Adaptations of Arctic and Alpine Plants to

Adaptations of Arctic and Alpine Plants to Environmental Conditions Author(s): L. C. Bliss Source: Arctic, Vol. 15, No. 2 (Jun., 1962), pp. 117-144 Published by: Arctic Institute of North America Stable URL: http://www.jstor.org/stable/40506981 . Accessed: 08/01/2014 06:21 Your use of the JSTOR archive indicates your acceptance of the Terms & Conditions of Use, available at . http://www.jstor.org/page/info/about/policies/terms.jsp

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ADAPTATIONS OF ARCTIC AND ALPINE PLANTS TO ENVIRONMENTAL CONDITIONS* L. C. Blissf Introduction one considersextremeenvironments and plant adaptationsthat have evolvedfromthe selectionof species populationsby various environmental the first desertand tundravegetationare frequently factors, to receiveattention. Tundra,as used here,refersto the treelessexpansesbeyondclimatic timberline bothin thenorth(arctictundra)and on highmountains(alpine As tundra). delimitedby Polunin (1951), arcticregionslie northof whichever of the followingis situatedfarthestnorth:(1) a line 50 miles north of coniferousforestor taiga; (2) northof the presentday northernlimit ofmicrophanerophytic growth(i.e.,trees2 to 8 m. in height,but excluding bushes in unusually favourablesites); or (3) north of the northern lineusingtheformulaV = 9 - 0.1K,whereV is themeanof Nordenskjöld the warmestmonthand Κ is the mean of the coldestmonthin degrees Centigrade.Absoluteboundariesbased upon these or any othercriteria are farfromperfect,thoughtheyserve as a usefulguide fordelimitation. Sincere appreciationis made to the NationalScience Foundationfor grantsG3891and G5119,whichsupporteda part of the researchreported is made to W. D. Billingsand A. Love here.Appreciativeacknowledgement andtoDorisLöve and B. Bilokurforsupplying themanuscript, forreviewing of severalRussianpapers. translations Floristics featuresof the tundrasis the relativelysmall One ofthe characteristic In his flora that has been selected out by the severe environments. 230 66 Polunin Flora" Arctic families, recognizes (1959) "Circumpolar to Löve division of the 892 and According Tracheophyta. species genera, ofthe arcticspeciesare endemic.Löve further (1959),probablytwo-thirds *Thispaper, Life totheAAASSymposium waspresented withsomemodifications, 1960. December New York UnderExtreme City, Conditions, ofIllinois. ofBotany, University fDepartment 117


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ADAPTATIONS OF ARCTIC AND ALPINE PLANTS

statedthatofthisfloraof600speciesonlyabout200are roughlycircumpolar in the alpine tundra. witha numberof speciesextendingto mid-latitudes of in number There is a strikingreduction species with increasing and a of latitudethatresultsfroman increasingseverity the environment arctic in the reductionofland area and availablesoil.Thereare 604 species partsofAlaska and Yukon (Porsild1951).The Greenlandfloraincludes590 species,about490 ofwhichare indigenous(Böcheret al. 1957). In Iceland, 540 speciesare knownwith387 of themindigenous(Löve and Löve 1956). Accordingto Porsild (1957), 340 speciesare foundin the CanadianArctic Archipelago;143 species occur in Spitsbergen(Höeg 1956), 97 in Peary Land, NorthGreenland(Holmen 1957), 65 in northernEllesmereIsland and Calder1953) and 49 specieson EllefRingnesIslandwith (Bruggemann Queen Elizabeth probablyfewerspecieson otherislandsoftheNorthwestern Islands (Savile 1961). Woodyplantsdecrease rapidlygoingnorthwardin the CanadianArcticArchipelago(Porsild1951). Fewer figuresare availableforalpinefloras,thoughthe followinggive some suggestionof the numbers.Hedberg (1957) listed 377 species representing44 vascular plant familiesfor the East Africanalpine flora. 250 speciesforthe Coloradoalpine Rydberg(1914) reportedapproximately 37 per centof the Coloradoalpine and Holm about stated that flora, (1927) These are conservativefigures,for the in Arctic. were found the species workofWeberand othersin thepast 10 yearshas providednumerousnew alpinerecords(Weber1955,1961a,1961b). Some of thesenew recordsare Weber ofspeciesquite commonin theArctic.In a personalcommunication desert to be in Colorado seem that 65 of the over reported alpine species small a are but derived.Annuals percentage present, representonly very ofthe alpineflora(Holm 1927,Little1941,Daubenmire1943). This is also trueforthe Arctic(S0rensen1941,Porsild1951,Bliss 1956). Went (1948, 1953) reportedthat75 per centofthenumerousalpineannualsin theSierra Nevada have close relativesin the desertsbelow. He feltthat the desert and alpineclimateshave in common:a shortgrowingseason,highinsolation rates,limitedmoisturesupply,and extremesin daily temperature. In the PresidentialRange in New Hampshirethereare approximately 70 alpinespecies,nearlyall ofwhichalso occurin theArctic.Thus,although thanthealpineflora theflorais small,it is decidedlymorearcticfloristically Measureof the westernmountains.This is also true forthe cryptogams. mentsofenvironmental factorsby the authorshowthatthe alpineenvironmentis morelike thatfoundin Labradorand Alaska thanthatin thewestern alpine areas. Vascular plantsseem to reach theirmaximumaltitudesin the Himalayas,whereStellariadecumbensoccursat 20,130ft. (Swan 1961). Other high altituderecordsare givenby Webster(1961). Althoughthe tundra and tropicalregions, florasare smallwhencomparedwiththoseoftemperate are the data presenteddo showthatvascularplants adaptedto survivein at highlatitudesand highaltitudes. veryextremeenvironments



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Anotherfeatureof the tundrais the low degree of endemism.When restricted geographicareas are consideredthenumberofendemicsin arctic and alpinetundrasis quite low (usuallyless than5 per centof the flora). Whereasthe numberof endemicsin the continental NorthwestTerritories and in Ungava, as well as in Greenlandis low, a higherpercentageof endemismis foundin theCanadianArcticArchipelago(Porsild1951). This as an indicationof a greaterage of the florain the last maybe interpreted namedregion,whichagrees withHultén's (1937) refugiumideas for the ArcticArchipelagoduringthePleistocene,a theoryalso supportedby Löve (1959). The importanceof autecologicaland cytogeneticalstudies in and present areas ofperiglacialsurvival,subsequentmigration, establishing Böcher were discussed distribution by patterns (1951). Communitydynamicsin relationto environment have a profound Intense frostaction processes or congeliturbation effecton soil and vegetationof arcticregions.The same processesoperate but are seldomif ever to a smallerextentin manyalpine environments, This has led some encounteredin temperateand tropicalenvironments. to state that new interpretations regardingsuccessionand investigators of regional climaxneed to be developedin the Arcticwiththe elimination climaticclimaxconceptsas used by Clements(1916) and land surfaceand soil stabilityconceptsas used by Cowles (1911) in temperateregions (Hopkinsand Sigafoos1950,Sigafoos1951,Raup 1951). Certainlyintense in boththevegetationand soils and the comfrostactioncreatesinstability munitiesmayremainin a stateof considerablefluctuation (Sigafoos1951). it seemsunrealisticto In manyareas wheretheprocessesare less intensive, factorsacting separatefrostactionphenomenafromtheotherenvironmental of which are end the and interacting products upon species populations, mosaic of the form a which stable vegetation part communities, relatively pattern. Climaxand successionalconceptsas appliedto tundravegetationhave beenreviewedbyChurchilland Hanson(1958).Theyconcludedthatsteadystatecommunity patternsthatcorrespondto relativelylong enduringpatternsofenvironmental gradientsrepresentclimaxtypes.Phasic cyclesthat occur in these communities resultingfromfrostactionare consideredby of thisbroad conceptof climaxas long themto be withinthe framework as theyare in succession.The writerfollows as thecyclesare notdirectional theseconceptsof directionalchangein successionleadingto a steady-state or climaxin whichphasiccyclesmayoccur.The problemsare in differenticyclesas influencedin part by the atingdirectionalfromnon-directional The of congeliturbation. populationsof species seem ratherwell intensity adaptedto the varyingdegreesof frostaction,whichallows the eventual The necessityto evaluate the developmentof ratherstable communities. role of frostactionphenomenain relationto successionand steady-state in the tundrais notmetwithin temperateregions. communities


