Soil CO2 flux dynamics in the two main plantation forest types in subtropical China

Science of the Total Environment 444 (2013) 363–368

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Soil CO2 flux dynamics in the two main plantation forest types in subtropical China Xinzhang Song a, b, Huanying Yuan a, b, Mark O. Kimberley c, Hong Jiang a, b,⁎, Guomo Zhou a, b, Hailong Wang a, b,⁎⁎ a b c

The Nurturing Station for the State Key Laboratory of Subtropical Silviculture, Zhejiang A&F University, Lin'an, 311300, China Zhejiang Provincial Key Laboratory of Carbon Cycling and Carbon Sequestration in Forest Ecosystems, Zhejiang A&F University, Lin'an, 311300, China Scion, Private Bag 3020, Rotorua 3046, New Zealand

H I G H L I G H T S ► ► ► ► ►

We investigate soil CO2 flux in Chinese fir and Moso bamboo plantations. Soil CO2 flux in both forest types shows similar daily and seasonal dynamic patterns. CO2 flux in Chinese fir forest is more sensitive to temperature than Moso bamboo. Higher CO2 flux was observed in the Moso bamboo than in the Chinese fir forest. This may influence the carbon sequestration capacity of these two forest types.

a r t i c l e

i n f o

Article history: Received 11 September 2012 Received in revised form 1 December 2012 Accepted 3 December 2012 Available online 29 December 2012 Keywords: Chinese fir Moso bamboo Plantation Soil CO2 fluxes Soil respiration Subtropical

a b s t r a c t Chinese Fir and Moso bamboo are the two most important forest plantation species in subtropical China. However, information on greenhouse gas emissions from these forests is still scarce. A field study was carried out to compare soil CO2 flux dynamics in Chinese Fir and Moso bamboo forests over a 12-month period using the LI-8100 Soil CO2 Flux System. The soil CO2 flux in both forest types showed similar daily and seasonal dynamic patterns with the highest soil CO2 efflux at 14:00–16:00 in summer and the lowest in winter. Moso bamboo forest showed significant higher (Pb 0.01) annual mean soil CO2 fluxes (52.9 t CO2 ha−1 yr−1) than Chinese fir forest (27.9 t CO2 ha−1 yr−1). The large difference in soil CO2 fluxes may potentially influence the carbon cycle of the two forest types at the ecosystem scale. The CO2 flux from the soil showed a significant positive correlation (P b 0.0001) with soil temperature at 5 cm depth, a significant negative correlation (P b 0.01) with air relative humidity, and no significant correlation with soil moisture in either forest types. The Q10 value of soil respiration was higher in Chinese fir than Moso bamboo forest, indicating that soil respiration under Chinese fir forest will be more sensitive to temperature change. This study contributes to better understanding of the role Moso bamboo and Chinese fir forests may play in carbon cycle and global warming mitigation. © 2012 Elsevier B.V. All rights reserved.

1. Introduction Globally, the pool of carbon in soils is greater than the pool contained in vegetation or the atmosphere, and changes in soil carbon content can therefore greatly affect the global carbon budget (Raich and Schelsinger, 1992; Bellamy et al., 2005). Soil respiration is a major flux in the global

⁎ Correspondence to: H. Jiang, Zhejiang Provincial Key Laboratory of Carbon Cycling and Carbon Sequestration in Forest Ecosystems, Zhejiang A&F University, Lin'an, 311300, China. Tel.: +86 571 6374 2866; fax: +86 571 6374 2899. ⁎⁎ Correspondence to: H. Wang, Zhejiang Provincial Key Laboratory of Carbon Cycling and Carbon Sequestration in Forest Ecosystems, Zhejiang A&F University, Lin'an, 311300, China. Tel.: +86 571 63705212; fax: +86 571 63740889. E-mail addresses: [email protected] (H. Jiang), [email protected] (H. Wang). 0048-9697/$ – see front matter © 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.scitotenv.2012.12.006

carbon cycle, second only to gross primary productivity (Box, 1978; Raich and Schelsinger, 1992). Therefore, even a small change in the soil respiration flux may have considerable implications for the rate of change in atmospheric CO2 and therefore for climate change. The effect of increased atmospheric CO2 and associated global warming on forest soil carbon stocks is complex involving both positive and negative feedbacks. Firstly, plant photosynthesis accelerates under elevated atmospheric CO2 conditions, leading to increased accumulation of soil carbon (DeLucia et al., 1999; Lichter et al., 2008), but also increases the rate of soil respiration partially cancelling this effect (Jackson et al., 2009). Secondly, because increases in temperature accelerate soil respiration it is feared that global warming may increase the release of soil organic carbon (SOC) to the atmosphere (Cox et al., 2000). However, the impacts of climate warming on soil decomposition dynamics have not been fully resolved and it is unclear whether locally derived respiration/temperature relationships can be used to predict

