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有证据表明,森林土壤中存在一个对全球CO_2收支具有潜在影响的内部CO_2汇。在氮高沉降地区已表现出土壤空气中CO_2的比例越低,其向地上大气释放的CO_2越少的趋势。而且在氮沉降发生的林缘,尤其是云杉林,土壤中CO_2浓度低,但往郁闭的林内则呈逐渐增加的趋势。在过去的30年中,森林土壤维持内部CO_2汇运转的能力局限于1000～1500kg/hm~2氮的累积量。超过了此限量,土壤内部的CO_2汇将随着氮的淋溶而成为另外一个CO_2源。这种“氮饱和”在斯堪的纳维亚南部郁闭的森林内并不常见,而是在高大气氮沉降的林缘发生。最初,土壤CO_2梯度从林缘向郁闭的林内增加,现在则相反。
There is evidence that there is an internal CO 2 sink in forest soils that has the potential to affect the global CO 2 budget. In the region of high nitrogen deposition, the lower the proportion of CO 2 in soil air, the less CO 2 it releases to the upper atmosphere. In the forest margin where nitrogen deposition occurred, especially in the spruce forest, the concentration of CO 2 in the soil was low, but it gradually increased toward the closed forest. In the past 30 years, the ability of forest soils to maintain the internal CO 2 transport has been limited to the accumulation of 1000 ~ 1500 kg / hm 2 nitrogen. Beyond this limit, CO 2 sinks within the soil will become another source of CO 2 with leaching of nitrogen. This “nitrogen saturation” is uncommon in a canopy forest in southern Scandinavia, but occurs at a forest margin where high atmospheric nitrogen settles. Initially, the soil CO 2 gradient increased from the forest margin to the canopy forest, which is now the opposite.