Cyanobacteria & Soil Fertlity.pdf

If you want to explore the role of Cyanobacteria in soil fertility in general & Azolla-Anabena association in particular, you can visit this PowerPoint Presentation.

1. Cyanobacteria (blue green algae), Azolla and Anabaena
azollae association, nitrogen fixation, factors affecting
growth, blue green algae and Azolla in rice cultivation.
By
Dr. N. Sannigrahi, Associate Professor,
Department of Botany,
Nistarini College, Purulia,
D.B. Road, Purulia (W.B) India

2. CYANOBACTERIA
Cyanobacteriaorbluegreenalgaearetheoneofmostsuccessfulau-
totrophicorganismsonearthwhichhavemasteredalltypesof
environments—freshwater,seawater,saltmarshes,moistrocks,tree
trunks,moistsoils,hotsprings,frozenwaters.
Cyanobacteriaarethemostselfcontainedphotosyntheticorganisms.They
can,therefore,liveundereverytypeofenvironmentandoneverytypeof
substrate.Becauseofthisfact,theyareoneoftheearliestcolonizersof
barrenareas.Manyofthemhavetheabilityofnitrogenfixation.
Cyanobacteriamaybeunicellular,colonialorfilamentous.Eachfilament
consistsofasheathofmucilageandoneormorecellularstrandscalled
trichomes.
Singletrichomefilamentsmayfurtherbeoftwotypes,homocystous(=
undifferentiated,e.g.,Oscillatoria)andheterocystous(=differentiated,
havingheterocysts,e.g.,Nostoc).Spirulinahasaspirallycoiledfilament.
Coloniesdevelopinsomecases,e.g.,Nostoc

3. CYANOBACTERIA

4. CYANOBACTERIA
Flagellaareabsentbutglidingmovementsareknowninanumberof
cyanobacteria.
Cyanobacterialcellsarelargerandmoreelaboratethanbacteria.Cell
structureistypicallyprokaryotic—oneenvelopeorganizationwith
peptidoglycanwall,nakedDNA,70Sribosomeandabsenceofmembrane
boundstructureslikeendoplasmicreticulum,mitochondria,Golgibodies,
plastids,lysosomes,sapvacuoles.
Thecellwallisfourlayeredwithpeptidoglycanpresentinthesecondlayer.
Theouterpartoftheprotoplastcontainsanumberofphotosynthetic
thylakoids.Itiscalledchromoplasm.Thethylakoidsliefreelyinthe
cytoplasm.Theirmembranescontainchlorophylla,carotenesand
xanthophylls.Chlorophyllbisabsent.
Attachedtothethylakoidmembranesaresmallgranulesknownas
phycobilisomes.Thelatterpossessaccessoryphotosyntheticpigments
knownasphycobilins.Thephycobilinsareofthreetypes—phycocyanin
(blue),allophycocyanin(blue)andphycoerythrin(red).

5. CYANOBACTERIA
Anaked,circular,doublestrandedDNAliescoiledgenerallyinthecentral
partofthecytoplasmknownascentroplasm.ThecoiledupDNAis
equivalenttoasinglechromosomeofhigherorganisms.Itisoftencalled
nucleoid.Likebacteria,smallcircularDNAsegmentsmayalsooccurin
additiontonucleoid.
Theyareknownasplasmidsortransposons.70Sribosomeoccurhereand
there.Semicirculargroupofcoiledmembranesoftenattachestheplasma
membranewiththenucleoid.Itisknownaslamellasome.Fourtypesof
inclusionsoccurinthecells.Theyareα-granules(cyanophyceanstarch),β-
granules(lipiddroplets),volutingranulesandpolyhedralbodies(ribulose
biphosphatecarboxylase).
Insteadoftypicalvacuolesorsapvacuoles,gasvacuolesorpseudo-
vacuolesarefound.Eachgasvacuoleconsistsofanumberof
submicroscopicunitscalledgasvesicles.Gasvacuolesfunctionaslight
screen;providebuoyancyregulatingmechanismandpneumaticstrength.

