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Abstract
The composition of soil organic matter (SOM) was characterized in longleaf pine (Pinus palustris) stands managed with regular broadcast fire (Burned) or pine straw raking (Unburned) in the Coastal Plain of Georgia, USA. Proton nuclear magnetic resonance spectroscopy revealed that soil-water extractions isolate a dissolved organic matter pool (DOM) that is younger and faster-cycling than in-situ soil leachate DOM. One year of soil respiration monitoring captured higher carbon dioxide flux in Burned than Unburned stands. Burned stand soils experience higher inputs of recently-fixed carbon (C) with SOM reflecting more fresh plant litter. Unburned stand SOM was dominated by more microbially-processed, but persistent, C due to annual biomass removal during pine straw harvest. Our results show that soil C can persist for centuries to millennia, even in ecoregions facing rapid C loss to decomposition and leaching and highlight some methodological challenges of assessing SOM pools in this system and others.