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Variation of soil respiration and its environmental factors in Hulunber meadow steppe
Acta Ecologica Sinica 35 (2015) 1–4
Contents lists available at ScienceDirect
Acta Ecologica Sinica j o u r n a l h o m e p a g e : w w w. e l s e v i e r. c o m / l o c a t e / c h n a e s
Variation of soil respiration and its environmental factors in Hulunber meadow steppe Xu Wang, Yuchun Yan, Shu Zhao, Xiaoping Xin *, Guixia Yang, Ruirui Yan Hulunber Grassland Ecosystem Research Station, Institute of Agricultural Resources and Regional Planning, Chinese Academy of Agricultural Sciences, Beijing 100081, China
A R T I C L E
I N F O
Article history: Received 19 November 2012 Revised 21 June 2013 Accepted 6 September 2013 Available online Keywords: Meadow steppe Soil respiration Temperature Soil water content Q10
A B S T R A C T
In order to understand the variations of soil respiration with the controlling environmental factors, continuous monitoring was carried out in Hulunber meadow steppe by an automated chamber system, LI8150, from 2009 to 2011. The results showed that soil respiration exhibited an apparent diurnal variation and seasonal dynamics. Diel maximum soil respiration often appeared between 13:00 and 14:00, while the minimum occurred between 4:00 and 5:00 in the morning. Soil respiration in the growing season from May to September was higher than that in the non-growing season. The peak value often occurred in July and August and the lowest was close to zero in winter. Soil respiration had a significant exponential relationship with soil temperature at 5 cm depth (P < 0.01), which could explain the 86.1–91.1% variation in soil respiration. A significant linear relationship was indicated between soil respiration and soil water content at 10 cm depth (P < 0.05). Soil respirations in 2009, 2010 and 2011 were estimated to be 465.0 gC m−2, 539.2 gC m−2 and 553.2 gC m−2 respectively. In addition, the temperature sensitivities of soil respiration (Q10) were calculated as 3.32, 3.55 and 4.05, respectively. The value of Q10 could cause a lower evaluation derived from observation in a short time, such as considering only the growing season. Field observation of soil respiration should cover all the possible time in the whole year, including the growing and non-growing seasons. © 2014 Ecological Society of China. Published by Elsevier B.V. All rights reserved.
1. Introduction Grassland is one of the main types of territorial ecosystem, occupying 25% of the land area [1]. The total carbon storage of grassland is about 266.3 Pg and 89.4% is stored in soil [2]. Soil respiration is the main approach for soil organic carbon (SOC) to release from soil. It is a crucial linkage of the carbon cycle and playing an important role for climate change [3]. It is very important to explore the variation of soil respiration with its controlling factors for deep understanding of the mechanism of carbon cycle in grassland and quantifying carbon balance in region [4]. The grassland occupies 41% of the total land area in China, and have strong spatial heterogeneity in vegetation, soil, water and heat conditions, which cause a distinct spatial heterogeneity of soil respiration, thus enhanced the difficulty for the accurate estimation of soil carbon flux in large scale. Therefore, further research on soil respiration should be carried out in different regions and different grassland types. At present, although there have been much domestic research on soil respiration of grassland ecosystem [5–11],
* Corresponding author. Hulunber Grassland Ecosystem Research Station, Institute of Agricultural Resources and Regional Planning, Chinese Academy of Agricultural Sciences, Beijing 100081, China. Tel.: +86(010)82109615. E-mail address: [email protected] (X. Xin).
the study and long-term observation on soil carbon flux remains insufficient in Hulunber meadow steppe, as China’s largest temperate meadow steppe, based on 3 years continuous observation on soil respiration by soil carbon flux automatic measurement system in Hulunber Grassland Ecosystem Research Station. This study focused on the characteristics of soil respiration with its environmental controlling factors in Hulunber temperate meadow steppe, which may provide scientific basis and data support for accurate estimation of regional carbon budget.
