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Climate-relatedchangesofsoilcharacteristicsaffectbacterialcommunitycompositionandfunctionofhighaltitudeandlatitudelakesCARINAROFNER1,HANNESPETER1*,NURIACATALAN2,3,FABIANDREWES1†,RUBENSOMMARUGA1andMARIATERESAPEREZ11LakeandGlacierEcologyResearchGroup,InstituteofEcology,UniversityofInnsbruck,Technikerstraße25,Innsbruck,Austria,2Limnology,DepartmentofEcologyandGenetics,UniversityofUppsala,Uppsala,Sweden,3CatalanInstituteforWaterResearch(ICRA),EmiliGrahit101,Girona17003,SpainAbstractLakesathighaltitudeandlatitudearetypicallyunproductiveecosystemswhereexternalfactorsoutweightherelativeimportanceofin-lakeprocesses,makingthemidealsentinelsofclimatechange.Climatechangeisinducingupwardvegetationshiftsathighaltitudeandlatituderegionsthattranslateintochangesinthepoolsofsoilorganicmatter.Uponmobilization,thisallochthonousorganicmattermayrapidlyalterthecompositionandfunctionoflakebacterialcommunities.Here,weexperimentallysimulatethispotentialclimate-changeeffectbyexposingbacterio-planktonoftwolakeslocatedabovethetreeline,oneintheAlpsandoneinthesubarcticregion,tosoilorganicmatterfrombelowandabovethetreeline.Changesinbacterialcommunitycomposition,diversityandfunctionwerefol-lowedfor72h.Inthesubarcticlake,soilorganicmatterfrombelowthetreelinereducedbulkandtaxon-specificphosphorusuptake,indicatingthatbacterialphosphoruslimitationwasalleviatedcomparedtoorganicmatterfromabovethetreeline.Theseeffectswerelesspronouncedinthealpinelake,suggestingthatsoilproperties(phosphorusanddissolvedorganiccarbonavailability)andwatertemperaturefurthershapedthemagnitudeofresponse.Therapidbacterialsuccessionobservedinbothlakesindicatesthatcertaintaxadirectlybenefitedfromsoilsources.Accordingly,thesubstrateuptakeprofilesofinitiallyrarebacteria(copiotrophs)indicatedthattheyareoneofthemainactorscyclingsoil-derivedcarbonandphosphorus.Ourworksuggeststhatclimate-inducedchangesinsoilcharacteristicsaffectbacterioplanktoncommunitystructureandfunction,andinturn,thecyclingofcarbonandphosphorusinhighaltitudeandlatitudeaquaticecosystems.Keywords:allochthonousorganiccarbon,bacterialproduction,dissolvedorganicmatter,diversity,heterotrophic,phosphoruslimitation,terrestrialvegetation,treelineReceived26July2016;revisedversionreceived17October2016andaccepted25October2016IntroductionClimatechangealtersecosystempropertiesandtherebythreatensbiodiversityandecosystemfunctioning.Lakeecosystemsintegratechangesinthesurroundingland-scapeandatmosphere,actingassentinelsofclimatechange(Sommaruga-W€ograthetal.,1997;Carpenteretal.,2007;Phametal.,2008;Williamsonetal.,2008;Adrianetal.,2009).Severalphysicalpropertiesoflakestendtoresponddirectlytoclimaticforcing,suchaswatertemperatureandthedurationoficecover(Adrianetal.,2009;O’Reillyetal.,2015).Chemicallakecharacteristicsoftenintegratecatchmentprocessessuchasrockweatheringandterrestrialprimaryproductiv-ity.Ecosystemproperties,suchasprimaryandbacterialsecondaryproductivity,diversityoftaxa,andtaxaturnoverintegratebothphysicalandchemicalalter-ationsovertime(Wagner&Adrian,2009).Lakesathighaltitudeandlatitudeareparticularlyvulnerabletoclimatechange(Woodwardetal.,2010).Theseremoteecosystemsaretypicallysmall,olig-otrophic,andice-coveredforseveralmonths,amplify-ingthedirectandindirecteffectsofclimatechange(Grimmetal.,2013).Comparedtoanexpectedglobalmeansurfacetemperatureincreaseof1.0–3.7°Cuntiltheendofthe21stcentury,surfacetemperaturesinalpineandsubarcticregionsareexpectedtoincreaseby~3–6°C(Beniston,2005)and2.2–8.3°C(Collinsetal.,2013),respectively.Moreover,snowpackdura-tionisprojectedtodecrease(R€ais€anen&Eklund,*PresentaddressStreamBiofilmandEcosystemResearchLabora-tory,EcolePolytechniqueFederaledeLausanne(EPFL),Lausanne,Switzerland†PresentaddressARGELimnologie,AngewandteGew€asser€okologieGesmbH,Innsbruck,AustriaCorrespondence:CarinaRofner,tel.+4351250751720,fax+4351250757199,e-mail:carina.rofner@uibk.ac.atDNASequenceshavebeendepositedattheNCBISequenceReadArchiveunderaccessionnumber:SRP077041.2331©2016TheAuthors.GlobalChangeBiologyPublishedbyJohnWiley&SonsLtd.ThisisanopenaccessarticleunderthetermsoftheCreativeCommonsAttributionLicense,whichpermitsuse,distributionandreproductioninanymedium,providedtheoriginalworkisproperlycited.GlobalChangeBiology(2017)23,2331–2344,doi:10.1111/gcb.135452011;Stegeretal.,2012),whereasthefrequencyandmagnitudeofextremeprecipitationordroughteventswillincrease(Fischer&Knutti,2015).Finally,climatechangeinducesrangeexpansionsofmanyplantandanimaltaxaattheiraltitudinalandlatitudinalextremes(Grabherretal.,1994;Lenoiretal.,2008;Harschetal.,2009).Suchshiftsinlocalplantcoverandplantcommunitycomposition(Sturmetal.,2001;Parmesan&Yohe,2003;Hinzmanetal.,2005;Lenoiretal.,2008;Pearsonetal.,2013),andtheirconse-quencesonsoilorganicmattercontentandcomposi-tion(Reussetal.,2010;Classenetal.,2015),arewelldocumented.However,observationalandexperimen-talknowledgeontheeffectsofthetreelineshiftandtheconcomitantchangesinsoilchemicalcharacteris-ticsonlakeecosystemsathighaltitudeandlatituderegionsismissing.Heterotrophicbacteriaplayacen