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Carbon sinks in terrestrial ecosystems can be significantly increased by afforestation, which will slow global warming. However, it is still unclear how different plantations influence the carbon sink and how they respond to environmental factors, especially in drylands. In this study, eddy correlation method (EC) was used to measure carbon and water fluxes and environmental factors of two artificial forests (<i>Larix principis-rupprechtii</i> and <i>Pinus tabulaeformis</i>) in the dryland of Northwest China, and the responses of evapotranspiration (ET), net ecosystem exchange (NEE), gross primary productivity (GPP), and ecosystem respiration (RECO) to environmental factors were also assessed. Results showed that the <i>L. principis-rupprechtii</i> forest ecosystem had higher water use efficiency (WUE), light use efficiency (LUE), GPP, and RECO than the <i>P. tabulaeformis</i> forest ecosystem. However, the proportion of net ecosystem production (NEP) to GPP in the <i>P. tabulaeformis</i> forest ecosystem (62.89%) was higher than that in the <i>L. principis-rupprechtii</i> forest ecosystem (47.49%), indicating that the <i>P. tabulaeformis</i> forest ecosystem had the higher carbon sequestration efficiency. In addition, the CO₂ and H₂O fluxes in the <i>L. principis-rupprechtii</i> forest ecosystem were more sensitive to environmental factors, compared with the <i>P. tabulaeformis</i> forest ecosystem. Further, the RECO of the <i>L. principis-rupprechtii</i> forest ecosystem was more sensitive to temperature changes, which implies that the <i>L. principis-rupprechtii</i> forest ecosystem will release more CO₂ than the <i>P. tabulaeformis</i> forest ecosystem with a warming climate. Therefore, the <i>P. tabulaeformis</i> forest ecosystem may have better carbon sequestration potential. These results are important for understanding the effects of climate change on the CO₂ and H₂O cycles in coniferous plantation ecosystems in drylands.