2. Materials and methods 2.1. Site description Hulunber meadow steppe is located in gentle hilly area of the greater Khingan Range, with a temperate semi-arid continental climate characterized with a long cold winter, short cool summer, dry windy spring and fall of early frost and sudden drop in temperature. Annual average temperature is from −5 to 0 °C, with great temperature difference between day and night and large annual temperature range. The average temperature of the coldest month (January) is between −18 and 30 °C, and that of the hottest month (July) is between 16 and 21 °C. The accumulated temperature (≥10 °C) is 1780–1820 °C, frost-free period 85–155 d. The precipitation is
http://dx.doi.org/10.1016/j.chnaes.2014.12.001 1872-2032/© 2014 Ecological Society of China. Published by Elsevier B.V. All rights reserved.
strongly heterogeneous in temporal distribution and annual precipitation is around 250–350 mm, of which 75% is assembled during the period from June to September. The main zonal vegetations include Filifolium sibiricum meadow steppe, Stipa baicalensis meadow steppe, and Leymus chinensis meadow, respectively located in the upper, middle and bottom of the hills, among which Stipa baicalensis meadow steppe is the typical vegetation. The soil is chernozem or dark chestnut. The experiment was carried out in Hulunber Grassland Ecosystem Research Station (N 49°19′, E 120°03′, alt. 628 m), located at Xieertala Farmland in Hailar District of Hulunber, Inner Mongolia Autonomous Region. The experiment site occupies an area of about 3.34 × 104 m2, which was enclosed at the end of 2006. Before enclosed, the field was grazed by the dairy cows. The dominant vegetation are consisted of Stipa Baicalensis, Leymus chinensis, Pulsatilla turczaninovii, Carex L. etc. 2.2. Field observation The measurements have been conducted from 2009 to 2011. Soil respiration was measured every 2 hours (once a hour in 2009) by an automatic measurement system (LI-8150, Licor Ltd, USA), which consists of an infrared analyzer, a multiplexer and five long-term observation chambers (20 cm in diameter). The chambers were set randomly in the field, keeping at least 10 m separation among them. The soil cycle were inserted into the soil at 3–5 cm depth for ensuring the air tightness of the chamber. The aboveground green plants were clipped regularly and maintain natural condition of the soil surface within the chambers. The environmental factors such as air temperature, humidity, pressure, solar radiation, wind speed, six levels (at 5 cm, 10 cm, 15 cm, 20 cm, 40 cm, 80 cm depth) of soil temperature and three levels (at 5 cm, 10 cm, 20 cm depth) of soil water content and rainfall were also monitored simultaneously by a nearby automated meteorological station. The monitoring frequency was every half an hour.
Soil temperature at 5cm depth °C
X. Wang et al./Acta Ecologica Sinica 35 (2015) 1–4 30 28
a
26 24 22 20 18 16
14 2009-07-24 00:00:00
Soil respiration rate µmolm-2 s-1
2
6.0
2009-07-25 00:00:00
2009-07-26 00:00:00
2009-07-27 00:00:00
2009-07-26 0:00:00
2009-07-27 0:00:00
b
5.5 5.0 4.5 4.0 3.5
2009-07-24 0:00:00
2009-07-25 0:00:00
Time Fig. 1. Diurnal variation of soil respiration and soil temperature at 5 cm depth at site in Hulunber grassland.
