Prescribed fire and pine straw: Soil carbon dynamics in longleaf pine (Pinus palustris) under two common management strategies

• All Burned Stand SOM pools were younger and more plant-derived than Raked Stand pools. • An increase in dPyC was not detected until ∼ 8 months post-Rx fire. • Carbon in in-situ DOM was more processed and older than in extractable DOM. • Contrary to expectations, MAOM contained more recently-fixed C than POM. Pyrogenic carbon (PyC) is an important persistent C pool in forests managed with prescribed (Rx) fire, however the details of its post-fire redistribution from soil to aquatic systems remain poorly understood. We established a study in longleaf pine stands under two management types: one with Rx fire (Burned) and one without Rx fire (Raked). Lysimeters were installed immediately post-Rx fire and used to collect leachate for fourteen months. Subsamples from soil cores were fractionated into particulate organic matter (POM) and mineral associated organic matter (MAOM) or extracted to obtain dissolved organic matter (DOM). Leachate DOM, bulk soil, soil organic matter (SOM) fractions, and extract DOM were analyzed for total C, total N, δ 13 C, δ 15 N, and radiocarbon. There was a spike in Burned Stand DOM aromatic functional groups (from 1 H nuclear magnetic resonance spectroscopy) eight months post-fire suggesting the PyC underwent a compositional shift, likely due to chemical or biological degradation, before entering the DOM pool. MAOM was younger and more vertically mobile than POM, suggesting it cycles more rapidly whereas POM cycles more slowly. We also found that in the Burned Stand, SOM and DOM were more characteristic of fresh plant material compared with the Raked Stand, which had regular litter removal and herbicide application. This indicates that different management strategies of longleaf pine can have significant effects on SOM dynamics, including dissolved PyC, which could be important for managing forests for C storage.