Sensitivity of deep soil C to climate change: Mineralization of soil organic matter at different moistures in an Amazonian PODZOSOL
Résumé
Changesinsoilswaterregimewillbeakeycomponentoffuture
climatechange.Whilemany
recentstudiesfocusedontheeffectoftemperatureonsoilCd
ynamicsmuchlessstudiesare
devotedtotheimpactofwaterregimes,althoughsoilmoisture
stronglyinfluencesmicrobial
activity(Moyano
et
al.
,2013).BphhorizonsofAmazonianpodzolsrepresentahugesto
ckof
organiccarbon,i.e.,13.6PgC(Montes
et
al
.,2011).Thesehorizonsareoftenwater‐‐saturated,
whichishypothesisedtolimitdecomposition.Predictedchanges
inclimateforthisAreawill
resultindrierandmorevariableswaterregimesascomparedto
thepresentsituation.Weinves‐
tigatedhowheterotrophicrespir
ationofthedifferentsoilhor
izonsofthesesoilsreactstosoil
moisture.Forthisweincubatedundisturbedsoilcoresfromthe
OH,E,Bph,andIIMsoilhori‐
zonsatdifferentmatricpotentials(pF0,1.7,2.5,3.5,4.2)
andmonitoredtheCmineralisationby
measuringtheevolvedCO
2
usingaμGC.TheresultsshowedverylittlevariationofCmin
eraliza‐
tionrateswithintheconsidered
rangeofmatricpotentials.Th
isisexplained,fortheBphhori‐
zons,bythedominanceofsoilporesbyverysmall(dia<0.95
μm)pores,whichremainwater
saturatedevenatpF4.2.Absenc
eofimpactofmatricpotential
variationsmayalsobeexplained
byotherfactorslimitingdecompositioninthesesoils.Wedisc
ussthepossibleimpactsofpre‐
dictedvariationsofthewaterre
gimeofthese.Soilswithclim
atechangechangingclimateonthe
stabilityoftheirC