Molecular and compound specific isotope compositions of apolar lipids were characterized in soil mesocosms incubated for 1 year with or without 13 C-labelled plant residues and earthworms, in order to investigate, at the molecular scale, the effect of earthworms on the fate of organic matter (OM) in soils. Molecular and isotope composition of long chain alkanes in casts confirmed that earthworms preferentially ingest soil fractions rich in plant debris. Apolar lipid specific isotope composition allowed calculation of the proportion of carbon derived from the labelled residues (C lab ). Casts displayed higher C lab values than surrounding soil while soil without earthworm exhibited intermediate C lab . The odd-over-even predominance (OEP) of alkanes suggested they are probably less degraded in casts than in the surrounding soil. Taken together, OEP and C lab values suggested that besides high incorporation of plant residues, earthworms may also favor the preservation of plant apolar lipids in their casts. Additionally, chain length and isotope pattern of alkanes further suggested root lipids were probably less degraded than shoot lipids. High 13 C-incorporation level for the bacterial biomarker hopene provided evidence for intense recycling of plant OM and suggested further contribution of bacterial necromass to soil OM.

中文翻译：

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蚯蚓培养1年后对土壤非极性脂质特征的影响

在有或没有 13 C 标记的植物残留物和蚯蚓的土壤中层环境中，对非极性脂质的分子和化合物特定同位素组成进行表征，以在分子尺度上研究蚯蚓对有机物命运的影响(OM) 在土壤中。铸件中长链烷烃的分子和同位素组成证实，蚯蚓优先摄取富含植物碎片的土壤部分。非极性脂质特定同位素组成允许计算来自标记残留物的碳比例 (C lab )。铸件显示出比周围土壤更高的 C lab 值，而没有蚯蚓的土壤表现出中等的 C lab 值。烷烃的奇偶优势 (OEP) 表明它们在铸件中的降解程度可能低于在周围土壤中的降解。综合起来，OEP 和 C 实验室值表明，除了高度掺入植物残留物外，蚯蚓还可能有利于在其模型中保存植物非极性脂质。此外，烷烃的链长和同位素模式进一步表明根脂质可能比茎脂质降解更少。细菌生物标志物希望烯的高 13 C 掺入水平为植物 OM 的强烈循环提供了证据，并表明细菌坏死对土壤 OM 的进一步贡献。