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Communities of mites (Acari) in litter and soil under the invasive red oak (Quercus rubra L.) and native pedunculate oak (Q. robur L.)

Communities of mites (Acari) in litter and soil under the invasive red oak (Quercus rubra L.) and... Because of thoughtless decisions or unintentional introduction, alien species disturb native ecosystems.redoak(Quercus rubra),amongotheralienwoodyplants,isstillusedtorehabilitatedegradedlandbecauseofitsbetterresistancetopollutionandfastergrowth,ascomparedtonativetree species.Soilmites,especiallyoribatida,aregoodbioindicatorsofecosystemdisturbance,sothemain goalofthisstudywastoexploretheinfluenceofinvasiveandnativeoaksonmitecommunities.forest standsdominatedby40-year-oldQ. rubraor35-year-oldQ. roburwerecompared.over2300soilmites wereextractedfrom20soiland20littersamples.mitedensitiesinthecommunitieswerehigherinred oaklitter,whichisprobablyaresultofthethickerlayerofshedleaves.changesinspeciescomposition oforibatidcommunitieswereobservedinlitter,incontrasttoalackofdifferencesinsoil.Theseobservationsareconsistentwithotherresearchesoninvasivewoodyplants.weexpectthatovertimethese changes will also be noticeable in the soil and will increase in litter. Keywords: invasivespecies,woodyplant,Quercus rubra,Quercus robur, soilmites,oribatida inTroducTion Somealienintroducedplantspeciesexpandtheirrangeveryquickly,threatening biodiversity,sotheyareclassifiedasinvasiveplants.Theproblemofinvasivespeciesisalarming,astheprocessofinvasionisirrevocableandcanleadtocatastrophic results (gniazdowska2005).invasivealienspeciesareregardedtodayasthegreatest threat to the biodiversity and stability of ecosystems (soLarz2007). redoak(Quercus rubra) was introduced to Poland in the 19th century from North America.itstillisandwasusedinthepastforafforestationofareasdestroyedby humanactivity,forplantingasanornamentaltreeinparks,inforestsasanadmixture, andforestablishingshelterbelts.Thechoiceofredoakisusuallyjustifiedbyitsrapid growthandgoodqualityofwoodincomparisontothenativeoaks(gazda2003). otherrelevanteconomiccharacteristicsofredoakincludeitsmodestenvironmental requirements, resistance to pollution (kaTzur & hauBoLd-rosara 1996), and aestheticvalue(beautifulredleavesinautumn).currentobservationsshowthatredoak seedlings are able to eliminate other plants by creating dense patches in the undergrowth. nowadays,surveysonplantinvasivenessarefocusedondisturbancesincirculation of water and nutrients (crooks2002;ehrenFeLd2003;ashTonetal.2005), reaction of microorganisms (level of soil enzymes) (kourTev et al. 2002; Lankau 2010),productionofallelopathiccompounds(gniazdowska2008;ensetal.2009; canToretal.2011),rateofexpansionandimpactonplantcommunities(chmura & sierka2006;Tokarska-guzik etal.2006),andevenmathematicalmodellingaiming to predict invasiveness (kivánek & Pysek2006).nevertheless,theimpactof invasive species on the abundance and composition of invertebrates is rarely studied (gerBeretal.2008). mitesinhabitingthesoilareanimportantpartoftheecosystem,playingacrucial role in organic matter decomposition and nutrient cycling. Participation of Oribatida inthetotalnumberofsoilmitesrangesfrom60%to90%.Theyareapivotalelement in the detritus food chain (LeBrun1979)andcanbeusedasindicatorsofchanges in the environment (e.g. niedBala1983).usingthemasbioindicatorsprovidesan opportunity to replenish information about the state of the soil based on plant and chemicalindicators.itisstillunclearwhatcausesthealienplantstobecomeinvasive, so monitoring of organisms performing a vital role in maintaining ecosystem balance is required. untilnow,inPoland,onlyskuBala & mierny(2009)havetestedthecondition of soil mites under Fallopia sachalinensis (Reynoutria sachalinensis), one of the mostdangerousinvasivealienspecies.Theresultshaveconfirmedtheassumption thatthewayitoccupiesaterrain,i.e.virtuallycompletedisplacementoftheexistent flora,coincideswithadeclineinbiodiversityofsoilmitecommunities,especiallyof thegroupsthatfeedondiversesubstrates:thesaprophagousoribatidaandAstigmata. Simplificationoftheenvironmentresultsinagreaterproportionofpredatorymites (mesostigmata, Prostigmata) within the mite communities. Stopping the spread of plantinvadersisaseriousproblem,particularlyinenvironmentsmodifiedbyhumans (e.g. maureLetal.2010).Amajorthreatposedbyredoakisitscompetitionwiththe nativespecies,i.e.aneffectsimilartothatofFallopia spp. inthisstudyweinvestigatedtheproblemofinvasivewoodyplantsatthestage ofyoungtrees(35­40yearsold),whichwouldbehelpfulinplanningasecondpart oftheexperimentondevelopmentofinvasivenessbyincludingolderageclassesof foreststands.wetestedwhetherredoak­aninvasiveplantinPoland­affectsthe biodiversity of native soil mesofauna in less fertile soils. Our goal was to answer the followingquestions: 1.isthedensityofvarioussoilmitegroupslowerinthesoilandlitterunderthe invasiveredoak,comparedwiththenativepedunculateoak(Quercus robur L.)? 2.isthesoilandlitterunderredoakdominatedbydifferentoribatidspeciesthan thesoilandlitterunderthenativeoak? 3.isthespeciesrichnessandspeciesdiversityoforibatidcommunitiesinsoil andlitterunderredoaklowerthaninunderthenativeoak? mATeriALAndmeThodS A40-year-oldstandwithpredominanceofQuercus rubra(90%)anda35-yearold stand with predominance of Q. robur(70%)werecompared,bothlocatedsoutheast of rybnik (southern Poland, upper Silesia). geographical coordinates of the selectedareasare50°03'58"n, 18°34'09"eand 50°03'55"n,18°34'24"e,respectively.Toeliminatetheinfluenceofsomeotherfactors,resultingfromgeographical differences(likelytoaffecttheanalysis),weselectedforeststandsthatareonly295m apart,bothonpooracidbrownsoilaccordingtodatafromtheBureauofforestmanagementandgeodesyincracow(BuLigL).Suchachoicewasdictatedbydifferent reactions of soil mites to soil parameters (e.g. nieLsenetal.2008)andtheobservation made by nicoLini & ToPP(2005),whodiscoveredthatnutrientuptakebyredoakon highlyfertilesoilhadalesssignificantnegativeimpactonthepoolofnutrientsfor soilmicroorganismsandmitesthaninasoildeficientinnutrients. on24April2010,wetookrandomly10soiland10littersamplesfromeach foreststandwithinarandomlyselectedsquareplot(10m×10m).Thesampleswere