20Droughtconsistentlyaltersthecompositionof

AcceptedArticleThisarticlehasbeenacceptedforpublicationandundergonefullpeerreviewbuthasnotbeenthroughthecopyediting,typesetting,paginationandproofreadingprocess,whichmayleadtodifferencesbetweenthisversionandtheVersionofRecord.Pleasecitethisarticleasdoi:10.1111/gcb.14113Thisarticleisprotectedbycopyright.Allrightsreserved.DR.RAULOCHOAHUESO(OrcidID:0000-0002-1839-6926)DR.MANUELDELGADO-BAQUERIZO(OrcidID:0000-0002-6499-576X)Articletype:PrimaryResearchArticlesDroughtconsistentlyaltersthecompositionofsoilfungalandbacterialcommunitiesingrasslandsfromtwocontinentsRunninghead:ConsistentdroughteffectsonsoilmicrobesRaúlOchoa-Hueso1,2*,ScottL.Collins3,ManuelDelgado-Baquerizo4,KellyHamonts1,WilliamT.Pockman3,RobertL.Sinsabaugh3,MelindaD.Smith5,AlanK.Knapp5,SallyA.Power11HawkesburyInstitutefortheEnvironment,WesternSydneyUniversity,LockedBag1797,Penrith,NewSouthWales,2751,Australia.2AutonomousUniversityofMadrid,DepartmentofEcology,2DarwinStreet,Madrid,28049,Spain.3DepartmentofBiology,UniversityofNewMexico,Albuquerque,NM87131,USA.4CooperativeInstituteforResearchinEnvironmentalSciences,UniversityofColorado,Boulder,CO80309,USA.5DepartmentofBiologyandGraduateDegreePrograminEcology,ColoradoStateUniversity,FortCollins,Colorado,80523,USA*Correspondingauthor:[e-mail]:[phone]AcceptedArticleThisarticleisprotectedbycopyright.Allrightsreserved.Keywords:Drought;Enzymeactivities;Microbialcommunity;Rainfallmanipulation;Soil-bornepathogensPapertype:PrimaryresearcharticleABSTRACTTheeffectsofshort-termdroughtonsoilmicrobialcommunitiesremainlargelyunexplored,particularlyatlargescalesandunderfieldconditions.Weusedsevenexperimentalsitesfromtwocontinents(NorthAmericaandAustralia)toevaluatetheimpactsofimposedextremedroughtontheabundance,communitycomposition,richnessandfunctionofsoilbacterialandfungalcommunities.Thesitesencompasseddifferentgrasslandecosystemsspanningawiderangeofclimaticandsoilproperties.Droughtsignificantlyalteredthecommunitycompositionofsoilbacteriaand,toalesserextent,fungiingrasslandsfromtwocontinents.Themagnitudeofthefungalcommunitychangewasdirectlyproportionaltotheprecipitationgradient.Thisgreaterfungalsensitivitytodroughtatmoremesicsitescontrastswiththegenerallyobservedpatternofgreaterdroughtsensitivityofplantcommunitiesinmorearidgrasslands,suggestingthatplantandmicrobialcommunitiesmayresponddifferentlyalongprecipitationgradients.Actinobateria,andChloroflexi,bacterialphylatypicallydominantindryenvironments,increasedtheirrelativeabundanceinresponsetodrought,whereasGlomeromycetes,afungalclassregardedaswidelysymbiotic,decreasedinrelativeabundance.TheresponseofChlamydiaeandTenericutes,twophylaofmostlypathogenicspecies,decreasedandincreasedalongtheprecipitationgradient,respectively.Soilenzymeactivityconsistentlyincreasedunderdrought,aresponsethatwasattributedtodrought-inducedchangesinmicrobialcommunitystructureratherthantochangesinabundanceanddiversity.OurresultsprovideevidencethatdroughthasawidespreadeffectontheassemblyAcceptedArticleThisarticleisprotectedbycopyright.Allrightsreserved.ofmicrobialcommunities,oneofthemajordriversofsoilfunctioninterrestrialecosystems.Suchresponsesmayhaveimportantimplicationsfortheprovisionofkeyecosystemservices,includingnutrientcycling,andmayresultintheweakeningofplant-microbialinteractionsandagreaterincidenceofcertainsoil-bornediseases.Keywords:Drought;Enzymeactivities;Microbialcommunity;Rainfallmanipulation;Soil-bornepathogens.INTRODUCTIONMicroorganismsplayfundamentalrolesasprimaryproducersanddecomposersandprovideimportantecosystemservicessuchasorganicmatterdecompositionandnutrientcyclingandstorage(vanderHeijdenetal.,2008;Bardgett&vanderPutten,2014).Thestructureandactivityofmicrobialcommunitiesinsoilsisinfluencedbysubstrateproperties,particularlysoilpHandorganicmattercontent,andvegetationtype(Fierer&Jackson,2006;Delgado-Baquerizoetal.,2016a);atlargerspatialandtemporalscaleslong-termclimaticphenomenasuchasincreasingaridityhavealsobeenassociatedwithlowerbacterialandfungalabundanceandlowermicrobialdiversity(Maestreetal.,2015).However,muchlessisknownabouthowshort-termclimaticprocesses,includingthemoreextremedroughteventsforecast(Cooketal.,2015),willaffectmicrobialcommunitiesandtheecosystemservicestheymediate.Climatemodelsforecastwidespreadchangesinprecipitationregimes,includinglonger,moreintensedroughts(McLaughlin,2014),causingdesertificationandpromotingtheexpansionofdrylandsglobally(Huangetal.,2016).Field-basedclimatechangestudieshavetraditionallyfocusedonabovegroundresponses(e.g.,plantproductivity,biomassandcommunitycomposition)oflocalstudies,whereasbelowgroundresponses,particularlythoseAcceptedArticleThisarticleisprotectedbycopyright.Allrightsreserved.ofmicrobialcommunities,havereceivedmuchlessattention(Wilcoxetal.,2015,2017).Experimentalapproachesacrossmultiplesitesandcontinents,wherecontrastingclimaticandedaphicconditionsmaymediatetheimpactsofchangingprecipitationregimes,areequallyneededtoaccuratelypredicttheresponseofmicrobialcommunitiestoextremedrought(Grimeetal.,