Nitrogen is one of the three essential nutrients in the terrestrial ecosystem and is regarded as a main limited factor in the forest ecosystem.

氮是陆地生态系统中三大营养元素之一，在森林生态系统中被视作主要的限制生长因子。

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PO Bailey, who dishes up three meals a day, said it is essential to provide a diet high in vitamin C and nutrients when away for long periods.

士官柏利负责潜艇上的一日三餐。他说长期在外航行，饮食的维生素c含量要高，要有营养很关键。

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