the nitrogen cycle
noun [ S ] uk/ˈnaɪ.trə.dʒən ˌsaɪ.kəl/ us/ˈnaɪ.trə.dʒən ˌsaɪ.kəl/
氮循环
the process by which nitrogen is exchanged between different living organisms on earth and between living organisms and the environment, for example when plants take it from the air and animals eat the plants