Jun Shan Jie Liu Yongfeng Wang Xiaoyuan Yan Hongyan Guo Xiangzhen Li Rong Ji. Digestion and residue stabilization of bacterial and fungal cells protein peptidoglycan and chitin by the geophagous earthwormMetaphire guillelmi.Soil Biology and Biochemistry http://dx.doi.org-10.1016-j.soilbio.2013.03.009

Abstract

Microbial biomass is an important source of soil organic matter which plays crucial roles in the maintenance of soil fertility and food security. However the mineralization and transformation of microbial biomass by the dominant soil macrofauna earthworms are still unclear. We performed feeding trials with the geophagous earthworm Metaphire guillelmi using ¹⁴C-labelled bacteria (Escherichia coli and Bacillus megaterium) cells fungal (Penicillium chrysogenum) cells protein peptidoglycan and chitin. The mineralization rate of the microbial cells and cell components was significantly 1.2–4.0-fold higher in soil with the presence of M. guillelmi for seven days than in earthworm-free soil and 1–11-fold higher than in fresh earthworm cast material. When the earthworms were removed from the soil the mineralization of the residual carbon of the microbial biomass was significantly lower than that in the earthworm-free soil indicating that M. guillelmi affects the mineralization of the biomass in soil in two aspects: first stimulation and then reduction which were attributed to the passage of the microbial biomass through the earthworm gut and that the microorganisms in the cast could play only minor roles in the stimulated mineralization and residual stabilization of microbial biomass. Large amounts (8–29%) of radiolabel of the tested microbial biomass were assimilated in the earthworm tissue. Accumulation of fungal cells (11%) and cell wall component chitin (29%) in the tissue was significantly higher than that of bacterial cells (8%) and cell wall component peptidoglycan (15%). Feeding trails with ¹