Chemical and Isotopic Thresholds in Charring: Implications for the Interpretation of Charcoal Mass and Isotopic Data

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• 作者：Lacey A. Pyle ; William C. Hockaday ; Thomas Boutton ; Kyriacos Zygourakis ; Timothy J. Kinney ; Caroline A. Masiello
• 刊名：Environmental Science & Technology
• 出版年：2015
• 出版时间：December 15, 2015
• 年：2015
• 卷：49
• 期：24
• 页码：14057-14064
• 全文大小：401K
• ISSN：1520-5851

文摘

Charcoal plays a significant role in the long-term carbon cycle, and its use as a soil amendment is promoted as a C sequestration strategy (biochar). One challenge in this research area is understanding the heterogeneity of charcoal properties. Although the maximum reaction temperature is often used as a gauge of pyrolysis conditions, pyrolysis duration also changes charcoal physicochemical qualities. Here, we introduce a formal definition of charring intensity (CI) to more accurately characterize pyrolysis, and we document variation in charcoal chemical properties with variation in CI. We find two types of responses to CI: either linear or threshold relationships. Mass yield decreases linearly with CI, while a threshold exists across which % C, % N, and 未¹⁵N exhibit large changes. This CI threshold co-occurs with an increase in charcoal aromaticity. C isotopes do not change from original biomass values, supporting the use of charcoal 未¹³C signatures to infer paleoecological conditions. Fractionation of N isotopes indicates that fire may be enriching soils in ¹⁵N through pyrolytic N isotope fractionation. This influx of 鈥渂lack N鈥?could have a significant impact on soil N isotopes, which we show theoretically using a simple mass-balance model.