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Rapid degradation of pyrogenic carbon

Authors

  • Michael Zimmermann,

    Corresponding author
    1. Department of Forest and Soil Research, University of Natural Resources and Life Sciences Vienna, Vienna, Austria
    • Centre for Tropical Environmental and Sustainability Science and School of Earth and Environmental Sciences, James Cook University, Cairns, QLD, Australia
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  • Michael I. Bird,

    1. Centre for Tropical Environmental and Sustainability Science and School of Earth and Environmental Sciences, James Cook University, Cairns, QLD, Australia
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  • Christopher Wurster,

    1. Centre for Tropical Environmental and Sustainability Science and School of Earth and Environmental Sciences, James Cook University, Cairns, QLD, Australia
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  • Gustavo Saiz,

    1. Centre for Tropical Environmental and Sustainability Science and School of Earth and Environmental Sciences, James Cook University, Cairns, QLD, Australia
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  • Iain Goodrick,

    1. Centre for Tropical Environmental and Sustainability Science and School of Earth and Environmental Sciences, James Cook University, Cairns, QLD, Australia
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  • Jiri Barta,

    1. Department of Ecosystem Biology, Faculty of Science, University of South Bohemia, Ceske Budejovice, Czech Republic
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  • Petr Capek,

    1. Department of Ecosystem Biology, Faculty of Science, University of South Bohemia, Ceske Budejovice, Czech Republic
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  • Hana Santruckova,

    1. Department of Ecosystem Biology, Faculty of Science, University of South Bohemia, Ceske Budejovice, Czech Republic
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  • Ronald Smernik

    1. School of Agriculture, Food and Wine, The University of Adelaide, Urrbrae, SA, Australia
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Correspondence: Michael Zimmermann, tel. + 43 (0)1 47654 3144, fax + 43 (0)1 47654 3130, e-mail: michael.zimmermann@boku.ac.at

Abstract

Pyrogenic carbon (PC- charcoal, biochar or black carbon) represents a poorly understood component of the global carbon (C) cycle, but one that has considerable potential to mitigate climate change through provision of long-term soil C sequestration. Mass balance calculations suggest global PC production and stocks are not in balance, indicating a major gap in our understanding of the processes by which PC is re-mineralized. We collected PC samples derived from the same wood material and exposed to natural environmental conditions for 1 and 11 years. We subjected these materials to repeated laboratory incubation studies at temperatures of up to 60 °C, as ground surface temperatures above 30 °C and up to 60 °C occur regularly over a significant area of the tropics and sub-tropics. Mineralization rates were not different for the two samples and followed an exponential Arrhenius function that suggest an average turnover time of 67 years for conditions typical of a tropical savannah environment. Microbial biomass as measured by chloroform fumigation and DNA extractions was the same for the two samples, but abiotic CO2 production was lower for the fresh PC sample than that for the aged sample. Nuclear magnetic resonance spectroscopy, hydrogen pyrolysis and scanning electron microscopy demonstrate that the measured CO2 production originates dominantly from polycyclic aromatic compounds rather than any minor labile components. Therefore, rapid, sub-centennial rates of re-mineralization of PC on the soil surface in tropical and sub-tropical environments may represent a major and hitherto unidentified mechanism for balancing the PC production at the global scale.

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