6. CYANOBACTERIA

7. Anabaenaazollae ASSOCIATION
TheassociationbetweenAzollaandAnabaenaazollaeisasymbioticone,
whereintheeukaryoticpartnerAzollahousestheprokaryoticendosymbiontin
itsleafcavitiesandprovidescarbonsourcesandinturnobtainsitsnitrogen
requirements.
Biologicalnitrogenfertilizersplayavitalroletosolvetheproblemsofsoil
fertility,soilproductivityandenvironmentalquality.Anabaenaazollae,a
cyanobacteriumlivesinsymbioticassociationwiththefreefloatingwaterfern
Azolla.
ThesymbioticsystemAzolla-Anabaenacomplexisknowntocontribute40-60
kgNha
-1
perricecrop.Anabaenaazollecangrowphotoautotrophicallyand
fixesatmosphericnitrogen.ThenitrogenfixingcyanobacteriasuchasA.
azollaeandvariabiliswhenimmobilizedinpolyurethanefoamandsugarcane
wastehavesignificantlyincreasedthenitrogenfixingactivityandammonia
secretion.
Theinoculationofcyanobacteriainneecropsignificantlyinfluencedthe
growthofricecropbysecretionofammoniainfloodwater.Theuseofneem
cakecoupledwiththeinoculationofAzollagreatlyincreasedthenitrogen
utilizationefficiencyinricecrop.

8. Anabaenaazollae ASSOCIATION

9. Anabaenaazollae ASSOCIATION
InadditiontocontributingN,thecyanobacteriaaddorganicmatter,secrete
growthpromotingsubstancelikeauxinsandvitamins,mobilizeinsoluble
phosphateandimprovephysicalandchemicalnatureofthesoil.
Algalizationhasbeenshowntoamelioratethesaline-alkalisoils,helpin
theformationofsoilaggregates,reducesoilcompaction,andnarrowC:N
ratio.
Theseorganismsenablethecroptoutilizemoreoftheappliednutrients
leadingtoincreasedfertilizerutilizingefficiencyofcropplant.Mostofthe
cyanobacteriaactassupplementstofertilizerNcontributingupto30kgN
ha
-1
season
-1
.Theincreaseinthecropyieldvariesbetween5-25percent.

10. NITROGEN FIXATION
ApartfromCarbon,HydrogenandOxygen,Nitrogenisthemostprevalent
essentialmacro-elementinlivingorganismsusedtobuildaminoacids,
proteins,nucleicacids,cytochromes,chlorophylls,alkaloids,phytohormones
andmanyofthevitamins.Plantscompetewithmicrobesforlimitednitrogen
contentavailableinthesoil.Plantsmainlyabsorbnitrogenintheformof
nitrate(NO
3
–
)orammoniumions(NH
4
+
)fromthesoil.
Thenitrateismoreabundantinwelloxygenated,non-acidicsoils,while
ammoniumispredominantinacidicorwaterloggedsoils.Theothersourcesof
availablesoilnitrogenmaybeaminoacidsfromdecayingorganicmatter,
animalexcreta(urea)andchemicalfertilizersthatcanbeabsorbeddirectlyby
theplants.Nitrogenisobtainedbytheplantsmainlyfromtheatmosphere.It
occursasfreediatomic(N
2)moleculesintheair.Itishighlyinertgas.Itcannot
beuseddirectlybythehigherplants,andthereforehastobefixed.
Thephenomenonofconversionoffreenitrogen(molecularandelemental)into
nitrogenouscompounds(tomakeitavailabletotheplantsforabsorption)is
callednitrogenfixation.Nitrogenfixationiscarriedoutbyphysicochemical
andbiologicalmeans.About10%ofnaturalnitrogenfixationtakesplaceby
physicochemicalmethodsand90%bybiologicalmethods.

11. NITROGEN FIXATION

12. NITROGEN FIXATION
 Theconversionofatmosphericnitrogenintothenitrogenouscompounds
throughtheagencyoflivingorganismsiscalledbiologicalnitrogenfixation.
Theprocessiscarriedoutbytwomaintypesofmicroorganism:thosewhich
liveinclosesymbioticassociationwithotherplantsandthosewhichare“free
living”ornon-symbiotic.Biologicalnitrogenfixation(BNF)istheprocess
wherebyatmosphericnitrogenisreducedtoammoniainthepresenceof
nitrogenese.Nitrogeneseisabiologicalcatalystfoundnaturallyonlyincertain
microorganismssuchasthesymbioticRhizobiumandFrankia,orthefree-
livingAzospirillumandAzotobacterandBGA.
 Amongtheearth’sorganisms,onlysomeprokaryoteslikebacteriaand
cyanobacteriacanfixatmospherenitrogen.Theyarecallednitrogenfixersor
diazotrophs.Theyfixabout95%ofthetotalglobalnitrogenfixedannually(-
200millionmetrictones)bynaturalprocess.
 FREELIVING:Azotobacter,Beijerinckia(bothaerobic)and
Clostridium(anaerobic)aresaprophyticbacteriathatperformnitrogenfixation.
Desulphovibrioischemotrophicnitrogenfixingbacterium.
Rhodopseudomonas,RhodospirillumandChromatiumarenitrogenfixing
photoautotrophicbacteria.Thesebacteriaaddupto10-25kg,of
nitrogen/ha/annum.

