ECOLOGY•Activity8•LivingonEarth
©2011TheRegentsoftheUniversityofCalifornia
SGI Ecology: Activity 8 • Living on Earth
The Nitrogen Cycle
1
ECOLOGY•Activity8•LivingonEarth
©2011TheRegentsoftheUniversityofCalifornia
Why is nitrogen important?
• Nitrogenisessentialtolivingorganisms
• Itisfoundinallaminoacids,whichmakeupproteins
• ItispartofDNAandRNA
ECOLOGY•Activity8•LivingonEarth
©2011TheRegentsoftheUniversityofCalifornia
Where does nitrogen come from?
• Nitrogenisfoundinmanychemicalforms(ammonia,nitrates,etc),onlysomeofwhichcanbeusedbyorganisms
• Nitrogenmakesup78%oftheair,butmostorganismscannotusenitrogendirectlyfromtheair
• Nitrogeniscycledbetweentheatmosphere,organisms,anddifferentreservoirsinaprocesscalledthenitrogencycle
• Duringthiscyclenitrogenistransformedintoseveralchemicalforms
ECOLOGY•Activity8•LivingonEarth
©2011TheRegentsoftheUniversityofCalifornia
The Nitrogen Cycle
ECOLOGY•Activity8•LivingonEarth
©2011TheRegentsoftheUniversityofCalifornia
Nitrogen-fixing Bacteria• Nitrogen‐fixingbacteriatransformatmosphericnitrogen(N2)intoammoniumcompounds(NH4
+)
• Symbioticnitrogen‐fixingbacterialiveinrootsoflegumefamilyplant(soy‐beans,peanuts,etc)
• Othertypesofnitrogen‐fixingbacteriaarefoundinthesoil
ECOLOGY•Activity8•LivingonEarth
©2011TheRegentsoftheUniversityofCalifornia
Organisms and Nitrogen• Plantsandotherproducersassimilatenitrogen,transformingitfromnitrate(NO3
–)orammonium(NH4
+)ionstoformbiomass.
• Consumersobtainnitrogenfromeatingproducers,orfromeatingotherorganismsthathaveeatenproducers.
ECOLOGY•Activity8•LivingonEarth
©2011TheRegentsoftheUniversityofCalifornia
Decomposers and Nitrogen
• Decomposers,primarilybacteriaandfungi,breakdowndeadorganisms.
• Decomposerstransformnitrogenfromorganismsintoammonium(NH4
+)whichgoesintothesoil.
ECOLOGY•Activity8•LivingonEarth
©2011TheRegentsoftheUniversityofCalifornia
Nitrifying Bacteria
• Nitrifyingbacteriabreakdownammonium(NH4
+)intonitrite(NO2–)
andthenintonitrate(NO3
–)
• Nitrate(NO3–)
isassimilatedbyorganismsortransformedbydenitrifyingbacteria
ECOLOGY•Activity8•LivingonEarth
©2011TheRegentsoftheUniversityofCalifornia
Denitrifying Bacteria
• Nitrate(NO3–)inthesoil
istransformedbydenitrifyingbacteriaintoatmosphericnitrogen(N2).
• DenitrifyingbacteriaalsoproduceN2O,whichcontributestothegreenhouseeffect.
ECOLOGY•Activity8•LivingonEarth
©2011TheRegentsoftheUniversityofCalifornia
Atmospheric Nitrogen
• Atmosphericnitrogen(N2)cannotbeuseddirectlybymostproducersorconsumersandmustbetransformedbybacteria.
ECOLOGY•Activity8•LivingonEarth
©2011TheRegentsoftheUniversityofCalifornia
Leaching• Nitrateionsarelostfromthesoilthroughleaching.
• Water‐solublenitrateionsmovewithwaterthroughthesoilandcancontaminatenearbygroundwaterorbodiesofwater.
• Leachingcanleadtopoorsoilconditionsandeutrophicationofcontaminatedwaterbodies.
ECOLOGY•Activity8•LivingonEarth
©2011TheRegentsoftheUniversityofCalifornia
The Nitrogen Cycle