collectedusingasteelcylinderof137cm3involumeand7.5cminheight.Thefallen leavesandhumuswereregardedasthelitterlayer.itshouldbenotedthatthislayer was1­3cmthick.onaverage,litterunderredoakwasthickerthanunderpedunculateoak.Thesamplesofsoilandlitterwereseparatedinthefield,thentransportedto thelaboratory,andplacedintheTullgrenapparatus.extractedmaterialwasdivided into4miteorders:oribatida,Prostigmata,Astigmata,andmesostigmata.onlyadult oribatida were determined to the species level. in total, 2307 specimens ofAcari werecollected,including1024oribatidmitesof52species.ThelistoforibatidspeciesrecordedattheforeststandsisgiveninAppendixi.Taxonomicnomenclature follows suBías(2004). Analyses of mite communities were based on density of mites of each order (mean number of individuals per 1 m2),separatelyforthesoilandlitter.Toassess thesignificanceofdifferencesinmitedensitybetweentheforeststands,thekruskalwallistestwasused.Toassessthesignificanceofdifferencesinmitedensitybetween allpairsofsites,themultiplecomparisontestwasdone.Theuseofnonparametric testswasdictatedbytheheavilyskewedmitedensitydistributionsintheexamined sites and the fact that attempts to transform the data to normal distribution did not givetheexpectedresults.Torecognizethepotentialinfluenceofoakstandsonoribatidspeciescommunities,thespeciesrichness,evenness,anddiversityindiceswere calculated.Theexpectedtotalspeciesrichnessinthestudiedstandswasestimated usingnon-parametric,incidence-basedestimators:1storderjackknifeand2nd order jackknife.estimatorswerecomputedusingSpeciesdiversityandrichnessivsoftware.inordertocomparethespeciescompositionofcommunitiesfoundindifferent habitats,clusteranalysiswasconducted(basedoneuclideandistances).correspondence analysis was performed to evaluate relationships between species density and habitat.StatisticalanalyseswerecarriedoutusingSTATiSTicA10.0software. Table1.meandensityofmites(individuals/m2 ± standard error) in soil and litter under Quercus rubra and Q. robur,andsignificanceofdifferences betweenthehabitats(kruskal-wallistest,N = 40) Quercus rubra soil 19500±3786.5 b 4444±1250.5b 23944±156.8b 6277±2281.7 8000±1500.3b 19333±13941.3b 1333±683.93a 444±231.3a 1722±520.2 16611 ± 1931.3 ab 12888±3335.8a 1722±441.7 2166±425.9ab 3166±1203.1ab 1555±528.9a 1888±469.9 ab 15055±3462.0 ab 11000±1662.1a 10.562 11.795 11.546 5.483 23.474 17.080 litter soil litter 0.014 0.008 0.009 0.139 <0.001 0.001 Quercus robur H p groupofmites Oribatida adults 11333±7837.6 a oribatidajuveniles 1666±1123.4a Oribatida total 1111±414.1 13000±4807.3 a mesostigmata Prostigmata 166±84.9a 1388±937.8a Astigmata Boldvaluesdenotesignificantdifferencesindensity(P<0.05).differentlettersdenotesignificantdifferencesbetweenhabitats,basedonamultiple comparison test. reSuLTS Statisticallysignificantdifferenceswereobservedinmeandensityofmites(individuals/m2) in the soil and litter under Quercus rubra and Q. robur with regard to mostmitegroups.Asregardsoribatidmites,theirdensityinredoaklitterwassignificantlyhigherthaninlitterunderthenativeoak.Thedensityoforibatidainthesoil inbothforeststandswasmuchlower.nostatisticallysignificantdifferencesinthis parameterbetweenforeststandswereobserved,butthenumbersoforibatidsinthe soil under Q. rubra were generally lower than in the soil under Q. robur. Numbers of prostigmatid and astigmatid mites in Q. rubra litter were also higher than in litter of thenativeoakandinbothcasesmuchhigherthaninsoillayers.Althoughdifferences indensitiesofmesostigmatawerenotsignificant,thepatternwassimilarasforthe abovegroupsofmites.highernumbersofmesostigmatidmiteswerenotedinthelitterunderredoakthanunderthenativespecies,andnumbersofthesemitesinthesoil under Q. rubra were lower than in the soil under Q. robur(Table1). Speciesrichness,diversity,andevennessindicesofcommunitiesweresimilar within the habitats (litter or soil) but differences between tree species were observed. numbersoforibatidspeciesinthelitterweregenerallyhigherthaninthesoil.furthermore,speciesdiversityandevennessindiceswerehigherinthelitterunderboth oaksthaninthesoil(Table2).Theestimatedtheoreticalnumberofspeciesinstudied sites was slightly higher (e.g. in litter under Q. rubra)orsignificantlyhigher(e.g. soil under Q. rubra)thanthenumberofobservedspecies.Theestimateswerehigher when2ndorderjackknifewasused(insteadof1storderjackknife)andrangedthen from37.6(litterunderQ. rubra)to56.0(litterunderQ. robur)(Table2).TheinTable2.observedandestimatedspeciesrichnessanddiversityoforibatidmitecommunitiesinthe soil and litter under Quercus rubra and Q. robur Parameter Quercus rubra soil Average number of species Totalnumberofspecies Shannonindex(H') evennessindex(J) jackknife1 order st Quercus robur soil 7.81 20 1.844 0.616 30.8±2.6 (54.0) 40.4 (122.0) litter 12.63 30 2.548 0.749 45.3±6.1 (51.0) 56.0 (86.6) litter 13.75 36 2.725 0.760 7.36 18 1.613 0.558 28.8±5.6 (60.0) 37.6 (108.8) 45.9±5.1 (27.5) 46.8 (30.0) jackknife2 order nd valuesaremeanestimates(±standarddeviation) Percentage increase in relation to the observed species numbers is given in parentheses creaseinrelationtothenumberofcollectedspeciesvariedbetween30%(litterunder Q. rubra)toover100%(soilunderQ. robur and Q. rubra)(Table2). clusteranalysisoforibatidcommunitiesshowssimilaritieswithintheanalysed soilorlitterlayeranddifferencesbetweenthem(fig.1).Thespeciescompositionof fig.1.dendrogramfor4comparedhabitats,basedonunweightedPairgroupmethodwithArithmeticmean(uPgmA)andeuclideandistancecoefficients oribatid communities in soil is much more similar than the species composition of oribatidfaunainlitterunderoaks. incorrespondenceanalysis,evaluatingrelationshipsbetweenspeciesdensityand habitat(fig.2),eigenvalueswerehighforaxis1(1=0.28)andaxis2(2=0.27). over92%ofthevariancewasexplainedbythefirst2axes.resultsoftheanalysis confirm the lack of valid differences in soil mite communities between the forest stands.ThedominantspeciesinthesoilinbothforeststandswasMicroppia minus minus (Paoli, 1908). it is a eurytopic (weigmann 2006) and cosmopolitan (suBías 2004)fungivorousgrazer(zaiTsevetal.2002),consideredasparthenogenetic(ciancioLo & norTon2006). Bycontrast,oribatidcommunitiesoflitterlayersofthe2comparedforeststands