Effects of the earthworm Eisenia andrei on methanogens in a cattle-impacted soil: A microcosm study

Cattle treading accompanied by a high input of organic matter was previously found to favour methanogenesis in soils at a site used as winter pasture in outdoor cattle husbandry. In this current study, the phylogenetic microarray AnaeroChip revealed high methanogenic diversity in a cattle-impacted soil with predominance of Methanosarcina, and presence of Methanoculleus, Methanobacterium, Methanocalculus, Methanobrevibacter, Methanosaeta, Methanothermobacter, Methanogenium, Methanohalobium, and Methanolobus. The bioturbation effects of an epigeic earthworm, Eisenia andrei, on the methanogenic microbial community in cattle-impacted soil were studied in a 6-month laboratory microcosm experiment. The microarray showed that the methanogenic community was changed by addition of earthworms to the soil. The abundance of 16S rRNA Methanosarcina gene copies decreased two fold in soil with worms compared to soil without worms after 2 months of incubation and decreased three fold after 4 and 6 months of incubation. The biomass of anaerobic microorganisms, as determined by unsubstituted non-ester-linked phospholipid fatty acid analysis, decreased in soil incubated for 4 and 6 months with worms. The abundance of the methyl-coenzyme M reductase (mcrA) gene, which is involved in CH4 production and is present in all methanogens, was not, however, changed by worms, and addition of worms even increased the rate of methane production. This study provides the first data concerning interactions between earthworms and methanogens in cattle-impacted pasture soil. The results of this laboratory microcosm experiment indicate that E. andrei changes the composition of the soil methanogenic community but does not reduce the total abundance of the methanogenic community and methane production rate. (C) 2011 Elsevier Masson SAS. All rights reserved.