Munksgaard, Niels C., McBeath, Anna V., Ascough, Philippa L., Levchenko, Vladimir A., Williams, Alan, and Bird, Michael I (2019) Partitioning of microbially respired CO₂ between indigenous and exogenous carbon sources during biochar degradation using radiocarbon and stable carbon isotopes. Radiocarbon, 61 (2). pp. 573-586.

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Abstract

Pyrolized carbon in biochar can sequester atmospheric CO₂ into soil to reduce impacts of anthropogenic CO₂ 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 CO₂ efflux rates, ¹⁴C concentration and δ¹³C values in CO₂ to quantify the contributions of biochar carbon and other sources of carbon to the CO₂ efflux. The ¹⁴C concentration in CO₂ showed that microbial degradation led to respiration of CO₂ sourced from indigenous biochar carbon (approximate to 0.5-1.4 μmoles CO₂/g biochar C/day) along with a component of carbon closely associated with the biochars but derived from the local environment. Correlations between ¹⁴C concentration, δ¹³C values and Ca abundance indicated that Ca²⁺ availability was an important determinant of the loss of biochar carbon.

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