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the effects of climate warming on soil respiration (Giardina and Ryan, 2000; Davidson and Janssens, 2006). The role that forests will play in mitigation of climate change through carbon sequestration will also be greatly influenced by forest management practices, and by global levels of deforestation and reforestation. Historically, deforestation has contributed significantly to the increase in atmospheric CO2. During deforestation, not only is there a release of carbon associated with the loss of forest biomass, but there can also be a longer term decline in SOC. This is because forest soils often contain higher stocks of organic carbon than soils of other land uses (Lal, 2005). There is less information on the effect on SOC of clearance of natural forest followed by conversion to managed plantation forest, although harvesting of temperate zone forests is associated with a loss of soil carbon especially from the forest floor layer which can take decades to recover under the regrowing forest (Nave et al., 2010). There are some evidence that soil carbon declines following conversion of natural to plantation forest in subtropical China. Implementation of intensive management practices, such as weeding, cultivation and mulching, can enhance soil respiration rates in forest plantations (Jiang et al., 2009; Liu et al., 2011; Zhang et al., in press). Zhou et al. (2006) found the SOC in a Moso bamboo (Phyllostachys pubescens) plantation declined by 34.7% 20 years after establishment before approaching a stable equilibrium status, while Wang et al. (2005) reported a 26.4% decline in SOC between a first and second generation Chinese fir (Cunninghamia lanceolata) plantation. The aim of this study was to determine soil respiration rates in subtropical Chinese plantation forests to improve our understanding of how these forests may contribute to climate change mitigation through carbon sequestration. In subtropical China, Chinese fir forest and Moso bamboo forest are the two most representative types of subtropical plantation forests established after clear cutting the evergreen broadleaf forest, a regional climax community. Chinese fir is a fast growing species prized for its wood quality, and has been widely planted for timber production in southern China (Yu, 2006), with plantations covering approximately 9.11 million ha and accounting for 30% of all plantations in China (Lei, 2005). Moso bamboo forests are the most important source of non-wood forest products in China and cover 3.37 million ha, accounting for 70% of China's bamboo forest area and 80% of the world's Moso bamboo area (Song et al., 2011). The most noticeable characteristic of these two types of plantation is their rapid growth rates. The annual carbon fixation of the tree crop at age 12 years was 5.10 t·ha − 1 in a Moso bamboo forest and 5.41 t·ha − 1 in a Chinese fir forest, these rates being higher than typical sequestration rates in tropical mountain rain forest (Zhao et al., 2009; Zhou and Jiang, 2004). This high annual rate of carbon accumulation makes plantations of Moso bamboo and Chinese fir become the most efficient forms among subtropical forest vegetation for carbon fixation, and they thus show considerable potential for mitigating climate change through carbon sequestration. Both types of forest have received increasing attention in recent decades and are regarded as important components in a government strategy of using forest plantations in southern China to address climate change (Song et al., 2011; Zhao et al., 2009). Most previous studies of carbon dynamics in Moso bamboo and Chinese fir forests have focused on stand productivity, storage and distribution of carbon (Xiao et al., 2007; Chen et al., 2009; Zhao et al., 2009). However, there has been no direct comparison and comprehensive assessment of the soil CO2 fluxes in these two main plantation types. Because soil respiration is a key part of the carbon cycle in forest ecosystems, this limits our understanding of the true role that forest plantations in southern China may play in mitigating climate change. The objectives of this study were to compare the dynamics of soil CO2 fluxes between the two major types of forest plantation in subtropical China, and to identify the environmental factors affecting them.