and the minimum between 4:00 and 5:00 am (Fig. 1a). This trend was well in accordance with the variation of temperature on soil surface (Fig. 1b), which indicated that temperature was the controlling factor of soil respiration in diurnal scale. 3.2. Seasonal variation of soil respiration
2.3. Statistical analysis The software SPSS13.0 was employed to do correlation and regression statistical analysis. The correlation coefficients between soil respiration and environmental factors were calculated by the Pearson method. The chart was modified by SigmaPlot 10.0. In addition, the value of Q10 was calculated on the exponential relation model [12], SR = aebT, Q10 = e10b, SR means soil respiration, T means temperature, a and b are simulation parameters. 3. Results
Soil respiration had significant seasonal variation characteristics in Hulunber meadow steppe during the observing period from 2009 to 2011, as showed in Fig. 2c. In general, soil respiration began to increase with the temperature increasing, and reached to a maximum in July and August, then decreased with the temperature decreasing deeply from September at the end of growing seasons. In winter, soil respiration tended to be steady and almost zero. The seasonal variation of soil respiration may be the result from the seasonal variation of temperature and distribution of rainfall, which happens mainly in July and August (Fig. 2a, 2b). 3.3. The correlations between soil respiration and the environmental factors
3.1. Diurnal variation of soil respiration The observation results showed that soil respiration in Hulunber meadow steppe had obvious diurnal variation characteristics (Fig. 1). In condition of stable sunny day (e.g. July 24th–27th in 2009), the variation of soil respiration was showed obviously in single peak curve in a day, with the maximum appearing from 13:00 to 14:00
Table 1 showed that the relationship between soil respiration and air temperature, soil temperature, soil water content, solar radiation, air pressure reached significant (P < 0.05) and very significant (P < 0.01) level, among which the correlation coefficients with soil
Table 1 Correlations between soil respiration and environmental factors.
r
Ta
T1
T2
T3
T4
T5
T6
W1
W2
W3
PAR
RAIN
RH
P
0.768**
0.813**
0.811**
0.800**
0.796**
0.754**
0.691**
0.700**
0.726**
0.619**
0.521*
0.193
0.046
−0.527*
Notes: r is correlation coefficient; Ta is air temperature (°C); T1–T6 mean soil temperature at 5 cm, 10 cm, 15 cm, 20 cm, 40 cm, 80 cm depth respectively (°C); W1–W3 mean soil water content at 5 cm, 10 cm, 20 cm depth (m3 m−3); PAR is photosynthetically available radiation (μmol m−2 s−1); RAIN is rainfall/mm; RH is relative humidity (%); P is atmospheric pressure (Pa). * P < 0.05, n = 552. ** P < 0.01.
X. Wang et al./Acta Ecologica Sinica 35 (2015) 1–4
ture could explain most variation of soil respiration. Based on the exponential relationship with soil temperature, soil respirations in Hulunber meadow steppe were estimated as 465.0 gC m −2 , 539.2 gC m−2 and 553.2 gC m−2 in 2009, 2010 and 2011 respectively. The Q10 of 2009, 2010 and 2011 were calculated as 4.05, 3.32 and 3.55.
Air temperature °C
40 20
a
0 -20
4. Discussion -40 -60 2009-01-01
2009-07-01
2010-01-01
2010-07-01
2011-01-01
2011-07-01
2012-01-01
2009-07-01
2010-01-01
2010-07-01
2011-01-01
2011-07-01
2012-01-01
2009-07-01
2010-01-01
2010-07-01
2011-01-01
2011-07-01
2012-01-01
60
Rain mm
50
b
40 30 20 10 0
2009-01-01
Soil respiration rate µmolm-2s -1
3
10 8
c
6 4 2 0
2009-01-01
Date Fig. 2. Seasonal variation of air temperature (a), rainfall (b) and soil respiration rate (c) during the period from 2009 to 2011.
temperature at 5 cm depth and soil water content at 10 cm depth were 0.81, 0.73 respectively, significantly higher than other factors. Soil temperature and moisture were the two factors which most closely related to soil respiration. 3.4. The influence of temperature and moisture on soil respiration Table 2 showed that there were very significant exponential relationships (P < 0.01) between diurnal average soil respiration and soil temperature at 5 cm depth in different years, and R2 ranged 0.86– 0.91. Meanwhile, there were also significant linear relationships (P < 0.05) between diurnal average soil respiration and soil water content at 10 cm depth with R2 from 0.60 to 0.77. Soil tempera-
Table 2 Regression models of soil respiration based on soil temperature, soil water content in the years 2009, 2010 and 2011. Year
2009 2010 2011
SR = aebT
SR = aW + b
a
b
R2
n
a
b
R2
n
0.254 0.365 0.362
0.140 0.121 0.127
0.861 0.911 0.910
208 206 138
20.91 23.49 36.28
−2.95 −2.18 −4.62
0.683 0.599 0.769
208 206 138
Notes: SR is soil respiration, T is soil temperature, W is soil water content, a and b are simulation parameters.
