Downloaded 21 times
Uploaded byRinaldo John
Nitrogen cycle
The nitrogen cycle describes the conversion of nitrogen between its various chemical forms and involves both biological and non-biological processes. Key processes include nitrogen fixation by bacteria and lightning which converts atmospheric nitrogen gas into ammonia; nitrification by bacteria which converts ammonia into nitrites and nitrates; assimilation by plants which use nitrates and ammonium for growth; ammonification by decomposers which converts organic nitrogen waste into ammonia; and denitrification by bacteria which converts nitrates back into nitrogen gas. Human activities like fossil fuel combustion, agriculture, and deforestation have significantly impacted the global nitrogen cycle.
More Related Content
![Sivasankaran_ppt_20250325_164726_0000[1] [Read-Only].pptx](https://cdn.slidesharecdn.com/ss_thumbnails/sivasankaranppt2025032516472600001read-only-250325154345-2453d5e0-thumbnail.jpg?width=640&height=640&fit=bounds)
More from Rinaldo John
Nitrogen cycle
- 1. Forms of Nitrogen •Urea CO(NH2)2 • Ammonia NH3 (gaseous) • Ammonium NH4 • Nitrate NO3 • Nitrite NO2 • Nitric oxide NO • Nitrous oxide N2O • Atmospheric Dinitrogen N2 • Organic N
- 2. Nitrogen • 78% ofthe air is nitrogen (N2) • Nitrogen is essential for organisms to make DNA, protein, amino acids, etc. • Yet, N2 is useless to plants and animals
- 3. How do organismsget nitrogen? • Two natural processes convert nitrogen gas into usable nitrogen: • Lightning • Nitrogen cycle
- 4. Nitrogen Cycle • 5main processes cycle nitrogen through the atmosphere, biosphere, and lithosphere: 1. Nitrogen fixation 2. Nitrification 3. Assimilation 4. Ammonification 5. Denitrification
- 5. 5 The Nitrogen Cycle •N2 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 N2 gas is converted to NH4 salts; nitrogen-fixing bacteria live free or in symbiotic relationships with plants • ammonification – bacteria decompose nitrogen- containing organic compounds to ammonia • nitrification – convert NH4 + to NO2 - and NO3 - • denitrification – microbial conversion of various nitrogen salts back to atmospheric N2
- 6.
- 7. 7 Insert figure 26.11 Nitrogenfixation through symbiosis
- 8.
- 9. The Nitrogen Cycle Nis cycled between: NH4 + (-3 oxidation state) and NO3 - (+5 oxidation state)
- 10. Nitrogen Reservoir Metrictons nitrogen Actively cycled Atmosphere N2 Ocean Biomass Soluble salts (NO3, NO2 -, NH4 +) Dissolved and particulate organics Dissolved N2 Land Biota Organic matter Earth’s crust 3.9 x 1015 5.2 x 108 6.9 x 1011 3.0 x 1011 2.0 x 1013 2.5 x 1010 1.1 x 1011 7.7 x 1014 No Yes Yes Yes No Yes Slow No Global Nitrogen Reservoirs
- 11.
- 12. Nitrogen Cycle • Nitrogenfixation • Bacteria (such as Rhizobium) convert gaseous nitrogen into ammonia, which is taken up by plants • N2 + 3H2 2NH3 Rhizobium nodules
- 13. Biological inputs ofnitrogen from N2 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. N2 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 mustalso protect nitrogenase from O2 complex is membrane associated slime production high levels of respiration conformation change in nitrogenase when O2 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(NH3) 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.
- 18. Nitrogen Cycle • Nitrification •Ammonia in soil converted by bacteria into nitrite ions (NO2 -) and nitrate ions (NO3 -)
- 19. Nitrification - Chemoautotrophicaerobic process Nitrosomonas Nitrobacter NH4 + NO2 - NO3 - Nitrosomonas: 34 moles NH4 + to fix 1 mole CO2 Nitrobacter: 100 moles NH4 + to fix 1 mole CO2 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 thefate of NO3 - 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.
- 22. Nitrogen Cycle • Assimilation •Plants use ammonia (NH3), ammonium ions (NH4 +), and nitrate ions (NO3 -) • Make DNA, amino acids, and protein • Animals get their nitrogen from eating plants
- 23. NH3 is assimilatedby cells into: proteins cell wall constituents nucleic acids Ammonia assimilation and ammonification Release of assimilated NH3 is called ammonification. This process can occur intracellularly or extracellularly proteases chitinases nucleases ureases
- 24.
- 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 (NH3) and ammonium ions (NH4 +)
- 26. - - - - + + HO 2 glutamate dehydrogenase NAD NADH = O glutamate - ketoglutarate + NH3 NH3 A At high N concentrations - - - - - - + + + = O glutamate glutamate glutamine - ketoglutarate NH3 NH3 NH3 NH2 ATP ADP + Pi glutamine synthetase Ferredoxin 2H+ 2e - glutamate- synthase (GOGAT) Transamination B At low N concentrations
- 27. Fate of ammonia(NH3) produced during nitrogen fixation plant uptake microbial uptake adsorption to colloids (adds to CEC) fixation within clay minerals incorporation into humus volatilization nitrification
- 28.
- 29. Nitrogen Cycle • Denitrification •Bacteria in the soil convert usable ammonia (NH3) and ammonium ions (NH4 +) back into nitrogen gas (N2) and nitrous oxide gas (N2O)
- 30. Denitrification NO, N2O depletethe ozone layer Reaction of N2O with ozone O2 + UV light O + O O + O2 O3 (ozone generation) N2O + UV light N2 + O* N2O + O* 2NO (nitric oxide) NO + O3 NO2 + O2 (ozone depletion) NO2 + O* NO + O2 returns fixed N to atmosphere: get formation of NO (Nitric oxide), N2O (Nitrous oxide) NO3 NO N2O N2
- 31. How are humansaffecting 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 humansaffecting the nitrogen cycle? • Excess livestock waste and fertilizer adds nitrous oxide (N2O) to the atmosphere • N2O is a greenhouse gas • May lead to global warming
- 33. Effects of HumanActivities 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 humansaffecting 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 • Nitrogencycle 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 • Nitrogenfixation: 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: Whena 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 (NH4 +). • 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 (NO2 -). Nitrobacter species are responsible for the oxidation of the nitrites into nitrates (NO3 -).
- 38. Nitrogen Cycle • Denitrification: Processoccurs when nitrates (NO3 -) reduced to gaseous nitrogen (N2), as by bacterial action on soil.
- 39. NITROGEN CYCLE N2 Crops Fertilizer Production Lightning Legume Nitrogen-Fixing Bacteria in soil& roots Nitrogen Fixation Ammonia Nitrates Nitrites Decomposers Denitrification Sheep (GAS )
- 40.
- 41. NO3 - NO2 - NON2O N2 Denitrification Nitrate reductase Nitrite reductase Nitrous oxide reductase +5 +3 +2 +1 0 2e- 1e- 1e- 1e-