[Characteristics of net ecosystem flux exchanges over Stipa krylovii steppe in Inner Mongolia]

Based on an entire year continuous measurement of surface fluxes by eddy covariance (EC) tower and micro-climate gradient observation system, the diurnal and seasonal dynamics of net ecosystem fluxes including carbon, water, and heat fluxes over Stipa krylovii steppe in Inner Mongolia were investigated. The results indicated that the diurnal pattern of carbon fluxes during growing season could be expressed as U curve. S. krylovii steppe ecosystem emitted CO2 before the sunrise and absorbed CO2 after the sunrise, with the maximum CO2 uptake around noon. The ecosystem had weaker CO2 uptake after the noon, and turned to emit CO2 after sunset. The CO2 uptake by S. krylovii steppe ecosystem reached the maximum in September, followed in August, and got the minimum in October. The diurnal dynamic patterns of sensible heat flux (Hs) and latent heat flux (LE) could be expressed as inverse U curves. The Hs and LE over S. krylovii steppe ecosystem were positive during the daytime, while Hs was negative and LE was close to zero during the nighttime. The ecosystem had the highest Hs and LE in May and September, respectively. In winter, the steppe acted as a weak carbon source, with the CO2 flux being small; while in summer, it became an obvious carbon sink.