Similar to other studies on soil respiration of grassland ecosystem [13–15], in diurnal scale, soil respiration exhibited a single peak curve variation in Hulunber meadow steppe, which reached highest at noon and lowest in the morning. Because there was almost no change on soil water content in a day, and the diurnal variation of soil respiration was tightly consistent with soil temperature in the surface layer (0–5 cm). It could be concluded that the diurnal variation of soil respiration was mainly dominated by soil temperature. Diurnal variation of air temperature and soil temperature were closely related with solar radiation. Generally, the maximum of air and soil temperature occurred at 13:00–14:00 and the minimum at 4:00–5:00 before the sunrise in bare soil condition, which showed a similar dynamics of diurnal soil respiration in our study. Maybe the simple structure of grassland vegetation, low height of canopy and little litter accumulation weakened the “block and delay effect” of solar radiation and heat conduction into soil [16,17]. Soil respiration during growing season from May to September was higher than that in non-growing season, and the maximum often occurred in July and August. It was consistent with the variation of temperature and rainfall during the same period. The exponential relationships on temperature could explain most variation of soil respiration. Many studies [15,18] had illuminated that the dominant factors of soil respiration were different in different types of grassland for the difference of water and heat conditions. For example, in alpine meadow steppe temperature was the controlling factor of soil respiration, and moisture was the main limiting factor in desert steppe [19], while in typical grassland in semiarid area, temperature and moisture co-affected soil respiration together [20]. The study area was located in the temperate meadow steppe, where annual rainfall reached around 350 mm. It was in better water conditions than typical grassland and desert steppe, and soil water content was not the limiting factor of soil respiration. Therefore, this indicated that the seasonal variation of soil respiration was mainly dominated by temperature in Hulunber meadow steppe. In addition, because the rainfall and heat assembled in the same period, the effect of temperature could not be peeled off when the relationship between soil water content and soil respiration was analyzed, which may explain why there was a significant linear relationship between them. So it is necessary to further research the co-affections and the individual contribution of temperature and moisture on soil respiration. Raich and Schlesinger found the Q10 value of soil respiration in global was approximately 2.4, and ranged 2.0–3.0 in temperate grassland [3]. Our study found that the Q10 was 3.32–4.05 in Hulunber meadow steppe, which is close to the value 3.7–3.9 in subalpine meadow steppe in western Sichuan [21], higher than the value 2.16– 2.98 in typical grassland in Xilin River Basin [11], and lower than the Q10 value 7.6 in alpine meadow steppe in Tibet Plateau [22]. The Q10 in different types of grassland and geographical distribution was much different, which was due to the controlling factors such as temperature [23,24], moisture [25,26], biomass and soil organic carbon [27] as well. Since Q10 is a key parameter for evaluating the carbon flux and carbon budgets, which directly determined the accuracy of the carbon balance assessment, the effect of biotic and abiotic factors should be jointly considered when quantifying the Q10 values in a large scale. In addition, most measurements of
4
X. Wang et al./Acta Ecologica Sinica 35 (2015) 1–4
soil respiration often were carried out within several months or even shorter time during the growing season, and lack in non-growing seasons especially in winter. Q10 value could be lower evaluated for the reason that the temperature sensitivity of soil respiration was higher in lower temperature conditions. Therefore, when estimating Q10, field observation of soil respiration should cover all the possible time in the whole year, including the growing and nongrowing seasons.
Acknowledgements
[10] [11]
[12] [13]
[14]
This work is supported by National Natural Science Foundation of China (No. 41101216); “973” Program (No. 2010CB833502); International S&T Cooperation Project of China (No. 2012DFA31290); Special Fund for Agro-scientific Research in the Public Interest (No. 201003061).
