Characteristics of Soil Respiration and its Environmental Factors of Poplar Plantation on Beach Land of the Yangtze River

Available online at www.sciencedirect.com

Procedia Environmental Sciences Sciences 8(2011) 18–29 Procedia Environmental 13 (2012) 18 – 29

Procedia Environmental Sciences www.elsevier.com/locate/procedia

The 18th Biennial Conference of International Society for Ecological Modelling

Characteristics of Soil Respiration and its Environmental Factors of Poplar Plantation on Beach Land of the Yangtze River J.X. Zhoua, M.Cuia*, L. Yinb b

a Institute of Desertification Studies, Chinese Academy of Forestry，Beijing，100091， China College of Environmental Science & Engineering, Hunan University, Changsha, 410082, China

Abstract

Soil respiration, especially of forest and wetland ecosystem, plays an important role in the global carbon cycle. Poplar plantation on beach land is a unique artificial ecosystem, which has characteristics of both ecosystems. The characteristics of soil respiration of poplar plantation are rarely reported. Soil CO2 release rates in artificial poplar plantation on beach land of Hunan and Anhui province were measured using Infra Red Gas Analysis(IRGA) technique, and the dynamics of soil respiration rate (SRR) and its controlling factors such as temperature, soil water content (SWC) and vegetation structure under the forest were analyzed. The results showed that the diurnal dynamics of soil respiration presented a single peaked curve with the maximum occurring around 11:00－13:00.The value order of Soil CO2 release rates was Jun-06＞Oct-05＞Mar-06＞Oct-05.The mean value of efflux was 2.285±0.752µmol m-2 s-1(P＜ 0.05,n=13), and the coefficient of variation is 0.544. It implied great spatial differences of SRR in the regions. The sensitivity of soil respiration to the temperature above ground superior to the soil temperature at 5cm-depth. Because the influence from exterior factors was little, the curve of soil temperature at 5cm-depth was gently, that led to indistinct responses of SRR to it. The value of Q 10 of the poplar plantation was 1.282±0.785(P＜0.05,n=13),less than the global level except for wetland. The relationship between SWC and SRR was not good, so the SWC was not a limiting but an influencing factor to the efflux of CO2.Influenced by the high SWC, the gross efflux of CO 2 was reduced. The vegetation structure was also one of the important controlling factors. © 2011 Published by Elsevier B.V. Selection and/or peer-review under responsibility of School of Environment,

© 2011Normal Published by Elsevier Ltd. Beijing University.

Keywords: poplar plantation; soil respiration rate; vegetation structure; soil water content; Q10 * Corresponding author. Tel.: +086-10-62884057; fax: +086-10-62884016. E-mail address: [email protected].

1878-0296 © 2011 Published by Elsevier B.V. Selection and/or peer-review under responsibility of School of Environment, Beijing Normal University. doi:10.1016/j.proenv.2012.01.002

