全 文 ：第27卷第5期
2008年10月
生态科学
EcologicalS ience
27(10)：295-299
0ct．2008
Theroleofshapeandsizeinthecologyf
phytoplankton
LuigiNaselli—Flores
DepartmentofBo anicalSciences,UniversityofPalermo，Italy．E-mail：luigi．naselli@unipa．it
Phytoplanktonisapolyphyleticgroupofhotosynthetic，
oxygenproducingprotoctistsandbacteriaad ptedto
persistin uspensionandliabletopassivemovementby
windandcurrent(Reynolds，2006)【lJ．Theyinhabit
almostall heaquaticecosystemsofthebiosphereand
showallenormously、)lridevariabilityofshape，size，
evolutionaryandphylogeneticposition，aswellenergy
andnutrientdemands．Theiramazingdiversityinan
apparentlyhomogeneousmedium,asthepelagic
environmentcanbeperceivedata firstight,caused
concel"nafewdecadesagoandpuzzledaquaticb ologists
foryears．Actually,thecontemporaryoccurrenceof
manyspeciescompetingforthesamefewresources
(apparently)violatedtheCompetitiveExclusion
Principles(Hutchinson，1961)圈．Nutrients(firstlyN
andP)andlightarethemainfactors，whichmaylimitthe
growthofphytoplanktondthesolutiontowhathas
beencalledtheHutchinson’sParadoxofthePlanktonlies
inthefacthataquaticenvironments，farfrombeing
homogeneous，alecharacterizedbygra ientsinenergy
andnutrientsdistribution,whichmayrap dlyhange
withinthegenerationtimefphytoplanktonspecies．To
obtainadequateccesstotheseunevenlydistributed
resourcesandgaintheSuccessinthecompetitivearena，
phytoplanktonspecieshavedevelopedas many
ecologicalstrategies舔thediffer nte vironmental
conditionsthatNaturecanoffer．
Factorsaffectingheabundanceofphytoplankton-
nutrientsa denergy
Thequantityofphytoplanktonttainablebiomassin
thepelagicis a functionofinorganicnutrients
concentrations．Carbon，oxygenandhydr genformup
to90％ofdrymatterofphytoplanktoncells．Moreover，
silica，whichconstituteshec llwallofdiatoms，may
significantlycontributeto dryweightin these
populations．Macronutrients(N，P，S，K，Mg，Ca，Na，
C11typicallyconstitutelesshan0．1％ofdryweight,
whilstmicronutrients(Fe，Mn，Cu，Zn，Me，Co，B，V，
etc．)arep sentintraces．Inspiteoftheirlowrelative
amounts，rnacro-andmicronutrientsaressentialfor
biomassproduction，andtheiroccurrenceinthe
surroundingmedium，assolublecompoundspresentas
diffusibleonsornon-dissociatedsmallmolecules，
maylimittheincreaseofbiomassccordingtothe
Liebig’SLawoftheminimum(i．e．thehigheramount
ofa tainablebiomassisdrivenbythelementpresent
inlowerconcentration)．
Phytoplanktonstoragestrategiesandadaptationstothe
widespectrumofnutrientconcentrationsinclude
nitrogenfixation，luxuryuptake，productionofalkaline
phosphatasesorevenheterotrophy，sinceseveral
speciescanutilizeorganiccarboncompounds01"
activelypreybacteria．Mixotrophyhasbeenfrequently
observedtohelphytoplanktonto escapeeither
carbonlimitationorlightlimitation，especiallyind 印
layers．Entrainmentintheverticalw termotionand
sinking，嬲well邪activeswimm ng，arethecommon
waysusedbyphytoplanktontoexploreth water
columnandseekfornutrients．
EnergyoriginatingfromtheSunandreachingthe
Earth’Ssurfaceismainlywithinthewaveband300-
3000am．TheSOcalledvisibleradiation，between400
and700nm，generallyepresents46—48％ofthis
万方数据
296 生态科学EcologicalScience 27卷
energyandcanbeusedforphotosynthesis：itis
thereforeusuallyreferredtoasphotosynthetically
activeradiation(PAR)．Thecomplexprocessesof
lightrefractionfr mthewatersurfacedownwardresult
inallattenuationofthequantityoflightpenetrming