[15]
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Contents lists available at ScienceDirect
Acta Ecologica Sinica j o u r n a l h o m e p a g e : w w w. e l s e v i e r. c o m / l o c a t e / c h n a e s
Variation of soil respiration and its environmental factors in Hulunber meadow steppe Xu Wang, Yuchun Yan, Shu Zhao, Xiaoping Xin *, Guixia Yang, Ruirui Yan Hulunber Grassland Ecosystem Research Station, Institute of Agricultural Resources and Regional Planning, Chinese Academy of Agricultural Sciences, Beijing 100081, China
A R T I C L E
I N F O
Article history: Received 19 November 2012 Revised 21 June 2013 Accepted 6 September 2013 Available online Keywords: Meadow steppe Soil respiration Temperature Soil water content Q10
A B S T R A C T
In order to understand the variations of soil respiration with the controlling environmental factors, continuous monitoring was carried out in Hulunber meadow steppe by an automated chamber system, LI8150, from 2009 to 2011. The results showed that soil respiration exhibited an apparent diurnal variation and seasonal dynamics. Diel maximum soil respiration often appeared between 13:00 and 14:00, while the minimum occurred between 4:00 and 5:00 in the morning. Soil respiration in the growing season from May to September was higher than that in the non-growing season. The peak value often occurred in July and August and the lowest was close to zero in winter. Soil respiration had a significant exponential relationship with soil temperature at 5 cm depth (P < 0.01), which could explain the 86.1–91.1% variation in soil respiration. A significant linear relationship was indicated between soil respiration and soil water content at 10 cm depth (P < 0.05). Soil respirations in 2009, 2010 and 2011 were estimated to be 465.0 gC m−2, 539.2 gC m−2 and 553.2 gC m−2 respectively. In addition, the temperature sensitivities of soil respiration (Q10) were calculated as 3.32, 3.55 and 4.05, respectively. The value of Q10 could cause a lower evaluation derived from observation in a short time, such as considering only the growing season. Field observation of soil respiration should cover all the possible time in the whole year, including the growing and non-growing seasons. © 2014 Ecological Society of China. Published by Elsevier B.V. All rights reserved.
1. Introduction Grassland is one of the main types of territorial ecosystem, occupying 25% of the land area [1]. The total carbon storage of grassland is about 266.3 Pg and 89.4% is stored in soil [2]. Soil respiration is the main approach for soil organic carbon (SOC) to release from soil. It is a crucial linkage of the carbon cycle and playing an important role for climate change [3]. It is very important to explore the variation of soil respiration with its controlling factors for deep understanding of the mechanism of carbon cycle in grassland and quantifying carbon balance in region [4]. The grassland occupies 41% of the total land area in China, and have strong spatial heterogeneity in vegetation, soil, water and heat conditions, which cause a distinct spatial heterogeneity of soil respiration, thus enhanced the difficulty for the accurate estimation of soil carbon flux in large scale. Therefore, further research on soil respiration should be carried out in different regions and different grassland types. At present, although there have been much domestic research on soil respiration of grassland ecosystem [5–11],
* Corresponding author. Hulunber Grassland Ecosystem Research Station, Institute of Agricultural Resources and Regional Planning, Chinese Academy of Agricultural Sciences, Beijing 100081, China. Tel.: +86(010)82109615. E-mail address: [email protected] (X. Xin).
the study and long-term observation on soil carbon flux remains insufficient in Hulunber meadow steppe, as China’s largest temperate meadow steppe, based on 3 years continuous observation on soil respiration by soil carbon flux automatic measurement system in Hulunber Grassland Ecosystem Research Station. This study focused on the characteristics of soil respiration with its environmental controlling factors in Hulunber temperate meadow steppe, which may provide scientific basis and data support for accurate estimation of regional carbon budget.
