C isotope values increase with soil depth is perhaps resulted from decomposition processes, while the increase
of 15N values with depth is usually related to a more intense microbial activity (e.g. [34,36]). However, Scheu and Falca [33] reported that 15N/14N ratios of earthworms vary little with soil depth in forest, due to the
movement of earthworms. In the present study, the VF was composed by four superimposed and separated perspex tubings, causing the earthworms not to move among the tubings. Thus, 15N- and 13C-enrichment of biofilms with depth implied the increase in the natural abundances of the organic food for earthworm, and led to 15N- and 13C-enrichment of the earthworms as the depth. These findings confirmed and complemented the findings that the N and C isotopic characteristics of the earthworms were influenced by that of growth substrates (sewage sludge).
C isotope values increase with soil depth is perhaps resulted from decomposition processes, while the increaseof 15N values with depth is usually related to a more intense microbial activity (e.g. [34,36]). However, Scheu and Falca [33] reported that 15N/14N ratios of earthworms vary little with soil depth in forest, due to the movement of earthworms. In the present study, the VF was composed by four superimposed and separated perspex tubings, causing the earthworms not to move among the tubings. Thus, 15N- and 13C-enrichment of biofilms with depth implied the increase in the natural abundances of the organic food for earthworm, and led to 15N- and 13C-enrichment of the earthworms as the depth. These findings confirmed and complemented the findings that the N and C isotopic characteristics of the earthworms were influenced by that of growth substrates (sewage sludge).
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