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Tedrow and Cantlon (1958) have shown that there are fairlygood betweenplantcommunities sitesand and soilson well-drained relationships on areas of shallow soils. Correlationsbetweensoils and vegetationon Tundraand Bog soils presentgreaterproblems.They reportedthatminor in climatehave a less profoundeffecton soil pattern regionaldifferences and vegetationthanthe local micro-variation in drainage.This can be well illustrated in themosaicpatternofvegetationin relationto micro-variation in drainageas controlledby microtopography (Figs. 1 and 2).

Fig. 1. Slightlyraised groundsupportinga communityof Betula nana ssp. eocilisand dwarfheath shrubs with cottongrasstussocks,Eriophorumvaginatumssp. spissum on the lower ground.Photographtaken on river terrace near Umiat, Alaska.

In alpinetundras,wherefrostactionis less evident,a greaterstability of soils and vegetationcan be recognized.The interrelationship between soil developmentand plant successionwas describedby Braun-Blanquet and Jenny(1926) forthecentralAlps.A pioneercommunity ofCarex firma and Dryas octopetalaon disintegrating limestoneis replacedby a transition ofKobresiamyosuroides community developedon soils classedas rendzina. The climaxvegetationdominatedby Carex curvulaoccurson climaxsoil characterized by beingacid, highlyleached,and containingmuch organic matter.A similarpatternof soil and vegetationdevelopmentin the alpine zone of othermountainswas reportedby Braun-Blanquet(1932). Anotherfeatureof community dynamicsin tundrasis that in some placesthereis a shiftin therelativeimportance(dominance)of the species comprisingthe existingflorain the stages of succession,ratherthan a



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of the vegetationin the serai stagesleading changein floristic composition to a stable community(Oosting1948,Müller 1952). In the High Arctic, physical environmentalfactorsexceed biological competition,the end productofwhichmaybe therandomoccurrenceofplantswithfewdistinct associations(Savile 1960). Two recentpapersin EnglishreviewmuchoftheRussianliteratureon tundraecology(Aleksandrova1960a,Tikhomirov1960). The formerpaper deals mainlywith the vegetationof Novaya Zemlya,whereas the latter includesall aspectsofRussiantundraecology.

Fig. 2. Raised rim of a depressed-centrepolygonsupportingSalix richardsoniiwith Carex aquatilis in the centreof the polygon.Coastal plain of northernAlaska approximately500 ft. east of the Colville River and 15 miles fromthe coast.

Environmentalfactors Soils In thevast area extendingfromscattered"islands"of alpinetundraat to broad expansesof arctictundrain highelevationsin low mid-latitudes thenorth,thereis a considerablerangeof environmental factors,including soils. Tundrasoilshave receivedconsiderableattention in Eurasia,especially bytheRussianpedologists. littleworkon tundra However,on our continent soilshas been done untilthe excellentstudiesof Tedrowand associatesin


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arcticAlaska. The arcticrepresentative ofmatureor zonal soils,the Arctic Brown soil (Tedrow and Hill 1955), is very restrictedin areal extent, occurringonlyunderconditionsof adequate drainage.A similarsoil type called sod-barerocksoil was describedby Karavaeva (1958) forthe alpine regionofeasternSayan,USSR. The Tundrasoilsand Bog soilsare northern extensionsof humicglei and bog soils respectively(Tedrow and Cantlon 1958,Tedrowand Harries1960). Bothsoil groupsare azonal.The dominant processoperatingin theTundrasoilsis a typeofgleizationat low temperatures;a processfoundalso in foreststo thesouth(Tedrowand Harries1960). resultsfrompédologieas In botharcticand alpine tundras,soil formation well as cryopedologic processes(frost-phenomena). If theconceptclimaxvegetationis restricted to communities developed and heathcommunities meadow undermesic,stablesoil conditions, upland associatedwithArcticBrownsoilsonlycouldbe designatedclimax(Tedrow and Harries 1960). This conceptof climax vegetationis too narrowas discussedin the community dynamicssection. in northern rateshave been investigated Organicmatterdecomposition Alaska by Douglas and Tedrow(1959). Theyreportedthatsoil temperature thansoil moisturein regulatingorganicmatterdecomis moreimportant are ofthesame order and foundthatannualratesofdecomposition position, ofmagnitudeas ratesoforganicmatterproduction per year. Alpinesoils in the RockyMountainshave been groupedinto 3 broad classes (alpineturf,alpinemeadow,alpinebog soils) by Retzer (1956). He statedthatthepresenceofkaolinitein thesoilsindicatesa ratheradvanced stage of weathering.A briefdescriptionof alpine soils in the Andes of Colombiawas presentedby Jenny(1948). He dividedthe soils into cold is greaterin mostalpine humusand podzoltypes.Soil profiledevelopment tundraregionsdue to betterinternaldrainagethatresultsin partfromthe and less intensivefrostaction. minorrole of permafrost Patternedgroundis a conspicuousfeatureof both arctic and alpine The extensiveliteratureregardingthe originof patterned environments. groundwas reviewedby Washburn(1956). Troll (1944) describedearth stonenets,and stonestripesas rangingfromsmall regularforms patterns, in the alpine zone of tropicalmountainswherenightlyfreezingoccursto is controlled themuchlargerformstypicaloftheArcticwheredevelopment by theseasonalcourseoffreezingand thawing. Low levels of plantgrowthin the Arctichave been attributedto low levels of soil nitrogen(Russell 1940a,S0rensen1941,WarrenWilson1954, 1957a). Russell (1940a) stated that nitrogendeficiencyresultsfromlow bacterialactivitydue both to low temperatureand low nutrientsupply. and where Certainlyplantgrowthis moreluxuriantaroundold settlements manuredby animals.Dadykin(1954) has carriedon extensivephysiological studieson rootsin cold soils in arcticRussia. He reportedthat nitrogen levels of plantsgrownin cold soils were equal to or greaterthannitrogen levels of controlplantsgrownin warmersoils.However,the low temperaof nitrogenintoorganiccompounds, turesreducethe assimilation probably



