The fungal feeding channel of the soil micro‐food web contributes to the transformation of exogenous C into soil C—A 13 C labelling microcosm experiment

Abstract Plant residue is an important carbon (C) source for soil communities that motivates underground C cycling. However, the effects of plant residue quantity on the structure of the soil micro‐food web and the transformation of exogenous C within the micro‐food web after increasing organic input are not known. Thus, a microcosm experiment was carried out to investigate the responses of soil micro‐food web (including microorganisms and nematodes) to different amounts of 13 C‐labelled maize residue addition treatments [without residue addition, 1/3 (1/3R), 2/3 (2/3R) and total residue addition (R)]. The abundances of residue 13 C in CO 2 ( 13 CO 2 ), soil organic C (SO 13 C), microorganisms ( 13 C‐microorganisms) and nematodes ( 13 C‐nematodes) were determined after 1, 7, 35 and 84 days. Increasing organic input changed the micro‐food web composition and increased the amount of 13 C‐bacteria, 13 C‐fungi and 13 C‐fungivores but not 13 C‐bacterivores. The result of the 13 C‐based network showed that bacterivores were positively correlated with omnivores‐predators at the early stage after increasing organic input, while fungivores were at the late stage. Greater 13 CO 2 /SO 13 C but lower SO 13 C/total 13 C input ratios were found in the R than in the 1/3R treatment at the early stage. At the late stage, the R treatment decreased both 13 CO 2 /total 13 C input and 13 CO 2 /SO 13 C ratios. We concluded that increasing organic input strengthened the trophic interactions between microorganisms and nematodes. The transformation of exogenous C from bacteria to bacterivores might accelerate the turnover of soil C pool, however, the C flow from fungi to fungivores and then to omnivores‐predators could contribute to the exogenous C sequestration in soil.