intoawaterbody，aswellasinaselectiveabsorption
ofthedifferentwavebands，proceedingalongdepth．In
thepelagicenvironment，verticallighattenuation
dependsotonlyondepthbutalsoonalgalbiomass
andsuspendedmatterpresentinthewatercolumn．As
conventionallydefined，photosynthesiswithnet
oxygenproductioninnaturalwatersontheaverage
occursinthelayerscomprisedbetweenthesurfacend
thedepthw eretheintensityofsurfacePARreaches
1％．Thislayerrepresentstheuphoticzone(z∞)ofa
waterbody．Itsdepthmayvaryfrom25·30min
ultraoligotrophicenvironmentstoafewcentimetersin
hypertrophicones．
Theportionofthewavebandbetween750and3000
nmconstitutesheinfraredradiation．Itcontributesto
theheatingoftheEarth’ssurfacendetermines
densitygradientsinthewatercolumns．Thestrengthof
thesegradients，governedbythegeographicalposition
andmorphologicalfeaturesofa givenwaterbody，
allowthewatermassestocirculatefromthesurfaceto
thebottomortopermanently，erratically，seasonally，or
evendailyseparatein othreedistincthorizontallayers：
thepilimnion(ormixingzone：‰x，whichinshallow
lakescorrespondstothemaximumdepthofthewater
column)，themetalimniona dthehypolimnion．The
physicalprocessesgoverningsuchtemperature-driven
segregationoftllewatermassesintothree(oreven
more)layersar offundamentalimportancein
limnology，andaredescribednd tailsnalltextbooks．
Theratiobetweenmixingdepthandeuphoticdepth
(蜀曲【／jr蜘)ismportantindetermininghowlongalgal
cellsentrainedthewatercolumnmotionwillbe
exposedtosufficientlighttoperformphotosynthesis．
Inparticular，ifZmix／ZeuSl，phytoplanktonorganisms
willalwaysreceiveenoughlighttophotosynthetise．
Conversely(z施／z∞>1)，phytoplanktonwillbe
exposedtofluctuatinglightslevelswithdarkperiods
directlyproportionaltothevalueofzIlIix／z∞．Valuesof
theratioabove2mayselectspecialadaptationstolow
lightconditionsormayfavorthoseorganismsableto
bedisentrainedfromtheverticalw termotions(e．g．
gas-vacuolatedcyanobacteria)．Eutrophicand
hypertrophicenv ronmentsbythecontractionoftheir
euphotiedepthduetotheincreasedphytoplankton
biomass，aswellasreservoirssubjecttowidewater-
levelf uctuationsbythedeepeningoftheirmixing
depth，areoftencharacterizedby m√z印>2and
generallyshowthe dominanceof buoyant
cyanobacteria(Naselli．Flores，2003)[31．
Lightlimitationmayftenconstituteasevereproblem．
Phytoplanktonreacttolightattenuationndvariation
initsspectralcompositioninseveralw ys．Insome
photoadaptings ecies，chlorophyllaconcentrationper
cellmayincreaseduringonecell-doublingbyafactor
of1．5to9．0．Awaytoincreasethespectralwidthof
lightabsorption，thesocalledchromaticdaptation，
callbeachievedbyraisingtheconcentrationsof
accessorypigments(antennaepigments)，especially
phycobiliproteins(cyanobacteriaandcryprophytes)
andxanthophylls(Padisfik，2003)【4】．Activeswimming
andbuoyancyregulationareusedbyotherspeciesto
selecttheoptimall yersofthewatercolumnfortheir
photosyntheticrequirements．Intra-specificphenotypic
plasticitymaalsoallowspeciestopersisttoacertain
degreeof nvironmentalvariabi ity．
Detailedaccountsonhekineticsofnutrientuptakeand
photonharvestingbyphytoplanktonreavailablein
severalbooks(e．g．Harris1986；Padisfik，2003；
Reynolds；1984．1997；2006)15,4．67，¨．
Morphologicaladaptationstothehabitatemplate
Thefactorsinvolvedin structuringphytoplankton
assemblagesinfreshwaterecosystemsarisefromthe
relationshipgeneratedbychemical，physicaland
biologicalparameterswhichtakeplacewithinthe