differsignificantly.ThehabitatofQ. rubra litter and the associated species are lo- fig.2.correspondenceanalysisbiplotshowingpositionsof52oribatidspeciesand4compared habitats.dominantspecies:chvoi=Chamobates (Xiphobates) voigtsi,Lfal=Lauroppia falcata falcata, mmin = Microppia minus minus, onov = Oppiella (O.) nova nova, rsub = Rhinoppia subpectinata,Sacu=Suctobelbella (S.) acutidens acutidens,Spal=Scheloribates (S.) pallidulus pallidulus,Ssub=Suctobelbella (S.) subcornigera subcornigera catedalongthepositivevaluesofaxis2,whereastheindexoftheQ. robur litter and associatedspeciesaresituatedalongthenegativepartofaxis2(fig.2). Twodominantspeciesweretypicalforredoaklitter.Scheloribates (S.) pallidulus pallidulus (koch,1841)isknownasaforestspecies (weigmann 2006) of broad cosmopolitandistribution,excludingAntarctica(suBías2004).Becauseofitsfeedingpreferencesithasbeenrecentlyspecifiedasaherbo-fungivorousgrazer(maLak 2010),whichconfirmsanearlieropiniononthespeciesassecondarydecomposer feeding mainly on fungi (schneideretal.2004).Theseconddominantspecies,Suctobelbella (S.) subcornigera subcornigera (forsslund,1941),isknownfromdifferent forestsoils,butisalsorecordedatruderalsites(weigmann 2006).itisaneurytopic species (weigmann 2006)ofholarcticdistributionextendingtotheorientandnew Zealand (suBías2004).Thespeciesisafungivorousbrowser(zaiTsevetal.2002), reproducing parthenogenetically (ciancioLo & norTon2006). Chamobates (Xiphobates) voigtsi (oudemans, 1902) and Rhinoppia subpec- tinata (oudemans, 1900) were characteristic for the litter layer under the native Q. robur.Theformerspecies,connectedwithacidforestsoils(weigmann 2006), is Palaearctic (suBías2004),regardedasaherbo-fungivorousgrazer(maLak2010). Thelatterspecies,R. subpectinata,iseurytopic(weigmann 2006), withaholarctic rangeexcludingtheeasternpartoforient(suBías2004).itisalsoincludedinthe feeding guild of fungivorous grazers (zaiTsevetal.2002). Several dominant species were not associated with any of the studied habitats. Oppiella (O.) nova nova (oudemans, 1902) is one of the most widely distributed oribatidsintheworld,occurringinvarioushabitats(suBías2004;weigmann 2006). itisknownasafungivorousgrazer(zaiTsevetal.2002)andcharacterizedbyparthenogenetic mode of reproduction (ciancioLo & norTon 2006). Suctobelbella (S.) acutidens acutidens (forsslund, 1941) is mainly known from acid soil forests (weigmann 2006). it is a fungivorous browser (zaiTsev et al. 2002), reproducing parthenogenetically (ciancioLo & norTon2006).Lauroppia falcata falcata (Paoli, 1908)isobservedindeciduouseuropeanforests(weigmann 2006).itbelongstothe feeding guild of omnivores (schneideretal.2004). diScuSSion inPoland,Article120,point1ofthenatureProtectionActof16April2004 (journalofLaws[dz.u.]no.92,item880)prohibitsintroductionofalienspecies ofplantsintothenaturalenvironment.however,thenationalforestholding"State forests"(PgLLP)allowstheintroductionofredoakanditsuseasanadditionalspeciesinestablishingofshelterbelts,basedonthe"Principlesofsilviculture".redoak soilrequirementsarelowerthanthoseofnativeoaks.Thistreespeciesisresistantto frostandindustrialpollution,thusrecommendedforpost-industriallandrestoration. itisstillrecommendedalsoforurbanplantingbecauseofitsdecorativevalue,also used as roadside trees (Bodyl2011).Amongforestersthereisaconvictionthatadditional alien species in unprotected forest are not harmful and should remain in place. Some foresters believe that to increase biodiversity it may sometimes be desirable to supplement reforestation and afforestation with alien species (BogaTko2010),which has no support from environmentalists. consideringtheproblemofinvasivewoodyplantspecies,gazda (2003)suggestedweshouldaskthequestion:whatpredisposesaspeciestobecomeinvasive? kowarik(1995)emphasizesthespecificityofinvasivewoodyplants,payingattentiontoalongerperiodoftheirdevelopment.inBrandenburg,theaveragetimefrom introduction of a species to its transition into an invasive species was 131 years for shrubs and 170 for trees, of which for the black cherry (Prunus serotina ehrh.) a minimum duration of 29 years was reported, and for walnut (Juglans regia L.), a maximumtimeof374years(kowarik1995). redoakwasbroughtintoPolandinthe19thcentury,whichmeansthattheperiod from the first introduction is about 100­200 years. how its invasiveness has developed?itshouldbenotedthatreichetal.(2005)observedwidespreadandrapid(within threedecades)changesinsoilsunderdifferenttreespeciesinanexperimentconducted inPoland.Thoseauthorsstudied14species,includingQuercus robur and Q. rubra,and observedthattreespeciesaffectedsoilsbothdirectly,throughthechemistryoftheirlitter,andindirectly,throughtheeffectoftheirlitterondetritivores(e.g.earthworms). resultsofthisstudysuggestthatthechangesinsoilmitecommunitiesin35-40year-oldforeststandsofinvasiveandnativeoakarenotremarkable.Theobserved influenceoftheinvasiveredoakonmitecommunitieswasweakerthanthatobserved by skuBala & mierny(2009)withregardtotheaggressiveplantinvaderReynoutria sachalinensis.withinstandsinvestigatedbyus,significantlyhigherdensitiesoforibatid,prostigmatid,andastigmatidmiteswereassociatedwithredoaklitter.Thisis probablyaresultofitsthickerlayer,whichcreatesmoremicrohabitatstobeoccupied. reichetal.(2005)foundthatthelitterproductionofredoakisovertwiceashighas thatofnativeoaks.Bycontrast,nosignificantdifferencesindensityofthesemites wereobservedinthesoil,butmeannumbersoforibatidandastigmatidmitesinthe soilundertheinvasiveoakwerelowerthanunderthenativeoak.formesostigmata, nosignificantdifferencesbetweentheinvestigatedhabitatswereobserved,although the same pattern of relationships was found. As regards the species composition of oribatid communities under the invasive andnativeoak,alackofimportantdifferenceswasnoticed.Someremarkabledifferencesinspeciescompositionwerefoundonlyinthelitterlayer.however,despite differences in composition of oribatid communities in the litter under invasive and nativeoak,theecologicalfunctionofdominantspeciesdidnotdiffer.inthelitterunder Q. rubra, one of the dominant species was Scheloribates pallidulus. Chamobates voigtsi reached high numbers in the litter under Q. robur.Bothspeciesareknownas