Nitrogen! It’s a cycle!

1. Nitrogen! It’s a cycle! Tara M. June 3rd, 2013

2. Content • Introduction • Plants and Nitrogen • Fixation • Mineralization/Immobilization • Nitrification • Denitrification • Video • Summary

3. Introduction • The nitrogen cycle is the process by which nitrogen is converted between its various chemical forms. • All life requires Nitrogen compounds ex: amino acids, proteins • Air (79% N) is a major reservoir, but most organisms can’t take-up/use N in this form • Plants must obtain N in “fixed “ forms such as nitrate or ammonia

4. The Nitrogen Cycle

5. Plants and Nitrogen • All plants need nitrogen to make • Amino acids • Proteins • DNA

6. Fixation- Bacteria • Conversion of Nitrogen to ammonia • Atmospheric N must be “fixed” in order to be taken up by plants, which can take up ammonia and nitrate • Most fixation is done by symbiotic or free-living bacteria • These bacteria contain the nitrogenase enzyme that combines gaseous N with H to produce ammonia • Rhizobium (symbiotic bacteria) live on the nodule of legumes and fix N in exchange for carbohydrates

7. Fixation –Atmospheric, Industrial • Atmospheric • Energy of lightning breaks nitrogen molecules and enables their atoms to combine with oxygen in the air forming nitrogen oxides. • These dissolve in rain, forming nitrates, that are carried to the earth. • Contributes roughly 5– 8% of the fixed nitrogen • Industrial • With an iron catalyst and great temperature and pressure H and N can be combined to form ammonia

8. Mineralization/Immobilization • Mineralization • Conversion of N compounds to ammonia • N from dead organic matter or animal waste is converted by enzymes in soil microbes and released as ammonium into the soil. • Immobilization • When microorganisms and plants assimilate ammonium into their cells to form proteins and nucleic acid • The N is being used by microbes and plants and is literally ‘immobilized’ in the cycle until the organism dies and it can be re-released to the soil.

9. Nitrification • Conversion of ammonia to nitrate via oxidation (2 step process) • Oxidation carried out by nitrifying bacteria • Nitrosomas- ammonia to nitrite • Nitrobacter- nitrite to nitrate • Legumes can also preform nitrification • Nitrites and nitrates reach the soil when the leaves of legumes are shed

10. Denirtification • Reduction of nitrates back to Nitrogen • Completes the cycle! • Preformed by bacterial species in anaerobic condition that use nitrate as an electron acceptor in place of oxygen during respiration

11. Summary • The nitrogen cycle is the process by which nitrogen is converted between its various chemical forms. • All plants need nitrogen to make amino acids, proteins and DNA • Fixation- conversion of atmospheric nitrogen to ammonia • Mineralization- conversion of N compounds to ammonia

12. Summary Cont. • Immobilization- when N has been assimilated into plant and microorganisms tissue matter and is not available in the soil • Nitrification- conversion of ammonia to nitrate • Denitrification- reduction of nitrates back to nitrogen