ecosystemi sel￡Nutrientandlightavailabilitycoupled
万方数据
!塑 三=旦!巫翌璺!!!!i：里12竖壁!堡!翌!!堕!塾竺!璺坐!塑垫!些箜212旦堕业丝塑!苎坐2翌121
谢thcompositionandabundanceofzooplanktonare
generallyreg棚edasthemainconstraintstothestructure
ofphytoplanktonssemblagesina givencosystem．
Manystudiesofreshwaterenvironmentshavea tributed
amajorroletooneorseveralofthesefactors．
Somerecentworkshavehighlightedt efactthathe
structureofphytoplanktonssemblagesseemtobe
betterxplainedbyphysicalf ctors(e．g．1ight
availabilityandmixingregime)，inducedbytrophic
andseasonalgr dients．
Phytoplanktonoffersa amazingmorphological
diversityandallthoseinvolvedinphytoplankton
researchhavecommonlyobservedthattheseorganisms
arepresentinvariousshapesandmayexpressaquite
llighvariability，bothintra-andinter-specific，intheir
morphology．Lewis(1976)‘81wasoneofthefirst
recognisingthecologicalvalueofmorphological
descriptorsinphytoplanktoninrelationtouptakeof
lightandnutrientsa d，asresultof,naturalselection
andcompetition．AfewyearslaterMargaleft9】(1978)
usedlife．formsasadeterminantofseasonalsuccession
ofphytoplanktonsuggestingthatmorphological
variabilityhasanadaptivevaluedirectedowardthe
bestfittingtoenvironmentalt mplate．Morerecently，
Reynolds(1997)■explainedindetailhowthediverse
ecologicalstrategiesadoptedbyphytoplanktoncanbe
relatedodifferencesi th irmorphology．
In orderto understandheadaptivevalueof
morphologicalfeaturestoacertainhabitatemplate，it
isimportantorecallthatphytoplanktonisgenerally
denserthanwaterandhasthetendencytosink
downwards．Onlygas—vacuolatedey nobacteriaanda
fewotherphytoplanktonspecies(e．g．Botryococcus
spp．，whichproducelipiddroplets)，havea relative
densitythatmakethemfloatingupwards．Other
phytoplanktonspeciesareneverisopycnicwiththe
mediumandthexistencea dlevelofabundanceof
singlespecieslargelydependsontheirownabilityin
travelingalongthewatercolumntoexploitnu rients
andharvestlight．Tobalanceth irnabilitytocontrol
horizontalpositionortoswimagainstsignificant
currents，phytoplanktonicalg ehavedevelopedawi e
varietyofadaptivestrategies．Inaddition，sincethey
representthesourceofnutritionforzooplankton，they
alsohavetocounteractthegrazingpressureexertedby
these‘herbivores．’
Theadaptivestrategiesshownbyphytoplanktonacton
mul iplel vels．Thespeciesinvolveddiffer
significantlyintheirphysiologicalab lities(i．e．，in
exploitingdifferentl velsofnutrientsandlight)，as
wellasintheirshapeandsize．Onthemorphological
traitsdependthepossibilitytobegrazedby
zooplanktonandthesinkingvelocityofplanktonic
algae；sinkingcanbedescribedbytheStokes’equation：
仇：—29r2(p—-p)
9r／O
where％isthesinkingvelocity【ms-!】，gisthe
gravitationalacceleration【ms-z】，，．istheradiusofthe
sinkingsphericalparticle【m】，∥isthespecificgravity
ofthesinkingparticle[kgm’】，Pisthespecificgravity
ofthefluidmedium【kgm’】and玎istheviscosityof
thefluidmedium[kg1s-I】．①isaspecies-specific
formresistancefactorbywhichthesinkingvelocityof
thealgadiffersfromthatofasphereofidentical
volumeanddensity．Thus，thevarietyofshapes
exhibitedbyphytoplanktonrepresentsa evolutionary
compromisedirectedbothtoanincreasedgrazing
resistanceandtoanoptimizationofs nkingvelocity．It
seemsimportantou derlinethathemodificationof
sinkingvelocityallowedbytheformresistancefactor
isnotawaytomerelyreducesinkinga dinsome
casesitcanincreasethevelocitytselfandfavor
sinking．
Theattentionpaidbyecologiststotheizeandshapes
