Surface reflectance properties of Antarctic moss and their relationship to plant species, pigment

40 Pages·2017·0.56 MB·English

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Faculty of Science - Papers (Archive) Faculty of Science, Medicine and Health
1-1-2002
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C. E. Lovelock
University of Queensland
Sharon A. Robinson
University of Wollongong, [email protected]
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Part of the Life Sciences Commons, Physical Sciences and Mathematics Commons, and the Social
and Behavioral Sciences Commons
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Lovelock, C. E. and Robinson, Sharon A.: Surface reflectance properties of Antarctic moss and their
relationship to plant species, pigment composition and photosynthetic function 2002.
https://ro.uow.edu.au/scipapers/48
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We investigated how surface reflectance properties and pigment concentrations of Antarctic moss varied
over species, sites, microtopography, and with water content. We found that species had significantly
different surface reflectance properties, particularly in the region of the red edge (approximately 700 nm),
but this did not correlate strongly with pigment concentrations. Surface reflectance of moss also varied in
the visible region and in the characteristics of the red edge over different sites. Reflectance parameters,
such as the Photochemical Reflectance Index (PRI) and Cold Hard Band (CBH) were useful discriminators
of site, microtopographic position and water content. The PRI was correlated both with the
concentrations of active xanthophyll-cycle pigments and the photosynthetic light use efficiency, Fv/Fm,
measured using chlorophyll fluorescence. Water content of moss strongly influenced the amplitude and
position of the red-edge as well as the PRI, and may be responsible for observed differences in
reflectance properties for different species and sites. All moss showed sustained high levels of
photoprotective xanthophyll pigments, especially at exposed sites, indicating moss is experiencing
continual high levels of photochemical stress.
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Bryum pseudotriquetrum, Ceratodon purpureus, chlorophyll, chlorophyll fluorescence, Grimmia antarctici,
Photochemical Reflectance Index, xanthophyll cycle pigments
DDiisscciipplliinneess
Life Sciences | Physical Sciences and Mathematics | Social and Behavioral Sciences
PPuubblliiccaattiioonn DDeettaaiillss
This article was originally published as: Lovelock, CE & Robinson, SA, Surface reflectance properties of
Antarctic moss and their relationship to plant species, pigment composition and photosynthetic function,
Plant Cell and Environment, 2002, 25(10), 1239-1250. Copyright 2002 Blackwell Publishing. The definitive
version can be found here through Blackwell Publishing.
This journal article is available at Research Online: https://ro.uow.edu.au/scipapers/48
1
Surface reflectance properties of Antarctic moss and their relationship to
plant species, pigment composition and photosynthetic function
5
RUNNINGTITLE: Surfacereflectanceofmoss
CatherineE.LovelockandSharonA.Robinson*
SmithsonianEnvironmental ResearchCenter,POBox28,EdgewaterMD21037,USA.
10 *InstituteforConservationBiology,UniversityofWollongong,Northfields Avenue,
Wollongong,NSW2522,Australia
Correspondenceabout this manuscript to:
15 DrCatherineLovelock
SmithsonianEnvironmental ResearchCenter
POBox28
EdgewaterMD21037,USA
Tel [phone],FAX[phone]
20 email [email protected]
2
Abstract
Weinvestigatedhowsurfacereflectanceproperties and pigment concentrations ofAntarctic
moss variedoverspecies,sites,microtopography,and withwatercontent. Wefoundthat species
hadsignificantlydifferent surfacereflectanceproperties,particularlyintheregionoftherededge
5 (approximately700nm),but this didnot correlatestronglywithpigment concentrations. Surface
reflectanceofmoss alsovariedinthevisibleregionandinthecharacteristics oftherededgeover
different sites. Reflectanceparameters,suchas thePhotochemical ReflectanceIndex(PRI)and
ColdHardBand(CBH)wereuseful discriminators ofsite,microtopographicpositionandwater
content. ThePRIwas correlatedbothwiththeconcentrations ofactivexanthophyll-cycle
10 pigments andthephotosyntheticlight useefficiency,F /F ,measuredusingchlorophyll
v m
fluorescence. Watercontent ofmoss stronglyinfluencedtheamplitudeandpositionofthered-
edgeas well as thePRI,andmayberesponsibleforobserveddifferences inreflectanceproperties
fordifferent species andsites. All moss showedsustainedhighlevels ofphotoprotective
xanthophyll pigments,especiallyat exposedsites,indicatingmoss is experiencingcontinual high
15 levels ofphotochemical stress.