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1. Introduction Soil respiration plays an important role in the global carbon cycle, and counts for about 50-75% of the total respiration of the Terrestrial ecosystem[1]. Forest ecological system has a larger CO2 negative flux, and is an important carbon pool[2]. Forest soil carbon storage is the most important part, which counts for 73%, of the global soil carbon [3].Through soil respiration , CO2 is released from the forest soil surface, that is an important link of forest carbon cycle and the main way of carbon output from forest ecological system[4], and also an important source of atmospheric CO 2 [5]. Forest soil respiration has become one of the important monitoring items in the established long-term CO2 flux monitoring stations[6]. So long-term continuous observation and study of forest soil surface CO2 flux and its influencing factors is an essential part of the whole forest ecological system carbon balance. The researches on forest soil respiration have been reported since the 1970s abroad [7], while domestic researchers focused on this study relatively late. So far, the research on forest soil respiration mainly distributed in the temperate and the warm temperate forest region of Beijing[8-10], the broad-leaved forest region of Changbai mountain[11-13], the broad-leaved mixed forest of Dinghu mountain foothills[4,5,7,14], the rainforests of Xishuangbanna and hainan jianfengling[15-17]. At the same time, Related research was reported at Natural secondary forest region of liupanshan[18] and Subtropical karst forest[19]. About the Wetland ecological system, now we only have the study of Meadow grassland soil respiration, but the characteristics of soil respiration of poplar plantation were rarely reported. In this paper, Soil CO2 release rates in artificial poplar plantation on beach land of Hunan and Anhui province were measured using Infra Red Gas Analysis(IRGA) technique, and the dynamics of soil respiration rate (SRR) and its controlling factors such as temperature, soil water content (SWC) and vegetation structure under the forest were analyzed. It will reveal the influencing environmental factors of soil respiration, and will also provide data base and scientific basis for accurate estimation of the input and output of carbon balance in this region. 2. Study area Beach land is a kind of micro-relief of plain rivers, where seasonal floods often happened. There are about 6.0×105 hm2 beach land along the middle and lower reaches of the Yangtze River[24], and located in the subtropical monsoon climate zone with abundant biological, climatic and soil resources. It is also one of relatively developed areas in China. In the early 1980s, people began to exploit the land resource, and tried to plant poplar trees on the beach land, which led to great development of the local economy and improvement of the ecological environment. In this study, we choose the beach land of the Yangtze River, where has been planted the poplar plantation, as our experimental sites to study the characteristics of soil respiration and its influencing factors of the poplar plantation on the beach land in Hunan and Anhui province. The basic conditions of the study sites were presented in the table 1. 3. Methods and materials 3.1. Design of field experiment Considering the different distribution characteristics of undergrowth, we conducted investigation of undergrowth firstly. Forty-eight plots of 1 m×1 m were set, and the number, height, and coverage of plants were recorded. And we calculated the dominance index of each spices. We choose 5 and 8 plots with dominant vegetation communities in the plantations of Hunan and Anhui Province respectively, to measure soil respiration rate of CO2. The experimental sites were generally selected in the flat and

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uniform places. The diurnal dynamics of soil respiration rate were measured by short-Term Chamber and Long-Term Chamber at the same time. The investigation of undergrowth was finished in 2005 July and September respectively, the soil respiration rate was measured every two hours in October 2005, March 2006, June, and October. Tab.1 General situation of the experimental sites Experimental site

Hunan

Anhui

Location

Junshan District of Yueyang City

Huaining county of Anqing City

Coordinate

N 29º31′40″ E 112º51′34″

N 33° E117°

Climate

Humid subtropical monsoon climate

Humid subtropical monsoon climate

Temperature

16.5－17.0℃

Annual average rainfall

1200.7－1414.6mm

Annual average relative humidity

80％

Time of the beach land under water

20－50d，the longest reached 130d

soil

Fluvo-aquic soil

Fluvo-aquic soil

Distance between rows and trees

4 m×5 m

3 m×10 m

Density

742 trees/hm2

477 trees/hm2

Year of plantation

2000

1989

Spices

Populus deltoides Marsh. × P.euramericana

Populus deltoides Marsh.× P.euramericana

Vegetation under plantation

grasses only，coverage 70－80%, mainly：Cynodon dactylon,Hemarthria

Bushes（Salix sp.and Broussonetia papyifera grasses) and grasses(nearly the same as in Hunan)

3.2. Sample collection and analysis of the gas The dynamics of CO2 concentration in soil was measured by dynamic chamber-IRGA method, instrument model is LI-8100(made in LI-COR company of American and gene Co., LTD offers).The measuring principle, measurement process and main characteristics of IRGA are detailed in references [25], this paper will no longer repeat it. Before measurement, we put the soil collar into the soil 25-35 mm depth, which was made of polyvinyl chloride (PVC). And then cut off all the plants and clear dead branches, but try our best not destroy the soil. Tamp down the base soil in case air leakage. To avoid the fluctuation of the respiratory rate in the short term caused by fixing the gas chamber, experiment began after 24 hours. Calculation formula of emissions flux of CO2 in soil: W   10VP0 1  0   1000  C  FC  RS T0  273.15  t  (1) In the formula, (cm3),

P0

FC

is emissions flux of CO2 in soil (µmol m-2 s-1), V is volume of the gas chamber

is pressure of gas chamber (KPa),

W0

is moisture content of gas chamber (mmol mol-1),

R

is

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T constant of gas, S is superficial area of soil in collar (cm2), 0 is temperature of gas in gas chamber (℃), C  t is the rate of concentration of CO2 changes with the moisture content (µmol-1 s-1).