ofphytoplanktonhasitsoriginin theneedto
categorizethemnotonlyonthebasisoftheir
phylogenetics，stillsubjecttomassivereappraisal，but
alsoonthefunctionalbasisoftheirrolesinaquatic
eeosystems．Twoainideasliesbeneathfunctional
万方数据
298 生态科学EcologicalScience 27卷
groupstheory：11 functionallywell—adaptedlgawill
belikelytotolerateth constrainingconditionsof
factordeficiencymoresuccessfullythanindividualsof
a lesswell—adaptedsp cies；2、ahabitatshown
typicallytobeconstrainedbylight，orCorNor
whatever,ismorelikelytobepopulatedbyspecies
witht eappropriatead ptationstobeabletofunction
there(thisofcoursedonotimplythatthosepecies
willbethere)．Asaconsequence，theterm‘functional
group’issensitiveothesetsofappropriatead ptive
specialismsandtheclustersofspeciesthathavethem．
Groupingphytoplanktonspeciesaccordingtotheir
ecologicalperformanceisthefirststeptoattempta
functionalclassificationoftheserganisms．Oneofthe
mostsuccessfulfunctionalcl ssification，addressed
towardanorderingofallphytoplanktontaxa，allowed
todescribeabout30ecologicalgroups(Reynoldseta1．，
2002)【Ⅻ．Thisordinationwellapproximatestheresults
obtainedby ividingthealgaeaccordingtotheir
morphologicaldescriptorsandselectedmorphological
traitsarerevealedaspowerfulpredictorsof ptimum
dynamicperformance．Asa con equence，algae
forminga singlefunctionalgroupveryoftenhave
similarmo phologies，asquantifiedbytheimensions
ofthealgal‘units’(cellsorco onies，asappropriate，
togetherwithanyperipheralmucilage)：surfaceareaO)，
volume(V)，andmaximallineardimension沏)are
powerfulpredictorsof ptimumdynamicperformance
underdifferentvironmentalconditions．Thus，
groupingphytoplanktono thebasisoftheselected
morphologicaltraitsallowstodistinguishamong
habitatswitha differentaccessibilityto ghtand
nutrientresources．Byplottingthelogarithmofms／v
againstthelogarithmoftheratios／v[1am“]foreach
phytoplanktonspecies，it ispossibletoidentifya
triangularportionoftheCartesianplane，whose
verticesrepresentthreedifferentvironmental
conditionsinrelationtonutrientsa dlightavailability
(Fig．1)．Inaccordancewiththeirdifferentabilitiesin
exploitingtheser sources，phytoplanktonspeciest d
t0bepositionedonthisplotandthethreecomers。
namedC，S，and＆summarizethethreemain
strategiesth ymayadopt．Inparticular，thecomerCis
occupiedbythemorcinvasivespecies，i．e．，those
investinginrapidgrowth；aroundthecomerS，the
moreacquisitivespecies，i．e．，thoseinvestingin
resourceconservation，aredisplaced；thecom rR
receivethemoreacclimatingspecies，i．e．，those
investinginefficientlightconversion．Itispossibleto
verifythatthosepeciescharacterizedbyelongatedor
needle-likeshape(e．g．，Planktothrixrubescens，
Closteriumaciculare)willbepositionedbytheir
morphologicaltraitsinthevicinityoftheRcomer；
thosehowingsphericalsh peandsmalldimensions
(e．g．，picoplankton)willtendtoaccumulateinth
vicinity．oftheCcomerandthosewitha larger
spherical(e．g．，Eudorinasp．) sl ghtlye lipsoidal
shape(e．g．， Eremosphaeratang nykae)will
concentratea oundheScomer．
Thecorrectinterpretationof the dominant
morphologicaltraitsinphytoplanktonssemblagesc n
supplyapowerfultooltoassesswaterquality，since
theseorganismswellintegratephysical，chemical，and
biologicalparametersoffreshwaterecosystems．In
addition，phytoplanktonassemblagescontainhigh
numberofspecies，makingd tausefulforstatistical
andnumericalapp ications．Theirresponset meis
