Location

 The eddy covariance tower was established at an experimental site (43°33'16"N, 116°40'17" E, 1250 m a.s.l) fenced from 2005 at the Inner Mongolia Grassland Ecosystem Station (43°38' N, 116°42' E, 1187 m a.s.l), which is administrated by the Institute of Botany, Chinese Academy of Sciences, located in the Xilin River Basin, Inner Mongolia. The vegetation type belongs to typical semiarid steppes.

Climatic

 The study area is semiarid continental climate. The mean annual air temperature is 0.8℃, with a range of temperature from -41.1℃ to 38.5℃, and annual precipitation is 336mm. The mean annual relative humidity is 57%, annual sunshine hour is 2617.54 hours and the average frost-free period is 100 days.

Vegetation and soil

 Leymus chinensis and Stipa grandis community are most widely distributed at this typical steppe ecosystem. Leymus chinensis community is composed of one constructive species (Leymus chinensis, a xerophilous rhizome grass) and other common species ( Stipa gradis, Koeleria cristata, Agropyron cristatum ). However, the four most dominant grasses of the Stipa grandis community are Stipa grandis, a xerophilous bunch grass and other three species, Koeleria cristata, Agropyron cristatum, and Cleistogenes squarrosa.

The eddy covariance tower was built in Leymus chinensis community fenced from 2005, which experienced intensive grazing over the last few decades before fenced. However, the experimental site has been clipped annually in early August to simulate grazing after it was fenced. Stipa gradis and Cleistogenes squarrosa dominated the site and the plant height is about 10-30cm.

The soil is chestnut soil, containing 74.9% sand, 15.2% silt and 9.8% clay. The soil thickness is more than 1m. Topsoil organic carbon and soil total nitrogen (0–10 cm) are 14.3gkg^-1 and 1.6gkg^-1, respectively.

Observation system

 The eddy covariance tower was built in Jun 2005 at a height of 5 m. The open-path eddy covariance system consists of an infrared gas analyzer (LI-7500, LICOR) and a three-dimensional sonic anemometer (CSAT3, CSI) (4 m above ground). The data of wind speed and gas concentration were sampled at 10 Hz. Continuous high frequency data were recorded and the covariance was calculated at 30 min intervals. Net radiation and photosynthetically active radiation were measured at 3.5 m above ground using a four-component net radiometer (CNR-1, Kipp&Zonen) and a quantum sensor (LI190SB, LICOR). Air temperature and relative humidity were measured at three levels (1.5 m, 2 m and 4m) with HMP45C (CSI). Rainfall was recorded continuously by a tipping bucket rain gauge (TE-525, CSI) 4 m above the ground. The top of 10 cm volumetric soil water content was measured by a TDR sensor (CS616, CSI). Soil temperature was measured with temperature probes (107, CSI) at three soil layers (5, 10 and 20 cm). Soil heat flux was determined with soil heat transducers (HFT-3, CSI) at 2 cm below the soil surface with three replicates. All micrometeorological data was recored every 30 min.

Principal Investigator

Shiping Chen

E-mail: spchen@ibcas.ac.cn