2. Materials and methods 2.1. Study site The study site was located in the Tianmu Mountain (30°18′30″N to 30°21′37″N and 119°24′11″E to 119°27′11″E) situated within the northwestern region of Zhejiang Province with a maximum elevation of 1506 m. The climate is representative of a subtropical monsoon region with a mean annual precipitation of 1420 mm and a mean annual temperature of 16.8 °C. Effective accumulated temperature greater than 10 °C is 2700° days, with July (24 °C mean temperature) and January (3 °C mean temperature) as the warmest and coldest months, respectively. Average annual sunshine hours are approximately 1940 h with an average of 234 frost-free days per year. Monthly mean air temperature and precipitation during the study period are shown in Fig. 1. The soil type is yellow red soil (Chinese system of soil classification), which is equivalent to Hapludult in USDA Soil Taxonomy (Soil Survey Staff of USDA, 1999). The soil is slightly acidic with a pH ranging from 4.7 to 6.0 (Wu et al., 2008). Both the Chinese fir and Moso bamboo plantations were established from native evergreen broadleaf forest about 60 years previously in sites of similar topography and soil type. The main management activity is harvesting by thinning in both plantations. In the Chinese fir plantation, trees are selectively harvested at an intensity of approximately 20% at about 15-year intervals. The Moso bamboo forest is harvested by thinning mature stems at age 6 or 7 years. In addition, a proportion of the bamboo shoots are selectively harvested each year. The Chinese fir forest contains trees with a greater range of ages while the bamboo forest contains plants within the age range 1–6 years. There has been no fertilizer application or weeding in either plantation. There are a few understorey species in both forests, principally Linderag lauca, Acer palmatum and Trachelospermum jasminoides in the Moso bamboo forest and Acer davidii, Nandina damestica, Camellia sinensis and Carex tristachya in Chinese fir forest.

2.2. Experimental design and measurement In May 2007, three 20 m×20 m measurement plots were established within each plantation. The culm height and external culm diameters at 1.3-m height above ground level or diameter at breast height (DBH) in each plot were measured. Soil samples were collected from 0 to 20 cm depth using stainless cutting ring samplers with 10 cm inner diameter from seven randomly selected locations in each plot and combined to form a composite sample. Soil bulk density was measured with cutting ring sampler method. The samples were brought back to the lab for further analysis. Soil total organic C content was determined using a potassium dichromate method. Soil total N concentration was measured using a semi-micro Kjeldhal method. Soil pH was determined using a pH meter on a 1:2 (w:v) soil/water extract. All methods described above for soil analysis are from Lu (1999). Stand and soil characteristics of both stands are summarized in Table 1. Within each plot, four randomly placed soil CO2 flux sampling PVC collars (10 cm inside diameter, inserted 5 cm from the ground surface into the soil) were installed. All PVC collars remained permanently installed throughout the experiment. Green plants growing inside each collar were cut carefully close to the soil surface with scissors before sampling. The soil CO2 flux was measured using the LI-8100 soil CO2 flux system (LI-COR Inc., Lincoln, NE, USA). Soil temperature and volumetric water content at 5 cm depth were measured adjacent to each respiration collar with two portable probes provided with the LI-8100. Other environmental factors, including air pressure, air relative humidity and air CO2 density, were also recorded automatically during experiment by the LI-8100. Measurements were carried out at 2-hour intervals between 8:00 and 18:00 on selected sunny days in May,

X. Song et al. / Science of the Total Environment 444 (2013) 363–368

Monthly mean air temperature Monthly cumulative precipitation

35

365

180 160

30

140 120 20

100

15

80 60

Precipitation (mm)

Temperature (oC)

25

10 40 5

20 0

0 Feb. Mar. Apr. May Jun.

Jul. Aug. Sep. Oct. Nov. Dec. Jan.

Time Fig. 1. Average monthly climatic data of the study site during experiment periods from February 2007 to January 2008.

where y is the soil respiration, t is the soil temperature at 5 cm depth, and a and k are the model coefficients. The temperature sensitivity parameter, Q10, was calculated from this model using the following equation (Liu et al., 2011; Luan et al., 2011):

or January. In both forests, the highest measured soil CO2 efflux was in August with maximums of 6.67 μmol CO2 m −1 s −1 for Moso bamboo and 4.98 μmol CO2 m−1 s−1 at 14:00 for Chinese fir. The two plantations also showed similar seasonal dynamics in soil CO2 fluxes (Fig. 3), being highest in summer with 6.30 μmol CO2 m −1 s −1 for Moso bamboo forest and 4.09 μmol CO2 m −1 s−1 for Chinese fir forest, followed by spring, and lowest in winter. The average annual CO2 flux from the soil in Moso bamboo forest was significantly higher than in Chinese fir forest as was the mean in every season. Mean annual soil CO2 effluxes were 3.82 μmol CO2 m −1 s −1 and 2.01 μmol CO2 m −1 s −1 in Moso bamboo forest and Chinese fir forest, respectively, these being the equivalent to an annual efflux of 52.90± 2.80(mean ± SD)t CO2 ha−1 yr−1 and 27.89 ±2.34 t CO2 ha−1 yr−1, respectively.

