67Soilmicrobiomeswithdistinctassembliesthrou

RESEARCHOpenAccessSoilmicrobiomeswithdistinctassembliesthroughverticalsoilprofilesdrivethecyclingofmultiplenutrientsinreforestedecosystemsShuoJiao1,2,WeiminChen1*,JieliWang1,NiniDu1,QiaopingLi1andGehongWei1*AbstractBackground:Soilmicrobiomesplayanimportantroleintheservicesandfunctioningofterrestrialecosystems.However,littleisknownoftheirverticalresponsestorestorationprocessandtheircontributionstosoilnutrientcyclinginthesubsurfaceprofiles.Here,weinvestigatedthecommunityassemblyofsoilbacteria,archaea,andfungialongvertical(i.e.,soildepthsof0–300cm)andhorizontal(i.e.,distancefromtreesof30–90cm)profilesinachronosequenceofreforestationsitesthatrepresentover30yearsofrestoration.Results:Inthesuperficiallayers(0–80cm),bacterialandfungaldiversitydecreased,whereasarchaealdiversityincreasedwithincreasingsoildepth.Asreforestationproceededovertime,theverticalspatialvariationinbacterialcommunitiesdecreased,whilethatinarchaealandfungalcommunitiesincreased.Verticaldistributionsofthesoilmicrobiomesweremorerelatedtothevariationinsoilproperties,whiletheirhorizontaldistributionsmaybedrivenbyagradienteffectofrootsextendingfromthetree.Bacterialandarchaealbeta-diversitywerestronglyrelatedtomulti-nutrientcyclinginthesoil,respectively,playingmajorrolesindeepandsuperficiallayers.Conclusions:Takentogether,theseresultsrevealanewperspectiveontheverticalandhorizontalspatialvariationinsoilmicrobiomesatthefinescaleofsingletrees.Distinctresponsepatternsunderpinnedthecontributionsofsoilbacteria,archaea,andfungiasafunctionofsubsurfacenutrientcyclingduringthereforestationofex-arableland.Keywords:Soilmicrobiome,Reforestation,Verticalspatialvariation,Multi-nutrientcyclingBackgroundWiththeirintensifiedusebyhumans,ecosystemsarefa-cingbiodiversitylossesandchangesintheirecosystemfunctioningandservices[1–5].Amongthemostseriousissuesisagriculturalintensification,whichisconsideredamajorthreattoglobalbiodiversity[6].Increasingcon-cernshavebeenraised,becauseagriculturalintensifica-tioncouldadverselyinfluencenaturalenvironmentsinmanyways,includinglarge-scalesoildegradation,lossofproductivity,increasedgreenhousegasemissions,accu-mulationofpesticides,anddiminishedavailabilityandqualityofwater[1,7].Reforestationofarablelandrepresentsoneofthemostwidelyusedrestorationstrat-egies,onethatcouldrestorenaturalecosystemfunction-ingandsoilproperties,butalsoinfluencebelowgroundmicrobialcommunitydynamics[8].Sincesoilmicroor-ganismsaremajorcomponentofterrestrialecosystems,itisoffundamentalimportancetodeterminethetem-poralchangesintheircommunitydynamics,aswellastheircontributionstosoilecologicalrestoration,duringthelong-termrestorationprocessofnaturalecosystems.Increasingattentionhasfocusedonthesignificanceofsoilmicrobiomeswithextremelycomplexdrivers,asacombinationofbacteria,archaea,andfungi[8,9].Soilmicrobiomesplayimportantrolesinecosystemfunc-tioning,suchasbyparticipatinginthebiogeochemicalcyclingofsoilnutrients[10,11];actingasdecomposers,mutualists,orpathogenstoinfluencethegrowthof*Correspondence:[e-mail];[e-mail]1StateKeyLaboratoryofCropStressBiologyinAridAreas,CollegeofLifeSciences,NorthwestA&FUniversity,Yangling712100,Shaanxi,People’sRepublicofChinaFulllistofauthorinformationisavailableattheendofthearticle©TheAuthor(s).2018OpenAccessThisarticleisdistributedunderthetermsoftheCreativeCommonsAttribution4.0InternationalLicense(),whichpermitsunrestricteduse,distribution,andreproductioninanymedium,providedyougiveappropriatecredittotheoriginalauthor(s)andthesource,providealinktotheCreativeCommonslicense,andindicateifchangesweremade.TheCreativeCommonsPublicDomainDedicationwaiver()appliestothedatamadeavailableinthisarticle,unlessotherwisestated.Jiaoetal.Microbiome(2018)6:146[12];andemittinggreenhousegasesthatmayaccelerateglobalclimatechange[13].Numer-ousstudieshavefocusedexclusivelyonthetop20cmofthesoilcolumnorless,inwhichthemicrobialbiomass,activity,anddiversityarethegreatest[14].Nevertheless,withitslargevolumethroughoutthedepthofthesoilprofile,thesubsurfacesoil(i.e.,deeperthan20cm)con-tainsnearly35%ofthetotalmicrobialbiomassandalsoharborsdiversemicrobes[15,16].Inparticular,thehugereservoirsofsubsurfacesoilmicrobiomescanplaypotentiallyimportantrolesinsoilformation,pollutantbiodegradation,andgroundwaterqualitymaintenance[14–17].Distinctmicrobialcommunitystructureshavebeenobservedbetweenthesurfaceandsubsurfacesoilsbecauseoftheirdifferentenvironments,forwhichmi-crobialdiversityvariedwithsoildepth[16–19].How-ever,thesestudiesfocusedonacertainmicrobialkingdom(i.e.,bacteriaorfungi)andthesoildepthhadarangeof0–100cm.Incontrast,littleisknownabouthowsubsurfacesoilmicrobiomesandpropertiesrespondtotherestorationprocessofnaturalecosystems,espe-ciallyinthedeepersoilprofiles(i.e.,100–300cm).Microbialdistributionshavebeenwellinvestigatedatglobal[10],continental[20],andregionalscales[21,22].Keyenvironmentalfactors,