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and theirderivatives.This was trueregardlessof the form nucleo-proteins of nitrogensupplied(nitrate,ammoniumnitrate,or organicnitrogen).He further statedthatboronand certainotherelementsaugmentthe yield of plantsgrownin cold soils.Whereasnitrogenappearsto be a limitingfactor in tundraplantgrowth,certainothersoil nutrientsseem to be presentin fairlyadequateamountsin somearcticand alpinesoils (Feustel et at. 1939, Böcher1949,Retzer1956,WarrenWilson1957a). Light intensity,duration,and quality Whereasrelativelyfew recordsof solar radiationhave been obtained in thetundras,solarradiationis exceedinglyimportant, because it not only affectssoil and air temperatures, and soil moisture,but also the humidity, within the The data available showthat,at least for energyflow ecosystem. in shortperiodsoftime,solarenergy theArcticmaybe equal to or exceed thatreceivedin mid-latitudes on a 24-hourbasis. Isolatedfiguresare rather but theydo give some generalindicationof environmental meaningless, conditions. Data fromvarioussources (S0rensen1941,Bliss 1956,Warren in the Arcticon level land, solar Wilson1960) show thatin mid-summer hr. (1 Langley= 1 gr.-cal./cm.2) . radiationrangesfrom318to510langleys/24 Solar radiationdata on Mt. Washingtongive a summeraverage of 436 hr. fromJuneto August (Haurwitz1937). Values obtainedby langleys/24 the writerfor 1959 range fromless than 100 in heavy fog to over 800 hr.on cleardaysin July.The highervalues are seldomattained langleys/24 mountain. forthisnearlyconstantly fog-bound at noonis usuallygreaterin the alpine In mid-summer lightintensity In general, thanin the arctictundradue to the thinneralpine atmosphere. on a 24-hourbasis,it appearsthatsolarradiationvalues in thearctictundra are ratherless thanin the alpine,thoughmanymoredata are needed. the lengthof day duringthe growingseason is of great Furthermore, In does not the alpinetundrasoftheUnitedStatesphotoperiod importance. exceed 15 to 16 hoursin summer,but in the Arcticat least 2 monthsof continuous lightprevail.FromtheworkofMooneyand Billings(1961) and othersit is becomingapparentthatmanypopulationsof arcticspecies are adapted to a 24-hourphotoperiodwhereas their alpine physiologically are counterparts adaptedto a shorterdaylength. ofultravioletlightin the alpineenvironment The greaterintensity has to state that this is the cause of the low growth led some investigators formof alpineplants.There are few,if any,experimental data to support thishypothesis. Temperature factorstemperature Ofthevariousenvironmental is themostimportant factorwithregardto plantgrowthand development in the tundra. limiting


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The physiologicalexplanationfor the criticaltemperatureeffectis twofoldaccordingto WarrenWilson(1957b).Withmean summerair temperatures frequentlyjust above 0°C, the temperaturesare near the lower cardinalpointformanymetabolicprocesses,and secondly,accelerationof increaseis greaterat low temperaphysiological processesby a temperature tures. A considerableamountofinformation in tundramicroon temperatures environments is containedin papersby S0rensen(1941),Cook (1955),Bliss (1956), WarrenWilson (1957b), Billingsand Bliss (1959), Aleksandrova (1960b), Conover (1960), and Marr (1961). Whereas temperaturesare relativelylow in the Arctic,they neverthelessshow normal day-time in themicroenvironment inversions withtemperature temperature gradients at In these severe where typical "night". environments, day-timetemperaturesat 0.7m.seldomexceed13° to 18°C. and morefrequently are 5° to 8°C, it is ofconsiderableinterestto notethatsoil surfacetemperatures in excess of 38°C. have been recordedby the writerin arcticAlaska as well as in thealpinetundrasofWyoming and Mt.Washington. soil-surface Night-time temperaturesfor the same dates were 4° to 7°C. Diurnal temperature extremesare thusconsiderable, usuallybeinggreaterin the alpine tundra on accountof the longernightperiod.Temperatureregimesin the microenvironment on north-and south-facing which slopes are quite different, encountered. helpsto explainthediversityofplantcommunities Mostofthetundraplantsare greatlyreducedin size,frequently forming a mat not higherthan 6 to 8 cm. Thus the above-ground partsare in the lower part of the microenvironment where considerablyhighertemperaturesprevail,whichpermitsmetabolicprocessesto proceedmore rapidly than would otherwisebe possible. Tundra plants are adapted by their caespitoseor low growthformto take advantageof the morefavourable thatprevailnear the ground.Frequentlythese temperature temperatures conditionsare not apparentwhentemperature data of weatherstationsin thearea are used.WarrenWilson(1957b)recordedleafand air temperature 1 cm.above thegroundwitha thermocouple. differences were Temperature less duringperiodsofmistor cloudbut stillmeasurable.In earlySeptember withshortperiodsof darknessleaf temperatures fell 1°C below air temperatures(WarrenWilson1957b). A strikingexampleof temperature stratification withina small clump of Saxifragaoppositifolia is citedby WarrenWilson (1957b). On June 23 at 1430 hrs. the air temperatureat 2 m. was 0.5°C, at 1 cm. above the insidetwo flowerbuds was 6°C. clumpit was 3.5°C. and the temperature Even greaterextremeswere recordedby Wulff(cited in Porsild1951) in northern Greenland(82°N.). Withtheair temperature at - 12°C, a reading of3.5°C. was recordedamongdead leaves in a tuftofsaxifrageand 10°C. in a darkclumpofmosses.Thesemicroenvironmental are notas temperatures extremeas in temperateregions,but in the tundrarelativelysmall temperatureincreasesbecomehighlysignificant withregardto plantmetabolic processes.



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The diurnalrhythms offlowering and pollinating agentsoftundraplants have been studiedby Shamurin(1958) at 71° N. near Ashkutz,USSR. He foundthattemperature factorcontrolling is the mostimportant flowering. Data presentedshow that flowersof many species open at minimalair of3° to 8°C. withmassopeningofflowersat 5° to 12°C. temperatures The mostintensivestudyof arcticplant temperatures knownto the writeris thatofTikhomirov et ai. (1960). Theygathereddata on 40 species of flowering plants at Tiksi, Yakutsk,USSR (71°35'N.). On sunnydays thetemperature found that ofplantpartsexceededtheair temperature they 2° to 5°C. on whereas by cloudydays planttemperatures may fall below thatof the air. Theyreportedthattemperatures insidewhiteflowerswere 0.7° to 2.0°C. higherthanadjacentair,and blue- and lilac-coloured flowers were 3.4° to 4.2°C. warmerthanthe adjacentair. Many temperatures are for of various a Sieversia glacialis plant includingroot presented parts temperatures. Tundraplantsare notonlyadaptedto take advantageofthefavourable balancein the microenvironment, but theycan also withstand temperature suddendropsin temperature to levels below freezing,oftenwithlittleor no ill effect.Porsild (1951) foundmasses of Epilobiumlatifoliumin full at - 3.5°C. The followingday, bloom,frozenstiffwiththe air temperature afterthawing,no evidenceof frostdamagecould be found.On Mt. Washingtonthe writerhas seen plantsin flowercoveredwithrimeice at temperaturesof-3° to - 1.5°C. Whentheice meltedtherewas no evidenceof damage.In June1959,Diapensia lapponicaand Rhododendron lapponicum werein bloomon Mt. Washington whena suddensnow stormoccurred.A continuoustemperature recordat theheightoftheplantsshowedtemperaturesrangingfrom-5° to - 0.5°C. (-0.5° predominated)during5 days, yet the flowerscontinuedbloomingand set seed followingsnow melt. If arcticand alpinespecieshad not acquiredthisphysiological adaptationto withstand severetemperature conditions associatedwithsuddenand violent theywouldhave been eliminatedfromthefloralongago,forsevere storms, stormsare characteristic ratherthanexceptionalin the tundra. The mostremarkabletoleranceto low temperatures of any plant in variousstagesofdevelopment seemsto be thatof Braya humilis.S0rensen (1941,p. 109) statesthat"Braya humilisoccupiesa unique positionamong all the seminiferous or infrucspecies of the area in that inflorescences tescencesat anystageofdevelopment maysurvivethe winterand continue theirdevelopment in the succeedinggrowingseason".S0rensenlike others, however,discountedthe reportsof a similarcapacityforwintersurvival offlowers andfruiting shootsofCochleariaofficinalis. thebulbils Apparently producedby some speciesalso can toleratelow wintertemperatures. S0rensen's (1941) excellent paper on temperaturerelations and on the developphenologyin Greenlandplantsincludesmuchinformation mentalstageof overwintering buds. He statedthatGreenlandspecieswith a morenorthern distribution frequently possessflowerbuds thatoverwinter in a veryadvancedstage of development. Floral organsin manyof these


