ESM 219 N Cycle _07

ESM 219 N Cycle _07 - ESM 219: F07 N cycle Nitrogen Cycling...

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1 ESM 219: F07 N cycle Nitrogen Cycling N 2 fixation – 85% biological (60% terrestrial, 40% marine) –N 2 + 8H + + 8e - 2 NH 3 + H 2 nitrogenase –Organ isms • Free-living (bacteria, many types) • Symbiotic, e.g. (many types) Rhizobia in legumes Frankia in trees N 2 fixation: pathway and stoichiometry. Azospirillum brasilense : a nitrogen fixing bacterium that lives in the soil rhizosphere (image = 7 microns)
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2 Azotobacter sp.: free living N sp.: free living N 2 fixer in soil (image width = 2 fixer in soil (image width = 2 microns). Here we see an X -section of a cyst, the resting section of a cyst, the resting stage analogous to an stage analogous to an endospore endospore Rhizobium trifolii (image width 2 microns) Note capsular material around this free living soil organism. Nitrogen fixation (continued) • Nodules –will have some in the lab next week……. • A few slides from our text (following) that show the process of bacteroid formation and the genes involved Rhizobium trifolii on root tip (image width 12 microns) --a clover symbiont
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3 Rhizobium trifolii (image width 8 microns) --microfibrils formed preceding root invasion Rhizobial bacteroids in Neptunia TEM Image: width = 4.7 microns The nod gene cluster on the Sym plasmid of Rhizobium leguminosarum biovar viciae (nodulates peas). The acetylene reduction assay for quantifying rates of dinitrogen fixation. Nitrogen Cycling (cont.) Immobilization = uptake of NH 4 + Ammonification = mineralization of organic N to ammonia O || urease NH 2 -C-NH 2 + H 2 O 2NH 3 + CO 2 Observations in immobilization / mineralization
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This note was uploaded on 08/06/2008 for the course ESM 219 taught by Professor Holden during the Fall '07 term at UCSB.

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ESM 219 N Cycle _07 - ESM 219: F07 N cycle Nitrogen Cycling...

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