Keywords: Bryumpseudotriquetrum,Ceratodonpurpureus,chlorophyll,chlorophyll
fluorescence,Grimmiaantarctici,Photochemical ReflectanceIndex,xanthophyll cyclepigments
3
Introduction
Solarradiationis essential forphotosynthesis andgrowthofplants.Thesurfacereflectance
characteristics ofleaves is keyindeterminingboththequantityandqualityofsolarradiationthat
5 is incident onleafinternal organs (Vogelmann1993).Althoughsolarradiationinthevisible
regiondrives photosynthesis,absorptanceofhighlevels ofvisibleradiationandradiationat other
wavelengths canbedamaging. At shorterwavelengths,absorbedUV-B (280-320nm)radiation
cancauselesions tonucleicacidandproteins. Excess levels ofvisibleradiation(400-750nm)
cancausephotoinhibitionofphotosynthesis (Cornic,Woo& Osmond1982). Highabsorptance
10 at longerwavelengths (>750nm)leads toincreases intemperaturethat canbedetrimental inarid
environments whereit is important forplants toconservewaterbylimitingtranspirationandto
maintainleaftemperatures closetothat ofairtemperatures (Gates et al.1965; Ehleringer1981).
Variationinabsorptanceofleaves has beenobserved(Ehleringer& Björkman1978; Vogelmann
1993)andspecializedadaptationofsurfacereflectanceproperties inplants is knowntofacilitate
15 photosyntheticcarbongain. Forexample,indesert ecosystems pubescent orwaxyleafsurfaces
that increasereflectancearecommon(Billings & Morris 1951,Ehleringer1981)and havebeen
demonstratedtobeimportant inprotectionfrom photoinhibitionofphotosynthesis (e.g.
Robinson,Lovelock & Osmond1993).Moreover,epidermal tissues oftenaccumulate
compounds that areeffectivescreens against UV-B radiation,therebydecreasingtheirreflectance
20 intheUVregion(e.g.Tevini 1993).
In this studywesurveyedthenatural variabilityofsurfacereflectanceinmoss in
continental Antarctica.At ourstudysiteinWilkes Land,easternAntarctic,conditions arecold
andusuallyveryarid,resultinginlichens dominatingtherocky,ice-freeareas. Themoss
4
communityis well developedfortheregion,but it is restrictedtomelt lakes,melt streams and
otherlocations wherefreewateris availableforat least someofthesummer(November-March).
Inwinterthemoss is coveredwithsnowand iceandis subject todisturbancefrom cryo-
perturbation,whichcauses highlycomplexmicroreliefofridges andvalleys withinthemoss
5 turves. Comparedtolowerlatitudes,levels ofUVradiationarelowinAntarctica. But,
Antarcticais experiencing largeincreases inincident UV-B radiationduetoreductions in
concentrations ofstratosphericozone(Frederick& Snell 1988).Increases inUVradiationare
havinglargeeffects ontheprimaryproductionoftheoceans (Neale,Davis & Cullen1998),and
couldalso beaffectingterrestrial vegetation.Theheat balanceofmoss,photosyntheticprocesses
10 andtheimpacts ofenhancedUVradiationarelikelytobepartiallydependent onmoss surface
reflectancecharacteristics andpigment composition. Thus,thefirst aim ofthis studywas totest
thehypothesis that moss species andmoss inhabitingdifferent environments havedifferent
surfacereflectancecharacteristics. Wemeasuredsurfacereflectanceat approximatelyonenm
intervals from 200-900nm ofthreedominant moss species overthreesites withdifferingwater
15 availabilities,andoverdifferences inmicrotopography.
Surfacereflectanceproperties ofvegetationareoftenusedas indicators ofphotosynthetic
functioninremotesensingofvegetation(reviewedinField,Gamon& Penuelas 1994).
