Partitioning of microbially respired CO 2 between indigenous and exogenous carbon sources during biochar degradation using radiocarbon and stable carbon isotopes

Niels C. Munksgaard, Anna V. McBeath, Philippa L. Ascough, Vladimir A. Levchenko, Alan Williams, Michael I. Bird

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    Abstract

    Pyrolized carbon in biochar can sequester atmospheric CO 2 into soil to reduce impacts of anthropogenic CO 2 emissions. When estimating the stability of biochar, degradation of biochar carbon, mobility of degradation products, and ingress of carbon from other sources must all be considered. In a previous study we tracked degradation in biochars produced from radiocarbon-free wood and subjected to different physico-chemical treatments over three years in a rainforest soil. Following completion of the field trial, we report here a series of in-vitro incubations of the degraded biochars to determine CO 2 efflux rates, 14 C concentration and δ 13 C values in CO 2 to quantify the contributions of biochar carbon and other sources of carbon to the CO 2 efflux. The 14 C concentration in CO 2 showed that microbial degradation led to respiration of CO 2 sourced from indigenous biochar carbon (≈0.5-1.4 μmoles CO 2 /g biochar C/day) along with a component of carbon closely associated with the biochars but derived from the local environment. Correlations between 14 C concentration, δ 13 C values and Ca abundance indicated that Ca 2+ availability was an important determinant of the loss of biochar carbon.

    Original languageEnglish
    Pages (from-to)573-586
    Number of pages14
    JournalRadiocarbon: an international journal of cosmogenic isotope research
    Volume61
    Issue number2
    Early online date5 Nov 2018
    DOIs
    Publication statusPublished - 1 Apr 2019

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