Nitrogen cycle

Nitrogen cycle

1. Forms of Nitrogen Urea  CO(NH 2 ) 2 Ammonia  NH 3 (gaseous) Ammonium  NH 4 Nitrate  NO 3 Nitrite  NO 2 Nitric oxide  NO Nitrous oxide  N 2 O Atmospheric Dinitrogen N 2 Organic N

2. Nitrogen 78% of the air is nitrogen (N 2 ) Nitrogen is essential for organisms to make DNA, protein, amino acids, etc. Yet, N 2 is useless to plants and animals

3. How do organisms get nitrogen? Two natural processes convert nitrogen gas into usable nitrogen: Lightning Nitrogen cycle

4. Nitrogen Cycle 5 main processes cycle nitrogen through the atmosphere, biosphere, and lithosphere: Nitrogen fixation Nitrification Assimilation Ammonification Denitrification

5. 5 The Nitrogen Cycle N 2 gas is the most abundant gas in the atmosphere, 79% of air volume. Involves several types of microbes 4 types of reactions: nitrogen fixation –atmospheric N 2 gas is converted to NH 4 salts; nitrogen-fixing bacteria live free or in symbiotic relationships with plants ammonification – bacteria decompose nitrogen- containing organic compounds to ammonia nitrification – convert NH 4 + to NO 2 - and NO 3 - denitrification – microbial conversion of various nitrogen salts back to atmospheric N 2

6. 6 Insert figure 26.10 Nitrogen cycle

7. 7 Insert figure 26.11 Nitrogen fixation through symbiosis

8. The Nitrogen Cycle

9. The Nitrogen Cycle N is cycled between: NH 4 + (-3 oxidation state) and NO 3 - (+5 oxidation state)

10. Nitrogen Reservoir Metric tons nitrogen Actively cycled Atmosphere N 2 Ocean Biomass Soluble salts (NO 3 , NO 2 - , NH 4 + ) Dissolved and particulate organics Dissolved N 2 Land Biota Organic matter Earth’s crust 3.9 x 10 15 5.2 x 10 8 6.9 x 10 11 3.0 x 10 11 2.0 x 10 13 2.5 x 10 10 1.1 x 10 11 7.7 x 10 14 No Yes Yes Yes No Yes Slow No Global Nitrogen Reservoirs

11. Nitrogen Cycle

12. Nitrogen Cycle Nitrogen fixation Bacteria (such as Rhizobium ) convert gaseous nitrogen into ammonia, which is taken up by plants N 2 + 3H 2  2NH 3 Rhizobium nodules

13. Biological inputs of nitrogen from N 2 fixation land - 135 million metric tons/ yr (microbial) marine - 40 million metric tons/yr (microbial) fertilizers - 30 million metric tons/yr (anthropogenic) Nitrogen must be fixed before it can be incorporated into biomass. This process is called nitrogen fixation. The enzyme that catalyzes nitrogen fixation is nitrogenase . N 2 fixing system Nitrogen fixation (kg N/hectare/yr) Rhizobium -legume Anabaena- Azolla Cyanobacteria-moss Rhizosphere assoc. Free-living bacteria 200-300 100-120 30-40 2-25 1-2 Rates of Nitrogen Fixation 1-2 kg N/hec/yr 2- 25 kg/N/hec/yr

14. Free-living bacteria must also protect nitrogenase from O 2 complex is membrane associated slime production high levels of respiration conformation change in nitrogenase when O 2 is present Azotobacter - aerobic Beijerinckia - aerobic, likes acidic soils Azospirillum - facultative Clostridia - anaerobic Examples of free-living bacteria:

15. Microorganisms fixing Azobacter Beijerinckia Azospirillum Clostridium Cyanobacteria Require the enzyme nitrogenase Inhibited by oxygen Inhibited by ammonia (end product)

16. Fate of ammonia (NH 3 ) produced during nitrogen fixation plant uptake microbial uptake adsorption to colloids (adds to CEC) fixation within clay minerals incorporation into humus volatilization nitrification } assimilation and mineralization

17. Nitrogen Cycle

18. Nitrogen Cycle Nitrification Ammonia in soil converted by bacteria into nitrite ions (NO 2 - ) and nitrate ions (NO 3 - )

19. Nitrification - Chemoautotrophic aerobic process Nitrosomonas Nitrobacter NH 4 + NO 2 - NO 3 - Nitrosomonas : 34 moles NH 4 + to fix 1 mole CO 2 Nitrobacter : 100 moles NH 4 + to fix 1 mole CO 2 Nitrification is important in areas that are high in ammonia (septic tanks, landfills, feedlots, dairy operations, over fertilization of crops). The nitrate formed is highly mobile (does not sorb to soil). As a result, nitrate contamination of groundwater is common. *Nitrate contamination can result in methemoglobenemia (blue baby syndrome).

