Methodologies based on ¹³C-enrichment (E), ¹³C-depletion (D) and ¹³C-natural abundance (NA) to estimate the stability of biochar in soil were critically examined. The stability of ¹³C-enriched biochar can be estimated by the quantitative recovery of excess ¹³C, either in the soil or in evolved CO₂. Both approaches have advantages and disadvantages. Recovery in the soil is a measure of both residual biochar ¹³C + ¹³C immobilised in soil organic matter during biochar decomposition. Variable proportions of organic- and inorganic-C are present in alkaline biochars, and few data exist on the uniformity of labelling, which is a basic requirement of the respired ¹³CO₂ and E methodology. The E technique has had limited application due to the cost and difficulty of obtaining a uniformly-enriched feedstock through continuous labelling of plants with ¹³CO₂ at a constant ¹³C enrichment. In contrast, the NA technique has been widely applied. The NA and D techniques are in situ methods that involve the addition of C₄-derived biochar to a C₃-soil or vice versa. Stability is estimated by a two-end-member mixing model that allows the proportion of evolved CO₂ derived from the biochar (Cdfb) to be estimated. The mixing model has recently been misused to estimate the Cdfb of ¹³C-enriched biochar, with ¹³C-abundance expressed as erroneously large δ values. ¹³C-based methods provide a yardstick against which rapid stability tests should be evaluated. While numerous laboratory incubation comparisons have been conducted, very few field-based data have been published.

中文翻译：

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用于量化土壤中生物炭稳定性的 13C 方法：批评

对基于¹³ C-富集 ( E )、¹³ C-消耗 ( D ) 和¹³ C-自然丰度 ( NA ) 的方法来估计土壤中生物炭的稳定性进行了严格检查。富含¹³ C 的生物炭的稳定性可以通过定量回收土壤中或释放的 CO _{2中的过量}¹³ C 来估计。两种方法都有优点和缺点。土壤中的恢复是衡量残留 biochar ¹³ C +  ¹³生物炭分解过程中固定在土壤有机质中的 C。碱性生物炭中存在不同比例的有机碳和无机碳，很少有关于标记一致性的数据，这是呼吸¹³ CO ₂和E方法的基本要求。由于通过在恒定的¹³ C 富集下用¹³ CO _{2连续标记植物来获得均匀富集的原料的成本和困难，} E技术的应用有限。相比之下，NA技术已被广泛应用。NA和D _技术是原位方法，包括将 C ₄衍生的生物炭添加到 C ₃土壤中，反之亦然。稳定性通过一个两端成员混合模型来估计，该模型允许估计源自生物炭 (Cdfb)的演化 CO _{2的比例。}混合模型最近被滥用来估计富含 13 C 的生物炭的 Cdfb ^，其中¹³ C 丰度表示为错误的大δ值。¹³基于 C 的方法提供了一个衡量快速稳定性测试的标准。虽然已经进行了许多实验室孵化比较，但很少有基于现场的数据发表。