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 C-13-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 C-13 in CO2 ((CO2)-C-13), soil organic C ((SOC)-C-13), microorganisms (C-13-microorganisms) and nematodes (C-13-nematodes) were determined after 1, 7, 35 and 84 days. Increasing organic input changed the micro-food web composition and increased the amount of C-13-bacteria, C-13-fungi and C-13-fungivores but not C-13-bacterivores. The result of the C-13-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 (CO2)-C-13/(SOC)-C-13 but lower (SOC)-C-13/total C-13 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 (CO2)-C-13/total C-13 input and (CO2)-C-13/(SOC)-C-13 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.