Tree taxa and pyrolysis temperature interact to control pyrogenic organic matter induced native soil organic carbon priming

Few studies have quantitatively assessed the interacting controls of taxa-specific properties and PyOM production temperature on native soil C (NSC) stabilization/de-stabilization dynamics (i.e. priming effects - PE) because of difficulty in distinctly assessing NSC reactivity apart from added PyOM-C. To quantify PyOM-induced PE, we incubated 13C-enriched jack pine (JP) or red maple (RM) wood and associated 13C-PyOM produced at 200 (PyOM200), 300 (PyOM300), 450 (PyOM450) and 600 (PyOM600) °C in soil from a northern temperate forest (Michigan, U.S.A.) for 10 months. We found that (1) net PE was negative with addition of both wood and PyOM from both taxa, with a 3-40% suppression in mineralization across treatments, (2) RM200, RM450, and RM600 exhibited initial positive PE in the first week of incubation, (3) PyOM300 of both taxa, the temperature associated with initial aromatization and carbohydrate conversion, induced the most negative PE and exhibited the largest increase in soil oxidative enzyme activity in JP300, (4) addition of sucrose to the incubations as labile C, offset negative PE in JP treatments but not in RM treatments and, (5) mean residence times of the fast cycling C pool of NSC were lower (1.4-1.6 d) for RM than for JP (2.9-8.3 d) additions. These results suggest that future changes in tree taxa dominance in fire prone systems could alter soil C stability though introduction of PyOM of distinct, taxa-specific, chemical properties that may be largely controlled by taxa specific temperature thresholds in thermochemical conversion of woody tissues to PyOM.