3.3. The determination of environmental factors The temperature and water content of soil were measured by connecting the temperature sensor and moisture sensor in the thermocouple of LI 8100 auxiliary instrument, at the same time of the measurement of soil respiration rate. 4. Results and analysis 4.1. The dynamics of soil respiration rate of poplar plantation in beach land Soil respiration plays an important role in forest ecological system, influenced by environmental factors, include temperature, soil moisture, root breathing and dead branches and leaves. These environmental factors change also reflects the change of plant phenology period [26]. The global storage of carbon in soil carbon library is twice as much as the carbon storage in atmosphere[27,28], so a small change in soil respiration would be made a strong effect on atmospheric carbon library. However, the soil as a huge library of carbon in the terrestrial carbon balance of payments have a lot of uncertainty, lead to lack of comprehensive when explain the characteristics of soil respiration in growing season only by environmental factors. For example, the length of the growing season largely influences the carbon flux of ecological system[29,30], so it is plant phenology period that influences the payment balance of soil respiration[31]. Considering the temperature changes are small ,the changes of soil respiration is not large also[17], in order to better research the relationship between soil respiration and environmental factor, and can better analysis the dynamic rule of soil respiration rate, we choose measured data in sunny for analysis. Mapping the dynamic changes rule of soil respiration on the computer. Using overall average moment estimators statistical methods (P < 0.05, n = 6) to calculate the repeated testing data[32], See Fig.1 Flux（µmol m-2 s-1）

6

Oct-05

Mar-06

Jun-06

Oct-06

5 4 3 2 1 0 9:00

11:00

13:00

15:00

17:00

20:00

23:00

2:00

5:00

7:00

时间（Time）

Fig.1 Diurnal dynamics of SRR in Poplar Plantation on Beach Land

From the change rule of the trend line, we can see that dynamics of soil respiration rate in poplar plantation was a single-peaked curve. The strongest of soil respiration was at 11:00－13:00, the most

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weak was at 2:00－5:00 a.m. There is a slow rise of soil respiration rate at 7:00 a.m. We can clearly see that from the dynamic trend line of soil respiration rate on mar 2006. See the date of Jun 2006, the maximum of soil respiration rate appeared at 17:00, in comparison to the other times experiment, the occurrence time of maximum have lag. The reason for the summer day high radiation energy, sunshine hours long, the sunshine percentage big; Vegetation have the strongest productivity in summer than other season, and the time of production dry matter by photosynthesis is the longest in a day of summer. Comprehensive above two aspects, and the soil respiration rate changes, the maximum dynamic time of occurrence in the summer relatively slowly. From the graph, it is known that soil respiration rate of jun 2006 is far greater than the rest 3 months, the reason is that time just to the growth peak time of a plant, temperature and soil moisture content have not become limit factor of soil respiration, the largest number of carbon products by the photosynthesis, so in this time made the carbon into the soil by plant is the biggest in a year, reflected in the soil respiration rate was bigger than the other times. The minimum of soil respiration rate appeared in October 2006. Investigate its reason, in a growing season, environmental factors in changes, such as the change of the temperature will cause the soil moisture, soil productivity, primary productivity of plant, carbon storage synchronous changes, and these factors of soil respiration rate changes with the season, In other words with plant phenology issue of the changes. For example, in the summer, soil temperature is high which made soil moisture content is likely to become the limit factor of soil respiration [33], or in winter, atmospheric temperature up to the lowest of a year, soil temperature more likely be limit factor of soil respiration[34].Our sample plots choose in beach land ecological system, where is land in winter and water in summer, so the soil moisture don't become the limit factor of soil respiration, so in plant growth season of summer, soil respiration rate higher than every other significant season. Also, in the autumn and winter, the plants in the end or the growth rests, nearly stop growth, and the temperature of soil is low that influences microbial activity, so that the soil respiration rate stay in lowest in all the phenology. In the spring, temperature picks up, plants start and began to grow, soil organisms also began activities, therefore, the respiration rate of soil in spring was higher than in the time of plant growth end o rests. From the graph, we can see that the soil respiration rate in October 2005 significantly greater than in October 2006, visible that soil respiration exist great interannual variability; Investigate its reason, the Yangtze river flood in 2005, the forest land flooded nearly two months and water back at september. And it is a drought year of 2006, forest land is not covered by water. It affects woodland soil water content higher in 2005 than in 2006, and the growth season of poplar is longer than 2006. So that the temperature, moisture content of soil and other micro environmental factors is superior than in 2006. Soil microbial activity violent that made leaves and plant root decomposition speedy, prompted release the CO2 from soil. 4.2. The influence of forest vegetation on soil respiration rate Different plant community made the temperature, humidity, content of soil organic matter and pH value and other ecological environment factors each are not identical, and the strength of soil respiration are also different[35]. Determining the rate of soil respiration in five advantage plant community in Hunan and eight in Anhui. Advantage of plant community situation see table 2. Different plant community have different soil respiration rate (figure 2), In hunan artificial poplar forest land, According to the size of the soil respiration rate alignment: cynodon dactylon and hemarthria ＞ leonurus artemisia ＞ Oenanthe javanica ＞ Cynodon dactylon and Daucus carota ＞ hemarthria. The average daily soil respiration rate respectively: 5.220µmol m-2 s-1、4.326µmol m-2 s-1、2.429µmol m-2 s1 、1.981µmol m-2 s-1、1.211µmol m-2 s-1. look at the changes of soil respiration rate in cynodon dactylon and hemarthria communities, the maximum respiratory rate 5.74µmol m-2 s-1, minimum 4.79µmol m-2 s-1, D-value 0.95µmol m-2 s-1. In the leonurus artemisia communities ， the maximum respiratory rate