2. Materials and methods 2.1. Site description Hulunber meadow steppe is located in gentle hilly area of the greater Khingan Range, with a temperate semi-arid continental climate characterized with a long cold winter, short cool summer, dry windy spring and fall of early frost and sudden drop in temperature. Annual average temperature is from −5 to 0 °C, with great temperature difference between day and night and large annual temperature range. The average temperature of the coldest month (January) is between −18 and 30 °C, and that of the hottest month (July) is between 16 and 21 °C. The accumulated temperature (≥10 °C) is 1780–1820 °C, frost-free period 85–155 d. The precipitation is
http://dx.doi.org/10.1016/j.chnaes.2014.12.001 1872-2032/© 2014 Ecological Society of China. Published by Elsevier B.V. All rights reserved.
strongly heterogeneous in temporal distribution and annual precipitation is around 250–350 mm, of which 75% is assembled during the period from June to September. The main zonal vegetations include Filifolium sibiricum meadow steppe, Stipa baicalensis meadow steppe, and Leymus chinensis meadow, respectively located in the upper, middle and bottom of the hills, among which Stipa baicalensis meadow steppe is the typical vegetation. The soil is chernozem or dark chestnut. The experiment was carried out in Hulunber Grassland Ecosystem Research Station (N 49°19′, E 120°03′, alt. 628 m), located at Xieertala Farmland in Hailar District of Hulunber, Inner Mongolia Autonomous Region. The experiment site occupies an area of about 3.34 × 104 m2, which was enclosed at the end of 2006. Before enclosed, the field was grazed by the dairy cows. The dominant vegetation are consisted of Stipa Baicalensis, Leymus chinensis, Pulsatilla turczaninovii, Carex L. etc. 2.2. Field observation The measurements have been conducted from 2009 to 2011. Soil respiration was measured every 2 hours (once a hour in 2009) by an automatic measurement system (LI-8150, Licor Ltd, USA), which consists of an infrared analyzer, a multiplexer and five long-term observation chambers (20 cm in diameter). The chambers were set randomly in the field, keeping at least 10 m separation among them. The soil cycle were inserted into the soil at 3–5 cm depth for ensuring the air tightness of the chamber. The aboveground green plants were clipped regularly and maintain natural condition of the soil surface within the chambers. The environmental factors such as air temperature, humidity, pressure, solar radiation, wind speed, six levels (at 5 cm, 10 cm, 15 cm, 20 cm, 40 cm, 80 cm depth) of soil temperature and three levels (at 5 cm, 10 cm, 20 cm depth) of soil water content and rainfall were also monitored simultaneously by a nearby automated meteorological station. The monitoring frequency was every half an hour.
Soil temperature at 5cm depth °C
X. Wang et al./Acta Ecologica Sinica 35 (2015) 1–4 30 28
a
26 24 22 20 18 16
14 2009-07-24 00:00:00
Soil respiration rate µmolm-2 s-1
2
6.0
2009-07-25 00:00:00
2009-07-26 00:00:00
2009-07-27 00:00:00
2009-07-26 0:00:00
2009-07-27 0:00:00
b
5.5 5.0 4.5 4.0 3.5
2009-07-24 0:00:00
2009-07-25 0:00:00
Time Fig. 1. Diurnal variation of soil respiration and soil temperature at 5 cm depth at site in Hulunber grassland.
