Warming, rather than drought, remains the primary factor limiting carbon sequestration.

Steppe ecosystems in arid and semiarid regions are particularly sensitive to climate change and strongly regulate the global carbon balance. However, carbon fluxes respond differently to climate change in different growing seasons, and the mechanism of this control is not yet clear. Therefore, we (i) obtained carbon flux data observed by a field eddy station in Inner Mongolia from 2006 to 2021; (ii) investigated the constraint effects of climatic factors on carbon fluxes; (iii) explored the response mechanisms of carbon fluxes to coupled changes in temperature and moisture; (iv) investigated the adaptation of steppe ecosystem to changes in temperature and drought. The results showed that (i) the steppe ecosystem was a carbon sink, with an average annual carbon fixation of 73.55 g C m yr and a roughly N-shaped carbon sink accumulation process within one year. (ii) The constraint effect of temperature and Vapor Pressure Deficit (VPD) on Net Ecosystem Productivity (NEP) and Gross Primary Productivity (GPP) was parabolic, with a clear optimum point. (iii) Temperature and moisture in the soil played a greater role in ecosystem carbon sequestration. Soil Water Content (SWC) could alleviate the inhibitory effect of temperature changes on the carbon sequestration of ecosystem. (iv) This ecosystem was capable of adapting well to changes in temperature and drought. However, warming, rather than drought, remains the primary factor limiting carbon sequestration. Specifically, it was GPP that drives the adaptation of ecosystem carbon sequestration to changes in temperature and drought, rather than Ecosystem Respiration (RECO). Although the steppe ecosystem has a good adaptation to changes in temperature and drought, it is still in the boundary region of warming. We hope that our study will deepen our comprehensive understanding of the relationship between temperature and moisture and ecosystem carbon fluxes and provide evidence for steppe ecosystem adaptation to climate change.