Carbon and water use efficiency (CUE and WUE) are crucial indicators of grassland ecosystem responses to climate change. Grass planting is one of the dominant methods of grassland restoration and agricultural production. However, how warming and reclamation impact grassland CUE and WUE remain unclear. Here we examined how warming affected carbon and water processes in natural alpine meadow and cultivated grassland, including gross ecosystem production (GEP), net ecosystem CO₂ exchange (NEE), evapotranspiration (ET), CUE and WUE. We deployed a seven-year warming experiment using open top chambers in alpine meadow and cultivated grassland on the Tibetan Plateau. Our results showed that the alpine meadow had a higher CUE and a lower WUE compared to the cultivated grassland under warming. Warming increased biomass production of the cultivated grassland in the beginning of the experiment but decreased it later in the experiment. Warming increased ET, did not affect GEP, and finally decreased WUE in the natural alpine meadow. In the cultivated grassland, warming decreased NEE, did not alter ER, and resulted the decrease in CUE. Our results highlight that reclamation decreases CUE and warming decreased WUE of alpine meadow. Although grass planting can increase biomass, the negative impacts of warming on carbon and water processes of cultivated grassland should be considered when reclaiming alpine meadow under warmer future.

碳和水的利用效率（CUE 和 WUE）是草原生态系统对气候变化响应的关键指标。种草是草地恢复和农业生产的主要方法之一。然而，变暖和开垦如何影响草原 CUE 和 WUE 仍不清楚。在这里，我们研究了变暖如何影响天然高寒草甸和耕地草地的碳和水过程，包括生态系统总产量 (GEP)、净生态系统 CO ₂交换量 (NEE)、蒸散量 (ET)、CUE 和 WUE。我们在青藏高原的高寒草甸和耕地草地上部署了一项为期七年的升温实验。我们的研究结果表明，与变暖的耕地草地相比，高寒草甸具有更高的 CUE 和更低的 WUE。变暖在实验开始时增加了耕地草地的生物量产量，但在实验后期降低了它。变暖增加了天然高寒草甸的ET，不影响GEP，最终降低了WUE。在耕地草地，变暖降低了NEE，没有改变ER，导致CUE降低。我们的研究结果强调，开垦降低了高寒草甸的 CUE，而变暖降低了高寒草甸的 WUE。虽然种草可以增加生物量，