): algae-lichen area. Data are means ± SD (n=3).
Fig. 1. Map of study area.

2. Materials and methods
Measurements were conducted at two desert ecosystems
located in the southern Dzungaria Basin of Xinjiang in China(Fig. 1) in July 2010. One location was in irrigation fields(44°17’N, 87°56’E), although seldom irrigated directlycompared with neighboring fields. Tamarix ramosissima
dominates in this site with fragment patchy distributions of saltaccumulations. The other site was located about 20 km awayfrom the first site (44°43’N, 87°90’E), which is covered byalgae-lichen in a patchy fashion with Haloxylon ammodendron
as the dominant shrub species. Soil CO2 fluxes weremeasured at bare soils, salt-accumulated area and litter-coveredarea at the irrigation field site (from 7:30 - 20:00 Hours, on 28July) and at algae-lichen area and litter-covered area in theother desert site (from 13:30 - 20:00 Hours on, 29 July and10:00 - 20:30 Hours, on 30 July). The soil surface at baresoils did not have any litter as well as the salt-accumulated area.
Air temperature and relative humidity were measured with athermo recorder (RS-13, TABAI Espec, Japan) at 15-minintervals. The maximum and minimum temperatures were36 and 16°C, respectively, with lowest relative humidity at
daytime being ~ 20%.
Soil CO2 fluxes were measured with a closed system which
was constructed from infrared gas analyzer (IRGA, LI-820,LICOR, USA), chamber (cylingder r=5.25cm, L=15.0cm) andair pump (EAP-01, Asone, Japan). The chamber was madeby white vinyl chloride column which didn’t allow sunlight topenetrate completely. Data of IRGA were recorded every
5seconds by the data logger (MR2031-MU, CHINO, Japan)
with soil temperature (at 5cm in depth) during eachmeasurement.
Soil temperature was measured withthermocouple sensor (SCN05-113, CHINO, Japan). Soil
CO2 fluxes Fc (µmol m-2 s-1) were calculated by the following
formulaPV ∆C(1)Fc(t ) =⋅RTS ∆tTable 1. Soil CO2 flux at daytime (12:00-18:00) in irrigation field anddesert site. Data are means ± SD (n=8-22). Different lower
case letters indicate significant differences by using Tukey-Kramer
test after one-way ANOVA (P<0.05).
sitedate
irrigation field 28 Julydesert29 July
30 July

surfacebare soilsalt accuµulation
litteralgae-lichen
litteralgae-lichen
litterFc (µµol µ-2 s-1)
0.01±0.19-0.04±0.19
1.01±0.24
0.03±0.35
0.40±0.14
0.16±0.10
0.52±0.15

ccacbcb

Where P is the air pressure (Pa), V is the chamber volume (m3),
R is the molar gas constant (8.314 Pa m3 K-1 mol-1), T is the airtemperature (K), S is the soil surface area (m2), C is CO2
concentration (µmol mol-1).

3. Results and Discussion
Diurnal changes of soil CO2 fluxes are shown in Figure 2.
Soil CO2 flux ranged from -0.8 to 1.4 µmol m-2 s-1. Soil CO2
releases under canopies at litter covered soil were higher thanother surface type in both sites (P<0.05). The soil CO2
release at the litter-covered area in the irrigation field site washigher than the desert site (P<0.05) and the average CO2 flux
during daytime (12:00 to 18:00) was 1.01 µmol m-2 s-1 (Table1). Zhang et al. (2007) had found out that soil respiration rate
at T. ramosissima community was higher than sites dominatedby H. ammodendron community throughout the year inwestern Dzungaria Basin. They also estimated the soilrespiration rate to be 2.02 and 0.65 µmol m-2 s-1 in July at T.
ramosissima and H. ammodendron community, respectively.
The higher CO2 release at the litter-covered area during thisstudy in the irrigation field site with T. ramosissima as thedominant shrub species was consistent with the results byZhang et al. (2007), although the CO2 release of this study waslower. In addition, soil CO2 fluxes measured in this study
were almost consistent with the soil respiration rate measured
at the same area by Zhu et al. (2008). However, soil CO2 flux

was found to be negative at bare soil and salt-accumulated areaat specific times. This was evident when the average soil
CO2 flux during daytime was -0.04 µmol m-2 s-1 atsalt-accumulated area (Table 1) with the minimum of -0.24µmol m-2 s-1 at 13:30. These negative values indicated thatsoil absorbs CO2 in this ecosystem. Xie et al. (2009) reported
that the rate of CO2 absorption by alkaline saline desert soils
increased with the increase in salinity and the soil CO2 fluxmeasured at saline desert in July ranged from -1 to 1 µmol m-2
s-1. In the irrigation field site, the salinity of surface soils atsalt-accumulated area was assumed to be higher than that atother area based on the surface salt accumulation features.
The higher soil CO2 absorption rate at salt-accumulated area
was thought to be attributed to the higher salinity of surface soil
although there was no significant difference in the rates
between bare soil and salt-accumulated area. CO2 absorption
via photosynthesis by soil crust may be ruled out in this study
since the chamber walls which were not transmissive reduced
most of the incident light. The results of soil CO2 flux atalgae-lichen area might have been caused by soil respiration
including dark respiration of soil crust communities. The
lower soil CO2 release at algae-lichen area might be thought tobe due to the low amount of organic matter, litter and roots,
including soil crust communities.
Generally, soil respiration increases with the increase in soil
temperature. Contrary to the notion that soil CO2 release
increases with the increase in soil temperature, results from thisstudy indicated that soil CO2 release decreased with theincrease of soil temperature (Fig. 3). Conant et al. (2004)
described that soil respiration is related to temperature, but soil
moisture can have an overriding influence particularly during
dry season in semiarid lands. Soil respiration increases with
the increase in soil moisture (Epron et al., 1999; Conant et al.,2004) and increases immediately after rewetting byprecipitation (Sponseller, 2007). Dark respiration on
projection area base for soil crust also increases with theincrease in thallus water content (Lange et al., 1998).
2230 July, 2010

1015-1202530Ts (℃)

3540

Fc (µµol µ-2 s -1)

Fc (µµol µ-2 s -1)

28 July, 2010
1015-12025303540Ts (℃)

Fig. 3. Relationship between soil CO2 flux and soil temperature inirrigation field site (left) and desert site (right). Closed circles(●) and dotted line: litter-covered area, closed triangles (▲) andbold line: bare soil, open triangles (▲) and thin line:
salt-accumulated area, open circles (○) and dashed line:
algae-lichen area.

Therefore, water availability is a major driver of soil CO2 flux
in semiarid ecosystems. Although there was no rainfall
during the measurement period, we found dew on the twigs ofT. ramosissima in early morning on 24th July in the site at theirrigation field. Agam and Berliner (2006) described that theamount of dew can exceed that of rainfall for plants and hence
adding water to the soil by dew formation and water absorption
in arid lands. In addition, soil surface may trap water in theearly morning, leading to water content at thin surface layer
decreasing gradually from morning to afternoon. Our results
suggested that temperature was not a major factor controllingsoil CO2 fluxes but water content at soil surface was more
important on soil CO2 flux in this ecosystem.

Acknowledgement
We are grateful to Prof. Chen Xi, Xinjiang Institute ofEcology and Geography CAS China, for his help in field
experiments. This study was supported by Grant-in-Aid for
Scientific Research (B) 21403001 from Japan Society for the
Promotion of Science (JSPS).
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