Understanding the Nitrogen Cycle: Essential Processes for Plant Growth
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The nitrogen cycle is a vital process where nitrogen is transformed between various chemical forms essential for life. Despite nitrogen being abundant in the atmosphere, plants need it in fixed forms like nitrate or ammonia to thrive. Key processes include fixation by bacteria, mineralization of organic compounds, nitrification to convert ammonia into nitrate, and denitrification, completing the cycle. This cycle supports the creation of amino acids, proteins, and DNA, making it crucial for all plants and life on Earth.
Understanding the Nitrogen Cycle: Essential Processes for Plant Growth
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Presentation Transcript
Nitrogen! It’s a cycle! Tara M. June 3rd, 2013
Content • Introduction • Plants and Nitrogen • Fixation • Mineralization/Immobilization • Nitrification • Denitrification • Video • Summary
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
Plants and Nitrogen • All plants need nitrogen to make • Amino acids • Proteins • DNA
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
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
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.
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
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
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
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
