Earthworms are keystone regulators of carbon exchange between terrestrial ecosystems and the atmosphere. However, exactly how earthworms regulate the composition of microbial and plant-derived carbon in soil organic matter remains poorly understood. Here we conducted a microcosm experiment with two species of endogeic earthworms (Drawida gisti and Metaphire guillelmi) to investigate their effects on cellular and extracellular-microbial residues versus fast and slow-decaying plant materials. We found that both species of earthworms reduced microbial residues (amino sugars or the protein content of extracellular polymeric substances (EPS)) and facilitated the decomposition of microbial residues rather than their formation. Neither earthworm species affected slow-decaying plant residues (lignin phenols). However, their effects on the fast-decaying fraction of plant residues (particulate organic matter (POM)) depended on the earthworm species. Principal component analysis (PCA) revealed that earthworms mediated two gradients between microbial and plant residues. The first gradient was between the nitrogenous fraction of microbial residues (e.g., amino sugars and EPS-protein) versus slow-decaying plant lignin, while the second gradient was between the fast-decaying POM versus EPS-polysaccharide. Our results suggest that earthworms play vital roles in mediating plant and microbial residue fractions in soil through their multifaceted mechanisms in regulating the chemical composition of organic carbon, and in understanding biological control of the global soil carbon cycle.

中文翻译：

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蚯蚓通过分解来调节土壤微生物和植物残留物


蚯蚓是陆地生态系统与大气之间碳交换的关键调节剂。然而，蚯蚓究竟如何调节土壤有机质中微生物和植物来源的碳的组成仍然知之甚少。在这里，我们对两种内生蚯蚓（Drawida gisti 和 Metaphire guillelmi）进行了微观实验，以研究它们对细胞和细胞外微生物残留物的影响，而不是快速和缓慢腐烂的植物材料。我们发现这两种蚯蚓都减少了微生物残留物（氨基糖或细胞外聚合物物质 （EPS） 的蛋白质含量），并促进了微生物残留物的分解而不是它们的形成。这两种蚯蚓物种都不会影响缓慢腐烂的植物残留物（木质素酚）。然而，它们对植物残留物的快速腐烂部分（颗粒有机物 （POM））的影响取决于蚯蚓物种。主成分分析 （PCA） 显示，蚯蚓介导微生物和植物残留物之间的两个梯度。第一个梯度是在微生物残基（例如氨基糖和 EPS 蛋白）的含氮部分与缓慢腐烂的植物木质素之间，而第二个梯度是在快速腐烂的 POM 与 EPS 多糖之间。我们的结果表明，蚯蚓通过其调节有机碳化学成分和了解全球土壤碳循环的生物控制方面的多方面机制，在介导土壤中的植物和微生物残留物组分方面发挥着至关重要的作用。