Significance of soil temperature and moisture for soil respiration in a Chinese mountain area

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Abstract

We measured soil CO2 efflux rate at 11 sites with different vegetation types, elevations and soil textures in a mountain area near Taiyuan city, China, over a period of 1 year. The aim was to understand the seasonal and spatial changes of soil respiration (Rs) and its responses to soil temperature (Ts) and soil water content (Ws).

During the experimental period the mean Ts of the sites at 10 cm depth ranged from about 0 to 26 °C, and the mean Ws of the surface 0–10 cm soil layer fluctuated between the levels of field water holding capacity (WHC) and less than 1/3 of WHC. The temporal course of Rs and Ts could be fitted with a three-parameter Gaussian equation, with the higher values in August and the lower values in March and December. The annual mean Rs (based on daily-weighted monthly mean Rs) was 3.08 ± 2.12 (mean ± S.D.), 3.85 ± 2.92, 3.62 ± 2.71, 2.47 ± 2.12, 3.45 ± 3.35, 3.56 ± 2.80, 3.65 ± 3.02, 4.27 ± 3.69, 4.63 ± 4.05, 3.79 ± 2.66 and 2.18 ± 1.47 μmol CO2 m−2 s−1 from site 1F (forest) to 11B (bare), respectively, and 3.51 ± 0.71 μmol CO2 m−2 s−1 across the 11 sites. Cumulative annual Rs (March to December) varied from 692.1 to 1472.0 g C m−2 yr−1, with an average of 1114.6 g C m−2 yr−1 across all 11 sites. The spatial variations (between-site and within-site) of Rs were significant, but there was no clear evidence for which factor mainly affected the spatial variation.

Temporal variations of Rs were dominantly controlled by Ts during most days of the year. However, during early summer, when Ws was limiting, Rs decreased dramatically and Ws exerted control over Rs. At all sites, Ts was the primary factor driving temporal variations in Rs. The functional relationships of Rs to Ts could be described well by exponential and Lloyd and Taylor equations. The coefficients of determination R2 of Ts to Rs in 11 sites varied from 0.55 to 0.84 for the exponential equation, and from 0.51 to 0.86 for the Lloyd and Taylor equation when the drought-affected data were excluded. The relationships of Ws to Rs could be described well by linear and power equations. The R2 of Ws to Rs in 11 sites ranged from 0.27 to 0.73, which were smaller than those of Ts to Rs, when the Rs was normalized using the fit of the Q10 function with Ts at 10 °C. Both the Q10 and R10 increased when dry-affected data were removed from the data sets. The Q10 ranged from 2.37 to 5.53 in 11 sites, and the R10 of the exponential equations varied from 1.27 to 2.90 μmol CO2 m−2 s−1, slightly lower than those of Lloyd and Taylor equations ranging from 1.34 to 4.34 μmol CO2 m−2 s−1. The calculated Q10 and R10 of each site at the seasonal time scale were negatively correlated with Ts and positively correlated with Ws. For all data sets, four two-variable equations including linear and non-linear ones could be used to model relationships of Rs to both Ts and Ws together, with the R2 ranging from a minimum of 0.58 to a maximum of 0.86 for individual site. Our research results can bear important implications for the study of CO2 efflux in similar semiarid regions.

Introduction

Soil respiration (Rs) is a major process controlling the carbon budget of terrestrial ecosystems and increased carbon sequestration in ecosystems may mitigate increasing atmospheric CO2 concentration. The total global emission of CO2 from soils is recognized as one of the largest fluxes in the global carbon cycle (Schlesinger and Andrews, 2000). Quantifying CO2 efflux and understanding the factors that underlie the seasonal and spatial variation in its magnitude are fundamental to our understanding of the behavior of the terrestrial ecosystem as a whole and to our ability to predict the likely consequences of climatic change (Raich and Schlesinger, 1992). The soil CO2 efflux differs among ecosystems and also varies with environmental conditions. To date, many measurements of soil CO2 efflux have been made in various ecosystems to estimate how much CO2 is released from soil and address the relationships between CO2 efflux and environmental conditions (Davidson et al., 1998, Qi and Xu, 2001, Xu and Qi, 2001). The soil respiration from different ecosystems has showed a temporal and spatial variation (Maestre and Cortina, 2003, Rayment and Jarvis, 2000, Mielnick and Dugas, 2000, Khomik et al., 2006, Saiz and Green, 2006) because of the influences of various factors such as soil temperature (Lloyd and Taylor, 1994), soil water (Gaumont-Guay et al., 2006b), vegetation (Buchmann, 2000), topography (Kang et al., 2003), and soil texture (Dilustro et al., 2005). So estimates of soil respiration rates at longer time scales and larger spatial scales require a better understanding of these factors in order to increase the reliability of regional estimates and improve the understanding of global terrestrial carbon fluxes (Kang et al., 2003). Microclimates induced by topography and vegetation covers in mountainous areas, where the soils and vegetation covers are often distributed across rugged surfaces, can affect soil respiration rate by constraining microsite factors, such as soil temperature (Ts) and soil water content (Ws). The interactions between topography and climate in a mountain area make it difficult to make estimates of soil CO2 efflux at the regional scale. The key to increasing the reliability of regional estimates of soil CO2 efflux and to understanding the temporal and spatial patterns of soil CO2 efflux is to obtain more Rs measurements in regional specific ecosystems or land covers at the appropriate spatial and temporal scales.