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4.79µmol m-2 s-1, minimum 3.84µmol m-2 s-1, D-value 0.95µmol m-2 s-1. In the Oenanthe javanica communities, the maximum respiratory rate 3.1µmol m-2 s-1, minimum 1.875µmol m-2 s-1 ， D-value 1.225µmol m-2 s-1. In Cynodon dactylon and Daucus carota communities, the maximum respiratory rate 2.275µmol m-2 s-1, minimum1.71µmol m-2 s-1, D-value 0.565µmol m-2 s-1. In the hemarthria communities, the maximum respiratory rate 1.36µmol m-2 s-1, minimum 0.88µmol m-2 s-1, D-value 0.48µmol m-2 s-1. The 1 soil respiration rate changing for 0.48µmol m-2 s- －1.225µmol m-2 s-1 in this forest land. Tab.2 The list of dominant plant species in Poplar Plantation on Beach Land Experimental site

Hunan

Anhui

Dominant plant species Cynodon dactylon +Daucus carota Cynodon dactylon +Hemarthria Hemarthria Leonurus artemisia Oenanthe javanica Carex sp.+Paederia scandens Triarrhena lutarioriparia+ Cynodon dactylon Hemarthria Cynodon dactylon +Poa annua Poa annua+ Triarrhena lutarioriparia Achyranthes aspera+ Poa annua Ranunculus sieboldi)+ Leonurus artemisia Polygonum hydropipex+ Cynodon dactylon

The rangeability of soil respiration is bigger in different plant community of Anhui than Hunan (figure 3). This is because the afforestation time was 11 years earler in Anhui than Hunan, and afforestation density is smaller in Anhui. So the undergrowth structure is more complicated caused by secondary succession and human effects ,and rangeability are greater than Hunan. See the figure, Poa annua+ Triarrhena lutarioriparia communities、Polygonum hydropipex + Cynodon dactylon communities have the maximum soil respiration, the next was Ranunculus sieboldii + Leonurus artemisia、Triarrhena lutarioriparia + Cynodon dactylon communities。Hemarthria、Cynodon dactylon 、 Poa annua and Achyranthes aspera + Poa annua communities have the same treed, and all of them was bigger than Carex sp+ Paederia scandens communities. Press from big to small order, the average daily soil respiration rate of plant community, respectively: 2.722µmol m-2 s-1、2.592µmol m-2 s-1、2.187µmol m-2 s-1、1.841µmol m-2 s-1 、 1.462µmol m-2 s-1 、 1.439µmol m-2 s-1 、 1.301µmol m-2 s-1 、 0.991µmol m-2 s-1. The soil respiration rate changing for 0.64µmol m-2 s-1－1.68µmol m-2 s-1. Comprehensive above analysis, The different vegetation structure makes the significant difference of soil respiration rate. Two comprehensive analysis, the respiration rate of beach land forest soil changing 1 1 for: 0.48µmol m-2 s- －1.225µmol m-2 s-1. Diurnal soil respiration rate was 0.991µmol m-2 s- －5.220µmol -2 -1 -2 -1 m s 。average was 2.285±0.752µmol m s (P＜0.05,n=13), Variation coefficient was 54.4%, It seen that Diurnal dynamics of soil respiration rate have great variations in the different space, this shows the vegetation structure is a factor which affected soil respiration rate. In comparison, the soil respiration in this ecological system is lower than the warm temperate zone forest region of Beijing (5.92±1.32µmol m-2 s-1)[9] and the rainforests of hainan jianfengling island (10.6853µmol m-2 s-1)[16], higher than forest region of Changbai mountain (205.85－395.69mg m-2 h-1)[11], nearly to the Broad-leaved mixed forest of Dinghu mountain foothills (488.99－700.57 mg m-2 h-1)[7].

