Ecosystem fires are stochastic and anthropogenic phenomena that affect critical soil processes. Nevertheless, environmental managers, policy-makers, and even scientists have often overlooked the induced transformations that fire does to soil organic matter (SOM), which sustains an ecosystem’s overall health. Here, we investigated the effects of simulated fire conditions on bulk SOM, water-extractable organic matter (WEOM), and vulnerability to microbial degradation. Sequential thermal decomposition experiments were carried out to investigate the effect of increasing temperature on C, N, δ13C, and δ15N of bulk SOM and WEOM. A microbial decomposition experiment was also done to determine the effects of burning on SOM degradability. Intermediate-intensity burns caused significant decreases in C and N concentrations in soils, as well as alterations in bulk SOM and WEOM properties. Conversely, the effects of low-intensity burns were less apparent in terms of bulk SOM content and stable C and N isotope composition. However, the results of the microbial decomposition experiment revealed that low-intensity burning resulted in elevated CO2 emission that were significantly correlated with C concentration, δ13C values, and the C/N ratio of WEOM. These results provide evidence that low-intensity burning can have important consequences for soils, altering its organic components and releasing significant amounts of greenhouse gases. Thus, particular focus must be given to managing ecosystem fires and evaluating their impacts, especially because fire is still widely used in agriculture and forest management with frequency projected to increase in the coming years.

中文翻译：

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燃烧后土壤有机质对微生物分解的脆弱性

生态系统火灾是影响关键土壤过程的随机和人为现象。然而，环境管理者、政策制定者，甚至科学家们经常忽视火对维持生态系统整体健康的土壤有机质 (SOM) 的诱导转变。在这里，我们研究了模拟火灾条件对散装 SOM、水可提取有机物 (WEOM) 和微生物降解脆弱性的影响。进行了连续热分解实验以研究温度升高对块状 SOM 和 WEOM 的 C、N、δ13C 和 δ15N 的影响。还进行了微生物分解实验以确定燃烧对 SOM 降解性的影响。中等强度的烧伤导致土壤中 C 和 N 浓度显着下降，以及散装 SOM 和 WEOM 属性的改变。相反，就大量 SOM 含量和稳定的 C 和 N 同位素组成而言，低强度烧伤的影响不太明显。然而，微生物分解实验的结果表明，低强度燃烧导致 CO2 排放增加，这与 C 浓度、δ13C 值和 WEOM 的 C/N 比显着相关。这些结果证明，低强度燃烧会对土壤产生重要影响，改变其有机成分并释放大量温室气体。因此，必须特别关注管理生态系统火灾并评估其影响，特别是因为火灾仍广泛用于农业和森林管理，预计未来几年其频率会增加。