CONICET | Buscador de Institutos y Recursos Humanos

Forest replacement by exotic plantations drive important changes at the level of theoverstory, understory and forest floor. In the Atlantic Forest of northern Argentina,large areas have been replaced by loblolly pine (Pinus taeda L.) monocultures. Plantand litter transformation, together with harvesting operations, change microclimaticconditions and edaphic properties. Management practices such as thinning promotethe development of native understory vegetations and could counterbalance negativeeffects of forest replacement on soil. Here, the effects of pine plantations and thinningon physical, chemical and microbiological soil properties were assessed. Bacterial,archaeal, and fungal community structure were analyzed using a metabarcodingapproach targeting ribosomal markers. Forest replacement and, to a lesser extent,thinning practices in the pine plantations induced significant changes in soil physicochemicalproperties and associated shifts in bacterial and fungal communities. Mostmeasured physical and chemical properties were altered due to forest replacement,but a few of these properties reached values similar to natural forests under thethinning operation. Fungal alpha diversity decreased in pine plantations, whereasbacterial alpha diversity tended to increase but with little statistical support. Shifts incommunity composition were observed for both fungal and bacterial domains, andwere mostly related to changes in plant understory composition, soil carbon, organicmatter, water content, pH and bulk density. Among several other changes, highlyabundant phyla such as Proteobacteria (driven by many genera) and Mortierellomycota(mainly driven by Mortierella) decreased in relative abundance in the plantations,whereas Acidobacteria (mainly driven by Acidothermus and Candidatus Koribacter) andBasidiomycota (mainly driven by the ectomycorrhiza Russula) showed the oppositeresponse. Taken together, these results provide insights into the effects of forestreplacement on belowground properties and elucidate the potentially beneficial effectof thinning practices in intensive plantation systems through promoting the understorydevelopment. Although thinning did not entirely counterbalance the effects of forestreplacement on physical, chemical and biological soil properties, the strategy helpedmitigating the effects and might promote resilience of these properties by the end of therotation cycle, if subsequent management practices compatible with the developmentof a native understory vegetation are applied.