Variationinreflectancehas beenobservedamongplant taxa(e.g.Gates et al.1965; Penuelas et
al.1993; Gamonet al.1995),duetodifferences inwaterandnutrient availability(e.g.Penuelas
20 et al.1994; Gamon,Serrano& Surfus 1997),environmental stress (e.g.Rock,Hoshizaki &
Millar1988),andbothseasonally(Running& Nemani 1988; Gamonet al.1995)anddiurnally
(Gamonet al.1990; Penuelas et al.1994; Gamonet al 1997). Changes insurfacereflectanceof
intact leaves havebeendirectlycorrelatedwithleafchemical composition(Jacquemoudet al.
5
1996)andchanges inphotosyntheticprocesses insomehigherplant taxa(Gamonet al.1990;
Gamonet al.1997,Gilmore& Ball 2000). But it is oftendifficult toreconcilephysiological
measurements,whichareoftenmadeat thescaleofindividual leaves and remotelysensed
measurements,whichareoftenmadeat thescaleofwholecanopies (Williams 1991; Fieldet al.
5 1994). Someofthedifficultyarises becausecanopies arecomplex. Canopies arecomposedof
layers ofleaves ofdifferent species that canhavearangeofproperties. Leaves within canopies
canhavevaryingdistributions,orientations,morphologies,internal structures,pigment
compositions,andepidermal characteristics,all properties that couldinfluencethesurface
reflectanceofthecanopy(Rocket al.1988; Fieldet al.1994;Voseet al.1995). At theleaflevel,
10 mosses areverysimpleconsistingofafewcell layers. But at ahigherlevel oforganization,
moss turves,althoughsmall incomparisontocanopies oftrees,arerelativelycomplex,
composedofmanyleafygametophytes packed togethertoform what canbethought ofas a
‘micro-canopy’. Inmosses,measurement ofphotosyntheticprocesses andsurfacereflectance
canbemadeat thesamescale. Thus,thesecondaim ofourstudywas totest thehypothesis that
15 spectral properties ofmoss aredirectlyrelatedtophotosyntheticprocesses and pigment
composition. Wewishedtounderstandwhethernon-destructivehyperspectral measurements
couldpotentiallybeusedtomapmoss species distributions andphysiological activityboth
spatiallyandtemporally.Herewedescribetests ofcorrelations amongsurfacereflectance
properties andcommonlyusedreflectanceindices andpigment concentrations,watercontents
20 andphotosyntheticfunctionofAntarcticmoss.
6
Materialsand methods
Moss was obtained from threesites aroundtheAustralianbaseCasey,Wilkes Land,continental
Antarctica(66º17’S,110º32’E).Twosites weredirectlyadjacent tothebase(RedShed and
5 Science),whiletheothersitewas 20km west at RobinsonRidge. Wateravailabilityvaries
across thesites. TheRedShedsiteis directlyadjacent toalargesummermelt lake,the
RobinsonRidgesiteis adjacent toamelt stream that flows intermittentlyoverthesummer
months,whileat theSciencesitewateris onlyavailablewhenoverlyingsnowmelts earlyinthe
summer. Temperaturealsovaries overthesites. RobinsonRidgeis cooler,andmoreexposed,
10 thantheRedShedandSciencesites (Melick, Hovendon& Seppelt 1997).Intheearly1990s the
Sciencesitewas exposed tocontaminationduetodepositionofcement dust duringconstruction
(Adamson,Adamson& Seppelt 1994).
At eachsiterepresentativesamples,approximately2cm2werecut from theturves over3
summerseasons (OctobertoFebruary)from 1996to1999. Thethreemost commonspecies,
15 Grimmiaantarctici Card.,Ceratodonpurpureus (Hedw.)Brid.,andBryumpseudotriquetrum
(Hedw.)Gaertn.,MeyerandScherb.weresampled.Thenecessity ofminimizingimpacts ofthe
study,theextent ofthemoss beds (smallerat Science)and thenatural distributionofthethree
moss species resultedindifferent representations ofeachspecies at eachsite(Table1). We
testedfordifferences betweenmoss species andtheinfluenceofsiteonpigment andsurface
20 reflectanceparameters usingsamples from all sites. Weusedasubset oftheRobinsonRidgeand
RedShedGrimmiaantarctici samples totest foreffects ofmicrotopography.