and the minimum between 4:00 and 5:00 am (Fig. 1a). This trend was well in accordance with the variation of temperature on soil surface (Fig. 1b), which indicated that temperature was the controlling factor of soil respiration in diurnal scale. 3.2. Seasonal variation of soil respiration
2.3. Statistical analysis The software SPSS13.0 was employed to do correlation and regression statistical analysis. The correlation coefficients between soil respiration and environmental factors were calculated by the Pearson method. The chart was modified by SigmaPlot 10.0. In addition, the value of Q10 was calculated on the exponential relation model [12], SR = aebT, Q10 = e10b, SR means soil respiration, T means temperature, a and b are simulation parameters. 3. Results
Soil respiration had significant seasonal variation characteristics in Hulunber meadow steppe during the observing period from 2009 to 2011, as showed in Fig. 2c. In general, soil respiration began to increase with the temperature increasing, and reached to a maximum in July and August, then decreased with the temperature decreasing deeply from September at the end of growing seasons. In winter, soil respiration tended to be steady and almost zero. The seasonal variation of soil respiration may be the result from the seasonal variation of temperature and distribution of rainfall, which happens mainly in July and August (Fig. 2a, 2b). 3.3. The correlations between soil respiration and the environmental factors
3.1. Diurnal variation of soil respiration The observation results showed that soil respiration in Hulunber meadow steppe had obvious diurnal variation characteristics (Fig. 1). In condition of stable sunny day (e.g. July 24th–27th in 2009), the variation of soil respiration was showed obviously in single peak curve in a day, with the maximum appearing from 13:00 to 14:00
Table 1 showed that the relationship between soil respiration and air temperature, soil temperature, soil water content, solar radiation, air pressure reached significant (P < 0.05) and very significant (P < 0.01) level, among which the correlation coefficients with soil
Table 1 Correlations between soil respiration and environmental factors.
r
Ta
T1
T2
T3
T4
T5
T6
W1
W2
W3
PAR
RAIN
RH
P
0.768**
0.813**
0.811**
0.800**
0.796**
0.754**
0.691**
0.700**
0.726**
0.619**
0.521*
0.193
0.046
−0.527*
Notes: r is correlation coefficient; Ta is air temperature (°C); T1–T6 mean soil temperature at 5 cm, 10 cm, 15 cm, 20 cm, 40 cm, 80 cm depth respectively (°C); W1–W3 mean soil water content at 5 cm, 10 cm, 20 cm depth (m3 m−3); PAR is photosynthetically available radiation (μmol m−2 s−1); RAIN is rainfall/mm; RH is relative humidity (%); P is atmospheric pressure (Pa). * P < 0.05, n = 552. ** P < 0.01.
X. Wang et al./Acta Ecologica Sinica 35 (2015) 1–4
ture could explain most variation of soil respiration. Based on the exponential relationship with soil temperature, soil respirations in Hulunber meadow steppe were estimated as 465.0 gC m −2 , 539.2 gC m−2 and 553.2 gC m−2 in 2009, 2010 and 2011 respectively. The Q10 of 2009, 2010 and 2011 were calculated as 4.05, 3.32 and 3.55.
Air temperature °C
40 20
a
0 -20
4. Discussion -40 -60 2009-01-01
2009-07-01
2010-01-01
2010-07-01
2011-01-01
2011-07-01
2012-01-01
2009-07-01
2010-01-01
2010-07-01
2011-01-01
2011-07-01
2012-01-01
2009-07-01
2010-01-01
2010-07-01
2011-01-01
2011-07-01
2012-01-01
60
Rain mm
50
b
40 30 20 10 0
2009-01-01
Soil respiration rate µmolm-2s -1
3
10 8
c
6 4 2 0
2009-01-01
Date Fig. 2. Seasonal variation of air temperature (a), rainfall (b) and soil respiration rate (c) during the period from 2009 to 2011.
temperature at 5 cm depth and soil water content at 10 cm depth were 0.81, 0.73 respectively, significantly higher than other factors. Soil temperature and moisture were the two factors which most closely related to soil respiration. 3.4. The influence of temperature and moisture on soil respiration Table 2 showed that there were very significant exponential relationships (P < 0.01) between diurnal average soil respiration and soil temperature at 5 cm depth in different years, and R2 ranged 0.86– 0.91. Meanwhile, there were also significant linear relationships (P < 0.05) between diurnal average soil respiration and soil water content at 10 cm depth with R2 from 0.60 to 0.77. Soil tempera-
Table 2 Regression models of soil respiration based on soil temperature, soil water content in the years 2009, 2010 and 2011. Year
2009 2010 2011
SR = aebT
SR = aW + b
a
b
R2
n
a
b
R2
n
0.254 0.365 0.362
0.140 0.121 0.127
0.861 0.911 0.910
208 206 138
20.91 23.49 36.28
−2.95 −2.18 −4.62
0.683 0.599 0.769
208 206 138
Notes: SR is soil respiration, T is soil temperature, W is soil water content, a and b are simulation parameters.