Q 10 ¼ a  expðkðt þ 10ÞÞ=a  expðkt Þ ¼ expð10kÞ:

3.2. The effect of environmental factors on soil CO2 fluxes

August, and November 2007, and January 2008, representing spring, summer, autumn, and winter, respectively. 2.3. Data analysis An exponential regression model was used to describe the relationship between soil respiration and soil temperature: y ¼ a  expðkt Þ

ð1Þ

ð2Þ

One way analysis of variance (ANOVA) and least significant difference (LSD) tests were performed to test the statistical significance of differences in the soil CO2 flux, soil temperature, soil moisture content and soil characteristics between the two plantations. Regression analysis was performed to determine the relationship between soil CO2 flux and environmental variables. Analyses were performed using the SPSS software (SPSS 13.0 for windows, SPSS Inc., Chicago, IL, USA). 3. Results 3.1. Soil CO2 flux dynamics of two plantations The soil CO2 flux in both forest types showed similar daily dynamics (Fig. 2). In May and August, the soil CO2 flux ascended gradually from 8:00, achieving a maximum rate at 14:00 or 16:00, and then descending, but there were no obvious daily fluctuations in October

The soil temperature at 5 cm depth in two plantations also showed similar seasonal dynamics (Fig. 3), being highest in summer and lowest in winter but there was no significant difference between forest types except in autumn. A significant (Pb 0.0001) exponential relationship was found between soil CO2 efflux and soil temperature in both Moso bamboo forest and Chinese fir forest, with a stronger correlation in Chinese fir forest (Fig. 4). The temperature sensitivity (Q10) of soil respiration was 2.18 and 3.13 in Moso bamboo and Chinese fir forest, respectively. Soil moisture did not show obvious seasonal variation and there was no significant correlation with the soil CO2 flux in either forest type. Correlations were tested between soil CO2 flux and environmental variables measured during the experimental period in August 2007 (Table 2). There were significant (P b 0.001) correlations between CO2 flux from the soil and air pressure but the correlation was positive in Moso bamboo forest and negative in Chinese fir forest. There was a significant (P b 0.01) negative correlation between soil CO2 efflux and air

Table 1 Stand and soil characteristics of study sites in the Moso bamboo forest (MB) and Chinese fir forest (CF) in Tianmu Mountain, Eastern China. Forest type

Altitude (m)

Mean stand density (trees ha−1)

Mean DBH (cm)

Mean height (m)

Soil pH

Soil total N (mg·g−1)

SOM (mg·g−1)

Soil bulk density (g·cm−3)

MB CF

431 330

4578 2300

8.1 14.0

17.5 11.2

5.0a 5.8b

2.3a 7.3b

87.8a 110.3b

1.4 1.3

DBH: diameter at breast height. SOM: soil organic matter.

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Soil CO2 flux (umol m-2 s-1)

a

May-2007 Aug-2007 Oct-2007 Jan-2008

8

b6

7

5

6

4

5 3 4 2

3 2

1

1

0

0 6

8

10

12

14

16

18

20

6

8

10

12

Time

14

16

18

20

Time

Fig. 2. Daily and seasonal variations of soil CO2 fluxes in Moso bamboo forest (a) and Chinese fir forest (b). Error bars are standard error of means, n = 12.

relative humidity in both two plantations. No significant correlation between soil CO2 flux and air CO2 density was observed in either forest type. 4. Discussion 4.1. Effect of environmental factors on soil CO2 fluxes

observed in Moso bamboo forest by Fan et al. (2009) and in Chinese fir forest by Zhang et al. (2007) in Hunan province in southern-central China. The obvious daily and seasonal variations in soil CO2 flux and significant (P b 0.0001) positive correlation between soil CO2 efflux and soil temperature in both plantations indicate that seasonal variation of soil temperature is a key factor affecting the soil CO2 flux. Previous observations in subtropical regions of China have reported similar findings (e.g. Tang et al., 2006; Sheng et al., 2010; Liu et al., 2011). The higher soil

