Abstract:This paper explore surface energy exchanges and their underlying mechanisms during the growing season in four grassland ecosystems in Qinghai-Tibetan Plateau and Mongolian Plateau through analyzing the 4—5-year continuous flux data obtained by the eddy covariance technique. The four ecosystems are a temperate steppe ecosystem in central Mongolia (KBU), a temperate steppe ecosystem in Inner Mongolia (NM), an alpine shrub-meadow ecosystem (HB) and an alpine steppe meadow (DX) in Qinghai-Tibetan Plateau along a precipitation gradient. The results show that the surface reflectivity (albedo) for short-wave radiation (αk) was lowest (0.12) in HB because of highest NDVI (0.58) and volumetric soil water content (28.3%) compared with those of other three ecosystems. The αk values in KBU, NM and DX decreased with the growth of plant, and increased as the plant senesced during the late growing season; but the seasonal variation of αk in HB exhibited an opposite trend to those at other three sites. The Bowen ratio decreased from 2.25 to 0.53 from the Mongolian Plateau to Qinghai-Tibetan Plateau with the increase of precipitation, suggesting that there is a shift of the sensible heat flux (H) dominated energy partitioning to the latent heat flux (LE) dominated energy partitioning. Vegetation growth played an important role in controlling energy exchange between grassland ecosystems and the atmosphere. The evaporative fraction of net-radiation (LE/Rn) was lower than H/Rn when NDVI was low; but with an increase in NDVI, LE/Rn increased whereas H/Rn decreased.