occurringinforestsandbelongtothesamefeedingguild:herbo-fungivorousgrazers. Suctobelbella subcornigerawasanotherdominantspeciesintheredoaklitter, whereas Rhinoppia subpectinata dominatesinthelitterunderthenativeoak.Both mite species occur in a broad range of habitats (eurytopic) and feed on similar substrates. S. subcornigeraisafungivorousbrowser,whereasR. subpectinata is a fungivorous grazer. itshouldbeemphasizedthatdespitehigherdensitiesoforibatidmitesinthelitterunderredoak,noremarkabledifferencesinmitespeciesrichnessanddiversity wereobservedbetweenlitterofbothoaks.Speciesrichnessoforibatidmitesinthe soilwasmuchlowerthaninthelitterunderbothoaks.however,itwasmoreunderestimatedincomparisonwithspeciesrichnessinthelitterlayer.itcanbeconcluded that changes in species composition of oribatid communities under invasive and nativeoaksproceedslowly.Thechangesinoribatidcommunitiesstartfromthelitter layer,becauseofitsspecificity.oribatidmitesfeedonhyphaeandsporesoffungi, decayingorganicmatter,andplantdebrisovergrown(predecomposed)bymycelium (maraunetal.2003).Themainsourceofthisfeedingmaterialisfoundinthelitter layer.Alldominantoribatidspeciesinthelitterlayerwerefungivores,whichproves thatfungidevelopedquitewellinlitterundernativeaswellasinvasiveoak.Thus, one of the most popular hypotheses of fungicidal effect of invaders (gniazdowska 2008)isnotcredibleatthisstageofoakstanddevelopment. ourresultssuggestdifferentconclusionsthanthoseobtainedinanexperiment conducted by nicoLini & ToPP(2005),concerningtheuseofredoakinrestoration of lignite opencast mines.They compared forest stands of red and native oak (Q. petraea)atthesameage(18years),plantedonsoilsofdifferentfertility.Thoseauthors found that red oak, because of its proprieties associated with environmental requirements,hasanegativeeffectonthedensityofsoilmesofaunainthepoorsoil (oribatidaandcollembola).Theysuggestedanexplanationthatwhenafast-growing tree,likeredoak,isplantedonapoorsoil,nutrientdepletioninsoilismuchquicker, as compared to slow-growing tree species.The depletion is due to increasing immobilization of nutrients in woody biomass of fast-growing trees and also increasing recalcitranceofitsorganicmatter.Allthishasasignificantimpactonreducingthe poolofnutrientsforsoilmicroorganismsandmites.Themechanismwouldnothave suchconsequencesinfertilesoils.Thismeansthatthoseauthorsobservednegative effectsmuchquickerthanwedidbecauseofinitialimpoverishmentofthesoil,which wouldbegreaterinaligniteopencastmineinrhineland.Themanagedforeststands studiedbyusweresituatedinthevicinityofacoalmineandurbanareaofrybnik, butthesoilwasnotmixedordepositedfromotherplacesasitwasinthecaseof restored land of the lignite mine. weconsideredabovetheageaspectofwoodyplantinvasiveness.Asecondimportant question posed by gazda(2003)is:whatmakestheenvironmentvulnerable to the invasion? vauramo & seTäLä(2010)paidattentiontothechoiceofplantsused inurbanareas.Thoseauthorsshowedthegreatpotentialofplantspeciesthatthey dividedintosomefunctionaltypes.Allthedistinguishedtypesarelikelytoalterthe soilorganismcommunitiesand,consequently,thedynamicsofnutrientsindisturbed soil(e.g.inthecity).Thussomeotherquestionarise.Arethedisturbancesincirculation of nutrients a direct consequence of the invasion of alien plants or they result from disturbance of the functioning of the soil animal communities, their biology andecology,ortheydependonavarietyofcoexistingfactors?Aninterestingpaper was presented by simBerLoFF & von hoLLe (1999)whoworkedontheproblemof enhanced susceptibility to further invasions of the areas already invaded (by another invasivealienspecies).Thoseauthorsgivemanyexamplesshowingthecomplexity ofthephenomenon,fromthestandpointoftheinvaderandofendemiclandwithits floraandfauna.Theyemphasizethatthecharacteristicsofalienorganismscannotbe definedingeneralbutinrelationtoaparticularsituation.consequently,reich et al. (2005)highlightthefactthatvegetation,soilorganisms,andsoilchemistryshould beviewedasco-developingcomponentsofterrestrialecosystems,evenondecadal scales.Thisalsoleadstoaconclusionaboutthenecessitytoincorporatedetailedsoil analysesinourresearchandcontinueobservationsinolderforeststands,whichis planned. As postulated by crooks(2002),thereisaneedforresearchinwhichthesites colonizedbyinvasiveplantsarecomparedwithnatural,undisturbedsites,toexamine comprehensivelytheimpactofspecificinvadersinthegivenconditionsonthenative environment. Our study area is situated within managed forests but still we can observedifferencesbetweentheforeststands,startingfromthelitterlevel.Thereis aneedtocontinuethesesurveysinthecontextofcollectingknowledgeonmechanismsoftheimpactofredoakasaninvasivewoodyplantinPolishconditions.our data will help to plan other experimentsthatwouldhelptodevelopmethodsforcontrollingtheexpansionofparticularinvasivealienspeciesincertainconditions.The resultspresentedarepartofalargerresearchprojecttakingintoaccountforeststands in the same area (Silesia) but with longer impact on the ecosystem. concLuSionS Thedensityofallgroupsofmitesand(toasmallerextent)theirspeciesrichness werehigherintheforeststanddominatedbytheinvasiveoakthaninthenativeoak forest.Twofactsmayexplaintheobservedrelationship.ingeneral,thelitterlayeris occupiedbyhighernumbersoforibatidmitesthanthesoillayer,whilelitterproductionofredoakishigherthanthatofnativeoak. morespecimensandspeciesoforibatidawereobservedinthelitteroftheinvasiveoakthaninthatofthenativeoak.Anoppositesituationwasobservedwith regardtothesoillayer,butthedifferenceswerenotremarkable.Theprobablereason forthisphenomenonisashorttimeoftheimpactoftheinvader.Threetofourdecadesappeartohavenosignificantimpactonthesoillayer. The species compositionof oribatidcommunities in the soil layer under both speciesofoaksissimilar,whereastheoribatidfaunainthelitterunderinvasiveand nativeoaksdifferssignificantly.however,theecologicalroleofdominantmitespeciesfoundinlitterofbothoakswassimilar.weexpectthatovertimechangeswillbe more noticeable between the stands and between both analysed levels. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Biological Letters de Gruyter

Communities of mites (Acari) in litter and soil under the invasive red oak (Quercus rubra L.) and native pedunculate oak (Q. robur L.)

