()微生物是人类的朋友 微生物是自然界物质循环的关键环节; Sunlight E Consun N E Figure 25.1 The now of energy (E)and nutrients(N)in ecosystems. Energy flows through he system(it is obtained continuously from the sun). whereas nutrients in the environment must be re- cycled for new life to continue 微生物是自然界物质循环的关键环节； (一) 微生物是人类的朋友