Linking Pyrogenic Organic Matter Reactivity in Soil to its Charring Temperature and Wood Source

Abstract:

Understanding the link between the chemical and structural properties of pyrogenic organic matter (PyOM) and its subsequent reactivity in soil is critical to predict how future increases in forest fire frequency and intensity will affect C and N cycling. Herein, we present results from a laboratory incubation that investigated the effects of wood species and charring temperature on the decomposition of PyOM and native soil organic carbon (SOC) dynamics in a sandy soil from a northern temperate forest (University of Michigan Biological Station, Pellston, MI, USA). PyOM was produced from highly ¹³C/¹⁵N-labeled red maple (RM; Acer rubrum) and jack pine (JP; Pinus banksania) at 0 (native wood), 200, 300, 450 and 600 °C. PyOM amendments to soil were at 11 % total soil C. After 3 months of this ongoing incubation, ¹³CO₂ evolution indicates that both pyrolysis temperature and species played a significant role in PyOM and native SOC mineralization. For both species, PyOM-C mineralization decreased with increasing temperature and PyOM ≥200 °C additions decreased SOC mineralization relative to controls.. In addition, PyOM-C mineralization of RM-derived PyOM was enhanced relative to JP-derived PyOM at temperatures <600 °C. Soils with added RM-derived PyOM exhibited significantly lower SOC mineralization at 300 and 450 °C than from JP-derived PyOM additions. These results highlighting interactive temperature and species effects are consistent with our detailed spectroscopic, elemental and isotope analysis of the PyOM samples across this pyrolysis gradient, which shows significant physicochemical changes at 300 °C for JP and between 300 and 450 °C for RM. Efforts will be made in this paper to link PyOM structural and chemical properties to the PyOM and native SOC turnover rates.