Biological Letters , Volume 50 (2) – Dec 1, 2013

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Publisher
de Gruyter
Copyright
Copyright © 2013 by the
ISSN
1644-7700
eISSN
1734-7467
DOI
10.2478/biolet-2013-0011
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Abstract

Because of thoughtless decisions or unintentional introduction, alien species disturb native ecosystems.redoak(Quercus rubra),amongotheralienwoodyplants,isstillusedtorehabilitatedegradedlandbecauseofitsbetterresistancetopollutionandfastergrowth,ascomparedtonativetree species.Soilmites,especiallyoribatida,aregoodbioindicatorsofecosystemdisturbance,sothemain goalofthisstudywastoexploretheinfluenceofinvasiveandnativeoaksonmitecommunities.forest standsdominatedby40-year-oldQ. rubraor35-year-oldQ. roburwerecompared.over2300soilmites wereextractedfrom20soiland20littersamples.mitedensitiesinthecommunitieswerehigherinred oaklitter,whichisprobablyaresultofthethickerlayerofshedleaves.changesinspeciescomposition oforibatidcommunitieswereobservedinlitter,incontrasttoalackofdifferencesinsoil.Theseobservationsareconsistentwithotherresearchesoninvasivewoodyplants.weexpectthatovertimethese changes will also be noticeable in the soil and will increase in litter. Keywords: invasivespecies,woodyplant,Quercus rubra,Quercus robur, soilmites,oribatida inTroducTion Somealienintroducedplantspeciesexpandtheirrangeveryquickly,threatening biodiversity,sotheyareclassifiedasinvasiveplants.Theproblemofinvasivespeciesisalarming,astheprocessofinvasionisirrevocableandcanleadtocatastrophic results (gniazdowska2005).invasivealienspeciesareregardedtodayasthegreatest threat to the biodiversity and stability of ecosystems (soLarz2007). redoak(Quercus rubra) was introduced to Poland in the 19th century from North America.itstillisandwasusedinthepastforafforestationofareasdestroyedby humanactivity,forplantingasanornamentaltreeinparks,inforestsasanadmixture, andforestablishingshelterbelts.Thechoiceofredoakisusuallyjustifiedbyitsrapid growthandgoodqualityofwoodincomparisontothenativeoaks(gazda2003). otherrelevanteconomiccharacteristicsofredoakincludeitsmodestenvironmental requirements, resistance to pollution (kaTzur & hauBoLd-rosara 1996), and aestheticvalue(beautifulredleavesinautumn).currentobservationsshowthatredoak seedlings are able to eliminate other plants by creating dense patches in the undergrowth. nowadays,surveysonplantinvasivenessarefocusedondisturbancesincirculation of water and nutrients (crooks2002;ehrenFeLd2003;ashTonetal.2005), reaction of microorganisms (level of soil enzymes) (kourTev et al. 2002; Lankau 2010),productionofallelopathiccompounds(gniazdowska2008;ensetal.2009; canToretal.2011),rateofexpansionandimpactonplantcommunities(chmura & sierka2006;Tokarska-guzik etal.2006),andevenmathematicalmodellingaiming to predict invasiveness (kivánek & Pysek2006).nevertheless,theimpactof invasive species on the abundance and composition of invertebrates is rarely studied (gerBeretal.2008). mitesinhabitingthesoilareanimportantpartoftheecosystem,playingacrucial role in organic matter decomposition and nutrient cycling. Participation of Oribatida inthetotalnumberofsoilmitesrangesfrom60%to90%.Theyareapivotalelement in the detritus food chain (LeBrun1979)andcanbeusedasindicatorsofchanges in the environment (e.g. niedBala1983).usingthemasbioindicatorsprovidesan opportunity to replenish information about the state of the soil based on plant and chemicalindicators.itisstillunclearwhatcausesthealienplantstobecomeinvasive, so monitoring of organisms performing a vital role in maintaining ecosystem balance is required. untilnow,inPoland,onlyskuBala & mierny(2009)havetestedthecondition of soil mites under Fallopia sachalinensis (Reynoutria sachalinensis), one of the mostdangerousinvasivealienspecies.Theresultshaveconfirmedtheassumption thatthewayitoccupiesaterrain,i.e.virtuallycompletedisplacementoftheexistent flora,coincideswithadeclineinbiodiversityofsoilmitecommunities,especiallyof thegroupsthatfeedondiversesubstrates:thesaprophagousoribatidaandAstigmata. Simplificationoftheenvironmentresultsinagreaterproportionofpredatorymites (mesostigmata, Prostigmata) within the mite communities. Stopping the spread of plantinvadersisaseriousproblem,particularlyinenvironmentsmodifiedbyhumans (e.g. maureLetal.2010).Amajorthreatposedbyredoakisitscompetitionwiththe nativespecies,i.e.aneffectsimilartothatofFallopia spp. inthisstudyweinvestigatedtheproblemofinvasivewoodyplantsatthestage ofyoungtrees(35­40yearsold),whichwouldbehelpfulinplanningasecondpart oftheexperimentondevelopmentofinvasivenessbyincludingolderageclassesof foreststands.wetestedwhetherredoak­aninvasiveplantinPoland­affectsthe biodiversity of native soil mesofauna in less fertile soils. Our goal was to answer the followingquestions: 1.isthedensityofvarioussoilmitegroupslowerinthesoilandlitterunderthe invasiveredoak,comparedwiththenativepedunculateoak(Quercus robur L.)? 2.isthesoilandlitterunderredoakdominatedbydifferentoribatidspeciesthan thesoilandlitterunderthenativeoak? 3.isthespeciesrichnessandspeciesdiversityoforibatidcommunitiesinsoil andlitterunderredoaklowerthaninunderthenativeoak? mATeriALAndmeThodS A40-year-oldstandwithpredominanceofQuercus rubra(90%)anda35-yearold stand with predominance of Q. robur(70%)werecompared,bothlocatedsoutheast of rybnik (southern Poland, upper Silesia). geographical coordinates of the selectedareasare50°03'58"n, 18°34'09"eand 50°03'55"n,18°34'24"e,respectively.Toeliminatetheinfluenceofsomeotherfactors,resultingfromgeographical differences(likelytoaffecttheanalysis),weselectedforeststandsthatareonly295m apart,bothonpooracidbrownsoilaccordingtodatafromtheBureauofforestmanagementandgeodesyincracow(BuLigL).Suchachoicewasdictatedbydifferent reactions of soil mites to soil parameters (e.g. nieLsenetal.2008)andtheobservation made by nicoLini & ToPP(2005),whodiscoveredthatnutrientuptakebyredoakon highlyfertilesoilhadalesssignificantnegativeimpactonthepoolofnutrientsfor soilmicroorganismsandmitesthaninasoildeficientinnutrients. on24April2010,wetookrandomly10soiland10littersamplesfromeach foreststandwithinarandomlyselectedsquareplot(10m×10m).Thesampleswere