Energy and CO2 exchanges and influencing factors in spring wheat ecosystem along the Heihe River, northwestern China

Spring wheat (Triticum aestivum Linn.) is an important crop for food security in the desert-oasis farmland in the middle reaches of the Heihe River in northwestern China. We measured fluxes using eddy covariance and meteorological parameters to explore the energy fluxes and the relationship between CO2 flux and climate change in this region during the wheat growing seasons in 2013 and 2014. The energy balance closures were 70.5% and 72.7% in the 2013 and 2014 growing season, respectively. The wheat ecosystem had distinct seasonal and diurnal dynamics of CO2 fluxes with U-shaped curves. The accumulated net ecosystemic CO2 exchanges (NEE) were -111.6 and -142.2 g C/m(2) in 2013 and 2014 growing season, respectively. The ecosystem generally acted as a CO2 sink during the growing season but became a CO2 source after the wheat harvest. A correlation analysis indicated that night-time CO2 fluxes were exponentially dependent on air temperature and soil temperature at a depth of 5 cm but were not correlated with soil-water content, water-vapour pressure, or vapour-pressure deficit. CO2 flux was not correlated with the meteorological parameters during daytime. However, irrigation and precipitation, may complicate the response of CO2 fluxes to other meteorological parameters.