Location
Shapotou Desert Experiment and Research Station (Shapotou station) is supported by Cold and Arid Cold and Arid Regions Environmental and Engineering Institute, Chinese Academy of Sciences, and located in Zhongwei county in the Ningxia Hui Autonomous Region at the southeast edge of the Tengger Desert (37°28＇N, 105°00＇E, 1320m.a.s.l）with an elevation of 1320 m, which is an ecotone between steppified desert and desertified steppe. The flux station is conducted in the carbon flux experimental fields of the Shapotou station, located in the Xiaohongshan area of Zhongwei county (37°29′46.74＂N, 104°25′32.9＂E), west 60 km of the Shapotou station, with an elevation of 1665m, which is typical desert vegetation.
Climatic
Shapotou area is belonging to the temperate zone with typical desertified climate. The annual mean temperature is nearly 10.0 ℃，with the lowest mean monthly temperature of -6.9℃ in January and maximum mean monthly temperature 24.3 ℃ in July and sunshine hours are 2730 and plant growing period is 150-180 days. Total annual mean precipitation 186 mm and approximately 80% is falling between May and September. The evapotranspiration potential during the growing season is 2900 mm. Days of annual frostless season is179. Average annual wind velocity is 2.9 m s-1.
Vegetation and soil
The study area is an ecotone between steppified desert and desertified steppe and the dominant species are sub-shrubs, shrub and herb. The predominant native plants are Reaumuria soongorica, Salsola passerina, Caragana stenophylla, Oxytropis aciphylla, Caragana korshinsikii, Ceratoides lateens, Hedysarum scoparium, Artemisia sphaerocephala, Artemisia ordosica, Agriophyllum squarrosum, Stipa breviflora, Enneapogon brachystachyus, Carex stenophylloides, Tragus berteronianus, Cleistogennes songorica. Predominant typically shrubs under the flux station are Reaumuria soongorica and Salsola passerina, with the vegetation cover of 30%. The height of Reaumuria soongorica and Salsola passerina are nearly 40 and 30 cm, respectively. The soil is Aeolian sandy soil. Bulk density is 1.37 g cm-3, with a sand, clay and silica content of 65.3%, 30.3% and 4.4%, respectively. Soil organic matter was1.49 g/kg and soil nitrogen was 1.08g/kg.
Observation system
Eddy covariance system in the carbon flux experimental fields of the Shapotou Station was conducted from July 2009. A fast respond (10 HZ) three-dimensional sonic anemometer (CSAT3, Campbell Scientific, Logan, UT, USA) was used to measure the fluctuations in wind speed, wind direction and temperature and an open-path infrared gas analyzer (LI-7500, LiCor, Lincoln, NE, USA) measured concentrations of water vapor and CO2, which were both mounted 3 m above the soil surface. A data logger (CR5000, Campbell Scientific, Logan, UT) was used to record 10 Hz raw data. Air temperature (Tair) and humidity were measured at a height of 0.5, 1, 2 and 4 m on a tower (HMP45C, Vaisala Inc., Helsinki, Finland). A four-component net radiometer (Rn) (CNR-1, Kipp & Zonen, the Netherlands) was placed 1.5 m above the soil surface. Two self-calibrating soil heat flux sensors (HFP01) were placed 5 cm below the soil surface. Soil temperature (109-L, Campbell Scientific Ltd., Edmonton, Alberta, Canada) was measured at five depths (0.05, 0.10, 0.15, 0.20, 0.40 m). Soil water content (SWC) (EnviroSMART, Campbell, Scientific Ltd., Edmonton, Alberta, Canada) profile was measured at seven depths (0.10, 0.20, 0.30, 0.40, 0.60, 0.80, 1.0 m). Average soil temperature (TCAV) was determined at a depth of 0.20 m. Precipitation was measured by a raingauge (TE525MM, Texas Electronics Inc., Dallas, T X, USA).
Principal Investigator
Xinrogn Li
E-mail: lxinrong@ns.lzb.ac.cn