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species take 2 years to develop,withfloralinitiationin the 1st year and floralexpansionwithinthe buds in the secondsummer.These species are thusadaptedto burstintoflowerand vegetativegrowthas soon as spring temperaturespermit.This rapid flowerexpansion with the arrival of favourabletemperatures is a good adaptationto the all-too-short growing season.S0rensenfurther offloralorgansin theArctic statedthatformation adaptation. maybe inducedby low temperature-thermoperiodical in cold tundrasoils has been reportedby Porsild Root stratification (1951) and Bliss (1956). Roots are typicallyconfinedto the warmerand In contrast,alpine slightlybetterdrainedsoil layersabove the permafrost. plantspossessrootsthatpenetratemoredeeplyintothe soil (Daubenmire 1941,Holchet al. 1941,Bliss 1956) fordrainageis generallymuchbetterand ifpresent, is quitedeepduringthegrowingseason (Retzer1956). permafrost,

Fi*. 3. Wind-prunedSalix brachycarpagrowingon the leeward side of a rock. Alpine fellfieldin the Medicine Bow Mountains,Wyoming,at an altitude of 11,000ft.

Alaska the roottipsofArctaDuringmuchofthesummerin northern and grostislatifolia Eriophorumvaginatumssp. spissumfollowedwithin 0.5 to 1.5 cm.ofthe retreating frostlevel in a saturatedsoil whosetemperatures were between0° and 1°C (Bliss 1956). Dadykin (1954) reported that youngroots of Calamagrostislangsdorffii and Rosa aciculariswere of0°C. foundnearthesurfaceofthefrozenlayerin soil witha temperature He furtherstated (afterGrigorieva)that roots of Rubus chamaemorus, Carex globularis,and Equisetumsilvaticumwere removedfromthe frozen starchgrains soil,immediately fixed,and thattheserootswereaccumulating



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and thatmeristematic cells were foundin metaphaseand anaphase stages of nucleardivision.Dadykinhas demonstrated water absorptionby roots in frozengroundwhere part of the water remainedin the liquid state in the soil as well as in the root. because ofhighosmoticconcentration Relativelyhighosmoticvalues have been reportedforbotharcticand alpineplantsas comparedwithtemperate-region species.Wagerand Wager (1938) reportedthatosmoticvalues forEast Greenlandplantsare higher in winterthanin summer,and thatthe springdropin values is associated with temperature rise and the utilizationof food reserves.They further lowerosmoticvalues statedthatplantscoveredbywintersnowhave slightly than plants growingin exposed situations.Heilborn (1925) related the winds higherosmoticvalues ofplantsin theEquadorianparamoto stronger and loweratmospheric pressurewhencomparedwithplantsat lower altitudes.Accordingto him,these factorscontrolthe water economyof the plants,whichis reflectedin the highervalues for exposed shrubs (25 to 29 atm.) thanforrosetteswiththicktap roots (12-17atm.). Otherinvestigatorshave related the higherosmoticvalues of alpine plants to low temperatures(Meier 1916). Mooney and Billings (1961) concludedthat the primaryrestrictive of arcticand alpine populationsof Oxyria factorlimitingthe distribution to be relativelyhigh summertemperature.Under these digynaappears reservesare depletedowingto low photosynthetic conditions, carbohydrate is supportedby the findings at This hypothesis economy hightemperatures. ofDahl (1951) foralpineplantsin Fennoscandiaand Müller(1928) on arctic plantsin west Greenland. rates of plant growthin As a last pointto be made on temperature, and in those species northernAlaska were correlatedwith temperature, correlations in whichgrowthwas relativelylarge, statistically significant were found(Bliss 1956). Wind Windis an ever-present environmental factorin botharcticand alpine tundraswithwind-pruned vegetationa commonsight,especiallyon exposed ridgesand slopesin the Alpineand in the High Arctic (Fig. 3). Although windspeed is greatlyreducednear the ground,the low statureand sparse cover of the vegetationenable the wind to be more effectivethan with tallerand morestratified of vegetationmats and vegetation.Wind-erosion cushionshas been discussedby Whitehead(1954) and Billingsand Mooney (1959) foralpinevegetationand by Hopkinsand Sigafoos(1950) in Alaska. Billingsand Mooney (1959) postulateda natural cycle involvingwinderosionand frostheavingin the degradationof peat hummocksthrough frostscars to sortedpolygonson which,afterflooding, peat accumulation is againinitiated.Thus any community thatmightbe called "climax"is of shortduration.The importanceof wind in the formation and degradation of hummocksin the alpine zone of the Old Man Range in New Zealand was discussedby Billingsand Mark (1961). Whitehead(1954) statedthat



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in theItalian adaptativesignificance caespitosegrowthformshave a definite Alps. He also indicatedthat wind may affectgrowthrates throughtemperaturechanges. as well as air temperin reducingleaf temperatures Windis effective of low microclimate ature,thusupsettingthemorefavourabletemperature arcticand alpine vegetationaccordingto WarrenWilson (1959). He concluded thatthe potenteffectof wind on tundravegetationis a resultof is due less of plantgrowthto wind,and thatthe sensitivity the sensitivity as theyaffect to excessivetranspiration conditions and moreto temperature net assimilation and shootgrowthrates.Althoughwind speeds are greatly reducedwithinclumpsof tundraplantsin the summer(WarrenWilson branches,especiallyin the alpine 1959), the abundanceof winter-killed tundra,testifiesto the lack of snow cover and strongwinds in winter (Bliss 1956). Bliss (1960) reportedthat transpiration rates for tundrashrubsare and related to air low, directly vapor pressuredeficit,and temperature, windspeedsbelow6 m.p.h.,butinverselyproportional to windspeedsabove 6 to 8 m.p.h.and cloud cover.Relativelylow transpiration ratesfortundra have been other workers plants reportedby (Wulff1902, Stocker 1931, in Cartellieri1940,Hygen 1953,Dadykin 1954). Transpiration differences 3 species of Vacciniumwere relatedto morphological structureand leaf anatomyaccordingto Hygen (1953). He furtherreportedthat cuticular losseswere quitelow in thexerophytic Vacciniumvitis-idaea, transpiration but quite highin wet-sitespeciessuch as Pinguiculavulgaris. It has been statedthat,in general,tundraplantsappear to be able to absorbwater in adequate amountsto meet the demandsof transpiration (Dadykin1954,WarrenWilson1959), thoughdroughthas been reportedin somestudies(Michelmore1934,Böcher1949,Whitehead1951),and Webster (1961) concludedthat water supplymay be the most importantlimiting factorintheupperaltitudinal limitsofflowering plantsinhighalpineregions. The importanceof wind in seed dissemination has been discussedby Porsild (1951), Tikhomirov(1951), and Gavriliuk(1961). Snow cover Snowbankor snowflush vegetationis commonlyfoundin the tundra of mountainousareas where wintersnow accumulationin large driftsis favouredby strongwinds and heavy snowfall.In most low-arcticand alpinetundrasthereis a ratherspecializedfloraassociatedwithsnowbanks of species (Polunin1948,Gjaerevoll1956,and others).The microzonation and vegetationis largelythe resultof adaptationsto depthand durationof snowcover(Billingsand Bliss 1959).These plantsmustbe able to complete at least a vegetativelifecyclein a fewweeks and even thatcannotoccur everyyear.Some speciesbegingrowthunderas muchas 50 to 100 cm. of snow (Billingsand Bliss 1959,Mooneyand Billings1960) whereasother species await the meltingof the snow beforestartingto grow.Kovakina



