55Spatialscaleaffectstherelativeroleofstoc

RESEARCHOpenAccessSpatialscaleaffectstherelativeroleofstochasticityversusdeterminisminsoilbacterialcommunitiesinwheatfieldsacrosstheNorthChinaPlainYuShi1†,YuntaoLi1†,XingjiaXiang1,RuiboSun1,TengYang1,DanHe1,KaopingZhang1,YingyingNi1,Yong-GuanZhu2,JonathanM.Adams3andHaiyanChu1*AbstractBackground:Therelativeimportanceofstochasticityversusdeterminisminsoilbacterialcommunitiesisunclear,asarethepossibleinfluencesthatalterthebalancebetweenthese.Here,weinvestigatedtheinfluenceofspatialscaleontherelativeroleofstochasticityanddeterminisminagriculturalmonoculturesconsistingonlyofwheat,therebyminimizingtheinfluenceofdifferencesinplantspeciescoverandincultivation/disturbanceregime,extendingacrossawiderangeofsoilsandclimatesoftheNorthChinaPlain(NCP).Wesampled243sitesacross1092kmandsequencedthe16SrRNAbacterialgeneusingMiSeq.Wehypothesizedthatdeterminismwouldplayarelativelystrongerroleatthebroadestscales,duetothestronginfluenceofclimateandsoildifferencesinselectingmanydistinctOTUsofbacteriaadaptedtothedifferentenvironments.Inordertotestthemoregeneralapplicabilityofthehypothesis,wealsocomparedwithanaturalecosystemontheTibetanPlateau.Results:Ourresultsrevealedthattherelativeimportanceofstochasticityvs.determinismdidvarywithspatialscale,inthedirectionpredicted.OntheNorthChinaPlain,stochasticityplayedadominantrolefrom150to900km(separationbetweenpairsofsites)anddeterminismdominatedatmorethan900km(broadscale).OntheTibetanPlateau,determinismplayedadominantrolefrom130to1200kmandstochasticitydominatedatlessthan130km.Amongtheidentifiabledeterministicfactors,soilpHshowedthestrongestinfluenceonsoilbacterialcommunitystructureanddiversityacrosstheNorthChinaPlain.Together,23.9%ofvariationinsoilmicrobialcommunitycompositioncouldbeexplained,withenvironmentalfactorsaccountingfor19.7%andspatialparameters4.1%.Conclusions:Ourfindingsrevealedthat(1)stochasticprocessesarerelativelymoreimportantontheNorthChinaPlain,whiledeterministicprocessesaremoreimportantontheTibetanPlateau;(2)soilpHwasthemajorfactorinshapingsoilbacterialcommunitystructureoftheNorthChinaPlain;and(3)mostvariationinsoilmicrobialcommunitycompositioncouldnotbeexplainedwithexistingenvironmentalandspatialfactors.Furtherstudiesareneededtodissecttheinfluenceofstochasticfactors(e.g.,mutationsorextinctions)onsoilmicrobialcommunitydistribution,whichmightmakeiteasiertopredictablymanipulatethemicrobialcommunitytoproducebetteryieldandsoilsustainabilityoutcomes.Keywords:Deterministic,Stochastic,Bacterialdiversity,βNTI,SoilpH,PCNM*Correspondence:[e-mail]†Equalcontributors1StateKeyLaboratoryofSoilandSustainableAgriculture,InstituteofSoilScience,ChineseAcademyofSciences,71EastBeijingRoad,Nanjing210008,ChinaFulllistofauthorinformationisavailableattheendofthearticle©TheAuthor(s).2018OpenAccessThisarticleisdistributedunderthetermsoftheCreativeCommonsAttribution4.0InternationalLicense(),whichpermitsunrestricteduse,distribution,andreproductioninanymedium,providedyougiveappropriatecredittotheoriginalauthor(s)andthesource,providealinktotheCreativeCommonslicense,andindicateifchangesweremade.TheCreativeCommonsPublicDomainDedicationwaiver()appliestothedatamadeavailableinthisarticle,unlessotherwisestated.Shietal.Microbiome(2018)6:27DOI10.1186/s40168-018-0409-4BackgroundSoilmicrobialdiversitypatternshavebeenwelldocu-mentedinawidevarietyofhabitats[1–3].Fromaninitialfocusonthedescriptionofpatterns,attentionisnowturn-ingtowardstheunderlyingprocessesinfluencingthestructureofmicrobialcommunities[4,5].Croplandsoilsrepresentarelativelyneglectedareaintermsofbothpat-ternsandprocessesinmicrobialcommunityecology.Des-pitetheimportanceofcroplandsoilsforglobalfoodsupply,therehasbeenrelativelylittleattentionpaidinun-derstandingwhatprocessesinfluencethestructureofmi-crobialdistributionpatterns[6–8].Understandingthestructuringofsoilcommunitiescouldhavepracticalimpli-cationsforcropproductivityandfoodproduction[9–11].Inattemptingtounderstandthefactorsgivingstruc-turetonaturalandagriculturalsoilmicrobialcommuni-ties,studieshaveemphasizedtwofundamentaltypesofprocess:(1)Deterministicprocesses,wherebyspeciesofbacteriaoccurwhereverthereisauniquepotentialnicheinwhichtheycansurviveinthefaceofcompetition[12].Inits“extreme”form,eachspeciesispredictablypresentwhereverasuitablenicheexists.Thishasbeensummarizedas“everythingiseverywhere,buttheenvir-onmentselects”[13].(2)Stochasticprocesses,wherebymanyspeciesexistinthesameorstronglyoverlappingniches,butdonoteliminateoneanotherduetotheircompetitiveabilitiesbeingcloselybalanced(inaccord-ancewithneutraltheory[14]).Inthissituation,therela-tiveabundanceofspeciesdriftswithchancefluctuationsinpopulations.Stochasticprocessesalsoincludetheleg-acyofpastdisturbanceeventscausingmoredramaticnonselectivecrashesinpopulations,followedbytheva-gariesofdispersaleventsleadingtospeciesarrivingun-predictably.Inanextremestochasticscenario,bacterialspeciesareoftenabsentfromplacesinwhichtheycouldpotentiallysurviv