collectedusingasteelcylinderof137cm3involumeand7.5cminheight.Thefallen leavesandhumuswereregardedasthelitterlayer.itshouldbenotedthatthislayer was1­3cmthick.onaverage,litterunderredoakwasthickerthanunderpedunculateoak.Thesamplesofsoilandlitterwereseparatedinthefield,thentransportedto thelaboratory,andplacedintheTullgrenapparatus.extractedmaterialwasdivided into4miteorders:oribatida,Prostigmata,Astigmata,andmesostigmata.onlyadult oribatida were determined to the species level. in total, 2307 specimens ofAcari werecollected,including1024oribatidmitesof52species.ThelistoforibatidspeciesrecordedattheforeststandsisgiveninAppendixi.Taxonomicnomenclature follows suBías(2004). Analyses of mite communities were based on density of mites of each order (mean number of individuals per 1 m2),separatelyforthesoilandlitter.Toassess thesignificanceofdifferencesinmitedensitybetweentheforeststands,thekruskalwallistestwasused.Toassessthesignificanceofdifferencesinmitedensitybetween allpairsofsites,themultiplecomparisontestwasdone.Theuseofnonparametric testswasdictatedbytheheavilyskewedmitedensitydistributionsintheexamined sites and the fact that attempts to transform the data to normal distribution did not givetheexpectedresults.Torecognizethepotentialinfluenceofoakstandsonoribatidspeciescommunities,thespeciesrichness,evenness,anddiversityindiceswere calculated.Theexpectedtotalspeciesrichnessinthestudiedstandswasestimated usingnon-parametric,incidence-basedestimators:1storderjackknifeand2nd order jackknife.estimatorswerecomputedusingSpeciesdiversityandrichnessivsoftware.inordertocomparethespeciescompositionofcommunitiesfoundindifferent habitats,clusteranalysiswasconducted(basedoneuclideandistances).correspondence analysis was performed to evaluate relationships between species density and habitat.StatisticalanalyseswerecarriedoutusingSTATiSTicA10.0software. Table1.meandensityofmites(individuals/m2 ± standard error) in soil and litter under Quercus rubra and Q. robur,andsignificanceofdifferences betweenthehabitats(kruskal-wallistest,N = 40) Quercus rubra soil 19500±3786.5 b 4444±1250.5b 23944±156.8b 6277±2281.7 8000±1500.3b 19333±13941.3b 1333±683.93a 444±231.3a 1722±520.2 16611 ± 1931.3 ab 12888±3335.8a 1722±441.7 2166±425.9ab 3166±1203.1ab 1555±528.9a 1888±469.9 ab 15055±3462.0 ab 11000±1662.1a 10.562 11.795 11.546 5.483 23.474 17.080 litter soil litter 0.014 0.008 0.009 0.139 <0.001 0.001 Quercus robur H p groupofmites Oribatida adults 11333±7837.6 a oribatidajuveniles 1666±1123.4a Oribatida total 1111±414.1 13000±4807.3 a mesostigmata Prostigmata 166±84.9a 1388±937.8a Astigmata Boldvaluesdenotesignificantdifferencesindensity(P<0.05).differentlettersdenotesignificantdifferencesbetweenhabitats,basedonamultiple comparison test. reSuLTS Statisticallysignificantdifferenceswereobservedinmeandensityofmites(individuals/m2) in the soil and litter under Quercus rubra and Q. robur with regard to mostmitegroups.Asregardsoribatidmites,theirdensityinredoaklitterwassignificantlyhigherthaninlitterunderthenativeoak.Thedensityoforibatidainthesoil inbothforeststandswasmuchlower.nostatisticallysignificantdifferencesinthis parameterbetweenforeststandswereobserved,butthenumbersoforibatidsinthe soil under Q. rubra were generally lower than in the soil under Q. robur. Numbers of prostigmatid and astigmatid mites in Q. rubra litter were also higher than in litter of thenativeoakandinbothcasesmuchhigherthaninsoillayers.Althoughdifferences indensitiesofmesostigmatawerenotsignificant,thepatternwassimilarasforthe abovegroupsofmites.highernumbersofmesostigmatidmiteswerenotedinthelitterunderredoakthanunderthenativespecies,andnumbersofthesemitesinthesoil under Q. rubra were lower than in the soil under Q. robur(Table1). Speciesrichness,diversity,andevennessindicesofcommunitiesweresimilar within the habitats (litter or soil) but differences between tree species were observed. numbersoforibatidspeciesinthelitterweregenerallyhigherthaninthesoil.furthermore,speciesdiversityandevennessindiceswerehigherinthelitterunderboth oaksthaninthesoil(Table2).Theestimatedtheoreticalnumberofspeciesinstudied sites was slightly higher (e.g. in litter under Q. rubra)orsignificantlyhigher(e.g. soil under Q. rubra)thanthenumberofobservedspecies.Theestimateswerehigher when2ndorderjackknifewasused(insteadof1storderjackknife)andrangedthen from37.6(litterunderQ. rubra)to56.0(litterunderQ. robur)(Table2).TheinTable2.observedandestimatedspeciesrichnessanddiversityoforibatidmitecommunitiesinthe soil and litter under Quercus rubra and Q. robur Parameter Quercus rubra soil Average number of species Totalnumberofspecies Shannonindex(H') evennessindex(J) jackknife1 order st Quercus robur soil 7.81 20 1.844 0.616 30.8±2.6 (54.0) 40.4 (122.0) litter 12.63 30 2.548 0.749 45.3±6.1 (51.0) 56.0 (86.6) litter 13.75 36 2.725 0.760 7.36 18 1.613 0.558 28.8±5.6 (60.0) 37.6 (108.8) 45.9±5.1 (27.5) 46.8 (30.0) jackknife2 order nd valuesaremeanestimates(±standarddeviation) Percentage increase in relation to the observed species numbers is given in parentheses creaseinrelationtothenumberofcollectedspeciesvariedbetween30%(litterunder Q. rubra)toover100%(soilunderQ. robur and Q. rubra)(Table2). clusteranalysisoforibatidcommunitiesshowssimilaritieswithintheanalysed soilorlitterlayeranddifferencesbetweenthem(fig.1).Thespeciescompositionof fig.1.dendrogramfor4comparedhabitats,basedonunweightedPairgroupmethodwithArithmeticmean(uPgmA)andeuclideandistancecoefficients oribatid communities in soil is much more similar than the species composition of oribatidfaunainlitterunderoaks. incorrespondenceanalysis,evaluatingrelationshipsbetweenspeciesdensityand habitat(fig.2),eigenvalueswerehighforaxis1(1=0.28)andaxis2(2=0.27). over92%ofthevariancewasexplainedbythefirst2axes.resultsoftheanalysis confirm the lack of valid differences in soil mite communities between the forest stands.ThedominantspeciesinthesoilinbothforeststandswasMicroppia minus minus (Paoli, 1908). it is a eurytopic (weigmann 2006) and cosmopolitan (suBías 2004)fungivorousgrazer(zaiTsevetal.2002),consideredasparthenogenetic(ciancioLo & norTon2006). Bycontrast,oribatidcommunitiesoflitterlayersofthe2comparedforeststands differsignificantly.ThehabitatofQ. rubra litter and the associated species are lo- fig.2.correspondenceanalysisbiplotshowingpositionsof52oribatidspeciesand4compared habitats.dominantspecies:chvoi=Chamobates (Xiphobates) voigtsi,Lfal=Lauroppia falcata falcata, mmin = Microppia minus minus, onov = Oppiella (O.) nova nova, rsub = Rhinoppia subpectinata,Sacu=Suctobelbella (S.) acutidens acutidens,Spal=Scheloribates (S.) pallidulus pallidulus,Ssub=Suctobelbella (S.) subcornigera subcornigera catedalongthepositivevaluesofaxis2,whereastheindexoftheQ. robur litter and associatedspeciesaresituatedalongthenegativepartofaxis2(fig.2). Twodominantspeciesweretypicalforredoaklitter.Scheloribates (S.) pallidulus pallidulus (koch,1841)isknownasaforestspecies (weigmann 2006) of broad cosmopolitandistribution,excludingAntarctica(suBías2004).Becauseofitsfeedingpreferencesithasbeenrecentlyspecifiedasaherbo-fungivorousgrazer(maLak 2010),whichconfirmsanearlieropiniononthespeciesassecondarydecomposer feeding mainly on fungi (schneideretal.2004).Theseconddominantspecies,Suctobelbella (S.) subcornigera subcornigera (forsslund,1941),isknownfromdifferent forestsoils,butisalsorecordedatruderalsites(weigmann 2006).itisaneurytopic species (weigmann 2006)ofholarcticdistributionextendingtotheorientandnew Zealand (suBías2004).Thespeciesisafungivorousbrowser(zaiTsevetal.2002), reproducing parthenogenetically (ciancioLo & norTon2006). Chamobates (Xiphobates) voigtsi (oudemans, 1902) and Rhinoppia subpec- tinata (oudemans, 1900) were characteristic for the litter layer under the native Q. robur.Theformerspecies,connectedwithacidforestsoils(weigmann 2006), is Palaearctic (suBías2004),regardedasaherbo-fungivorousgrazer(maLak2010). Thelatterspecies,R. subpectinata,iseurytopic(weigmann 2006), withaholarctic rangeexcludingtheeasternpartoforient(suBías2004).itisalsoincludedinthe feeding guild of fungivorous grazers (zaiTsevetal.2002). Several dominant species were not associated with any of the studied habitats. Oppiella (O.) nova nova (oudemans, 1902) is one of the most widely distributed oribatidsintheworld,occurringinvarioushabitats(suBías2004;weigmann 2006). itisknownasafungivorousgrazer(zaiTsevetal.2002)andcharacterizedbyparthenogenetic mode of reproduction (ciancioLo & norTon 2006). Suctobelbella (S.) acutidens acutidens (forsslund, 1941) is mainly known from acid soil forests (weigmann 2006). it is a fungivorous browser (zaiTsev et al. 2002), reproducing parthenogenetically (ciancioLo & norTon2006).Lauroppia falcata falcata (Paoli, 1908)isobservedindeciduouseuropeanforests(weigmann 2006).itbelongstothe feeding guild of omnivores (schneideretal.2004). diScuSSion inPoland,Article120,point1ofthenatureProtectionActof16April2004 (journalofLaws[dz.u.]no.92,item880)prohibitsintroductionofalienspecies ofplantsintothenaturalenvironment.however,thenationalforestholding"State forests"(PgLLP)allowstheintroductionofredoakanditsuseasanadditionalspeciesinestablishingofshelterbelts,basedonthe"Principlesofsilviculture".redoak soilrequirementsarelowerthanthoseofnativeoaks.Thistreespeciesisresistantto frostandindustrialpollution,thusrecommendedforpost-industriallandrestoration. itisstillrecommendedalsoforurbanplantingbecauseofitsdecorativevalue,also used as roadside trees (Bodyl2011).Amongforestersthereisaconvictionthatadditional alien species in unprotected forest are not harmful and should remain in place. Some foresters believe that to increase biodiversity it may sometimes be desirable to supplement reforestation and afforestation with alien species (BogaTko2010),which has no support from environmentalists. consideringtheproblemofinvasivewoodyplantspecies,gazda (2003)suggestedweshouldaskthequestion:whatpredisposesaspeciestobecomeinvasive? kowarik(1995)emphasizesthespecificityofinvasivewoodyplants,payingattentiontoalongerperiodoftheirdevelopment.inBrandenburg,theaveragetimefrom introduction of a species to its transition into an invasive species was 131 years for shrubs and 170 for trees, of which for the black cherry (Prunus serotina ehrh.) a minimum duration of 29 years was reported, and for walnut (Juglans regia L.), a maximumtimeof374years(kowarik1995). redoakwasbroughtintoPolandinthe19thcentury,whichmeansthattheperiod from the first introduction is about 100­200 years. how its invasiveness has developed?itshouldbenotedthatreichetal.(2005)observedwidespreadandrapid(within threedecades)changesinsoilsunderdifferenttreespeciesinanexperimentconducted inPoland.Thoseauthorsstudied14species,includingQuercus robur and Q. rubra,and observedthattreespeciesaffectedsoilsbothdirectly,throughthechemistryoftheirlitter,andindirectly,throughtheeffectoftheirlitterondetritivores(e.g.earthworms). resultsofthisstudysuggestthatthechangesinsoilmitecommunitiesin35-40year-oldforeststandsofinvasiveandnativeoakarenotremarkable.Theobserved influenceoftheinvasiveredoakonmitecommunitieswasweakerthanthatobserved by skuBala & mierny(2009)withregardtotheaggressiveplantinvaderReynoutria sachalinensis.withinstandsinvestigatedbyus,significantlyhigherdensitiesoforibatid,prostigmatid,andastigmatidmiteswereassociatedwithredoaklitter.Thisis probablyaresultofitsthickerlayer,whichcreatesmoremicrohabitatstobeoccupied. reichetal.