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ZOL 355 (10)
Lecture 9

ZOL 355 Lecture Notes - Lecture 9: Nitrogen Fixation, Limiting Factor, Autotroph


Department
Zoology
Course Code
ZOL 355
Professor
P.Ostrom
Lecture
9

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Nitrogen Cycling
Background
Importance
o Important component of proteins
o Base of DNA
o A limiting nutrient and controls
primary production
Not in sufficient quantities
Necessary for growth
Nitrogen reservoirs and nitrogen limitation
o In the atmosphere is N2
Can be used in this form
o Very few organisms can use nitrogen
o Nitrogen is not biologically available
Important terminology
When N enters a plant, we call this N uptake
If nitrogen is limiting then fertilizers have nitrogen in them
Forms of N used by plants
o Ammonium (NH4+) an ion
o Nitrate (NO3-)
o Urea (NH2)2CO)
o Nitrite (NO2-) not very abundant
o Ammonia (NH3) a gas
Reservoir
Size (1015 g)
Atmosphere
3,900,000
Ocean
23,348
Land
Soil: 460
Biota: 14.2
Nucleotide bases
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Bacteria, algae and plants can uptake ammonium, nitrate or urea across
the cell wall of their roots
Nitrogen synthesis
o N uptake and Synthesis
o NH4+ - movement in to the cell NH4+ - amino acids - biomass
o NO3- - movement in to the cell NH4+ - amino acids - biomass
o Urea - movement in to the cell NH4+ - amino acids - biomass
o Synthesis of the amino acid glutamic acid from NH4+
Reactions of the Nitrogen Cycle
Nitrogen fixation
o N2 - NH4+ - protein - biomass
o Nitrogen Fixation
o Plants an’t fix nitrogen
Only bacteria conduct N2 fixation
Can only fix nitrogen if they have a symbiotic relationship with
photosynthetic bacteria
o Plant nodules containing an abundance of N2 fixing bacteria
Cowpea
Soybean nodules and symbiotic bacteria
o Importance of N2 fixation for Sonoran Desert plants
Bacteria crust
o Question for exam: how does nitrogen control photosynthesis
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