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b

c

d

e Flux(µmol m-2 s-1)

Flux(µmol m-2 s-1)

a 7 6 5 4 3 2 1

4

a

b

c

d

e

f

g

h

3.5 3 2.5 2 1.5 1 0.5 0

0 09:00 11:00 13:00 15:00 17:00 20:00 23:00 02:00 05:00 07:00

09:00 11:00 13:00 15:00 17:00 20:00 23:00 02:00 05:00 07:00

时间(Time)

时间(Time)

Fig.2 Diurnal dynamics of SRR in Hunan

Fig.3 Diurnal dynamics of SRR in Anhui

a: Cynodon dactylon +Daucus carota ； b: Cynodon dactylon +Hemarthria ；c: Hemarthria；d: Leonurus artemisia； e: Oenanthe javanica

a: Carex sp.+Paederia scandens ； b: Triarrhena lutarioriparia+ Cynodon dactylon；c: Hemarthria； d: Cynodon dactylon +Poa annua； e: Poa annua+ Triarrhena lutarioriparia；f: Achyranthes aspera+ Poa annua； g: Ranunculus sieboldi)+ Leonurus artemisia ； h: Polygonum hydropipex+ Cynodon dactylon

4.3. The relationship between temperature and soil respiration rate Correlation coefficient between soil respiration rate and surface temperature (R2 = 0.6773) was higher than the temperature of 5cm underground (R2 = 0.1523) in Hunan forest (figure 4). Index equation can be good to illustrate the point. When the temperature is lower the soil respiration scatterplot gathered in fitting curve, with the temperature increase the scatterplot deviating increase. Investigate its reason, the main source of organic matter in forest come from litter and grazing livestock manure on the surface, the organic matter soil is relatively low. Organic matter in under the action of microbial decomposition finally to be the CO2, and the activity of microorganism and a series of biochemical reaction rate is obviously positive related to the temperature[36], and right now the soil water content changes on the small or basic stability so that the temperature become the key factor of the CO 2 emissions. At the same time the temperature of 5cm by small influence of external environment temperature, the temperature change relatively gentle, CO2 emissions to its response flux is not very obvious. So the correlation of CO2 emissions and the surface temperature was higher than with the soil temperature, and correlation coefficient is high. Soil respiration rate of forest compared to the correlation of soil temperature at 5cm depth in Anhui, it has the high correlation with temperature of the earth's surface (figure 5). Like the forest land in Hunan, as when the temperature is lower, the community of the soil all respiration scatterplot gathered in fitting curve, as temperature grow, the deviating increase. The correlation of soil respiration rate and soil temperature at 5cm depth is bad, the main reason of soil temperature at 5cm depth have little effect by external environment temperature, the temperature change are small. From the graph, The daily change range of soil temperature at 5cm depth are small (both within in 5℃), can cause CO2 emissions to its response flux is not obvious. And reasonable vertical distribution of trees, shrubs and herbs, effective for reducing the surface temperature variations by undergrowth flare and wind. So it can accurately with the

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3.5

Flux(µmol m-2 s-1)

