Bomb ¹⁴ C for tracing biochar mineralization in soil

Abstract

Improving our understanding of biochar carbon (C) stability in soil is crucial given its potential for soil C sequestration. However, challenges with isotopic labeling of biochar restrict our ability to determine its fate in soil. Atmospheric nuclear bomb tests in the 1960s resulted in a ¹⁴ C spike in tree rings, providing an opportunity to address this challenge. Here, we present a method that utilizes the elevated levels of ¹⁴ C in wood from tree rings formed between 1964 and 1967 as a tracer to determine the proportion of biochar C in mineralized soil. Biochar was produced using wood from the ¹⁴ C enriched tree rings as feedstock and thereafter used in a mineralization experiment capturing the emitted CO ₂ . We demonstrate that the bomb ¹⁴ C-enrichment in the biochar is high enough to differentiate between CO ₂ originating from either biochar or soil organic matter mineralization. The method can be used to address questions on biochar persistence, its interactions with soil organic matter and research that is needed to explore the potential to use biochar for C sequestration in soils.