Wood source and pyrolysis temperature interact to control PyOM degradation rates

Wednesday, 16 December 2015
Poster Hall (Moscone South)
Pierre-Joseph Hatton1, Timothy R Filley2, Subhasish Chatterjee3, Apolline Auclerc4, Mark Gormley5, Keyvan Dastmalchi3, Ruth E Stark3, Knute J Nadelhoffer6 and Jeffrey A Bird5, (1)University of Michigan Ann Arbor, Ann Arbor, MI, United States, (2)Purdue University, Earth, Atmospheric, and Planetary Sciences, West Lafayette, IN, United States, (3)City University of New York, Department of Chemistry, New York, NY, United States, (4)Universite de Lorraine, Lab Sols & Environnement UMR 1120, Vandoeuvre-les-Nancy, France, (5)Queens College, CUNY, Queens, NY, United States, (6)Univ of Mich- Eco & Evol Bio, Ann Arbor, MI, United States
Surprisingly little is known about how shifts in tree species composition and increased forest fire frequency and intensity will affect one of the most stable pools of soil organic matter, i.e. the pyrogenic organic matter (PyOM or char). In a previous study, we showed that wood source and pyrolysis temperature interact to control PyOM structure and potential reactivity for two tree species common in high-latitude forests, jack pine (JP) and red maple (RM). Here, we investigate whether these differences affect PyOM turnover by examining the fates of 13C/15N-enriched JP wood and PyOM pyrolyzed at 300 (JP300) and 450 °C (JP450) and RM pyrolyzed at 450 °C (RM450). The substrates were applied 1–3 cm below the O/A interface of a well-drained Spodosol in a long-term forest fire study located at the University of Michigan Biological Station (Pellston, MI, USA).

13C-CO2effluxes from the first 996 days of decay showed a significant wood source by pyrolysis temperature interaction on PyOM field mineralisation rates, with RM450 mineralising twice faster than JP450 during the first 90 days. Increasing pyrolysis temperature substantially decreased field mineralization rates during the first 996 days, with mineralisation rates 24 and 80 times slower for JP300 and JP450 compared with JP wood. After 1 year, (i) bacterial groups were large sinks for PyOM-derived C as pyrolysis temperature increased and as substrate use efficiency decreased; (ii) potential phenol oxidase and net peroxidase activities were unaffected by the PyOM addition, although net peroxidase activities measured tended to lesser for soils amended with JP450 and RM450; and (iii) Collembola detritivores appeared less likely to be found for soils amended with JP450 and RM450. PyOM-derived C and N recoveries did not differ after 1 year; we will present 3-y recovery data.

Our results suggest that the composition of angiosperms (e.g. RM) and gymnosperms (e.g. JP) in high-latitude forests is an underappreciated but essential determinant of soil PyOM stocks and reactivity, with angiosperms yielding more degradable PyOM. Considering the wood source by pyrolysis temperature interaction on PyOM will help providing more comprehensive large-scale assessments of PyOM stocks and reactivity potentials under current and future climate conditions.