Fulx(µmol m-2 s-1)

passage of time. So the correlation of CO2 emissions daily change and surface temperature are better than with the soil temperature, high correlation coefficient. The Q10 of soil respiration is a convenient index to measure the sensitive degree of soil respiration and temperature changes, namely the temperature increase every 10 ℃, the soil respiration rate increase multiples. According to the statistical analysis on small and medium-sized sample, calculate the confidence interval of Q10 is 1.282 + /-0.785: (P < 0.05, n = 13). With the temperature rise every 10℃, the release strength of CO2 increases 128.2 + 78.5% in the beach land of poplars. The value greater than Beijing mountain area (1.51) [9], and nearly to the tropical rain forest in Xishuangbanna (2.03-2.36) [17] , lower than Changbai mountain forest land (2.44) [17] and Dinghu mountain forest (1.86-3.24) [4]. The lower Q10 is mainly due to the reasons of water in summer and land in winter natural feature of the middle and lower Yangtze River, make beach ecological system air relative humidity value on the high side (7090%), and also the soil water content keep in the high level (about 35%), the woodland soil structural is bad, that made solid, gas and liquid imbalance, which restricted the soil respiration intensity of temperature sensitivity. 3 2.5 2 1.5

y = 1.5913e 0.024x R 2 = 0.6773

1 0.5 0 0

5

10

15

20

25

30

3.5 3 2.5 2 1.5

y = 1.2549e 0.0365x R 2 = 0.1523

1 0.5 0 0

地表温度 Soil surface temperature(℃)

5

10

15

20

25

地下5cm处温度 Soil temperature at 5cm depth(℃)

4 3.5 3 2.5 2 1.5

y = 2.0213e 0.0259x R 2 = 0.759

1 0.5 0 0

5

10

15

20

25

Flux(µmol m-2 s-1)

Flux(µmol m-2 s-1)

Fig.4 Relationship between SRR and soil surface temperature, soil temperature at 5cm depth in Hunan Poplar Plantatio 4 3.5 3 2.5 2

y = 0.8626e 0.0854x R 2 = 0.1877

1.5 1 0.5 0 0

地表温度 Soil surface temperature(℃)

5

10

15

20

地下5cm处温度 Soil temperature at 5cm depth(℃)

Fig.5 Relationship between SRR and soil surface temperature, soil temperature at 5cm depth in Anhui Poplar Plantation

4.4. Relationship between SRR and SWC Kucera and Kirkham [37] noted that in soil humidity is reduced to under the condition of wilting water permanent or more than the field capacity, CO 2 emissions in soil surface will reduce.Soil water on the influence of soil respiration is mainly through plants and microbes on the physiological activities of the energy supply and microorganisms, the body of the soil redistribution, permeability and the diffusion of

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Flux(µmol m-2 s-1)

7

Flux(µmol m-2 s-1)

gases, etc of the adjustment and the control of the realization of the [36]. In the study, the linear equation analysis, the result is the area of artificial soil respiration rate poplars beaches with 5 cm of underground water content in poor correlation (figure 6, figure 7). Appear this kind of circumstance, on the one hand may be due to the determination of soil water content data is less, can't accurately model the out its and soil CO2 flux relations; On the other hand, the discretion of the soil water content on soil hole permeability has a great influence, is plant roots and aerobic soil microorganisms and the necessary condition of the soil water content, high will limit the spread of O 2 in the soil. This time soil at state, don't think gas and oxygen plant roots of microbial activity is restrained, the decomposition rate of soil organic matter, the soil of CO2 produced less. The soil respiration rate and water dispersible point that two forest land, figure 5 cm soil moisture content in high (30-40%), and the soil hole permeability is poor, restricted the soil CO2 gas emissions, so the soil respiration rate was sensitive to the change of water content, but also in the soil respiration rate of a tropical, subtropical forests in the cause of much lower. y = 14.386x - 1.655 R 2 = 0.0708

6 5 4 3 2 1

4

y = 5.0518x - 0.0076 R 2 = 0.0581

3.5 3 2.5 2 1.5 1 0.5 0

0 0

0.1

0.2

0.3

0.4

0.5

土壤5cm处含水量 Soil humidity at 5cm depth(%) Fig.6 Relationship between SRR and SWC at 5cm depth in Hunan Poplar Plantation

0

0.1

0.2

0.3

0.4

0.5

土壤5cm处含水量 Soil humidity at 5cm depth(%) Fig.7 Relationship between SRR and SWC at 5cm depth in Anhui Poplar Plantation

