Abstract
By living in permanent burrows and incorporating organic detritus from the soil surface, anecic earthworms contribute to soil heterogeneity, but their impact is still under-studied in natural field conditions. We investigated the effects of the anecic earthworm Lumbricus centralis on fresh carbon (C) incorporation, soil organic matter composition, protists, and nematodes of a Cambisol under grassland. We used plant material labelled with stable isotope tracers to detect fresh C input around earthworm-occupied burrows or around burrows from which the earthworm had been removed. After 50 days, we sampled soil (0–10 cm depth) in concentric layers around the burrows, distinguishing between drilosphere (0–8 mm) and bulk soil (50–75 mm). L. centralis effectively incorporated fresh C into the drilosphere, and this shifted soil organic matter amount and chemistry: total soil sugar content was increased compared to unoccupied drilosphere and bulk soil, and the contribution of plant-derived sugars to soil organic matter was enhanced. Earthworms also shifted the spatial distribution of soil C towards the drilosphere. The total abundance of protists and nematodes was only slightly higher in earthworm-occupied drilosphere, but strong positive effects were found for some protist clades (e.g. Stenamoeba spp.). Additional data for the co-occurring anecic earthworm species Aporrectodea longa showed that it incorporated fresh C less than L. centralis, suggesting that the two species may have different effects on soil C distribution and organic matter quality.
Highlights
Anecic earthworms forage at the soil surface for organic detritus which they bring inside their vertical burrows and translocate large amounts of organic matter belowground (Hale et al 2005; Nuutinen 2011)
We focused on L. centralis (Bouché), which is morphologically and ecologically similar to the widespread L. terrestris
L. centralis specimens from the burrows under labelled maize had on average higher δ13C (1.67±11.85 ‰) than isotopic control specimens (−21.00±0.13‰), but there was a very high variability
Summary
Anecic earthworms forage at the soil surface for organic detritus which they bring inside their vertical burrows and translocate large amounts of organic matter belowground (Hale et al 2005; Nuutinen 2011). Together with the earthworms’ excreta, the soil near the burrows forms the ‘drilosphere’, a microhabitat that acts as a hotspot of many edaphic processes, such as C and N incorporation (Andriuzzi et al 2013; Fahey et al 2013), mineralization (Don et al 2008), and nitrification and denitrification (Parkin and Berry 1999). These functions are associated with, and partly driven by, enhanced biological activity. The soil around burrows of Lumbricus terrestris supports bacterial communities that can respond rapidly to the earthworm-mediated input of fresh organic detritus (Tiunov and Scheu 1999).
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