Despite the importance of soil organic matter (SOM) in the global carbon cycle, there remain many open questions regarding its formation and preservation. The study of individual organic compound classes that make up SOM, such as lipid biomarkers including n-alkanes, can provide insight into the cycling of bulk SOM. While studies of lipid biomarkers, particularly n-alkanes, have increased in number in the past few decades, only a limited number have focused on the transformation of these compounds following deposition in soil archives. We performed a systematic review to consolidate the available information on plant-derived n-alkanes and their transformation from plant to soil. Our major findings were (1) a nearly ubiquitous trend of decreased total concentration of n-alkanes either with time in litterbag experiments or with depth in open plant–soil systems and (2) preferential degradation of odd-chain length and shorter chain length n-alkanes represented by a decrease in either carbon preference index (CPI) or odd-over-even predominance (OEP) with depth, indicating degradation of the n-alkane signal or a shift in vegetation composition over time. The review also highlighted a lack of data transparency and standardization across studies of lipid biomarkers, making analysis and synthesis of published data time-consuming and difficult. We recommend that the community move towards more uniform and systematic reporting of biomarker data. Furthermore, as the number of studies examining the complete leaf–litter–soil continuum is very limited as well as unevenly distributed over geographical regions, climate zones, and soil types, future data collection should focus on underrepresented areas as well as quantifying the transformation of n-alkanes through the complete continuum from plant to soil.

中文翻译：

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正构烷烃从植物到土壤的转化：综述

尽管土壤有机质 (SOM) 在全球碳循环中很重要，但关于其形成和保存仍存在许多悬而未决的问题。研究构成 SOM 的单个有机化合物类别，例如包括正烷烃在内的脂质生物标志物，可以深入了解大量 SOM 的循环。虽然脂质生物标志物，特别是正构烷烃的研究在过去几十年中有所增加，但只有少数人关注这些化合物在土壤档案中沉积后的转化。我们进行了系统审查，以整合有关植物源性n的可用信息-烷烃及其从植物到土壤的转化。我们的主要发现是 (1)正构烷烃的总浓度随垃圾袋实验中的时间或开放植物 - 土壤系统的深度而降低的趋势几乎无处不在，以及 (2) 奇链长度和较短链长度n 的优先降解- 烷烃表现为碳偏好指数 (CPI) 或奇偶优势 (OEP) 随深度下降，表明n 的退化-烷烃信号或植被成分随时间的变化。该审查还强调了脂质生物标志物研究之间缺乏数据透明度和标准化，使得对已发表数据的分析和合成既耗时又困难。我们建议社区转向更加统一和系统地报告生物标志物数据。此外，由于检查完整的叶-凋落物-土壤连续体的研究数量非常有限，并且在地理区域、气候带和土壤类型上分布不均，因此未来的数据收集应侧重于代表性不足的地区，并量化正构烷烃通过从植物到土壤的完整连续体。