5. Discussion By the influence of the fluctuation of temperature, or the changes of humidity, the vegetation communities appear annual changes. Environmental factors like water, fertilizer, climate, heat and etc, changed with seasons alternating, which make the vegetation communities’ phenology phase changes accordingly. Soil respiration rate changes with plant phenology and environmental factors’ change. The characteristics of the soil respiration rate can illustrate this point better. Assuredly, there are a lot of factors affecting soil respiration rate. This article only analyzed the temperature and moisture factors, in order to study the characteristics of soil respiration rate changes deeply, we should start form the atmosphere - soil - vegetation system, considerate various of ecological factors on soil respiration rate comprehensively in the future research. In the study of artificial poplar forest soil respiration rate, we found that an exponential model can show the soil respiration response to temperature change better. Compared with the soil temperature at 5cm depth, the relationship between the soil respiration rate and surface temperature is better. Meanwhile, the different structures of vegetation make the dynamics of soil respiration differently. It shows the existence of spatial heterogeneity in the soil respiration. Researchers use the Q10 values of soil to illustrate the relationship of soil respiration with temperature changes. The current values of Q10 reported existed some difference. Rich and Schlesinger made a comprehensive study and then found that the value was 2.4. The Q10 value of the global scale (not including wetlands) based on temperature was 1.5. In our research, the Q10 value of soil respiration in the ecosystem of artificial poplar on beach land ranged between 1.110-

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1.459, which was lower than the global scale’s level(not including wetlands), which showed that Q10 in poplar plantation on the Yangtze River beach land varies with the vegetation coverage. The optimal soil moisture condition for soil respiration is usually close to the maximum field capacity, because most of the large pores are filled with air when the soil is at this state, which is conducive to the spread of O2, and the small pores are mostly occupied by water, easy to the spread of the soluble matrix. When the soil is too dry or too wet, the soil respiration will be inhibited. Results of regression analysis showed that the correlation between soil moisture content at 5cm depth and soil CO2 release was not significant. The reason is that our study areas belong to typical subtropical humid climate, annual precipitation is about 1200-1500 mm, soil moisture is too high, and restrained soil respiration. It can be identified that the soil moisture is not but the temperature in the plantation is, the limiting factor for soil CO2 release in the poplar plantation. But high water content will reduce the total soil respiration. Anyway, when study the soil respiration rate in a certain ecological type area, we must do a systematic, comprehensive planning and long-term pointing monitoring. That is the only way to achieve good results. So it is clearly not enough that we use the test results of 5 and 8 dominant vegetation communities in the two study areas to characterize all of the characteristics of the soil respiration of the artificial poplar plantation. And that is also the reason why the coefficient of variation or CV value of soil respiration rate we measured is pretty big. Additionally, when we went to work in the field, the climate is warm. So in the scatter chart of relationship between soil respiration rate and temperature, there is no distribution curve in the low temperature area. At the same time, in the research of soil respiration, except water and temperature, factors like soil fertility, the CO2 concentration, and people’s activity can also make a great influence on the intensity of soil respiration. We should consider these factors and renew our research in the further work. Acknowledgements Financial supports from National Natural Science Foundation of China (41071334) are highly appreciated. References [1] Hanson PJ, Edwards NT, Garten CT, Andrews JA. Separating root and soil microbial contributions to soil respiration: A review of methods and observations. Biogeochemistry 2000;48:115－46. [2] Zhang XQ，Wang WJ，Zu YG et al.. The Difference between Different Components of Soil Respiration in Several Types of Forests in Northeastern China. Journal of Northeast Forestry University 2005;33(2):46－8. [3] Yi ZG，Yi WM. Proceeding of studies on soil respiration of forest ecosystem. Ecology and Environment 2003;12(3):361－5. [4] Zhou CY, Zhou GY, Zhang DQ et al.. Study on CO2 efflux and their controlling factors in the forest of Dinghushan. Science in China Series D:Earth Sciences 2004;34:175－82. [5] Yi ZG, Yi WM, ZHou G Y, et al.. Soil carbon effluxes of three major vegetation types in Dinghushan Biosphere Reserve. Acta Ecologica Sinica 2003;23(8):1673－8. [6] Yang YS, Chen GS, Wang XG et al.. Response of soil CO2 efflux to forest conversion in subtropical zone of China. Acta Ecologica Sinica 2005;25(7):1684－90. [7] Zhou CY, Zhang DQ, Wang SY et al.. Diurnal variations of fluxes of the greenhouse gases from a coniferous and broadleaved mixed forests oil in Dinghushan. Acta Ecologica Sinica 2004;24(8):1741－5. [8] Liu SH, Fang JY, MAKOTO K. Soil respiration of mountainous temperate forests in Beijing, China. Acta Phytoecologica Sinica 1998;22(2):119－26.

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