The daily patterns of variation in soil CO2 flux found in this study were strongly related to soil temperature. Similar results have been

a

10 8

6 6

4

4

2

0 30 25

Soil temperature (°C)

0.078x y=0.990e 2 R =0.887, p<0.0001

8

Soil CO2 flux (umol m-2 s-1)

Soil CO2 flux (umol m-2 s-1)

MB CF

2

0

b

6 5

y=0.302e

R =0.755, p<0.0001

4

20

0.114x

2

3 15 2 10

1

5

0

0 May-2007

Aug-2007

Nov-2007

Jan-2008

Time Fig. 3. Seasonal variation of soil CO2 fluxes and soil temperature in Moso bamboo forest and Chinese fir forest.

0

5

10

15

20

Soil temperature at 5 cm depth

25

30

(oC)

Fig. 4. Relationship between soil CO2 flux and soil temperature at 0.05 m depth in Moso bamboo forest (a) and Chinese fir forest (b).

X. Song et al. / Science of the Total Environment 444 (2013) 363–368 Table 2 Relationships between soil the CO2 flux and environmental variables in the Moso bamboo forest (MB) and Chinese fir forest (CF). Environment factor

Forest type

Regression equation

R2

P

Air pressure

MB CF MB CF MB CF

Y = 1.196x − 107.4 y = −4.430x + 432.4 Y = −0.025x + 8.352 y = −0.090x + 13.58 Y = −0.003x + 7.659 y = −0.024x + 16.97

0.67 0.70 0.48 0.86 0.07 0.20

b0.001 b0.001 b0.01 b0.001 >0.05 >0.05

Air relative humidity Air CO2 density

respiration Q10 value in Chinese fir forest suggests that the soil CO2 flux in Chinese fir forest was more sensitive to temperature change than in Moso bamboo forest. This may be partly related to the higher levels of soil organic matter and nutrients in the Chinese fir forest (Table 1) as a positive correlation between soil respiration and SOC has been reported (Sheng et al., 2010; Yang et al., 2011). It would be expected that under future scenarios of global warming, soils of Chinese fir forest may contribute increasingly more CO2 emissions to the atmosphere than those of Moso bamboo forest. No significant correlation was found between soil CO2 fluxes and soil moisture in either forest type. Similar results have been reported for Schima superba and Chinese fir plantations in Fujian province in the southeast of China (Sheng et al., 2010), and for a Chinese fir plantation in Hunan province in southern-central China (Zhang et al., 2007). However, other studies have found significant positive correlations between soil CO2 flux and soil moisture in subtropical areas under a variety of land uses (Yang et al., 2007; Sheng et al., 2010; Liu et al., 2011). These conflicting observations suggest that the relationship between soil respiration and soil moisture is complicated and warrants further investigation. The significant (P b 0.01) negative correlation between soil CO2 efflux and air relative humidity in both two plantations indicates that a high level of air relative humidity can restrain soil CO2 emissions in both forest types. A possible reason is that high relative air humidity in forests can restrict the air flow thus to some extent limiting CO2 emissions from the soil. 4.2. Effect of forest type on soil CO2 fluxes In this study, the Moso bamboo forest showed a significantly higher annual mean soil CO2 efflux (52.90 t CO2 ha−1 yr−1) than the neighboring Chinese fir forest (27.89 t CO2 ha−1 yr −1), which may partially be due to the different land cover (forest type) and management practices. Although both Chinese fir and Moso bamboo plantations were converted from the same native evergreen broadleaf forest approximately 60 years ago, there are significant differences in soil and stand characteristics between Chinese fir and Moso bamboo plantations (Table 1) because of the land cover change (forest type) and implementation of different management practices. Land use and cover change would alter the quality and quantity of plant-derived organic carbon inputs to the soil, and physical–chemical properties and microbial activities of soils, which would consequently influence soil respiration. Differences in the soil CO2 flux among forest types in subtropical regions of China have been observed in other studies (Table 3) and indicate that soil CO2 emission is strongly regulated by forest type. Observations from four Moso bamboo forests (Fan et al., 2009; Liu et al., 2011; Wang et al., 2011; the current study) and six Chinese fir forests (Fang et al., 2005; Yang et al., 2007; Wang et al., 2009; Sheng et al., 2010; Zhu et al., 2010; the current study) on various sites in subtropical China show a significantly higher (P b 0.05) mean annual soil CO2 effluxes in Moso bamboo forest (44.5 t CO2 ha−1 yr−1) than Chinese fir forest (24.2 t CO2 ha−1 yr −1) (Table 3). The soil respiration rate for Chinese fir forest reported here is comparable to global estimates for temperate coniferous forests or dry tropical forests which average about 25 t CO2 ha−1 yr−1, much lower than those for moist tropical

