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The Biogeochemical Cycles Nitrogen Cycle Biology I Ecology What is Nitrogen? • Nitrogen - most abundant element in the Earth’s atmosphere. • Nitrogen cannot be absorbed directly by plants & animals until it is converted into compounds they can use. Nitrogen Cycle Steps • Step 1- Nitrogen Fixation- Special bacteria convert nitrogen gas (N2) to ammonia (NH3) which the plants can use. –Assimilation • Step 2- Nitrification- Nitrification is the process which converts ammonia into material which the plants can use as nutrients. • Step 3- Ammonification- After living organisms have used nitrogen, decomposers convert the nitrogen-rich waste compounds into simpler ones . • Step 4- Denitrification- Final step in which other bacteria convert the simple nitrogen compounds back into nitrogen gas (N2), to be released into the atmosphere How do humans affects the Nitrogen Cycle? • Nitric Oxide (NO) is released into the atmosphere when any type of fuel is burned. This includes byproducts of internal combustion engines. • Nitrous Oxide (N2O) is released into the atmosphere through bacteria in livestock waste and commercial fertilizers applied to the soil. • Removing nitrogen from the Earth’s crust and soil when we mine nitrogen-rich mineral deposits. • Discharge of municipal sewage adds nitrogen compounds to aquatic ecosystems which disrupts the ecosystem and kills fish. Nitrogen in the air nitrogen fixing plant eg pea, clover animal protein plant made protein root nodules (containing nitrogen fixing bacteria) denitrifying bacteria nitrates absorbed dead plants & animals urine & faeces decomposition by bacteria & fungi nitrates bacteria (nitrifying bacteria) ammonia nitrites bacteria Nitrogen in the air nitrogen fixing plant eg pea, clover animal protein plant made protein root nodules (containing nitrogen fixing bacteria) dead rabbit denitrifying bacteria nitrates absorbed dead plants & animals urine & faeces decomposition by bacteria & fungi nitrates bacteria ammonia nitrites (nitrifying bacteria) bacteria
