Effects of Pyrolysis Temperature and Soil Depth on Pyrogenic Carbon Dynamics from a Forest Soil of Sierra Nevada, California.

Pyrogenic organic carbon (PyC) is found in soils as a heterogenous mixture of thermally altered residues, ranging from slightly charred plant biomass to soot. Although the stability of PyC in soils is known to be controlled by PyC's physicochemical characteristics as well as the pyrolysis temperature of the source material, it is unclear how PyC dynamics differ in surface (0-10cm) and subsurface (below 10 cm) soils. In this study, we conducted a 6-month laboratory incubation study to investigate the interactive effects of pyrolysis temperature and soil depth on PyC losses in a fine-loamy, temperate forest soil. We followed the fate of dual-labeled ¹³C and ¹⁵N jack pine PyC produced at 300^oC and 450^oC and incubated in surface (0-10 cm) and subsurface (50-70 cm) forest soils in the dark at 55% soil field capacity and 25^oC. Losses of PyC as ¹³CO₂ and in ¹³C-dissolved organic carbon (DOC) leached from soils were measured periodically during the incubation study using a Thermo Scientific GasBench interfaced to a Delta V Plus isotope ratio mass spectrometer (IRMS) and total organic C analyzer interfaced to a PDZ Europa 20-20 IRMS. PyC formed at 300^oC mineralized faster than that formed at 450^oC, whereas soil depth had no effect on the mineralization rates of PyC, suggesting that pyrolysis temperature is a more important than soil depth as a driver of PyC loss in Sierra Nevada forest soils. We will also present data on the influence of pyrolysis temperature and soil depth on the proportion of PyC in the DOC pool.