Preferential degradation of leaf- vs. root-derived organic carbon in earthworm-affected soil

Abstract

Earthworms are integral parts of many ecosystems and may play a decisive role in determining whether soils function as carbon (C) sink or source. However, information on how earthworms affect the composition and stability of soil organic matter (SOM) is scarce. Particularly their effect on organic matter deriving from leaves and roots with distinct composition and, thus, susceptibility to decomposition and stabilization remains unclear. Here, we combine cutin- and suberin-derived lipids as specific markers for leaf- and root-derived SOM with their 13C composition and physical fractionations of soil. We show that earthworms overprint the protective role of organo-mineral associations and aggregates to favor the accumulation of root- relative to leaf-derived SOM. This gradual accumulation contributes to the often-observed dominance of root-derived organic matter in soil and emphasizes the need to consider molecular level effects of earthworms on SOM dynamics.