Similar to other studies on soil respiration of grassland ecosystem [13–15], in diurnal scale, soil respiration exhibited a single peak curve variation in Hulunber meadow steppe, which reached highest at noon and lowest in the morning. Because there was almost no change on soil water content in a day, and the diurnal variation of soil respiration was tightly consistent with soil temperature in the surface layer (0–5 cm). It could be concluded that the diurnal variation of soil respiration was mainly dominated by soil temperature. Diurnal variation of air temperature and soil temperature were closely related with solar radiation. Generally, the maximum of air and soil temperature occurred at 13:00–14:00 and the minimum at 4:00–5:00 before the sunrise in bare soil condition, which showed a similar dynamics of diurnal soil respiration in our study. Maybe the simple structure of grassland vegetation, low height of canopy and little litter accumulation weakened the “block and delay effect” of solar radiation and heat conduction into soil [16,17]. Soil respiration during growing season from May to September was higher than that in non-growing season, and the maximum often occurred in July and August. It was consistent with the variation of temperature and rainfall during the same period. The exponential relationships on temperature could explain most variation of soil respiration. Many studies [15,18] had illuminated that the dominant factors of soil respiration were different in different types of grassland for the difference of water and heat conditions. For example, in alpine meadow steppe temperature was the controlling factor of soil respiration, and moisture was the main limiting factor in desert steppe [19], while in typical grassland in semiarid area, temperature and moisture co-affected soil respiration together [20]. The study area was located in the temperate meadow steppe, where annual rainfall reached around 350 mm. It was in better water conditions than typical grassland and desert steppe, and soil water content was not the limiting factor of soil respiration. Therefore, this indicated that the seasonal variation of soil respiration was mainly dominated by temperature in Hulunber meadow steppe. In addition, because the rainfall and heat assembled in the same period, the effect of temperature could not be peeled off when the relationship between soil water content and soil respiration was analyzed, which may explain why there was a significant linear relationship between them. So it is necessary to further research the co-affections and the individual contribution of temperature and moisture on soil respiration. Raich and Schlesinger found the Q10 value of soil respiration in global was approximately 2.4, and ranged 2.0–3.0 in temperate grassland [3]. Our study found that the Q10 was 3.32–4.05 in Hulunber meadow steppe, which is close to the value 3.7–3.9 in subalpine meadow steppe in western Sichuan [21], higher than the value 2.16– 2.98 in typical grassland in Xilin River Basin [11], and lower than the Q10 value 7.6 in alpine meadow steppe in Tibet Plateau [22]. The Q10 in different types of grassland and geographical distribution was much different, which was due to the controlling factors such as temperature [23,24], moisture [25,26], biomass and soil organic carbon [27] as well. Since Q10 is a key parameter for evaluating the carbon flux and carbon budgets, which directly determined the accuracy of the carbon balance assessment, the effect of biotic and abiotic factors should be jointly considered when quantifying the Q10 values in a large scale. In addition, most measurements of
4
X. Wang et al./Acta Ecologica Sinica 35 (2015) 1–4
soil respiration often were carried out within several months or even shorter time during the growing season, and lack in non-growing seasons especially in winter. Q10 value could be lower evaluated for the reason that the temperature sensitivity of soil respiration was higher in lower temperature conditions. Therefore, when estimating Q10, field observation of soil respiration should cover all the possible time in the whole year, including the growing and nongrowing seasons.
Acknowledgements
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This work is supported by National Natural Science Foundation of China (No. 41101216); “973” Program (No. 2010CB833502); International S&T Cooperation Project of China (No. 2012DFA31290); Special Fund for Agro-scientific Research in the Public Interest (No. 201003061).
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