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Carbon avail-ability and temperature control the post-snowmelt.pdf

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SoilBiology&Biochemistry32(2000)441±448www.elsevier.com/locate/soilbioCarbonavailabilityandtemperaturecontrolthepost-snowmeltdeclineinalpinesoilmicrobialbiomassDavidA.Lipson*StevenK.SchmidtRussellK.MonsonDepartmentofEnvironmentalPopulationandOrganismicBiologyUniversityofColoradoBoulderCO80309-0334USAAccepted8April1999AbstractInColoradoalpinedrymeadowsoilsmicrobialbiomasshasbeenobservedtoincreaseduringfallandwinterandtorapidlydeclineaftersnowmeltinthespring.IthasbeenshownthatthesemicrobialpopulationdynamicsarelinkedtoNavailabilitytoalpineplantsbuttheunderlyingmechanismshavenotbeenexplained.Wehypothesizedthat:(1)freeze-thaweventsinthespringcausereductionofthemicrobialbiomass(2)thewintermicrobialcommunityissensitivetoprolongedtemperaturesabove08Cand(3)theincreaseofbiomassinfallanditsdeclineinspringareduetochangesinCavailability.Weperformedlaboratoryexperimentstotestthee€ectoftemperatureregimeonsoilmicrobialbiomassrespirationandCavailabilityandmadeseasonalmeasurementsofCpools.Soilmicrobialbiomasswasuna€ectedbyfreeze-thaweventsinwhichrealisticratesoffreezingandthawingwereused.Somesigni®cante€ectswereobservedatfasterfreezingrates.Despitethistolerancetotemperature¯uctuationsthewintermicrobialcommunityshowedsensitivitytoprolongedtemperaturesabove08C.Thise€ectmayhavebeencausedindirectlybyane€ectoftemperatureonsubstrateavailability.TwoweekincubationsatincreasedtemperaturescausedareductioninthequantityofextractableorganicCinthesoil.Thesoilconcentrationsofcelluloseandhotwater-solubleorganicCwere