Abstract
BackgroundEpigeic earthworms are key organisms in organic matter decomposition because of the interactions they establish with microorganisms. The earthworm species and the quality and/or substrate availability are expected to be major factors influencing the outcome of these interactions. Here we tested whether and to what extent the epigeic earthworms Eisenia andrei, Eisenia fetida and Perionyx excavatus, widely used in vermicomposting, are capable of altering the microbiological properties of fresh organic matter in the short-term. We also questioned if the earthworm-induced modifications to the microbial communities are dependent on the type of substrate ingested.Methodology/Principal FindingsTo address these questions we determined the microbial community structure (phospholipid fatty acid profiles) and microbial activity (basal respiration and microbial growth rates) of three types of animal manure (cow, horse and rabbit) that differed in microbial composition, after being processed by each species of earthworm for one month. No differences were found between earthworm-worked samples with regards to microbial community structure, irrespective of type of manure, which suggests the existence of a bottleneck effect of worm digestion on microbial populations of the original material consumed. Moreover, in mesocosms containing cow manure the presence of E. andrei resulted not only in a decrease in bacterial and fungal biomass, but also in a reduced bacterial growth rate and total microbial activity, while no such reduction was found with E. fetida and P. excavatus.Conclusions/SignificanceOur results point to the species of earthworm with its associated gut microbiota as a strong determinant of the process shaping the structure of microbial communities in the short-term. This must nonetheless be weighed against the fact that further knowledge is necessary to evaluate whether the changes in the composition of microbiota in response to the earthworm species is accompanied by a change in the microbial community diversity and/or function.
Highlights
The aboveground net primary production, around 80–90%, enters the soil food web as dead plant material in most terrestrial ecosystems [1]
We found that the shifts in phospholipid fatty acid (PLFA) profiles were strongly influenced by the species of earthworm (Fig. 1b), irrespective of the type of manure (ANOVA F4,18 = 0.37, P = 0.83)
The first discriminant function contributed in differentiating the substrates processed by E. andrei from those processed by E. fetida and P. excavatus (Fig. 1b), accounting for 72% of the variance (ANOVA F2,18 = 57.38, P,0.001), whereas the second function mainly separated the substrates processed by E. fetida from those processed by P. excavatus (ANOVA F2,18 = 62.47, P,0.001; Fig. 1b)
Summary
The aboveground net primary production, around 80–90%, enters the soil food web as dead plant material in most terrestrial ecosystems [1]. Earthworms may affect the decomposition of organic matter through gut associated processes (direct effects), i.e. via the effects of ingestion, digestion and assimilation of the organic matter and microorganisms, which are released in earthworm casts [5,6]; and cast associated processes (indirect effects) that are more closely associated with the presence of unworked material and to physical modification of the egested material [7] Such indirect effects are derived from direct effects, and include processes such as the ageing of earthwormworked material (weeks to months), and mixing of such material with substrates that have not been processed by earthworms yet [8]. We questioned if the earthworm-induced modifications to the microbial communities are dependent on the type of substrate ingested
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