Enzymes, Manganese, or Iron? Drivers of Oxidative Organic Matter Decomposition in Soils
Enzymes, Manganese, or Iron? Drivers of Oxidative Organic Matter Decomposition in Soils
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DOI：
10.1021/acs.est.0c04212
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发表时间：
2020-11-03
影响因子：
11.4
通讯作者：
Keiluweit, Marco
中科院分区：
文献类型：
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作者：
Jones, Morris E.;LaCroix, Rachelle E.;Keiluweit, Marco
土壤有机质的氧化分解决定了碳的比例，无论是储存或排放到大气中的二氧化碳。将有机物完全转化为二氧化碳需要氧化机制，将复杂分子分解成可由微生物呼吸的较小的可溶性单体。目前的模型将氧化解聚主要归因于胞外酶的活性。在这里，我们表明，活性锰（Mn）和铁（Fe）的中间体，而不是其他测量的土壤特性，最好的预测在温带森林土壤中的氧化活性。结合生物测定，光谱学和湿化学分析，我们发现，在表面凋落物的氧化活性是最显着相关的活性锰（III）物种的丰度。与此相反，在下面的矿质土壤中的氧化活性是最显着相关的活性Fe（II/III）物种的丰度。阳性对照表明，Mn（III）和Fe（II/III）物质在产生氧化活性方面同样有效，但这意味着传统生物测定对Fe具有系统性偏见。结合起来，我们的研究结果突出了耦合的生物-非生物性质的氧化机制，锰介导的氧化占主导地位的锰丰富的有机土壤和铁介导的氧化占主导地位的铁丰富的矿质土壤。这些研究结果表明，微生物依赖于不同的氧化策略，这取决于在给定的土壤环境中的铁和锰的相对可用性。
Oxidative decomposition of soil organic matter determines the proportion of carbon that is either stored or emitted to the atmosphere as CO2. Full conversion of organic matter to CO2 requires oxidative mechanisms that depolymerize complex molecules into smaller, soluble monomers that can be respired by microbes. Current models attribute oxidative depolymerization largely to the activity of extracellular enzymes. Here we show that reactive manganese (Mn) and iron (Fe) intermediates, rather than other measured soil characteristics, best predict oxidative activity in temperate forest soils. Combining bioassays, spectroscopy, and wet-chemical analysis, we found that oxidative activity in surface litters was most significantly correlated to the abundance of reactive Mn(III) species. In contrast, oxidative activity in underlying mineral soils was most significantly correlated to the abundance of reactive Fe(II/III) species. Positive controls showed that both Mn(III) and Fe(II/III) species are equally potent in generating oxidative activity, but imply conventional bioassays have a systematic bias toward Fe. Combined, our results highlight the coupled biotic-abiotic nature of oxidative mechanisms, with Mn-mediated oxidation dominating within Mn-rich organic soils and Fe-mediated oxidation dominating Fe-rich mineral soils. These findings suggest microbes rely on different oxidative strategies depending on the relative availability of Fe and Mn in a given soil environment.