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(1958) reporteddevelopmentof new shootsincludingan accumulationof nitrogenunderless than 110 cm. of snow startingin January.This work was done on the Kola Peninsula,USSR. In some instances,species may remainundersnowfor2 or moreyears,unable to carryon manyphysiological processes.It is under such conditionsthat relativelylarge carbohydratereservesin rootsand rhizomesmaypermitsurvivalthatotherwise could not occur. Plants buried under wintersnow do have protectionduringcritical In summerthe meltwaterpreperiodsof highwindand low temperature. ventstheirbeing subjectedto soil drought(Billingsand Bliss 1959). In general,tundrashrubsare foundonlywherewintersnow cover prevails. Thus,shrubheightis quite well correlatedwithmean wintersnow depth. Accumulationof dirton snowbanksin the Arcticand its role in building a fineorganicsoil as well as the possibleincreasein soil nitrogenhas been presentedby WarrenWilson (1958). In the Alps thereare no annuals in theschneetälchen floraand vegetativereproduction is veryimportant since seedproduction doesnotoccureveryyear(Braun-BlanquetandJenny1926). Aspectsof adaptation Pollination The relationofair temperature to the diurnalpatternof flowering and pollinationby bumble-beesand flieswas studiedby Shamurin(1958) near of20 speciesofflowering Ashkutz,USSR. The fertilization plantsin southeasternChukotk,USSR is reportedto dependentirelyupon 2 species of bumble-bees(Gavriliuk1961),thoughin generalthereare indicationsthat thanin otherenvironments windand insectpollinationare less important Whereas (Löve 1959). Self pollinationthus seems to be most important. self pollinationmay be an importantmechanismin severe environments cross pollinationhelps wherelittletimecan be lost to chancepollination, to insuregreatergeneticdiversitywithinthe populations. Seed production Althoughviable seeds are producedby manytundraspecies,seeds of other tundra species fail to germinate(Nichols 1934, Söyrinki1938-9, S0rensen1941, Bliss 1958). Holch et al (1941) reportedthat rhizomes providethe best means of propagationof alpine plantsin Colorado.Seed undersevereconditionswas studiedby S0rensen(1941), who germination foundthat germination occurredeven thoughthe seeds remainedfrozen forhalfofeach 24-hourperiod.Environmental conditionsin the alpine and arctictundras,as in thedesert,seemto be adequateforseed production and in some There to be a considerable germination only years. appears productionof seedlingsin some yearsfollowedby severalyearsin whichfew if any seedlingsbecomeestablished.This differential survivalof seedlings can havea profound effect on vegetation patterns.Studiesin Coloradoalpine


130


areas indicatethatsoil droughtand needleice activityare the mostimportantenvironmental controls(Osburn 1961). Germination studiesby Bliss (1958) showedthatseeds of Salix plantthe seed seldom foliavar.monicaripenin Julyand germinate immediately; viable overwinter.The seed of Salix brachycarparipensin late remaining Augustand probablydoes notgerminateuntilthe following spring,forthe seeds remainviable over winter.The formerspecies growsin sites that are moistthroughout thesummer,whereasthelatterspeciesgrowsin sites thatare frequently ofviable Salix quite dryby August.The overwintering brachycarpaseed with germination occurringin moistsoil the following springmay be of importanceforsurvival.This patternis of interest,for speciesof Salix in generalproduceseed of shortviability.Fruitsof some arcticspeciesdo notmatureand dehisceuntilaftersnowcoversthe ground mechanismforseed dispersaland sub(Porsild1951). This is an important because snowbankcommunitiesare enrichedby sequent establishment windtransported soil and seeds thataccumulatein the snowduringwinter (Porsild 1951). Observationsby the author (Bliss 1956) in arcticand alpine tundras indicatethatflowering and seed productiondecreasewithan inintensity creasein the severityof environments caused by local microenvironmental conditions.Thus, local variationin floweringand fruitingas a resultof differences topographic (exposedridges,shelteredslopes,snowbankvegetabe as as tion) may great overlarge geographicareas such as the reduction in fruiting of some speciesfromthe Low Arcticto the High Arctic. The frequency ofapomictsis also quitehighin thetundra(Löve 1959). this mechanism of asexual seed productionenables the survival Certainly, of new vigorousand well-adaptedbiotypesthatbecause of sexual sterility could nototherwisesurvive.This permitsa rapidbuild up of a population of geneticallysimilarindividuals,which,if adaptedto the prevailingenvironmental couldpermitcolonizationof newlyavailablehabitats conditions, such as in the Arcticfollowingice retreat(Stebbins1950). Vivipary(germination ofa propagulewhileattachedto theparentplant) as in Polygonum viviparum,Saxifragacernua,and Poa alpina var. viviparais a means of that equips the progenyfor establishment reproduction duringthe same season. growing Polyploidy Althoughthe numberof speciesin the floradecreasesfrommiddleto highlatitudes,thereis an increasein thefrequency ofpolyploidy fromabout 30 to 35 per cent in warm temperateregionsto over 60 per cent in the Subarcticand Arcticand 70 to 80 per centin the arcticislands (Löve and Löve 1957). A highincidenceof polyploidyhas also been reportedforthe Mexican alpine flora(Beaman et al 1962). Stebbins(1950) reviewedthe literatureon polyploidyin the Arcticand concludedthat it is due to a combination of causes including:(1) a highpercentageof perennialherbs



