Hatten Jeff, Goñi Miguel
Department of Forest Engineering, Resources & Management, Oregon State University, Corvallis, Oregon, United States of America.
College of Earth, Ocean, and Atmospheric Sciences, Oregon State University, Corvallis, Oregon, United States of America.
PLoS One. 2016 Mar 24;11(3):e0151957. doi: 10.1371/journal.pone.0151957. eCollection 2016.
Wildfire greatly impacts the composition and quantity of organic carbon stocks within watersheds. Most methods used to measure the contributions of fire altered organic carbon-i.e. pyrogenic organic carbon (Py-OC) in natural samples are designed to quantify specific fractions such as black carbon or polyaromatic hydrocarbons. In contrast, the CuO oxidation procedure yields a variety of products derived from a variety of precursors, including both unaltered and thermally altered sources. Here, we test whether or not the benzene carboxylic acid and hydroxy benzoic acid (BCA) products obtained by CuO oxidation provide a robust indicator of Py-OC and compare them to non-Py-OC biomarkers of lignin. O and A horizons from microcosms were burned in the laboratory at varying levels of fire severity and subsequently incubated for 6 months. All soils were analyzed for total OC and N and were analyzed by CuO oxidation. All BCAs appeared to be preserved or created to some degree during burning while lignin phenols appeared to be altered or destroyed to varying extents dependent on fire severity. We found two specific CuO oxidation products, o-hydroxybenzoic acid (oBd) and 1,2,4-benzenetricarboxylic acid (BTC2) that responded strongly to burn severity and withstood degradation during post-burning microbial incubations. Interestingly, we found that benzene di- and tricarboxylic acids (BDC and BTC, respectively) were much more reactive than vanillyl phenols during the incubation as a possible result of physical protection of vanillyl phenols in the interior of char particles or CuO oxidation derived BCAs originating from biologically available classes of Py-OC. We found that the ability of these compounds to predict relative Py-OC content in burned samples improved when normalized by their respective BCA class (i.e. benzene monocarboxylic acids (BA) and BTC, respectively) and when BTC was normalized to total lignin yields (BTC:Lig). The major trends in BCAs imparted by burning persisted through a 6 month incubation suggesting that fire severity had first order control on BCA and lignin composition. Using original and published BCA data from soils, sediments, char, and interfering compounds we found that BTC:Lig and BTC2:BTC were able to distinguish Py-OC from compounds such as humic materials, tannins, etc. The BCAs released by the CuO oxidation procedure increase the functionality of this method in order to examine the relative contribution of Py-OC in geochemical samples.
野火对流域内有机碳储量的组成和数量有重大影响。大多数用于测量火灾改变的有机碳（即天然样品中的热解有机碳（Py-OC））贡献的方法旨在量化特定组分，如黑碳或多环芳烃。相比之下，氧化铜氧化程序会产生源自多种前体的多种产物，包括未改变和热改变的来源。在此，我们测试通过氧化铜氧化获得的苯羧酸和羟基苯甲酸（BCA）产物是否能有力指示热解有机碳，并将它们与木质素的非热解有机碳生物标志物进行比较。微观世界的O层和A层在实验室中以不同的火灾严重程度燃烧，随后培养6个月。分析了所有土壤的总有机碳和氮，并通过氧化铜氧化进行分析。所有BCA在燃烧过程中似乎都在某种程度上得以保存或生成，而木质素酚似乎根据火灾严重程度在不同程度上发生改变或被破坏。我们发现两种特定的氧化铜氧化产物，邻羟基苯甲酸（oBd）和1,2,4-苯三甲酸（BTC2），它们对燃烧严重程度反应强烈，并且在燃烧后微生物培养期间能抵抗降解。有趣的是，我们发现苯二酸和苯三甲酸（分别为BDC和BTC）在培养期间比香草基酚更具反应性，这可能是由于香草基酚在炭颗粒内部受到物理保护，或者是由于源自生物可利用的热解有机碳类别的氧化铜氧化衍生BCA。我们发现，当这些化合物通过各自的BCA类别（即分别为苯单羧酸（BA）和BTC）进行归一化，以及当BTC相对于总木质素产量（BTC:Lig）进行归一化时，它们预测燃烧样品中相对热解有机碳含量的能力会提高。燃烧引起的BCA的主要趋势在6个月的培养过程中持续存在，这表明火灾严重程度对BCA和木质素组成具有一级控制作用。利用来自土壤、沉积物、炭和干扰化合物的原始和已发表的BCA数据，我们发现BTC:Lig和BTC2:BTC能够将热解有机碳与腐殖质、单宁等化合物区分开来。氧化铜氧化程序释放的BCA增加了该方法的功能，以便研究热解有机碳在地球化学样品中的相对贡献。
