Azolla

Agricultural Microbiology

1. Azolla
Dr. S. PARTHASARATHY, M.Sc. (Agri)., Ph.D.
Assistant Professor (Plant Pathology)

2. INTRODUCTION
Morethan50%nitrogencanbesupplementedwhenAzolladual
croppedwithrice.
Azolla(alsoknownasmosquitofern,duckweedfern,orfairymoss)
isagenusinthefamilySalviniaceaeisregardedas“LiveNitrogen
ManufacturingFactory”because,itharborsnitrogenfixing
Cyanobacteria.
TheAzollasporophyte(generally0.5–7cminlenghtbutupto
40cm inA.nilotica)consistsofa
multibranchedrhizomegenerating,ontheventral
surface,adventitiousrootshangingdownintothewatertoabsorb
nutrientsdirectly.
AzollaCyanobacterialSymbioses

3. BLUE GREEN ALGAE
Nitrogen fixing BGA –called -cyanobacteria
Frequently abundant in soils fresh and salt waters
Blue green colourof the cell –cyanophycin–absence of
organized nuculeus
Rice ecosystem provides favorable for growth of BGA.
Someofthempossessapeculiarstructureknownas'heterocyst'and
allheterocystousformscanfixnitrogenfromair.
Recently,someblue-greenalgaewithoutheterocystshavealsobeen
foundtofixnitrogenunderspecialconditionslikelowoxygentension
Aulosira,Tolypothrix,Scytonema,Nostoc,Anabaenaand
Plectonema

4. Filament of BGA

5. Role of heterocysts
•Free living Anabaena azollaeonly develops 5-10% of its cells into
heterocysts
•However, when living in conjunction with Azolla, Anabaena azollae
will increase its heterocyst production up to 25-30%
Role
•Heterocystsfunctionasthesitesfornitrogenfixationunderaerobic
conditions
•Productionofnitrogenaseandotherproteinsfornitrogenfixation.
•Productionofenzymesthateliminateoxygenfromthecell.
•Rearrangementofthethylakoid,andtheup-regulationofglycolytic
enzymes

6. Azolla-Anabaena symbiosis
Azolla with Anabaena
TheBlueGreenAlgae-diazotrophiccyanobacteriaAnabaenaazollae
(Nostocaceae)presentasasymbiontwiththisAzollaferninthelowercavities
actuallyfixesatmosphericnitrogen

7. Anabaena azollae, although it can exist on its own, is usually found
within ovoid cavities inside the leaves of the water fern Azolla
The dorsal lobe is green and has nearly 2000-5000 immobilized cyanobacterial
symbiont (Anabaena azollae) within a central cavity.

8. Azolladual cropping enhance rice yield by 55 % and supplement
nitrogen by 50-75 %
Azollaas a component of INM
Extensivelyusedasbiofertilizerandgreenmanuringforricecultivation.
Azollacanpromoteaerobictransformationssuchasmethaneoxidation
throughenhancedaerationofthefloodwaterinricefields
Azollahasveryfastgrowingcharacter.Itdoublesitsbiomassin3-5
days
Azolla fixes 40-60 kg N/ha in rice crop

9. Anabaenaazollaeisasmallfilamentousphototrophic
cyanobacteriagenerallyseenasamulticellularorganismwithtwo
distinct,interdependentcelltypes.
1.Thefirstisasmall,circular,photoautotrophic“vegetative”cell
thatperformsoxygenicphotosynthesisandistypicallyblue
greenincolor.
2.Thesecondisaheterocyst;alarger,paler,morehomogenous
cellproducedbyAnabaenatofixatmosphericnitrogen.

10. There are 7 living species of
•Azollapinnata,
•Azollacaroliniana,
•Azollarubra,
•Azollafiliculoides,
•Azollanilotica,
•Azollamexicanaand
•Azollamicrophylla.
Azollapinnatais native to India but now many of these
species have been introduced.

11. Resting structure -Akinete
Underenvironmentalstress,suchaslightlimitation,coldtemperatures,or
phosphatestarvation,filamentouscyanobacteriasuchasAnabaena
azollaeformspecializedsporescalledakinetes
Anabaena filaments
Heterocyst
Akinete

12. Azollacanabsorbnitratesfromthewater,itcanalsoabsorbammonia
secretedbyAnabaenawithintheleafcavities.
•TheabilityofAzollatofixN
2isabout1.1kgN/ha/day.
•Thedoublingtimevariesbetween2and10daysformostspeciesand
maximumbiomassrangedbetween0.8to5.2tdrymatter/hawithan
averageof2.1t/ha.
Biological Nitrogen Fixation

13. Application
•Asgreenmanure,Azollaisgrownalonefortwotothreeweeksin
floodedfields.
•Afterwards,waterisdrainedoutandAzollafernisincorporatedin
thefieldbeforetransplantingofpaddy.Otherwise,4-5qoffresh
Azollaisappliedinstandingwateroneweekafterplantingof
paddy.
•DryAzollaflakescanbeusedaspoultryfeedandgreen.
•Azollaisalsoagoodfeedforfish.
•Itcanbeusedasabio-fertilizer,amosquitorepellent,inthe
preparationofsaladsandaboveallasabio-scavengerasittakes
awayallheavymetals.

14. Advantages of Azolla
1.Itcaneasilybeproducedinlargequantityrequiredasgreenmanureinallthe
seasons
2.ItcanfixatmosphericCO
2andnitrogentoformcarbohydratesandammonia
respectivelyandafterdecompositionitaddsavailablenitrogenforcrop
uptakeandorganiccarboncontenttothesoil.
3.Theoxygenreleasedduetooxygenicphotosynthesis,helpstherespirationof
rootsystemofthecropsaswellasothersoilmicroorganisms.
4.ItsolubilisesZn,FeandMnandmakethemavailabletotherice.
5.AzollasuppressestenderweedssuchasCharaandNitellainapaddyfield.
6.Azollareleasesplantgrowthregulatorsandvitaminswhichenhancethe
growthofthericeplant.
7.Azollacanbeasubstituteforchemicalnitrogenousfertilizerstoacertain
extent(25kg/ha)anditincreasesthecropyieldandquality.
8.Itincreasestheutilisationefficiencyofchemicalfertilizers.
9.Itreducesevaporationratefromtheirrigatedricefield.