关键词: 碳密度, 陆地生态系统, 空间格局, 影响因子

Abstract: Terrestrial ecosystems are a large carbon density and play an important role in the global carbon budget and mitigating global warming by carbon sequestration. To encourage additional carbon sequestration and storage in global vegetation and soils, we need to be clear about the distribution patterns of carbon density and the factors that influence these patterns. Therefore, the characteristics of the distribution patterns of carbon density in terrestrial ecosystems of the world and China are reviewed in this paper. At the global scale, the distribution of carbon in vegetation corresponds with the spatial pattern of biomass and generally decreases from low-latitude to high-latitude with the exception of boreal forests. In contrast, soil organic pools of carbon increase along the same gradient. The largest stores of carbon in biomass are in tropical and boreal forests, and the largest stores of soil carbon are in the high latitude ecosystems (boreal forest and tundra). Total carbon density of both vegetation and soils are highest in tropical and boreal forests. In the tropics more carbon is stored in vegetation than in soils, while in the boreal region far more carbon is stored in the soils. At the regional scale, these patterns might vary due to differences in climate, topography and human influence among regions. Several major factors, including climatic conditions, soil nutrients, biodiversity, climate and atmospheric CO2 changes, land use and cover changes, all contribute to the storage and maintenance of carbon. For example, carbon density will be high in regions where temperature and precipitation are favorable for abundant plant growth. The enhanced carbon sequestered in response to elevated levels of CO2 or nitrogen, or their combination, is less in species-poor than in species-rich regions. In a word, they can raise the carbon density in terrestrial ecosystems by directly or indirectly accelerating net primary production, or constraining respiration and decomposition. However, in spite of its great significance for explaining the present distribution patterns of carbon pools and estimating future changes, the mechanisms by which these processes occur are not fully understood. It is critical that we strengthen our research effort in this area of study. Although a great deal of effort has been put into the carbon density researches, there still remains much uncertainty regarding data collection, mechanistic explanations, and model construction in the relevant studies. In the future, we should establish a standardized and unified system to estimate carbon density, produce more accurate and useful models, and perform integrated studies at multi-scales and multi-resolutions levels.

Key words: Carbon pools, Terrestrial ecosystems, Distribution patterns, Influence factors