摘要
Regional droughts may become more frequent this century as a result of anthropogenic global climate change. Thus, it is becoming critically important to evaluate the water budget accurately in terrestrial ecosystems. The water budget, which represents an important index for drought, is widely used to characterize water cycle processes in terrestrial ecosystems and to inform management decisions regarding regional water resources. As a vital component of the terrestrial biosphere, grassland ecosystem plays crucial role in regional carbon sinks and sources especially that located in the Qinghai-Tibet Plateau. In this study, based on water balance method, seasonal variations of water budget were analyzed using flux data obtained from eddy covariance measurements from 2004 to 2011 in an alpine meadow in Damxung (DX), an alpine shrubland in Haibei (HBGC), and a Leymus chinensis grassland in Inner Mongolia (NMG). We found that seasonal variations of water budget were quite different among the three ecosystems. The average water budget were (− 81.48 ± 76.56) mm, (− 35.97 ± 81.70) mm, and (− 53.05 ± 56.91) mm for DX, HBGC, and NMG, respectively. Water surplus happened from June to August in DX with an amount of (52.04 ± 68.15) mm, while water deficit existed during the other months of the year with an amount of (− 133.51 ± 42.62) mm. There was little evidence of water deficit in HBGC at the yearly scale. However, seasonal water surplus occurred from May to September with an average of (30.11 ± 67.47) mm and water deficiency were noted during the other months of the year with an average of (− 66.08 ± 25.87) mm. Due to lack of precipitation in NMG, water deficiency occurred from January to March, and the amount of deficiency during this time period was (− 18.01 ± 17.95) mm. Although precipitation was ample from April to October, water deficiency still occurred in NMG as a result of high evapotranspiration (i.e., the deficiency was approximately (− 39.99 ± 70.49) mm). In addition, the water budget and net ecosystem productivity showed consistent trends during the study period. Net ecosystem productivity was relatively higher from June to August when there were ample precipitation and water surplus than that of months with water deficit. Further studies need to be done in the future to address the complex influence of rain intensity and soil water balance on ecosystem productivity.