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in whichpolyploidyis somewhathigher;(2) manygrassesand sedges in whichpolyploidyis frequent;and (3) widertolerancelimitsof polyploids foroccupyingnew habitats.However,some of the plantsfoundunderthe mostadverseconditionsare diploids (e.g., Silène acaulis, Oxyria digyna, Vacciniumuliginosum,and others),which shows Saxifragaoppositifolia, thatgenesforhardinessare presentin thediploidas well as in thepolyploid condition(Löve and Löve 1949,1957; Hagerup 1933). Gustafsson(1948) has viewedtheincreaseofpolyploidsin theArcticas a resultof thebreakdown of the diploidsexual mechanismleadingto vegetativereproduction ratherthan an increasein polyploidsdue to severe climaticconditionsas stipulatedby Hagerup (1932). Löve and Löve (1949) Followingan extensivereviewofthe literature, favouredthe hypothesisthatthe increasedfrequencyof polyploidsin the Arctic is due to the increasedgeneticalsuperiorityof polyploids.This hypothesisis based on data fromnumerouspapers,whichshow that the increasedtoleranceof plantstowardextremeconditions, as in the Arctic, resultsfromthe greaterphysiologicaland morphologicaladaptabilityof Relatedtothisis theworkofSokolovskayaand Strelkova(1960). polyploids. They reported,based upon 168 species,that the majorityof the diploid florawhereasthepolyploidspecies speciesbelongto theancientarcto-alpine of that arctic the flora that has spread over the Eurasiatic represent part Arcticduringpost-glacialtime. In evaluatingthe importanceof polyploidyin any environment one mustkeep in mindthe relativeproportionof generaand familiesknown to have a highincidenceof polyploidsas the Cyperaceae,Gramineae,and Rosaceae. Phenology Plantphenologycan be a usefultool in helpingto describemicroenvironmental differences betweenvarioushabitats.Bliss (1956) reportedthat manyspecieslivingin a givenhabitatbreak dormancy,flower,and fruit whereasthe same speciesexhibitdifferent together, cyclesof development in different habitats.This shows the controlof local microenvironmental factorson therateofplantdevelopment. Data on phenologyofarcticplants are also containedin the papers by Söyrinki(1938-9),S0rensen (1941), McClure (1943), and Alexsandrova(1960c). Limiteddata by Bruggemann and Calder (1953) and Savile (1959) indicatethatthegrowingseasoncomes earlierin the High Arctic(Alert82°30'N.) of the Canadian ArcticArchiInlet 63Ο2ΓΝ.and Coral Harpelagothanin the Low Arctic(Chesterfield bour 64°09' N.). This is in part due to the extentof snow cover,angle of incidenceand daylength.The establishment of phenologicalseasons for variouslocationsin the tundrawould be a veryusefultool in delimiting macro-and microenvironments, but it must await the gatheringof more detaileddata on phenologyforimportantspecies that occur in the arctic and alpine tundras.


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Gross morphology is ratherextensive.Worthy The literatureon tundraplantmorphology of specialmentionare paperson structureand biologyof arcticflowering plantsby Warmingand othersthatappearedin Meddelelserom Gr0nland of the East from1908 to 1921,and the sectionon biologicalmorphology Greenlandplantsby S0rensen(1941). in a very In general,manyarcticplantspossessbuds thatover-winter so thatwiththe adventof favourabletemadvancedstageof development occurrapidly.A conspicuousfeature peratures,shootgrowthand flowering to the of tundraplantsis the relativelylarge size of flowersin proportion vegetativeshoots (S0rensen 1941, Daubenmire1943). In alpine tundras the caespitosegrowthformis veryimportant(Daubenmire1943) as it is in theHighArctic.Some speciesin bothtundrashave fleshyleaves,though thisis probablymorecharacteristic of alpine species.Evergreenleaves are rathercommonin arcticplants.Thickcuticleand an abundanceofepidermal hairsare consideredby someto be adaptationsof alpineplants.According to Holch et al. (1941), epidermalhairsof alpineplantsabsorblarge quantitiesof lightthus reducingthe amountof lightreachingthe chlorophyll. visiblelightas reportedforsubalpinespecies However,thehairsmayreflect by Billingsand Morris (1951). Krog (1955) has reportedhighertemperaturesin willowcatkinswithhairs than in catkinspaintedblack. He felt thatlong-wave radiationfromthecatkinsis trappedby thehairsin addition to theirfunctioning as a black body.Thus specieswithhairsor dark scales couldflowerearlier,whentemperatures are stillnear freezing, thanspecies these characteristics. This be an in factor botharctic lacking may important and alpineplantspossessinghairsand darkscales,formanyofthesespecies do flowerearly(Bliss 1956). The importance ofhairsin bud development and the ripeningof seeds in pubescentracemeswas discussedby Tikhomirov et al (I960). The workofZhuikova(1959) on theKola Peninsula,USSR, has shown that in several species of Vacciniumthere are different formsof shrub habitats.Zhuikovaworkedon the branchingdevelopgrowthin different mentofindividualsfromseedlingto maturesize and foundthatin general and V. vitis-idaeado not plants of Vacciniumuliginosum,V. myrtillus, floweruntiltheyare 14 to 20 yearsold. Life-form The life-form spectrumof a floracan be used as a roughmeasureof theprevailingclimateand theselectiveactionofthe climateon thoseplant formsbestadaptedforsurvival.Raunkiaer(1934) reporteda chamaephyte climateforthe tundrasin whichchamaephytes constituteat least 20 per cent of the spectrum.Phanerophytes, buds more plantswithperennating than30 cm.abovetheground,and therophytes or annualsare eitherlacking or are at least quite minorin the tundra.The mostimportant groupsare



133

the percentthe chamaephytes and hemicryptophytes. As a generalization, age ofchamaephytes graduallyincreasesas theclimatebecomesmoresevere with increase in latitude- arctic,and an increase in altitude- alpine ofmanychamaephytes thecushiongrowth-form (Raunkiaer1934).Certainly is a formwelladaptedto takeadvantageofthehighersurfacetemperatures, reducedwindspeeds as well as beingadaptedto greatersurvivalin areas of littlesnow coverin winter.This growth-form has evolvedin unrelated plantfamiliesin the tundraand is a good exampleof parallelevolutionof a formwell adaptedforsurvivalin the severetundraenvironments (Bliss 1956). and respiration Photosynthesis dwarfnature of tundraplants and theirslow The characteristically Wager (1938) statedthatlow growthrateshave been variouslyinterpreted. and were morelimitingthanthe low carbohydrate synthesis temperatures and water.In contrast,S0rensen small supplyof nitrogen,soil nutrients, forsoilmoistureand nutrients, especiallynitro(1941) believedcompetition of the the inherent and specieswere causal. morphology developmental gen to low levels of have been related of low levels plant growth Though Wilson Warren 1954,1957a), Dadykin (1954) has nitrogen(Russell 1940a, but that low levelsofproteinsynthesis be shownthatnitrogen may adequate also discussedslownessofprotein the factor. Polunin be limiting may (1955) He reduced cell combined with elongationat low temperatures. synthesis in for arctic is no that there evidence stated further shortage carbohydrate plants.Thishas beenclearlyshownforarcticspecies(Russell1940b,Warren Wilson1954,1960),andforalpinespecies(Russell1948,Mooneyand Billings may help to accountforrapid 1960). High levels of solublecarbohydrates (Wager1941,Russell 1948,Midorikawa1959) springgrowthand flowering as well as an increasein cold resistanceof underground partsduringthe winter(Russell 1948). in theleaves of Oxyriadigyna oftotalcarbohydrate The concentration on JanMayenIsland showeda diurnalrhythm duringcontinuousdaylight averaged33 to 45 per centofthe (WarrenWilson1954).Totalcarbohydrate dryweightduringa 3-dayperiod.These values were considerablyhigher in the thanthoseobtainedforOxyrialeaves in England.A diurnalrhythm light.Kislyakova(1960) openingofstomatawas also foundundercontinuous has shownthat Vacciniumuliginosum,potato,and beans assimilateconon theKilskiiPeninsula,USSR (67°30'N.). Under in midsummer tinuously but clear skies at "night"assimilationrates are about 1 mg. CO2/dm.2/hr. is absentor nearlyso. By 4 a.m., undercloudyweather"night"assimilation Similarfindings ratesincreaseto a level of 3 to 15 mg.CO2/dm.2/hr. have been reportedby otherRussianbotanists(Dadykinand Grigorieva,Kostichev et ah, citedin Kislyakova1960). The annualcarbohydrate cycleand its relationto growthhas recently beendescribedfor3 alpinespeciesin Wyoming(Mooneyand Billings1960).


