The Nitrogen Cycle By: Rachel Brewer Kaci Kelley-Brown Jennifer Moats Dolleen Wiltgen What is nitrogen ? Periodic Table Nitrogen is in the Nonmetals Group • Where is nitrogen found in the environment? The largest single source of nitrogen is in the atmosphere . Nitrogen makes up 78% of our air! What happens to atmospheric nitrogen (N 2) in the nitrogen cycle? N N N N N N Atmospheric nitrogen is converted to ammonia or nitrates . N N Atmospheric Nitrogen (N 2) N N Nitrates (NO ) Ammonia (NH 3) 3 Nitrogen combines Nitrogen combines with Hydrogen to make with Oxygen to make Ammonia Nitrates N N Why does N atmospheric nitrogen N need to be converted? N N It is one of nature’s great ironies… Nitrogen is an essential component of DNA, RNA, and proteins—the building blocks of life. Although the majority of the air we breathe is nitrogen , most living organisms are unable to use nitrogen as it exists in the atmosphere ! How does N atmospheric N nitrogen get changed into a form that can be used by most living organisms? By traveling through one of the four processes in the Nitrogen Cycle ! (1) Nitrogen Fixation (4) Denitrification Nitrogen Cycle (3) Nitrification (2) Ammonification The first process in the nitrogen cycle is… Nitrogen Fixation ! (1) Nitrogen Fixation Nitrogen Cycle What is N N “nitrogen fixation” and what does it mean to say nitrogen gets “fixed”? “Nitrogen Fixation ” is the process that causes the strong two-atom nitrogen molecules found in the atmosphere to break apart so they can combine with other atoms. N Oxygen Hydrogen N Hydrogen N N N Oxygen N Nitrogen gets “ fixed ” when it is combined with oxygen or hydrogen. There are three ways that nitrogen gets “fixed” ! (a) Atmospheric Fixation (b) Industrial Fixation (c) Biological Fixation Bacteria Lightning “fixes” Nitrogen! Atmospheric Fixation (Only 5 to 8% of the Fixation Process) N The enormous energy of N O lightning breaks nitrogen Nitrogen molecules apart and enables combines the nitrogen atoms to combine with Oxygen with oxygen forming nitrogen Nitrogen oxides forms oxides (N 2O) . Nitrogen oxides (N 2O) Nitrogen dissolve in rain, forming (NO 3) oxides dissolve in rain and nitrates. Nitrates (NO 3) are change to carried to the ground with the nitrates rain. Plants use nitrates to grow! N N H Industrial Fixation Under great pressure, at N H a temperature of 600 3 degrees Celcius, and with the use of a Industrial Plant combines catalyst, atmospheric nitrogen and hydrogen nitrogen (N ) and 2 Ammonia is formed hydrogen are combined (NH 3) to form ammonia (NH 3). Ammonia can be used as a fertilizer . Ammonia is used a fertilizer in soil Biological Fixation (where MOST nitrogen fixing is completed) There are two types of “Nitrogen Fixing Bacteria” Free Living Bacteria Symbiotic Relationship Bacteria (“fixes” 30% of N 2) (“fixes” 70% of N 2) Free Living Bacteria Highly specialized bacteria live in the soil and have the ability to combine atmospheric nitrogen with hydrogen to make ammonia (NH ). N 3 N H NH3 Free-living bacteria live in soil and combine atmospheric nitrogen with hydrogen (NH 3) Nitrogen changes into ammonia Bacteria Symbiotic Relationship Legume plants Bacteria Bacteria live in the roots of legume family plants N and provide the plants with ammonia (NH 3) in exchange for the plant’s NH 3 carbon and a protected home. N Roots with nodules where bacteria live Nitrogen changes into ammonia. Most atmospheric nitrogen (N 2) is “fixed” and changed to ammonia (NH 3). Ammonia is highly toxic to many organisms. Can plants use ammonia? Very few plants can use ammonia (NH 3)… (1) Nitrogen Fixation (2) Ammonification …but, fortunately the second process Ammonification can help! What is ammonification ? Ammonification : Bacteria decomposers break down amino acids from dead animals and wastes into nitrogen ammonium . Bacteria decomposers break down amino acids into ammonium Why is ammonification necessary? Because plants cannot use the organic forms of nitrogen that are in the soil as a result of: (1) wastes (manure and sewage) (2) compost and decomposing roots and leaves How does ammonification occur? Microorganisms convert the organic nitrogen to ammonium. The ammonium is either taken up by the plants (only in a few types of plants) or is absorbed into the soil particles. Ammonium (NH 4) in the soil is stored up to later be changed into inorganic nitrogen , the kind of nitrogen that most plants can use. Bacteria converts organic nitrogen to ammonium (NH 4) Ammonium (NH 4) is used by some plants Bacteria Ammonium (NH 4) is stored in soil. What happens to ammonium (NH 4) stored in the soil? It travels through the third process of the nitrogen cycle called Nitrification ! (1) Nitrogen Fixation (3) Nitrification (2) Ammonification Nitrifying bacteria in the ground first combine ammonia with oxygen to form nitrites . Then another group of nitrifying bacteria convert nitrites to nitrates which green plants can absorb and use! Nitrifying bacteria in soil combine ammonia with oxygen Ammonia changes to nitrites Nitrifying bacteria in soil convert nitrites to nitrates Ammonia Nitrites Nitrates Plants absorb nitrates and grow! (NH 3) (NO 2) (NO 3) How does nitrogen reenter the atmosphere in the nitrogen cycle? Through the fourth process called denitrification ! (1) Nitrogen Fixation (4) Denitrification (3) Ammonification (2) Nitrification What does denitrification do ? Denitrification converts nitrates (NO 3) in the soil to atmospheric nitrogen (N 2) replenishing the atmosphere. Nitrogen in atmosphere (N 2) Nitrates (NO 3) in Soil How does the denitrification process work? Nitrates in soil Denitrifying bacteria live deep in soil and in aquatic sediments where conditions make it difficult for them to get oxygen. The denitrifying bacteria use nitrates as an alternative to oxygen, leaving free nitrogen gas as a byproduct. They close the nitrogen cycle! Nitrogen in atmosphere closes the nitrogen cycle! (N 2) (NO 3) Denitrifying bacteria live deep in soil and use nitrates as an alternative to oxygen making a byproduct of nitrogen gas. Other ways that nitrogen returns to the atmosphere… Emissions from industrial combustion and Volcano eruptions gasoline engines create nitrous oxides emit nitrous oxides gas (N O). 2 gas (N 2O). (a) (b) N2 N2O (4) Denitrification (1) Nitrogen Fixation (c) Nitrogen Cycle (3) Nitrification (2) Ammonification NO 3 NH 3 Ammonia is converted Organic nitrogen is to nitrites and nitrates. Nitrates in Soil converted to ammonium. (a) (b) N2 N2O (4) _____________ (1) _____________ (c) Nitrogen Cycle (3) ____________ (2) _____________ NO 3 NH Ammonia is converted Organic nitrogen is 3 to nitrites and nitrates. Nitrates in Soil converted to ammonium. You can find animated clip art at: http://office.microsoft.com/clipart.