13. NITROGEN FIXATION
•SYMBIOTICNITROGENFIXINGCYANOBACTERIA:
•AnabaenaandNostocspeciesarecommonsymbiontsinlichens,
Anthoceros,Azollaandcycadroots.Azollapinnata(awaterfern)has
Anabaenaazollaeinitsfronds.ItisofteninoculatedtoRicefieldsfor
nitrogenfixation.
•SYMBIOTICNITROGENFIXINGBACTERIA:
•Rhizobiumisaerobic,gramnegativenitrogenfixingbacterialsymbiontsof
Papilionaceousroots.SesbaniarostratahasRhizobiuminrootnodulesand
Aerorhizobiuminstemnodules.Frankiaissymbiontinrootnodulesof
manynon-leguminousplantslikeCasuarinaandAlnus.Xanthomonasand
Mycobacteriumoccurassymbiontintheleavesofsomemembersofthe
familiesRubiaceaeandMyrsinaceae(e.g.,Ardisia).Severalspeciesof
Rhizobiumliveinthesoilbutareunabletofixnitrogenbythemselves.
Theydosoonlyassymbiontsintheassociationofrootsoflegumes.
•Theprocessiscomplicatedmediatedbyaseriesofbiochemicalprocessto
reachthepleasure.

14. FACTORS OF NITROGEN FIXATION
ItisevidentthattheamountofBNFthattakesplaceinagivenforagecrop
communitycanvaryconsiderably.Thisimpliesthatvariousenvironmental
andmanagementfactorsinfluencethemagnitudeofBNFinagivenforage
cropcommunity.Whatarethesefactors?Ingeneral,virtuallyanyfactor
thataffectsthegrowthanddevelopmentoftheforagecropwillhavesome
impactonBNF.Thiswouldincludeawiderangeoffactorsincluding
air/soiltemperature,soilfertility,soilmoisture,pestdamage,weed
competition,andsoilpH.
SoilpH
SoilpHaffectsboththehostplantandthebacteriainvolvedinthe
symbioticrelationship.Withregardtotheforageplants,soilpHaffectsthe
uptakeofnutrientsfromthesoil.Ingeneral,asoilpHbetween6.0and7.0
providesthebestenvironmentforoptimumuptakebytheforageplant.
Therefore,maintainingthesoilpHinthisrangetendstopromoteoptimal
plantgrowthandoptimalBNFinmanyforagecrops.However,some
foragespeciesarebestadaptedtosoilpHvaluessomewhathigherorlower
thanthisrange.Theastuteforageproducershouldbecomefamiliarwiththe
preferredpHrangeoftheircrops.ThebacteriamostofteninvolvedinBNF

15. FACTORS OF NITROGEN FIXATION
inforages,thoseinthegenusRhizobium,areoftennegativelyaffectedby
soilpHvalueslessthan6.0.IfsoilpHislessthan6.0,andwhereitis
economicaltodoso,limestonemaybeaddedtoincreasesoilpHandthus
increaseBNF.Therearesomeexceptionstothisgeneralrule.Forexample
thesymbiosisbetweenredcloveranditsmicrosymbiontRhizobium
leguminosarumbiovartrifoliiappearstofunctionwellatpHvaluesless
than6.0.
SOIL FERTILITY
ReductionofBNFduetosoilfertilitywilloftenberelatedtoeitheran
excessofsoilnitratesoradeficiencyofsomeessentialnutrientlimiting
plantgrowthanddevelopment.Ingeneral,excesssoilnitratelevelswill
depressBNF.ThustheapplicationoffertilizerNtoforagecropsthatare
abletoutilizeBNFisrarelyrecommended.Ifthereisanysuspicionofsoil
nutrientdeficiencies,soiltestsshouldbeconducted.Ifsoiltestsindicatea
significantdeficiencyofessentialnutrients,appropriatefertilizer
applicationsareadvised.

