Permafrost carbon could produce a positive climate feedback. Until now, the ecosystem carbon budgets in the permafrost regions remain uncertain. Moreover, the frequently used models have some limitations especially regarding to the freeze–thaw process. Herein, we improved the IBIS model by incorporating an unfrozen water scheme and by specifying the parameters to estimate the present and future carbon budget of different land cover types (desert steppe, steppe, meadow, and wet meadow) in the permafrost regions. Incorporating an unfrozen water scheme reduced the mean errors in the soil temperature and soil water content by 25.2%, and the specifying leaf area parameters reduced the errors in the net primary productivity (NPP) by 79.9%. Further, the simulation results showed that steppes are carbon sources (39.16 gC/m²/a) and the meadows are carbon sinks (−63.42 gC/m²/a). Under the climate warming scenarios of RCP 2.6, RCP 6.0, and RCP 8.5, the desert steppe and alpine steppe would assimilated more carbon, while the meadow and wet meadow were projected to shift from carbon sinks to carbon sources in 2071–2100, implying that the land cover type plays an important role in simulating the source/sink effects of permafrost ecosystem carbon in the IBIS model. The results highlight the importance of unfrozen water to the soil hydrothermal regime and specific leaf area for the growth of alpine vegetation, and present new insights on the difference of the responses of various permafrost ecosystems to climate warming.

多年冻土碳可以产生积极的气候反馈。到目前为止，多年冻土地区的生态系统碳预算仍然不确定。此外，经常使用的模型有一些局限性，特别是在冻融过程方面。在此，我们通过合并未冻结的水方案并指定参数来估算多年冻土地区不同土地覆盖类型（沙漠草原，草原，草甸和湿草甸）的当前和未来的碳收支，从而改进了IBIS模型。结合使用非冻结水方案，可将土壤温度和土壤水分的平均误差降低25.2％，并且指定叶面积参数可将净初级生产力（NPP）的误差降低79.9％。此外，模拟结果表明，草原是碳源（39.16 gC / m ²/ a），草甸是碳汇（−63.42 gC / m ² / a）。在RCP 2.6，RCP 6.0和RCP 8.5的气候变暖情景下，沙漠草原和高山草原将吸收更多的碳，而草地和湿地草甸预计将在2071-2100年从碳汇转变为碳源，这意味着在IBIS模型中，土地覆盖类型在模拟多年冻土生态系统碳的源/汇效应中起着重要作用。结果突出了未冻结水对土壤热液状态和特定叶面积对于高山植被生长的重要性，并提供了关于各种多年冻土生态系统对气候变暖的响应差异的新见解。