134


It was foundthatthe carbohydrate contentof underground storageorgans was highestin thefall.At thestartofgrowthin thenextspring,the carbomust hydratelevel is somewhatreduced,whichindicatesthatdevelopment occurunderthe snow in the underground around organsat temperatures 0°C. When the snow meltsthereis a burstof growthat the expense of reserves(Billingsand Bliss 1959).Mooneyand Billings(1960) carbohydrate reservesin a 1-week reporteda 50-per-cent dropin rhizomecarbohydrate periodduringleaf expansionand the appearanceof flowerbuds forPolyThese reservesthat were laid down in the previous gonumbistortoides. year thus permitthe rapid rate of growthand floweringduringa 1- to 4-weekperiod.As in the Arctic,these alpine plantsno doubt have buds thatoverwinter in an advancedstageof development. Replacementof rhizomereservesoccurredfromflowering untilfall dormancyin all 3 species. and respirationrates from Althoughfield data on photosynthesis tundraplantsare quite limited,the data summarizedin Table 1 and those and respiration rates presentedbyPisek (1960) indicatethatnetassimilation are quite similarfor plants growingin different tundras.However,the physiological activityofdeciduousand evergreenleaves appearsto be quite different (Pisek and Knapp 1959,Pisek 1960). The latterpaper citeddata fromthe Kola Peninsula,USSR (Danilov and Mirimanjan1948), which showedthatnetassimilation rateswerehigherin arcticherbsand deciduous shrubsthan in evergreenshrubs.Respirationrates were also higherin deciduousthanin evergreenplantsaccordingto Pisek and Knapp (1959). Theirdata includedseveralalpine shrubs.Pisek and Knapp reportedthat measurableratesofrespiration occurin evergreenleaves of Rhododendron at 0°C. in winter,and thesummerrateswere higherin leaves ferrugineum of the presentyear when comparedwithrates fromolder leaves. Wager arcticleaves have on the (1941) concludedthatat the same temperature, thanleaves of temperateplants.This averagea higherrate of respiration is supportedby the findingsof Stocker (1935) and to a less degree by Scholander and Kanwisher (1959). The latter authors concluded that respiratorytemperaturecompensationmay be a minorfactorin arctic plants,though2 of the 9 species examinedshowed significantly higher ratesforarcticthanfortemperate respiration whenmeasured region-species at the same temperature. Bukharin(1961) reportedthatplantsfromseveral ecologicalhabitats were transplanted at variousaltitudes(340 to 1000 m.) in the Murmansk region.All specieswere reducedin growthand rate of development with increasein altitude;reductionsthatwere correlatedwithlower levels of caroteneat higheraltitudes.Nativespeciesin contrastfrequently had higher carotenelevels at higheraltitudesand definitecorrelationswere found betweencarotenelevel and developmental stage.It is knownthatcarotene rolein photosynthesis, playsan important oxidation-reduction and reactions, growth.If tundraplantspossesshighercarotenelevels especiallyin more severeenvironments, thismayhelp to explaindistribution patterns.This is certainlyworthfurther investigation.


135


Workingwiththe limitedarcticdata, WarrenWilson (1960) concluded thatnet assimilationrates of tundraplantsare about one-halfthe values reportedfortemperateregionplants,and that respirationis about 20 to statedthatlow tempera25 per centofthenet assimilatedrate.He further turesare basicallyresponsiblefordepressionof net assimilationin arctic ratherthanthelevels oflightintensity. environments Table 1. Net assimilationand respirationrates for detached leaves of arctic and alpine plants. Net assimilation Locality

Species

Carbohydrate increase gr.ldm.2/week

JanMayenIsland (71°N.)*

Oxyriadigyna

0.30

JanMayenIsland**

Oxyriadigyna(windyhilltop) 0. digyna(sheltered hillside) 0. digyna

0.34 0.46 0.54

CornwallisIsland (75°N.)**

Salix árctica

0 . 73

East Greenland(69°N.)t

Oxyriadigyna

0. 68

AlaskanArcticgrouptt

Oxyriadigyna

0.53

WesternAmericanalpinegrouptt Oxyriadigyna

0.31

0 . 53 0 . 50

Salix herbácea Sibbaldia procumbens

Respiration East Greenland(69°N.)t

Oxyriadigyna

0 . 06-0. 19

JanMayenIsland (7ΓΝ.)**

Oxyriadigyna

0.11

AlaskanArcticgrouptt

Oxyriadigyna

0. 16

0. 15 WesternAmerican alpinegrouptt Oxyriadigyna * Russell 1940. ** WarrenWilson 1960. tData of Wager (1941), adjusted by WarrenWilson (1960). whole plants were measuredwith tt Mooneyand Billings1961.Control-chamber-grown and respiration an infraredgas analyser.Data calculatedfromrates of photosynthesis givenin Fig. 15 of Mooneyand Billings.

Müller (1928) and Wager (1941) reportedthat light saturationfor several species in Greenlandoccurredbetween500 and 2,000ft. candles. Müller(1928) concludedthatat low lightintensities(150 to 650 ft.candles) and Salix glauca decreasedwith assimilation ratesforEpilobiumlatifolium increasefrom10° to 20°C. but at 1,900f.candles,assimilation a temperature increasedwith temperaturerise. Data presentedby Cartellieri (1940) showed that net assimilationrates were higherfor Ranunculusglacialis undercool, cloudyskies than on clear,warm days, and that assimilation


136


did not exceed fluctuations followedlightintensity as longas the intensity 2,800to 3,700ft.candles. The data of Mooney and Billings (1961) indicatethat variationin and respiration ratesforOxyriadigynaare quite well corphotosynthetic relatedwith ecotypicvariationwithinthis wide-ranging species. Of the many data presented,two exampleswill illustratethe point.The upper temperaturecompensationpoint for alpine populationsfromthe central occurred RockyMountainswas 35°C, whereastemperature compensation at 26°C. in the arcticpopulations.Light saturationwas not completeat 5,200ft.candlesin the LovelandPass Coloradoalpine plantswhereasthe plantsfromDonjek Mountains,Yukon Territorywere lightsaturatedat variation approximately 2,000ft.candles.A furtherstudyon physiological in arctic-alpine of that from midshows races populations Oxyriadigyna latitudealpineenvironments are photosynthetically moreefficient at lower concentrations of CO2 than populationsof the same species fromnear sea-levelat highlatitudes(Billingset ah 1961). Certainlymorecomparative physiologicalstudieson populationsof wide-ranging arctic-alpinespecies will shed a greatdeal of lighton the geneticallycontrolledphysiological mechanismsthatenable the plantsto survivein thesesevere and diverse tundraenvironments. Table 2. Net primaryproductionrates for Russian arctic tundra plant communities based on air-dryweights. Locality

LiakhovskiiIslandf (New SiberianIslands)

Vegetationtype

Shrubby-mossy tundra shoots roots Polygonalground mossytundra shoots roots

EuropeanRussiaff

Shrubby-mossy tundra shoots

Cover per cent

60.0

35. 0

-

gr./m.2

gr./m.2jday*

185.0 511.0

0.51 1.40

119.0 260.0

0.33 0.71

120.0

0.33

* Based on entireyear, t Aleksandrova1958. tfLavrenko et al. 1955.

Productivityand efficiency is available on plant Althougha considerableamountof information factorsaffecting growthand the variousenvironmental growth,relatively littleis knownaboutplantgrowthper unitarea or primaryproduction and of the producers.Estimatesof grossand net primaryproduction efficiency give a rathergood measureof the effectof the complexof environmental factorson thespeciescomprising a givenplantcommunity.



