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SamplingsitesweresituatedalongagradientofpollutiongoingfromthesmeltertotheNorth-East.AllsiteswerecoveredbyScotchpine(PinussilvestrisL.).Sampleswerecollectedfromthreelocationsthatweresituatedatintervalsofapprox.1,2and6kmfromthesmelter(furtherreferredtoassoilsA,B,andC).Thelocationshaveasimilarsoilstructure:sandywithapproximately2.5%ofclay(Koopmansetal.,1993).Samplesweretakenfromtheupper10cmofthesoilminerallayer(litterwasremoved).Oneitherlocationfourreplicateplotsweresampled.Fromeachreplicate15soilcores,4cmindiameterand10cmdepthweretakenandthenmixedandsieved(0.5cmmesh).
Preparationofsamples
Aftersieving,fieldmoistsoilfromeachplotwasdividedintosubsamplesofapprox.250gandeachofthemwasplacedina300mlplasticjar.Thesamplesweredividedintofoursets,eachcontainingfoursamples.Onesetwastreatedwithleadnitrate(1000mgPbkg)1dw),thesecondwastreatedwithsodiumchloride(6.67gNaClkg)1dw),thethirdwasheatedfor18hat50Candthefourthoneservedasanon-stressedcontrol.Aftertreatmentsampleswerekeptindarknessatatemperatureof20Cuntilmeasurement.Fromeachjarsamplesforrespiration,bacterialgrowthratemeasurementandchemicalanalysesweretaken.
Respiration
Twentyfourhoursbeforeeachmeasurement200gofsoilfromeachjarwasplacedinto±600mlglassbottlesanddrylucernemeal(alfalfa(Medicagosativa))wasaddedandmixedthoroughly.Lucernewasaddedinamountscorrespondingto3.2gCkg)1soil,whichwassufficienttoinducerespirationandoffsetnutrientlimitation.Withoutsubstrateadditiontherespirationisusuallytoolowtomeasuresignificantdifferenceswithin24h.CarbondioxideproductionwasmeasuredwithaGCapparatus(CarloERBAInstruments).Forthefirstmeasurementsampleswerepreparedasdescribedabovedirectlyafterapplicationofstressandterminationofdisturbance.
Measurementwasperformedasfollows:5gofsoilwasshakenwith40mlofmilliQ-waterinplastictubes,thencentrifugedandfilteredthroughglasswool.Supernatants(1.5ml)weredecantedintoeppendorftubes.Sampleswereincubatedfor2hat20Cwith3.75llradio