Endogeic earthworms shape bacterial functional communities and affect organic matter mineralization in a tropical soil

Abstract

Priming effect (PE) is defined as a stimulation of the mineralization of soil organic matter (SOM) following a supply of fresh organic matter. This process can have important consequences on the fate of SOM and on the management of residues in agricultural soils, especially in tropical regions where soil fertility is essentially based on the management of organic matter. Earthworms are ecosystem engineers known to affect the dynamics of SOM. Endogeic earthworms ingest large amounts of soil and assimilate a part of organic matter it contains. During gut transit, microorganisms are transported to new substrates and their activity is stimulated by (i) the production of readily assimilable organic matter (mucus) and (ii) the possible presence of fresh organic residues in the ingested soil. The objective of our study was to see (i) whether earthworms impact the PE intensity when a fresh residue is added to a tropical soil and (ii) whether this impact is linked to a stimulation/inhibition of bacterial taxa, and which taxa are affected. A tropical soil from Madagascar was incubated in the laboratory, with a 13 C wheat straw residue, in the presence or absence of a peregrine endogeic tropical earthworm, Pontoscolex corethrurus. Emissions of 12 CO 2 and 13 CO 2 were followed during 16 days. The coupling between DNA-SIP (stable isotope probing) and pyrosequencing showed that stimulation of both the mineralization of wheat residues and the PE can be linked to the stimulation of several groups especially belonging to the Bacteroidetes phylum. The ISME Journal (2012) 6, 213-222; doi:10.1038/ismej.2011; published online 14 July 2011 Subject Category: microbial ecology and functional diversity of natural habitats

Microbial Anaerobic Digestion (Bio-Digesters) as an Approach to the Decontamination of Animal Wastes in Pollution Control and the Generation of Renewable Energy

“…We observed a greater diversity of bacteria in vermicompost than windrow and ASP ( Figure 4). Our results support earlier reports that earthworms promote growth of bacteria [45] including Bacteroidetes, Verrucomicrobia, Firmicutes, and Proteobacteria [46]. There was also a trend for greater diversity of fungi in vermicompost and a relatively high abundance of fungi including Mortierella and Arthrobotrys supporting earlier reports [4,47].…”

The earthworm species Metaphire posthuma modulates the effect of organic amendments (compost vs. vermicompost from buffalo manure) on soil microbial properties. A laboratory experiment

“…Litter and OM decomposition rates are often stimulated in experiments comparing soils with and without earthworms [12]. It is therefore likely that earthworms stimulate microbial activity through the fragmentation and alteration of vermicompost in their gut and/or through the production of more easily degradable organic substances (i.e., the mucus) leading to priming effect processes [9]. These results can be seen in line with the niche construction, or feedback loop hypothesis applied to soil engineers [32].…”

Harmful or useful? A case study of the exotic peregrine earthworm morphospecies Pontoscolex corethrurus

“…In particular, the digestion process in the earthworm gut is known to enhance microbial activity (Barois and Lavelle, 1986;Drake and Horn, 2007). The feeding activity of P. corethrurus has been shown to result in increased microbial biomass and activity in casts after soil was passed through the gut and excreted (Barois, 1992;Barois and Lavelle, 1986;Bernard et al, 2012). Thus, P. corethrurus has provided a basis for the 'sleeping beauty' hypothesis where water and soluble-C in the form of intestinal mucus produced by the earthworm awakens dormant microbial communities in the gut, thereby increasing mineralization of the stable forms of SOM ingested (Lavelle et al, 1983).…”