Abstract: AimsGlobal warming could have profound effects on ecosystem carbon (C) fluxes in alpine ecosystems. The aim of our study is to examine the effects of gradient warming on net ecosystem carbon exchange (NEE).MethodsIn the Northern Tibetan Grassland Ecosystem Research Station (Nagqu station), Institute of Geographic Sciences and Natural Resources Research, Chinese Academy of Sciences, we conducted various levels of temperature increasing experiments (i.e., 2 °C and 4 °C increments). The warming was achieved using open-top chambers (OTCs). In total, there were three levels of temperature treatments (control, 2 °C and 4 °C increment), and four replicates for each treatment. The ecosystem NEE was monitored every five days during the growing season in 2015.Important findings Our findings highlight the importance of soil moisture in mediating the responses of NEE to climatic warming in alpine meadow ecosystem. The 4 °C warming significantly stimulated NEE,except for July measurements. The 2 °C warming had no effects on NEE during the growing season. Compared to the 2 °C warming, the 4 °C warming significantly stimulated NEE. The results showed that our targeted ecosystem acts as a carbon sink under 2 °C warming, whereas will act as a net carbon source under 4 °C warming in the future. This study provides basic data and theoretical basis for evaluating the alpine ecosystem’s responses to climate change.

Key words: global warming, alpine meadow, net ecosystem carbon exchange, carbon budget, Northern Xizang plateau