Carbon cycle of terrestrial ecosystem is an important link of global carbon cycle. Permafrost region is the largest soil carbon pool of terrestrial ecosystem. Its decomposition and carbon release under the background of climate warming may form positive feedback with climate change, thus accelerating global warming.
However, the ecosystem carbon budgets in the permafrost regions remain uncertain. Therefore, accurately predicting the response of permafrost ecosystem to global change depends on in-depth analysis of the regulation mechanism of terrestrial carbon cycle.
Using the dynamic vegetation model, combined with the data of soil water, heat and carbon flux at long-term observation points, a research team led by Prof. WU Tonghua from the Northwest Institute of Eco-Environment and Resources (NIEER) of the Chinese Academy of Sciences (CAS) systematically studied the global change of carbon cycle response of permafrost ecosystem.
They improved the integrated biosphere simulator (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.
At last, the future scenario climate data of different emission paths of CMIP5 are used to input into the model, to exploring the carbon budget and the effect of carbon source and sink in Qinghai-Tibet Plateau under future warming.
The result indicated that 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 were carbon sources (39.16 g C/m2/a) and the meadows were carbon sinks (-63.42 g C/m2/a). Under the climate warming scenarios of representative concentration pathways (RCP) 2.6, RCP 6.0, and RCP 8.5, the desert steppe and alpine steppe would assimilate 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 played an important role in simulating the source/sink effects of permafrost ecosystem carbon in the IBIS model.
This study highlights 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.
These results will fill our knowledge gap regarding the permafrost ecosystem carbon cycle under a warming climate.
This study has been published on CATENA entitled “Warming could shift steppes to carbon sinks and meadows to carbon sources in permafrost regions: Evidence from the improved IBIS model“.
This work was supported by the National Natural Science Foundation of China and the “Light of West China” Program of CAS.