(2005)foundthatthelitterproductionofredoakisovertwiceashighas thatofnativeoaks.Bycontrast,nosignificantdifferencesindensityofthesemites wereobservedinthesoil,butmeannumbersoforibatidandastigmatidmitesinthe soilundertheinvasiveoakwerelowerthanunderthenativeoak.formesostigmata, nosignificantdifferencesbetweentheinvestigatedhabitatswereobserved,although the same pattern of relationships was found. As regards the species composition of oribatid communities under the invasive andnativeoak,alackofimportantdifferenceswasnoticed.Someremarkabledifferencesinspeciescompositionwerefoundonlyinthelitterlayer.however,despite differences in composition of oribatid communities in the litter under invasive and nativeoak,theecologicalfunctionofdominantspeciesdidnotdiffer.inthelitterunder Q. rubra, one of the dominant species was Scheloribates pallidulus. Chamobates voigtsi reached high numbers in the litter under Q. robur.Bothspeciesareknownas occurringinforestsandbelongtothesamefeedingguild:herbo-fungivorousgrazers. Suctobelbella subcornigerawasanotherdominantspeciesintheredoaklitter, whereas Rhinoppia subpectinata dominatesinthelitterunderthenativeoak.Both mite species occur in a broad range of habitats (eurytopic) and feed on similar substrates. S. subcornigeraisafungivorousbrowser,whereasR. subpectinata is a fungivorous grazer. itshouldbeemphasizedthatdespitehigherdensitiesoforibatidmitesinthelitterunderredoak,noremarkabledifferencesinmitespeciesrichnessanddiversity wereobservedbetweenlitterofbothoaks.Speciesrichnessoforibatidmitesinthe soilwasmuchlowerthaninthelitterunderbothoaks.however,itwasmoreunderestimatedincomparisonwithspeciesrichnessinthelitterlayer.itcanbeconcluded that changes in species composition of oribatid communities under invasive and nativeoaksproceedslowly.Thechangesinoribatidcommunitiesstartfromthelitter layer,becauseofitsspecificity.oribatidmitesfeedonhyphaeandsporesoffungi, decayingorganicmatter,andplantdebrisovergrown(predecomposed)bymycelium (maraunetal.2003).Themainsourceofthisfeedingmaterialisfoundinthelitter layer.Alldominantoribatidspeciesinthelitterlayerwerefungivores,whichproves thatfungidevelopedquitewellinlitterundernativeaswellasinvasiveoak.Thus, one of the most popular hypotheses of fungicidal effect of invaders (gniazdowska 2008)isnotcredibleatthisstageofoakstanddevelopment. ourresultssuggestdifferentconclusionsthanthoseobtainedinanexperiment conducted by nicoLini & ToPP(2005),concerningtheuseofredoakinrestoration of lignite opencast mines.They compared forest stands of red and native oak (Q. petraea)atthesameage(18years),plantedonsoilsofdifferentfertility.Thoseauthors found that red oak, because of its proprieties associated with environmental requirements,hasanegativeeffectonthedensityofsoilmesofaunainthepoorsoil (oribatidaandcollembola).Theysuggestedanexplanationthatwhenafast-growing tree,likeredoak,isplantedonapoorsoil,nutrientdepletioninsoilismuchquicker, as compared to slow-growing tree species.The depletion is due to increasing immobilization of nutrients in woody biomass of fast-growing trees and also increasing recalcitranceofitsorganicmatter.Allthishasasignificantimpactonreducingthe poolofnutrientsforsoilmicroorganismsandmites.Themechanismwouldnothave suchconsequencesinfertilesoils.Thismeansthatthoseauthorsobservednegative effectsmuchquickerthanwedidbecauseofinitialimpoverishmentofthesoil,which wouldbegreaterinaligniteopencastmineinrhineland.Themanagedforeststands studiedbyusweresituatedinthevicinityofacoalmineandurbanareaofrybnik, butthesoilwasnotmixedordepositedfromotherplacesasitwasinthecaseof restored land of the lignite mine. weconsideredabovetheageaspectofwoodyplantinvasiveness.Asecondimportant question posed by gazda(2003)is:whatmakestheenvironmentvulnerable to the invasion? vauramo & seTäLä(2010)paidattentiontothechoiceofplantsused inurbanareas.Thoseauthorsshowedthegreatpotentialofplantspeciesthatthey dividedintosomefunctionaltypes.Allthedistinguishedtypesarelikelytoalterthe soilorganismcommunitiesand,consequently,thedynamicsofnutrientsindisturbed soil(e.g.inthecity).Thussomeotherquestionarise.Arethedisturbancesincirculation of nutrients a direct consequence of the invasion of alien plants or they result from disturbance of the functioning of the soil animal communities, their biology andecology,ortheydependonavarietyofcoexistingfactors?Aninterestingpaper was presented by simBerLoFF & von hoLLe (1999)whoworkedontheproblemof enhanced susceptibility to further invasions of the areas already invaded (by another invasivealienspecies).Thoseauthorsgivemanyexamplesshowingthecomplexity ofthephenomenon,fromthestandpointoftheinvaderandofendemiclandwithits floraandfauna.Theyemphasizethatthecharacteristicsofalienorganismscannotbe definedingeneralbutinrelationtoaparticularsituation.consequently,reich et al. (2005)highlightthefactthatvegetation,soilorganisms,andsoilchemistryshould beviewedasco-developingcomponentsofterrestrialecosystems,evenondecadal scales.Thisalsoleadstoaconclusionaboutthenecessitytoincorporatedetailedsoil analysesinourresearchandcontinueobservationsinolderforeststands,whichis planned. As postulated by crooks(2002),thereisaneedforresearchinwhichthesites colonizedbyinvasiveplantsarecomparedwithnatural,undisturbedsites,toexamine comprehensivelytheimpactofspecificinvadersinthegivenconditionsonthenative environment. Our study area is situated within managed forests but still we can observedifferencesbetweentheforeststands,startingfromthelitterlevel.Thereis aneedtocontinuethesesurveysinthecontextofcollectingknowledgeonmechanismsoftheimpactofredoakasaninvasivewoodyplantinPolishconditions.our data will help to plan other experimentsthatwouldhelptodevelopmethodsforcontrollingtheexpansionofparticularinvasivealienspeciesincertainconditions.The resultspresentedarepartofalargerresearchprojecttakingintoaccountforeststands in the same area (Silesia) but with longer impact on the ecosystem. concLuSionS Thedensityofallgroupsofmitesand(toasmallerextent)theirspeciesrichness werehigherintheforeststanddominatedbytheinvasiveoakthaninthenativeoak forest.Twofactsmayexplaintheobservedrelationship.ingeneral,thelitterlayeris occupiedbyhighernumbersoforibatidmitesthanthesoillayer,whilelitterproductionofredoakishigherthanthatofnativeoak. morespecimensandspeciesoforibatidawereobservedinthelitteroftheinvasiveoakthaninthatofthenativeoak.Anoppositesituationwasobservedwith regardtothesoillayer,butthedifferenceswerenotremarkable.Theprobablereason forthisphenomenonisashorttimeoftheimpactoftheinvader.Threetofourdecadesappeartohavenosignificantimpactonthesoillayer. The species compositionof oribatidcommunities in the soil layer under both speciesofoaksissimilar,whereastheoribatidfaunainthelitterunderinvasiveand nativeoaksdifferssignificantly.however,theecologicalroleofdominantmitespeciesfoundinlitterofbothoakswassimilar.weexpectthatovertimechangeswillbe more noticeable between the stands and between both analysed levels.

Journal

Biological Lettersde Gruyter

Published: Dec 1, 2013

References