Earthworm linings induce stronger lateral gradients of Ct, Nt, and cereal root growth from macropore towards bulk soil than root debris

As biochemical ‘ hotspot ’ in subsoil of arable fields with high total carbon and nitrogen (C t , N t ) contents, the biopore sheath is an attractive soil compartment for root growth. However, little is known about the modulating effects of either taprooted cover crops or anecic earthworms on the biopore sheath and root growth of following crops. A pot experiment was performed to measure C t and N t contents and homorhizous root growth of spring barley ( Hordeum vulgare L.) in the sheaths (up to 8 mm distance from macropore) compared to the bulk soil (20–36 mm distance) in 2.5 year old biopores. The biopore types are artificial macropores formerly colonized by either a taprooted perennial crop ( Cichorium intybus L.) (‘root type’) or an anecic earthworm ( Lumbricus terrestris L.) fed with chicory leaves (‘worm type’). Additionally, δ 13 C and δ 15 N were analyzed in the sheaths and bulk soil as an indicator for the organic matter degradation. Indicating the accumulation of organic matter, fewer heavier isotopes were found towards macropore. That coincided with a tendentially (root type) or significantly (worm type) increasing C t and N t content, and an increasing root length density (log RLD) of spring barley in worm type. Both pore types facilitate root growth in comparison to the bulk soil, but with stronger gradient in worm type. • Quantified homorhizous root growth in root or worm colonized biopores in subsoil. • Modulation of taproot or earthworm on biopore sheaths of large sized biopores. • δ 13 C and δ 15 N reflected the organic matter accumulation in the sheaths of root and worm type biopore. • Worm linings induced stronger gradients of C t , N t , and root growth across the sheath.