38Microbialchangeinwarmingsoils

SCIENCEsciencemag.orgGRAPHIC:K.SUTLIFF/SCIENCEByDanielB.MetcalfeSoilsarethelargestsingleterrestrialsourceofcarbondioxide(CO2),buttheseemissionsarehighlysensitivetoarangeoffactorsassociatedwithclimatechangeandhumanlanduse(1).ResearchershavelongsoughttobetterunderstandtheunderlyingdriversofsoilCO2emissions,butthedurationofexperimentsisalltoooftenconstrainedbyprojectdeadlinesandpersonnelcontracts,hamperingourabilitytounderstandandpredictthemanygradualbutimportantprocessesthatoccurinsoils(2).Onpage101ofthisissue,Melilloetal.(3)reportonanintriguing26-yearrecordofsoilrespirationresponsestowarminginatemperateforest.Theresultsfromthisunusuallylongtimeserieshighlightboththepotentialpitfallsofdrawinghastyconclusionsfromshort-termstudiesandtheimportanceoflong-termexperimentsinecosystemandclimatescience.Shiftsintheterrestrialcarbonstore,ofwhichsoilsconstitutearound70%,areoneofthemostimportantbutleastunder-stooddriversofvariationinatmosphericCO2levels(4,5).Soilcarbonissensitivetoawiderangeoffactors,ofwhichtempera-tureisoneofthemostimportantfromaclimatechangeperspective(6).Generally,warmconditionspromotemicrobialactiv-ity.Globalwarmingwouldthereforebeex-pectedtoincreasemicrobialbreakdownoforganiccarbonandsubsequentreleaseasCO2,butdemonstratingthisconclusivelyhasproveddifficult.Severalapproacheshavebeenusedtoexaminepatternsin,andregulatorsof,soilcarboncycling.Multiplecontrolledexperi-mentshaverepeatedlyshownincreasingsoilrespirationunderwarmerconditions(6,7).Acomprehensiveglobalsynthesisofsoilrespirationmeasurementsfoundanincreaseassociatedwithrisingairtempera-turessincethe1960s,buttheexactmecha-nismslinkingtemperatureandsoilcarboncyclingremainunclear(8).Furthermore,itisnotwellknownhowmuchsoilcarbonisreadilyavailableformicrobialbreakdownversushowmuchislockedupinrecalci-trantmaterialandtowhatextentthiscouldshiftwithclimatechange(6,9).Melilloetal.makeimportantadvancesinaddressingthesegapswithoneofthemostdetailedpicturesyetoftheresponsesofsoilmicrobesandcarboncyclingovermorethantwodecadesofexperimentalwarming.Theirresultswillbeinvaluableinongoingeffortstobetterpredictandmitigatecarbonlossesfromsoilsthatfacerapidwarmingassociatedwithclimatechange.Theauthorscomparesoilrespirationinforestplotsheatedwithburiedcableswithsoilrespirationinuntouchedplots.Thein-sightsderivedfromthesemeasurementsareamplifiedbyrepeatingthesemeasurementsforsolong.Theauthorsalsodrawfromawiderangeofshorter-termpublishedex-perimentsfromthesamesitetoelucidatethemechanismsthatcontrolobservedshiftsinrespirationbetweenplotsandovertime.Overthe26-yearperiodoftheexperiment,theyobservedthreemultiyearphasesofsoilrespiration(seethefigure).Inthefirstphase,soilrespirationsteadilyde-creasedunderwarmedconditions.Thiswasfollowedbyasecondphasewherewarminginducedlittlechangeinrespiration,andthenathirdphaseofsteadilyrisingrespira-tion.Atthetimeofpublication,theexperi-mentisenteringafourthphasewheresoilrespirationisagaingraduallydeclining.Theauthorsconcludethatdecades-longwarmingstimulatesphasesofminimalwarming-inducedrespiration,correspond-ingtowidespreadsoilmicrobialcommu-ECOLOGYMicrobialchangeinwarmingsoilsLong-termreorganizationofmicrobialcommunitiesleadstopulsesincarbonrelease19912001200720122016Phase1Phase2Phase3Phase43000(gCO2–Cm–2year–1)ChangesinsoilCO2emissionsinheatedplotsrelativetocontrolplotsTemperature5°CaboveambienttemperatureCarbonformsinsoilLabileandrecalcitrantMicrobialtypesinsoilFungiandbacteriaMicrobialcarbonstarvationDeclineinlabilecarbon,microbialbiomass,andsoilrespirationImpoverishedmicrobialcommunityReorganizedmicrobialcommunityInitialconditionsatonsetofwarmingContinuedmicrobialshiftRiseinbreakdownofligninandsoilrespiration19912001200720122016Phase1Phase2Phase3Phase43000Cm–2year–1)sinsoilsionsplotsolotsatureoveientatureMicrobialcarbonstarvationDeclineinlabilecarbon,microbialbiomass,andsoilrespirationImpoverishedmicrobialcommunityReorganizedmicrobialcommunityInitialconditionsatonsetofwarmingContinuedmicrobialshiftRiseinbreakdownofligninandsoilrespirationDeclineinligninandsoilrespirationCCCCCCCCCCCCCCCCCCDepartmentofPhysicalGeographyandEcosystemScience,LundUniversity,Sölvegatan12,SE22362,Lund,Sweden,andDepartmentofEcologyandEnvironmentalScience,UmeåUniversity,Linnaeusväg6,SE90187,Umeå,Sweden.Email:[e-mail]6OCTOBER2017•VOL358ISSUE635941Long-termreorganizationofsoilmicrobialcommunitiesunderwarmingIna26-yearwarmingexperiment,carbondioxideemissionsfromheatedplotschangedwithtimeasmicrobialcommunitiesreorganized.DA_1006Perspectives.indd4110/4/179:51AMPublishedbyAAASonOctober5,2017|PERSPECTIVESsciencemag.orgSCIENCEIMMUNOLOGYNeutrophilstakearound-tripImagingshedslightonneutrophildynamicsinsterileinflammationByHannahGarnerandKarinE.deVisserInflammationisabody’sresponsetoharmfulstimulithataimstoelimi-natethetriggerthatcausedtheini-tialinjuryandenabletissuerepair.Inflammationcanbeeitherpathogen-associatedorsterile.Sterileinflamma-tioncanbetriggeredbyacuteconditions,suchastrauma,toxinexposure,andis