20. What is the fate of NO 3 - following nitrification? accumulation (disturbed vs. managed) fixation within clay minerals leaching (groundwater contamination) dissimilatory nitrate reduction nitrate ammonification denitrification plant uptake microbial uptake biological uptake (assimilatory nitrate reduction) } Assimilatory nitrate reduction many plants prefer nitrate which is reduced in the plant prior to use however, nitrogen in fertilizer is added as ammonia or urea . assimilatory nitrate reduction is inhibited by ammonium nitrate is more mobile than ammonium leading to leaching loss microorganisms prefer ammonia since uptake of nitrate requires a reduction step

21. Nitrogen Cycle

22. Nitrogen Cycle Assimilation Plants use ammonia ( NH 3 ), ammonium ions (NH 4 + ), and nitrate ions (NO 3 - ) Make DNA, amino acids, and protein Animals get their nitrogen from eating plants

23. NH 3 is assimilated by cells into: proteins cell wall constituents nucleic acids Ammonia assimilation and ammonification Release of assimilated NH 3 is called ammonification . This process can occur intracellularly or extracellularly proteases chitinases nucleases ureases

24. Nitrogen Cycle

25. Nitrogen Cycle Ammonification Animals excrete excess nitrogen in their urine and feces Additional nitrogen is added to the soil when organisms die Decomposing bacteria and fungi convert the nitrogen in their waste into usable ammonia ( NH 3 ) and ammonium ions (NH 4 + )

26. At high N concentrations At low N concentrations

27. Fate of ammonia (NH 3 ) produced during nitrogen fixation plant uptake microbial uptake adsorption to colloids (adds to CEC) fixation within clay minerals incorporation into humus volatilization nitrification

28. Nitrogen Cycle

29. Nitrogen Cycle Denitrification Bacteria in the soil convert usable ammonia ( NH 3 ) and ammonium ions (NH 4 + ) back into nitrogen gas (N 2 ) and nitrous oxide gas (N 2 O)

30. Denitrification NO, N 2 O deplete the ozone layer Reaction of N 2 O with ozone O 2 + UV light O + O O + O 2 O 3 (ozone generation) N 2 O + UV light N 2 + O * N 2 O + O * 2NO (nitric oxide) NO + O 3 NO 2 + O 2 (ozone depletion) NO 2 + O * NO + O 2 returns fixed N to atmosphere: get formation of NO (Nitric oxide), N 2 O (Nitrous oxide) NO 3 NO N 2 O N 2

31. How are humans affecting the nitrogen cycle? Burning fuels release nitric oxide (NO) into the atmosphere Creates acid rain Harms vegetation Harms aquatic ecosystems Damages materials (metal, stone, etc.)

32. How are humans affecting the nitrogen cycle? Excess livestock waste and fertilizer adds nitrous oxide (N 2 O) to the atmosphere N 2 O is a greenhouse gas May lead to global warming

33. Effects of Human Activities on the Nitrogen Cycle We alter the nitrogen cycle by: Adding gases that contribute to acid rain. Adding nitrous oxide to the atmosphere through farming practices which can warm the atmosphere and deplete ozone. Contaminating ground water from nitrate ions in inorganic fertilizers. Releasing nitrogen into the troposphere through deforestation.

34. How are humans affecting the nitrogen cycle? Runoff from agricultural lands and sewage facilities adds nitrogen to aquatic ecosystems Results in algal blooms Leads to “dead zones”

35. Nitrogen Cycle Nitrogen cycle is the continuous sequence of natural processes by which nitrogen in the atmosphere and nitrogenous compounds in the soil are converted, as by nitrification and nitrogen fixation, into substances that can be utilized by green plants and then returned to the air and soil as a result of denitrification and plant decay.

36. Nitrogen Cycle Nitrogen fixation: The conversion of atmospheric nitrogen into nitrogenous compounds by bacteria (Rhizobia) found in the root nodules of legumes and certain other plants, and in the soil. Assimilation: Plants take nitrogen from the soil, by absorption through their roots in the form of their nitrate ions or ammonium ions. All nitrogen obtained by animals can be traced back to the eating of plants.

37. Nitrogen Cycle Ammonification: When a plant or animal dies, or an animal expels waste, the initial form of nitrogen is organic. Bacteria, or fungi in some cases, convert the organic nitrogen within the remains back into ammonium (NH 4 + ). Nitrification: The oxidation of the ammonium compounds in dead organic material into nitrites and nitrates by soil nitrobacteria, making nitrogen available to plants. Nitrosomonas species converts ammonia to nitrites (NO 2 - ). Nitrobacter species are responsible for the oxidation of the nitrites into nitrates (NO 3 - ).

38. Nitrogen Cycle Denitrification : Process occurs when nitrates (NO 3 - ) reduced to gaseous nitrogen (N 2 ), as by bacterial action on soil.

39. NITROGEN CYCLE N 2 Crops Fertilizer Production Lightning Legume Nitrogen-Fixing Bacteria in soil & roots Nitrogen Fixation Ammonia Nitrates Nitrites Decomposers Denitrification Sheep (GAS )

40. Nitrogen Cycle Assimilitory Nitrate Reduction Nitrification Nitrification Ammonification Nitrogen Fixation Denitrification Organic N NH 3 N 2 + N 2 O NH 4 + NO 2 - NO 3 -

41. NO 3 - NO 2 - NO N 2 O N 2 Denitrification Nitrate reductase Nitrite reductase Nitrous oxide reductase +5 +3 +2 +1 2e - 1e - 1e - 1e -