The manipulation of organic residues affects tree growth and heterotrophic CO2 efflux inatropical Eucalyptus plantation

Fast-growing plantationsareincreasinglybeingestablishedontropicalsoils,wherefertilityislargely supported bysoilorganicmatter(SOM)andwheredifferentmanagementoptionsofharvestorganicres- idues isthoughttoimpactthelong-termsustainabilityoftheseplantations.Theobjectivesofthisstudy were: (1)toquantifytheeffectofcontrastingmethodsoforganicresiduemanagementontreegrowth and soilCO2 effluxes inthefirst2yearsafterplantingand(2)toevaluatetheimpactoforganicresidue manipulations onthemineralizationofsoilorganicmatteroverthelengthoftheexperiment.Threetreat- ments weresetupin0.125haplotsandreplicatedinthreeblocksattheharvestingofaCongolese Euca-lyptus stand, resultinginanabovegroundorganicresiduemassrangingfrom0to6.3kgm_2. The mineralization ofSOMwasdeducedineachtreatmentbypartitioningsourcesofsoilCO2 effluxes using decomposition experimentsandbyupscalingspecificrootrespiration.SoilCO2 effluxes weregreatly affected byseasonsandorganicresiduemanipulation,althoughtherewerenosignificantchangesintop- soil watercontentandtopsoiltemperatureovermostofthestudyperiod.Abovegroundorganicresidue was thefirstcontributortosoilCO2 efflux inthetwotreatmentswithalitterlayer.Organicresidueman- agement didnotsignificantlyinfluencethemineralizationofSOMinourstudy,probablyduetothelow quality of Eucalyptus litter, ortothehypotheticallackofdissolvedorganiccarbontransfersfromlitterto soil. AstrongrelationshipwasfoundbetweencumulativeheterotrophicCO2 efflux andtreegrowth,sup- porting thehypothesisthattheearlygrowthof Eucalyptus trees inasandytropicalsoilislargelydepen- dent onthenutrientsreleasedbythedecompositionoforganicresidues. (Résumé d'auteur