Abstract
We measured soil respiration during two winters in three different ecotypes of the BOREAS northern study area. The production of CO2 was continuous throughout the winter and, when totaled for the winter of 1994–1995, was equivalent to the release of ∼40–55 g C/m2 from the soil surface. As soils cooled in the early winter, the CO2 production rate decreased in a manner that appeared to be exponentially related to shallow soil temperatures. This exponential relationship was not observed when soils began to warm, possibly indicating that there may be additional or different processes responsible for increased CO2 production during winter warming events. We also measured CO2 concentrations in soil gas and the Δ14C of the soil CO2. These measurements show that the CO2 produced in winter is not simply the return to the atmosphere of the carbon fixed during the previous growing season. We suggest that the wintertime production of CO2 originates, at least in part, from the decomposition of old organic carbon stored at depth in the soil.
Highlights
--40-55g C/m2fromthesoilsurfaceA.ssoilscooledin theearlywintert,heCO2 productionrate decreasedin a mannerthat appearedto be exponentiallyrelatedto shallowsoiltemperatureTsh.isexponentiraellationshwipasnotobservewdhensoils beganto warm,possiblyindicatingthattheremaybe additionaol r differentprocesses responsiblefor increasedCO2 productionduringwinter warmingevents.We measureCdO2concentratioinnssoilgasandtheA4Cof thesoilCO2.These measurementshowthat the CO2 producedin winter is not simplythe return to the atmosphereof the carbonfixedduringthe previousgrowingseasonW. e suggesthat the wintertimeproductionof CO2 originates,at leastin part, from the decompositionof old organiccarbonstoredat depth in the soil
A major focusof the Boreal Ecosystem-AtmospherSetudy (BOREAS) is to understandcarbon exchangebetween the boreal forestsand the atmosphereW. inter productionof CO2 is especiallycritical in understandingthe annual cyclingof carbon in these ecosystems[Frolkinget al., 1996] sinceit is knownto return to the atmospherea significantportion of the carbon fixed during the growingseason[Gouldenet al., this
In this paper we relate seasonaland interannual trends in soiltemperatureand moistureto variationsin soilrespiration andsoilgasCO2concentrationsW. e examinethe importance of CO2 productionand transportin controllingsoil gasCO2 concentrationsand fluxes.We useour soil respirationdata to estimatethe cumulativeseasonarlespiration.We report significandt epletionof 4Cin soilgasCO2andsuggestht atthe issue].Soil respiration,a processthat includescontributions CO2fluxesobservedthroughouthewintermustbe supported from plantsand microbialdecompositionof litter and organic by ongoingCO2 productionoriginating,at leastin part, from matter in soil,isa majorcontributorto winter CO2 production. the decompositionof old organiccarbonstoredat depthin the Winter soil respirationhasbeen estimatedto contribute20% soil
Summary
In August 1993 we establishedthree sites in three forest volume, and the surfacearea coveredby the chamber.Molar ecotypeson sandy and clay soils in the BOREAS northern fluxeswere basedon concentrationsadjustedfor temperature studyarea (NSA) near Thompson,Manitoba. The predomi- and pressure;no correctionfor water vapor was necessary nantspeciesof the threeecotypeswereoldblackspruce(OBS) because the circulated air was not dried. (piceamariana, on predominantlyclay soils),youngjack pine Closedchambersare not an accuratemethodfor measuring (YJP) (pinusbanksianao, npredominantlysandysoils),andold gastransportdrivenby advectiveprocessesb,ecausethe chamjack pine (OJP) (on predominantlysandysoils).Soilpitswere ber itselfdisruptsadvectionacrossand throughthe snowsurdug near the three eddycorrelationflux towersat OBS Closed chambers work best when vertical diffusion is the onlyNSA tower runningin winter), YJP, and OJP. Print of the OBS eddy correlation flux tower. Temperature and gas probeswere installedin the nine the naturalCO2fluxbyincreasingthe concentrationof CO2 at OBS pits dug in 1994.
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