CO2失汇与北半球中高纬度陆地生态系统的碳汇

 化石燃料消耗及热带林破坏导致约7.0PgC·a-1(1Pg＝109t)的CO2向大气排放，其中3.0～3.4PgC·a-1的CO2被用于大气CO2浓度的升高，约2.0PgC·a-1的CO2被海洋吸收，而陆地生物圈被认为是CO2净吸收与净排放基本达到平衡。因此，在人工源CO2中，尚有1.6～2.0PgC·a-1的CO2去向不明。这就是著名的CO2失汇之谜。大气成分监测、CO2通量测定以及模型模拟等方面的研究都表明，北半球陆地生态系统是一个重要的碳汇，但其值存在很大的不确定性，且具有较大的时空变化。全球温暖化、CO2施肥效应，氮和磷沉降的增加以及人工植被的扩大是形成碳汇的主要因素。为减少碳汇估计值的不确定性，除加强长期定位监测、改良现有估测模型外，重视研究土壤圈在碳循环中的作用至关重要。

THE CARBON SINK :THE ROLE OF THE MIDDLE AND HIGH LATITUDES TERRESTRIAL ECOSYSTEMS IN THE NORTHERN HEMISPHERE

About 7.0 Pg (1 Pg=109 t) of carbon is annually released to the atmosphere from fossil fuel combustion and the buring and clearance of tropical forests, of which 3-3.4 PgC of the carbon adds to the atmospheric carbon pool and about 2.0 PgC is uptaken by oceans. The terrestrial biosphere is considered to hold its carbon dynamic in balance with approximately equal rates of sequestration and emission. Therefore 1.6 to 2.0 PgC per year is unattributed and this is known as the ’missing sink’. Many studies, including the monitoring of atmospheric components, analysis of forest inventories, CO2 flux measurements and modeling simulations, have suggested that the mid- and high latitude terrestrial ecosystems of the Northern Hemisphere are functioning as a significant carbon sink, though with a large uncertainty and considerablly spatio-temporal heterogeneity. Global warming, CO2 fertilization, increasing nitrogen and phosphorus deposition, and the expansion and re-growth of forests are major factors impacting the size and distribution of these carbon sinks. Study on the role of soils in the carbon cycles-as well as long-term monitoring and improvement of existing carbon model simulations is a critical step required to reduce uncertainty in the size of this sink.