137

The limiteddata available indicatethat the values for the standing cropat theendofthegrowingseasonfortheArcticrangefrom0.01gr./m.2/ for day on CornwallisIsland fora Salix árcticabarrento 0.66 gr./m.2/day Carex rostratameadowat Abisko,Sweden.The generalrangeof net productionin theArcticis from0.20to 0.60 gr./m2/day based upon the entire year (see Bliss 1962a). Table 2 gives productionrates based on roots and shoots of arctic are quite comparableto those plants.The above groundratesofproduction fromotherarcticcommunities. The interesting and mostimportantpoint is the tremendous biomassof livingroots.From the methodsgiven,great care was employedin washingout the rootsfromthe soil to a depthof 25 to 36 cm. (Aleksandrova1958).It must,however,be keptin mindthatthese data forrootbiomassrepresent theproduction ofmanyyears. The data foralpineecosystems are quite similarto thoseforthe Arctic witha generalrangeof production from0.20 to 0.60 gr./m.2/day based on the entireyear.The values rangefrom0.06 gr./m.2/day near the centreof a late-melting snowbankin Wyomingto 0.57 gr./m.2/day in a Mt. Washratesare calculated ingtoncarexmeadow(see Bliss 1962a).Whenproduction on the lengthof the growingseason (50 to 70 days), the values forboth tundrasrangefrom1 to 3 gr./m.2/day. There is some indicationin theselimiteddata thatnet productionof shootsis slightly greaterin theArctic,at least in theLow ArcticofAlaska, in comparisonto the variousalpine ecosystems. This may resultfromthe arctic its with resultant longer photoperiod greaternumberof hoursavailable for photosynthesis a considerable during part of the shortgrowing season.The frequently observedgreaterheightof the same speciesin the Arcticas comparedwiththeiralpine counterparts may be relatedto this in difference diurnal assimilation in rates additionto the somesuggested what moresevere alpine environment, at least when comparedwith that ofnorthern Alaska (Bliss 1956). of the alpine plant communitieson Mt. Washingtonwas Efficiency the dry weightof the vegetationper metre2to calculatedby converting gram-calories per metre2using the caloric value of the respectivecommunitiesas determined withan oxygenbombcalorimeter. The caloricvalue per metre2was thendividedby one-halfof the solar radiationavailable duringthe growingseason (200.6 χ 106 calories per metre2),a 3-year averageforthe summitof Mt. Washington(Haurwitz1937). One-halfof the totalsolar radiationvalues are used in the calculationsfor only this amountof energyis in the rangeof visiblelightabsorbedby chlorophyll (Daubenmire1959). Solar energyof the growingseason is used, forit is the onlypart of the year duringwhichplantscan carryon assimilation. shrubheath meadowin Thus, efficiency percentageforthe Juncus-dwarf 1959 would be 81 χ 4,743dividedby 200.6 χ 106,or 0.19 per cent after by 100 (Table 3). multiplication The Mt. Washington efficiency percentagespresentedin Table 4 show little from fluctuation The relatively year to year in the same community.


138


rates of these alpine communitiesare comparableto those of efficiency severaltemperate thoughmuchmoreworkis necessary regioncommunities, in difbeforeprimaryproductionefficiency data forvariouscommunities ferentenvironments can be properlyevaluated. This seeminglycomparableefficiency of certainalpine communities withtemperate communities resultsin partfroma morecompleteutilization of the growingseason for growth.Most temperatecommunities produce largerstandingcrops,but this is achievedover a greaterportionof the year. Limiteddata available indicatethatthese alpine plant communities have highercaloricvalues thantemperateand tropicalplantcommunities, increasesthatare statistically significant (Golley1961). Table 3. Calculationof percentageefficiency of net productionin the Mt. Washington alpine tundra. Annualtotalsolarradiation(3-yearaverage) 1,077.3X 106 Annualsolarradiationavailableforphotosynthesis 538.6 X 106 Total solarradiationduringgrowing season(June-Aug.) 401.2 X 106 Solarradiationavailableforphotosynthesis during season 200.6 X 106 growing caloricvaluesofplantmaterialpermetre2 = ofefficiency percentage solarradiationin cal. permetre2

gr.-cal./m.2 gr.-cal./m.2 gr.-caL/m.2 gr.-cal./m.2

in Efficiency per cent* Vegetation1959

gr./m.2

cal./gr.

Juncus-dwari shrubheathmeadow 81 4,743 Carexmeadow 203 4,802 * Based on one-halfof the total solar energyvalue.

Entire year

Growingseason

0 . 07 0.18

0.19 0.48

Froma recentanalysisof40 species (entireplantsamples)of vascular fromMt. Washingtonit is apparent plantsand 15 species of cryptogams that the caloric and lipid (ether extract) values are high,especiallyin evergreenshrubs, (Bliss 1962b). Caloric values for evergreenshrubs averaged 5078±69, deciduous shrubs 4915±52, herbs 4567±32, mosses 4410±70,and lichens4324±59 cal./gr.ovendrywt.It seemsthatthesehigh caloricvalues can be accountedforin partby the relativelyhighlipidpercentages,whichrangefrom3.72±0.5 in the evergreenshrubsto 1.41±0.1 in theherbs.It is postulatedthatthesehighpercentagesoflipids,assuming thatsome are in the formof foodreservesas well as structuralmaterials, oftundraplantsreferred mayaccountfortheratherhighratesofrespiration to earlierand therapidratesofgrowthand development whentemperatures become favourablein the spring;an importantadaptationmechanismif substantiated work. by further In conclusion, thoughthetundrais characterized by havinga veryshort growingseason withlow air and soil temperatures, and thoughwind as it affectsthe air and planttemperatures is important togetherwiththe low utilizationlevel of nitrogen,tundraplants seem amazinglyefficient with This is in partdue to theutilizationof a large regardto energyconversion.


139


the use of portionof the growingseason for growthand development, reservesof the previousyear, and the higher considerablecarbohydrate caloric values of the species. The biomass productionof shoots ranging from1 to 3 gr./m.2/day duringthe growingseason is comparableto the of temperateregions.These points values foundin numerouscommunities earlierin thepaper,showthattundraplantsare quite and thosementioned in whichtheygrowand reproduce. well adaptedto theenvironments of net primaryproductionfor various ecosystemsbased on usable Table 4. Efficiency solar radiationduringgrowingseason. Plant material

Community

Typhamarsh-Minnesota* Zizania aquáticamarsh-Minn.* nutensold field-Minn.* Sorghastrum old field-Michiganf Poa compressa - Michiganf old field Poa compressa

Usable solar radiation gr.-cal.jm.2

Efficiency per cent

gr./m.2

cal.jgr.

1680 (shoots) 580 (shoots) 160 (shoots) 385 (shoots) 385 (shoots) 1023 (roots)

4,000 4,000 4,000 4,080 4,080 3,300

337 X 106 337 X 106 337 X 106 471 X 106

1.99 0.68 0.19 0.33

X 106

1.06

4,640 4,689 4,745

200.6 X 10e 200.6 X 106 200.6 X 106

0.18 0.25 0.49

4,764 4,743 4,802

200.6 X 106 200.6 X 106 200.6 X 106

0.19 0.19 0.48

471

Mt. Washington 1958 Juncus-dwarf shrubheathfellfield Juncus-dwarf shrubheathmeadow Carexmeadow

80 (shoots) 109 (shoots) 208 (shoots)

Juncus-dwarf shrubheathfellfield Juncus-dwarf shrubheathmeadow Carexmeadow * From Bray et al 1959. tFrom Golley 1960.

80 (shoots) 81 (shoots) 203 (shoots)

1959

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