rapid，asisrecoverytime，withrecolonizationaftera
disturbanceoftenmorerapidthanforothero ganisms．
Theythuscouldprovideapowerfulmonitoringtool，
oncetheprocessesgoverningtheirrelativemportance
arefullyunderstood．
Refefences
IIl Reynolds，C．S．(2006)Ecologyofphytop ankton．
CambridgeUniv．Press，CambridgeandNewYork．
121 Hutehimon,G．E．(1961)111eparadoxoftheplankton．
AmericanNaturalist95，137-145．
ISl Naselli·Flores，L．(2003)Man-madelakesin
Mediterraneansemi．aridclimate：thes仃angecaseofDr
DeepLakeandMrShallowLake．Hydrobiologia506-509，
13．21．
万方数据
!塑 生型型箜坐堕皇壁!堡翌!型!垒竖型!丝!垫些型型堕业塑!些竺 翌
【4J Padisfik，J．(2003)Phytoplankton．In0’Sullivan,P．E．&
Reynolds，C．S．(editors)ncLakesHandbook1．
LimnologyandLimneticEcology：251-308．Blackwell
ScienceLtd．Oxford．
151 Harris，G．P．(1986)phytoplanktonecology：structure，
functionandfluctuationChapmanandHall．NewYork．
【6l Reynolds，C．S．(1984)111eecologyoffreshwater
phytoplankton．CambridgeUniv．Press，Cambridgeand
NewYork．
【717 Reynolds，C．S．(1997)Vegetationprocessesinthepelagic．
AModelforEcosystemTheory．ECI．0Idendorf．
10
1
广-1
蔓
L．一
象
0．1
【8l Lewis，W．M．Surface／volumeratio：implicationfor
phytoplanktonmorphology．Science192，885—887．
19】 Margalef,＆(1978)Lifeformsofphytoplanktonas
survivalalternativesn锄unstableenvironment．
OceanologicaActa1，493—509．
f10lReynolds，C．S．，V．Huszar,C．KruLL．Naselli—Flores&S．
Melo(2002)Towardsafunctionalcl sificationof he
freshwaterphytoplankton．JournalofPlanktonResearch
24：417-428．
S
o
Chlasp．
o
oEudsp．
}0
M／csp．
o
roZsp．O．01一卜⋯⋯⋯一t。一f一一⋯r一一⋯一⋯一1
1 10 100 1000
mS矿1
Fig．1．C—S—Rstrategicordinationofs mes lectedgreenalgaep rformedaccordingtomorphologicaltra ts．Aphsp．：
Aphanizomenonsp．；Ankjud：Ankyrajudayi；Aulgra：Aulacoseiragranulata；Botbra：Botryococcusbraunii；
Cerhir：Ceratiumhirundinella；Chlosp．：Chlorella； asp．：Chlamydomonassp．；Cl aci：Closterium
aciculare；Dic：Dictyospaheriumsp．；Eretan：Eremosphaeratanganyikae；Eudsp．：Eudorinas ；Micsp．：
Microcystissp．；Monsp．：Monoraphidiumsp．；Mousp．：Mougeotiasp．；Plasp．：Planktothrixsp．；Scequa：
Scenedesmusquadricauda；Synsp．：Synechococcussp．；Tabsp．：Tabellariasp．；Volsp．：Volvoxsp．；s：
individualorco onysurface；V：individualorcolonyvo ume；m：individualorcolonym ximallinear
dimension．
≯她啵。肋
幻y镪n。盎胁晚鼢
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o
万方数据
The role of shape and size in the ecology of
phytoplankton
作者： Luigi Naselli-Flores
作者单位： Department of Botanical Sciences,University of Palermo,Italy
刊名： 生态科学
英文刊名： ECOLOGICAL SCIENCE
年，卷(期)： 2008,27(5)

参考文献(10条)
1.Reynolds,C.S Ecology of phytoplankton 2006
2.Margalef,R Life forms of phytoplankton as survival alternatives in an unstable environment 1978
3.Lewis,W.M Surface/volume ratio:implication for phytoplankton morphology[外文期刊]
4.Reynolds,C.S Vegetation processes in the pelagic.A Model for Ecosystem Theory 1997
5.Reynolds,C.S The ecology of freshwater phytoplankton 1984
6.Harris,G.P phytoplankton ecology:structure,function and fluctuation 1986
7.Padisak,J Phytoplankton 2003
8.Naselli-Flores,L Man-made lakes in Mediterranean semi-arid climate:the strange case of Dr Deep
Lake and Mr Shallow Lake[外文期刊] 2003
9.Hutchinson,G.E The paradox of the plankton[外文期刊] 1961
10.Reynolds,C.S;V.Huszar;C.Kruk;L.NaseUi-Flores S.Melo Towards a functional classification of the
freshwater phytoplankton[外文期刊] 2002


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