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Table 3 Annual soil CO2 flux amount of major forest ecosystems in the subtropical regions of China. Forest types

Annual soil CO2 fluxes References (t CO2 ha−1 yr−1)

Moso bamboo forest Moso bamboo forest Moso bamboo forest Moso bamboo forest Chinese fir forest Chinese fir forest Chinese fir forest Chinese fir forest Chinese fir forest Chinese fir forest Castanopsis kawakamii plantation Schima superba plantation Pinus massoniana forest Pine forest Mixed pine and broadleaf forest Secondary evergreen broadleaf forest Monsoon evergreen broadleaf forest Evergreen broadleaf forest Evergreen broadleaf forest Natural forest Secondary forest

52.90 33.94 41.17 49.87 27.89 31.52 16.66 15.85 35.27 18.04 34.60 40.37 36.63 37.00 38.00 22.79 41.00 50.38 42.20 68.24 46.16

This study Fan et al. (2009) Liu et al. (2011) Wang et al. (2011) This study Fang et al. (2005) Yang et al. (2007) Wang et al. (2009) Sheng et al. (2010) Zhu et al. (2010) Yang et al. (2007) Sheng et al. (2010) Yang et al. (2004) Yi et al. (2007) Yi et al. (2007) Xiao (2003) Yi et al. (2007) Yang et al. (2007) Liu et al. (2011) Sheng et al. (2010) Sheng et al. (2010)

forests which average 46 t CO2 ha−1 yr−1 (Raich and Schelsinger, 1992), but slightly higher than Japanese plantation forest which average about 20 t CO2 ha−1 yr−1 (Ishizukaa et al., 2006). It is also lower than the rate of most other subtropical Chinese forest types such as evergreen broadleaf forest (Table 3). These moderate levels of soil respiration for Chinese fir are not consistent with a significant decline in SOC. However, this may not be true for Moso bamboo which has a high soil CO2 efflux compared with most other forest types. Previous studies have found that autotrophic respiration (root respiration) comprise about 28.3% and 40.2% of total soil respiration in Moso bamboo forest (Fan et al., 2009) and Chinese fir forest (Chen et al., 2005), respectively. Therefore, the mean annual CO2 flux from the soil excluding autotrophic respiration in Moso bamboo forest is about twice that of Chinese fir forest (31.9 t CO2 ha−1 yr−1 compared with 14.5 t CO2 ha−1 yr−1). It has been reported in a number of previous studies that soil organic carbon content decreased following land use change from the native evergreen broadleaf forests to Moso bamboo plantations (Zhou et al., 2006). We expect that the relatively high soil respiration in Moso bamboo plantations may have contributed to the decline of soil organic carbon content in these forests. Of course, soil carbon sequestration is dependent on carbon inputs and outputs. The measurement about soil respiration only represents the soil carbon outputs and thus cannot comprehensively reflect soil carbon sequestration. Therefore, further research is required to verify this expectation. It is possible that the high soil CO2 emissions especially for Moso bamboo forest may be influenced by management activities such as cultivating, thinning and harvesting operations (Zhou et al., 2006; Liu et al., 2011). More research is required to determine whether this is so and to develop management regimes that are associated with reductions in soil CO2 emissions. 5. Conclusions The soil CO2 efflux in Moso bamboo forest and Chinese fir forest showed similar daily and seasonal dynamic patterns with the highest soil CO2 efflux at 14:00–16:00 in summer and the lowest in winter. Moso bamboo forest showed significantly higher (P b 0.01) annual mean soil CO2 fluxes than Chinese fir forest. The CO2 flux from the soil showed a significantly positive correlation (P b 0.0001) with soil temperature, a significantly negative correlation (P b 0.01) with relative humidity, and no significant correlation with soil moisture in either forest type. The Q10 value of soil respiration was higher in Chinese fir than

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