16. FACTORS OF NITROGEN FIXATION
CLIMATE
Virtuallyanyaspectofclimatethataffectscropgrowthratewillalsoaffect
BNF.Specifically,factorssuchaslowair/soiltemperature,lackof
sunshine,ordroughtwilllikelyreduceBNF,atleasttemporarily.While
climatecontroliscurrentlybeyondthecontroloftheforageproducer,some
managementstepscanbetakentominimizetheeffectofclimate.Planting
datecanbeselectedtoalleviateproblemswithexcessivelycoldorwarm
soils.Timelyirrigationcanbeusedtominimizetheimpactofdroughty
periods.
Inadditiontotheaforesaidfactorsinthecontextofbiologicalnitrogen
fixation,thedifferentotherfactorslikethedegreeofthemicrobes,their
associationalongwiththeothergrowthfactors.ItincresesPhosphorous
pentoxidetoofferphosphorousintothesoil.Allthesefactorsplay
synergisticallytoexpeditetheprocessoftheenrichmentofthesoilfertility
inthisregard.

17. RICE CULTIVATION & BGA
 Bluegreenalgae(BGA)areprokaryoticphototrophicorganismsthat
canfixtheatmosphericnitrogenbiologically,andweredirectlyappliedasa
bio-fertilizersinagriculturalfieldsspecificallyPaddyfield.Sincetheyare
havingtheabilitytofixnitrogen,theyareformulatedwithvarious
adsorbentsforthepurposeofenhancingthecropgrowthalongwith
maintainingthesoilfertilityandothersoilfactorsresponsiblefor
productivity.headsorbentformulatedmixedbluegreenalgaeenhancedthe
paddyplantgrowthundergreenhousecondition.
 Bluegreenalgalspeciesthatthrivedinricefieldreleasesmall
quantitiesofammoniaasthemajorfertilizingproduct,andsmall
nitrogenouspolypeptidesduringactivegrowth,whereasmostofthefixed
productsaremadeavailablemainlythroughautolysisanddecomposition.
 Cyanobacteriaalsoimprovesoilcharacteristicsbymodifyingtexture
sizeandsubsequentaerationandenhancingcarboncontentandwater
holdingcapacity.Suchorganismsareoneofthemajorcomponentsofthe
nitrogenfixingbiomassinpaddyfields.Theimportanceofcyanobacteria
inagricultureforpaddycultivationisdirectlyproportionaltotheirabilityto
fixnitrogenandotherpositiveeffectsforplantsandsoil.

18. RICE CULTIVATION & BGA

19. APPLICATION OF Azolla
Generally,theAzollamatisusedasfertilizerasitcontainsAnabaena
azollaeanditcanincreasethesoilfertilityinpaddyfield.Proper
applicationofthismatcanensure600kg/year/Hectarenitrogenfixationin
ricefield.Thiscanbeappliedinthefollowingtimeperiods:
Beforetheapplicationofseedinthericefield,
Beforethetransplantationfromthenurserytothemaincropfield,
TheapplicationofAzollaecantoleratetheresistanceofheavymetalslike
Hg,Asetc,
Azollaematcanreducetheweeddevelopmentinthericefield,
ThedeathoftheAzollaematcanaddmorenitrogen,Phosphorousand
Potassiuminthesoil.
\Thus,thericefieldreclamationcanbeensuredforthesustainable
productivityofthesoilbymaintainingthehealthofthesoilintheprocess
ofcultivation.

20. THANKS TO VISIT THE PAGE
•References:
•1. Fundamental Botany-Sen & Giri
•2. A text of Fungi-Vasistha,
•3. A Textbook of Microbiology-R.P. Singh,
•4.Textbook of Microbiology-Dubey & Maheswari,
•5. Soil Microbiology-N.S. Subba Rao,
•6. Agricultural Microbiology-G. Rangaswami,
•7. Google for images,
•8. Different WebPages for information.
•Disclaimer:ThisPPThasbeenmadetoenrichfreeonlinestudy
resourceswithoutanypleasureoffinancialinterest.