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