Additionallywetestedtheinfluenceofmoss watercontent onsurfacereflectance. We
used4samples ofG.antarctici from microtopographicridges at RobinsonRidge. Wemeasured
7
thesurfacereflectanceofthesamples whentheyweredry,andafterthey hadbeenrehydrated
withafinemist ofwaterfor5minutes. Excess waterwas blottedfrom themoss before
measurements.Moss re-hydraterapidly,regainingfull physiological activityinonetotwo
minutes (Robinsonet al.2000).
5
Measuringsurfacereflectance
Weusedanintegratingspherefittedtoascanningspectrophotometer(GBC UV-Vis 918,
GBC Australia)tomeasurespectral reflectanceofmoss between200–900nm at approximately
10 1nm intervals on2cm2areas ofmoss canopy. Themoss turfsamples werelargeenoughto
completelyfill thesampleapertureoftheintegratingsphere. Tomaintainmoss canopy
architecture(gametophytearrangement)thesamples wereheldinplacebywithina1cm deep
highlyreflectivesampleholder.Forsomesamples this requiredshavingtissuefrom thebasal
portionofthesampleusingarazorbladeuntil theturfwas 1cm thick.Thedepthand packingof
15 thesamples resultedintransmittanceofthroughthesamplebeingnegligible.Reflectance
measuredthereforerepresents themoss canopywithgreenphotosynthetictissueofbetween2-5
mm depthand8-5mm ofnon-photosynthetictissuebelow.From theentirereflectancespectra,
usingsubsets ofthetotal 87spectra(Table1),wepresent meanreflectanceat keywavelengths
andalsocalculatereportedindices usedinremotesensingvegetation(Table2).TheColdHard
20 Band(CHB,Gilmore& Ball 2000)has beenfoundtocorrelatewiththeformationofa
chlorophyll-proteincomplexinleaves that protects against freezingdamage.ThePhotosynthetic
ReflectanceIndex(PRI,Gamonet al.1990,1997)was developedtoreflect changes in
concentrations ofthexanthophyll cyclepigments that areformedwhenplants arestressed. The
amplitudeofthereflectancechangeat thered-edge( )andthepositionofthered-edge( )
(cid:1)RE
RE
8
werecalculatedfrom thefirst derivativeofthespectra(Horler,Dockray& Barber1983).Other
reflectanceindices usedbyarangeofresearchers werealsocalculated(e.g.Vogelmann,Rock&
Moss 1993; Gitelson& Merzylak1997; Lichtenthaler,Gitelson& Lang1996; Carter1991,
1993).
5
Pigment,water andphotosyntheticcharacteristics
Priortomeasurement ofthereflectancespectra,asubset oftheG.antarctici samples weredark
adaptedfor20minutes afterwhichthechlorophyll fluorescenceparameterF /F was measured
v m
10 usingaPAM 2000(H.Walz,Effeltrech,Germany). Afterthereflectancespectraweremeasured,
thephotosyntheticallyactiveapices ofthemoss wereremovedusingarazorbladeand thetissue
was frozeninliquidnitrogen. Samples werereturnedtoAustraliainliquidnitrogenand then
storedat –80˚C inafreezerpriortopigment analysis. Forchlorophyll and carotenoid
determination,samples (50-100mgfreshweight)weregroundwithliquidnitrogenandsandina
15 mortarandpestleandthenextractedin(1.5ml)100%acetone.Thesamples weretransferredtoa
micro-centrifugetubecontaining1mgsodium bicarbonateandkept oniceinthedarkfor20
minutes. Aftercentrifugation(13,000rpm for5minutes)thepellet was re-extractedin0.5ml
80%acetoneusingapolypropylenetissuegrinder(CrownScientific,Australia). Afterafurther
20minutes onice,thesamplewas centrifugedas aboveandthesupernatants from each
20 extractioncombinedandmadeupto3ml with100%acetone. Chlorophylls and carotenoids
werethenquantifiedbyhigh-pressureliquidchromatography(HPLC)usingamethodadapted
from Gilmore& Yamamoto(1991).Thesamples (30-70µl)wereinjectedintoaShimadzu
HPLC system (Shimadzu,Australia)at aflowrateof2ml min-1. Solvent A