Advances in the carbon sink potential of terrestrial ecosystems in China

The "carbon peak and carbon neutrality" concept has become a major demand for global climate governance and ecological civilization construction in China. Understanding the potential of terrestrial carbon sequestration and its response to climate change and human activities is very important for accurately predicting the impacts of future climate change on terrestrial ecosystems and is the basic premise for human beings to cope with climate change. Based on the perspective of terrestrial ecosystem carbon storage and carbon sinks, this paper summarizes the carbon storage of forest, shrub, grassland, farmland and wetland ecosystems of China, thus assessing the carbon sink potential of the Chinese terrestrial ecosystem and its response to different climate change scenarios and human activities. The evaluation results varied greatly due to different research methods and data. The average biomass carbon density of China's forests and grasslands was approximately 55.7 and 4.8 Mg C ha(-1), respectively, which were lower than the average values of the global forests (94.2 Mg C ha(-1)) and grasslands (7.2 Mg C ha(-1)), mainly due to larger areas of young forests and extensive grazing. The average biomass carbon density of the wetland was approximately 4.1 Mg C ha(-1), which varied greatly for different types of wetland vegetation, and the highest value was located in coastal wetland vegetation (9.6 Mg C ha(-1)). The biomass carbon density of shrub and farmland was approximately 4.8-9.6 and 3.06-7.1 Mg C ha(-1), respectively. The carbon sink potential of China's main terrestrial ecosystems (forest, shrub, grassland and farmland) estimated by different methods varied greatly. According to the eighth (2009-2013) and ninth (2014-2018) inventory data of China's forest resources and other inventory data, the latest result of the carbon storage increase rate of China's terrestrial ecosystem was estimated to be approximately 0.28 PG C a(-1). Ecological engineers should greatly promote the carbon sink potential of terrestrial ecosystems. The terrestrial ecosystem carbon sink of six major national ecological engineering projects in China reached approximately 132 Tg C a(-1), of which more than half (74 Tg C a(-1), 56%) was attributed to the implementation of ecological engineering projects. The carbon sink increase was approximately 14.7 and 14 Tg C a(-1) from the conversion of farmland to grassland engineering area and natural forest protection engineering area, respectively, and approximately 7.0-12 Tg C a(-1) in each of the other five engineering areas. Thus, it is necessary to constantly improve the assessment methods of terrestrial ecosystem carbon reserves and carbon sinks and constantly update the assessment results based on the latest data. The shortcomings of the existing studies are put forward in this paper. (1) Integrated research on the carbon sink function of China's terrestrial ecosystems in different periods and different emission scenarios in the future is insufficient, especially on the sink potential of different kinds of major ecological projects in the same region. (2) Impact research on nitrogen deposition and its interaction with climate change and atmospheric CO2 concentration on the carbon sink potential of China's terrestrial ecosystems is still insufficient, especially regarding the carbon sink potential of major national ecological projects. (3) Research on the climate change risk of carbon sequestration in China's terrestrial ecosystems has not been conducted. Finally, this research identifies research activities on carbon storage and carbon sinks in China's terrestrial ecosystems in the future, including carbon sink potential and a risk assessment of major national ecological projects, the simulation technology of the regional terrestrial ecosystem carbon budget with high spatial heterogeneity, and the dynamic downscaling method and correction technology of meteorological data under different climate change scenarios, to provide scientific support for the systematic management optimization scheme of increasing sinks in China's terrestrial ecosystem and to serve the strategy of national carbon neutrality.