Soil respiration is a critical hydrological process that plays an important role in the terrestrial carbon cycle. Associate Professor CHEN ShuTao and his colleagues from the School of Environmental Science and Engineering at Nanjing University of Information Science and Technology set out to estimate annual soil respiration from terrestrial ecosystems in China. They have tabulated published estimates of annual soil respiration and developed an empirically based, semi-mechanistic model that includes climate and soil properties. They found that the highest and lowest annual soil respiration rates appear in southeastern China and northwestern China, respectively, which is in accordance with the spatial patterns of mean annual air temperature and annual precipitation. They also determined that annual soil respiration from terrestrial ecosystems in China varied from 4.58 to 5.19 Pg of carbon per year (1 Pg = 1×1015 g or 1×109 tonnes) between 1970 and 2009. Their work, entitled "Interannual variability in soil respiration from terrestrial ecosystems in China and its response to climate change", was published in SCIENCE CHINA Earth Sciences, 2012, VOL 55 (10).
With the exception of gross photosynthesis, soil respiration (e.g., soil CO2 emissions) exceeds all other terrestrial-atmospheric carbon exchanges. Quantifying the spatio-temporal pattern of soil respiration from terrestrial ecosystems in China is critical to provide a theoretical basis for evaluating the carbon budget. Great uncertainty remains from previous annual soil respiration estimates for terrestrial ecosystems in China, with a difference of 1 Pg of carbon per year between the highest and lowest values. Moreover, few studies have focused on the relationship between interannual variability in soil respiration and climatic factors. The need to develop a soil respiration model that includes increased field measurement data covering a wide range of plant functional types and biomes is urgent.
Based on in situ measurements, global soil respiration data sets have been compiled. These data sets include measured annual soil respiration from China and other countries, covering most types of terrestrial ecosystems. A annual soil respiration model was established using a range of predictors, data including mean air temperature, total annual precipitation and soil organic carbon storage. The data sets used in estimating soil respiration include climate (mean annual air temperature and precipitation) data sets from 1970 to 2009 and topsoil (0 cm) property data sets obtained from the Second State Soil Survey. Data on the annual precipitation at ~670 weather stations from 1970 to 2009 were obtained from the National Meteorological Information Center, China. By linking the model to the spatial database, the annual soil respiration from terrestrial ecosystems in China was estimated from 1970 through 2009.
The variability of annual soil respiration shows clear spatial patterns in the data. Three distinct regions can be characterized by differences in their annual soil respiration; these regions can be geographically identified as southeastern China, northwestern China, and northern and northeastern China. The highest and lowest annual soil respiration rates appeared in southeastern China and northwestern China, respectively, in accordance with the spatial patterns of mean annual air temperature and annual precipitation. Annual soil respiration from terrestrial ecosystems in China varied from 4.58 to 5.19 Pg of carbon per year between 1970 and 2009. During this time period, annual soil respiration was estimated to be 4.83 Pg carbon per year on average. Annual soil respiration in China accounted for 5% of the global annual soil respiration.
A significant linear relationship between annual soil respiration and annual precipitation was found. Precipitation may influence soil respiration by affecting vegetation growth and root activity. In this regard, precipitation is therefore an important factor controlling the terrestrial carbon cycle. Interannual variability in mean air temperature also influences the variability in annual soil respiration. This relationship suggests that, under a scenario of warming, increasing variability in mean annual air temperature incurs greater variability in annual soil respiration.