As the second largest geographic unit in China, the Loess Plateau is characterized by its rugged surface and non-uniform land covers. So it is very important to understand CO2 efflux from this special ecosystem. However, the information of this ecosystem on soil respiration has not yet been represented. Our study area is located in the eastern part of Loess Plateau of China. The objectives of this study were (1) to examine the seasonal patterns of soil CO2 efflux from 11 sites in this mountain area, to understand whether there is any difference in soil respiration among the sites, (2) to estimate the amount of soil CO2 efflux from this area, (3) to characterize the spatial variation of soil CO2 efflux across the 11 sites, and (4) to identify the relationships between soil CO2 efflux and Ts, as well as Ws, in this mountain area.

Section snippets

Studied area and experimental site

The experimental area, about 36 km from Taiyuan city, Shanxi province, is situated in the Tianlong Mountain area (N37°44′; E112°22′), i.e., the eastern part of Loess Plateau, China. Since 1992 this area has been a national nature reserve with an area of 26766 ha. The region is characterized by a monsoon continental climate. Mean annual precipitation for the area, based on the 30-year climate record from 1971 to 2000 at Jinyuan district of Taiyuan city, is 478 mm, ranging from 257 mm in 1972 to 809 

Temporal variations

Temporal variations of Ts at 10 cm depth in 11 sites, though slightly different, showed a distinct “bell-shape” trend (Fig. 1a), with contrasting values between 0 and 3 °C in early spring and early winter, and 20–23 °C in summer. The low values were observed in December and in March. The maximal values occurred mostly in summer months. But the values were different between sites (Table 1), depending on slope orientation, elevation, vegetation type, Ws, and so on. The Ts was 2–3 °C higher in 1F, 2S,

Conclusions

The annual mean Rs from all measured data (March to December) among 11 sites obviously differed and ranged from 2.50 ± 1.62 (mean ± S.D., 11B, n = 26) to 5.19 ± 4.29 (9G, n = 29) μmol CO2 m−2 s−1. Temporal variability of Rs in this area, ranging from less than 1 μmol CO2 m−2 s−1 in the early spring and winter to larger than 10 μmol CO2 m−2 s−1 in summer, was positively related with seasonal variability of Ts and Ws. The average Rs (the daily-weighted monthly mean Rs) in 11 sites ranged from 2.18 (11B) to 4.63 (9G) 

Acknowledgements

The authors thank You Longfeng, Chen Jianwen, Liu Xiaxia, Wang Haixia, and Tang Yi for their valuable help in fieldwork. We thank Xue Xinfei for help with soil organic carbon analysis and Prof. Zhang Feng for statistical assistance. This study was funded mainly by Shanxi Foundation for Returned Overseas Scholars and Natural Science Foundation of Shanxi (20031062) and Shanxi University. We also thank the two anonymous reviewers for their insightful comments and suggestions on the initial

References (36)

  • B.E. Law et al.

    Spatial and temporal variation in respiration in a young ponderosa pine forest during a summer drought

    Agric. For. Meteorol.

    (2001)
  • F.T. Maestre et al.

    Small-scale spatial variation in soil CO2 efflux in a Mediterranean semiarid steppe

    Appl. Soil Ecol.

    (2003)
  • P.C. Mielnick et al.

    Soil CO2 flux in a tall grass prairie

    Soil Biol. Biochem.

    (2000)
  • M.B. Rayment et al.

    Temporal and spatial variation of soil CO2 efflux in a Canadian boreal forest

    Soil Biol. Biochem.

    (2000)
  • G. Vincent et al.

    Spatial and seasonal variations in soil respiration in a temperate deciduous forest with fluctuating water table

    Soil Biol. Biochem.

    (2006)
  • J. Wu et al.

    Year-round soil and ecosystem respiration in a temperate broad-leaved Korean Pine forest

    For. Ecol. Manag.

    (2006)
  • W. Borken et al.

    Site and temporal variation of soil respiration in European beech, Norway spruce, and Scots pine forests

    Global Change Biol.

    (2002)
  • Z.H. Cheng et al.

    A study on vegetation resources in Tianlong Mountain, Shanxi province

    J. Mountain Sci.

    (2000)
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