氮循环的一个关键组成部分就是——在大气中，将纯净的氮固定为成含氮化合物的形式——这或多或少要完全依赖于生物(闪电仅起一点儿作用)。
One crucial part of this cycle-the fixing of pure nitrogen from the atmosphere into useful nitrogen-containing chemicals-depends more or less entirely on living things (lightning helps a bit).
其中一些气体，如，氮，氧，氩， 氖等，作为空气的永久组成成分，总是以固定的比例存在于大气中。
Some of them, such as nitrogen, oxygen, argon, neon, and so on, may be regarded as permanent atmospheric components that remain in fixed proportions to the total gas volume.
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