Temperature sensitivity of soil respiration in different ecosystems in China

Abstract

Understanding the sensitivity of soil respiration to temperature change and its impacting factors is an important base for accurately evaluating the response of terrestrial carbon balance to future climatic change, and thus has received much recent attention. In this study, we synthesized 161 field measurement data from 52 published papers to quantify temperature sensitivity of soil respiration in different Chinese ecosystems and its relationship with climate factors, such as temperature and precipitation. The results show that the observed Q₁₀ value (the factor by which respiration rates increase for a 10 °C increase in temperature) is strongly dependent on the soil temperature measurement depth. Generally, Q₁₀ significantly increased with the depth (0 cm, 5 cm, and 10 cm) of soil temperature measuring point. Different ecosystem types also exhibit different Q₁₀ values. In response to soil temperature at the depth of 5 cm, alpine meadow and tundra has the largest Q₁₀ value with magnitude of 3.05 ± 1.06, while the Q₁₀ value of evergreen broadleaf forests is approximately half that amount (Q₁₀ = 1.81 ± 0.43). Spatial correlation analysis also shows that the Q₁₀ value of forest ecosystems is significantly and negatively correlated with mean annual temperature (R = −0.51, P < 0.001) and mean annual precipitation (R = −0.5, P < 0.001). This result not only implies that the temperature sensitivity of soil respiration will decline under continued global warming, but also suggests that such acclimation of soil respiration to warming should be taken into account in forecasting future terrestrial carbon cycle and its feedback to climate system.

Introduction

Soil respiration is a major process controlling carbon loss from terrestrial ecosystems. On a global scale, soil respiration was estimated to produce 80.4 Pg C y⁻¹ (petagram carbon per year) with a range of 79.3–81.8 Pg C y⁻¹ (Raich et al., 2002), accounting for 60–90 percent of total respiration of global terrestrial ecosystems (Schimel et al., 2001), which is more than 11 times the current rate of fossil fuel combustion (Marland et al., 2000). Accordingly, small changes in the magnitude of soil respiration could have a large effect on the concentration of CO₂ in the atmosphere. For example, a recent study suggested that autumnal atmospheric CO₂ zero-crossing date has significantly advanced due to the stimulation of soil respiration driven by rising temperature in the Northern Hemisphere (Piao et al., 2008).

Several factors can profoundly influence soil respiration, such as soil quality, N deposition, climate condition, and human disturbance (Davidson and Janssens, 2006, Davidson et al., 2006, Mo et al., 2008, Qi et al., 2002). Among these factors, climate change, particularly global warming has been suggested to be the major cause of accelerating global soil carbon loss (Jones et al., 2003). Such increase in soil respiration in response to rising temperature is expected to provide a positive feedback to global warming (Cox et al., 2000, Jenkinson et al., 1991, Raich and Schlesinger, 1992), but there are large uncertainties in the magnitude of this feedback (Friedlingstein et al., 2006). Our current poor understanding of the temperature sensitivity of soil respiration is one of the major sources of the uncertainty estimated by different climate–carbon coupling models (Fierer et al., 2006, Jones et al., 2003, Lenton and Huntingford, 2003). For example, terrestrial carbon models such as Roth-C, CENTURY and TEM generally assume a constant temperature sensitivity of soil respiration regardless of the characteristics of the ecosystems (Jenkinson et al., 1991, Tian et al., 1999), although a previous study suggested that Q₁₀, the factor by which soil respiration increases with a 10 °C rise in temperature, is likely to vary across different ecosystems and climatic conditions (Raich and Schlesinger, 1992).

China has climate regimes ranging from perennial snow on the high western mountains to deserts in the western lowlands, and from cold temperate regions in the northwest to warm and humid tropics along the southern coast (Fang et al., 2001a). The different climates support a set of ecosystems ranging from the boreal coniferous forest in the northeast to the tropical monsoon rain forest in the south. Such wide climatic variability, topographic complexity, and natural ecosystem diversity have provided a unique field for examining temperature sensitivity of soil respiration for different ecosystems and climatic conditions. During the last 10 years, the number of studies of soil respiration sensitivity to temperature has increased rapidly in China (Fig. 1). According to these field measurements, temperature sensitivity of soil respiration in China varies from the Q₁₀ value of 0.93 for the cropland in Shenyang city, Liaoning Province (Wang et al., 2006b) to that of 6.27 for the evergreen needleleaf forest in Li county, Sichuan Province (Chen et al., 2007). Although these previous studies have significantly improve our understanding on temperature sensitivity of soil respiration at the site level, the sensitivity of soil respiration to temperature at the country and regional scale is not still clear. This insufficient knowledge further limits our ability to assess the role of Chinese terrestrial ecosystems in the global carbon balance. For example, a significant increase in China's vegetation productivity has been widely observed by satellite data (Fang et al., 2003), but the net carbon exchange between China's terrestrial ecosystems and the atmosphere still remain largely uncertain (Fang et al., 2007). Thus, it is imperative to synthesize previously reported temperature sensitivity of soil respiration at different sites across China.

In this study, we analyzed temperature sensitivity of soil respiration for different ecosystems and their relationship with climate factors (temperature and precipitation) in China utilizing field measurement based Q₁₀ value that were assembled from 161 sites reported by previous literature. In the first analysis, we discussed the effects of the depth of soil temperature measuring point on the estimation of Q₁₀ value. In the second analysis, we evaluated Q₁₀ values for different ecosystems in China. In the third analysis, we investigated the change in temperature sensitivity of soil respiration in response to temperature and precipitation change. In the last analysis, we discussed the potential role of China's terrestrial ecosystem as carbon sink or source over the last two decades based on the Q₁₀ values in different ecosystems estimated in this study and historical change in vegetation productivity derived from previous study (Piao et al., 2005).