Title: The effects of fire on soil carbon dynamics

Abstract: Fire is a common, widespread phenomenon in many parts of the world, and has multiple, complex effects on soil chemical and physical processes. Fire can transform the chemical composition of bulk soil organic matter (SOM) and its soluble component and convert organic matter into more stable forms of organic carbon collectively known as pyrogenic carbon (PyC). Although much progress has been made in describing the thermal transformations in bulk SOM and estimating PyC stocks and mineralization rates, there is limited data available on the thermally induced chemical changes of the soluble portion of SOM. Additionally, the controls of PyC persistence in soils remain unclear. In this talk, I will present results from my past and ongoing research work that examined: 1) changes in the distribution of carbon functional groups in water-extractable organic matter from soils heated at low and intermediate temperatures; and 2) the effects of pyrolysis temperature and soil depth on PyC mineralization rates and PyC-induced soil organic carbon priming. I will show that the water-extractable organic matter from soils heated at 250oC became more enriched in aliphatic C structures, whereas the water-extractable organic matter from soils heated at 350oC became more enriched in aromatic C. PyC mineralized faster and inhibited the losses of ‘native’ organic carbon from surface soils when formation temperature of PyC decreased from 450 oC to 300 oC. Taken together, my results suggest fire intensity, formation temperature and soil depth should be considered by predictive models that incorporate fire effects on SOM and PyC cycling in soils.