Main Content

The World of Protozoa, Rotifera, Nematoda and Oligochaeta

Ref ID : 6150

Daniel L. Mummey, Matthias C. Rillig, and Johan Six; Endogeic earthworms differentially influence bacterial communities associated with different soil aggregate size fractions. Soil Biol.Biochem. 38:1608-1614, 2006

Reprint

In File

Notes

Endogeic earthworm activities can strongly influence soil structure. Although soil microorganisms are thought to be central to earthworm-facilitated aggregate formation, how and where within the soil matrix earthworm-facilitated influences on soil microbial communities are manifested is poorly defined. In this study we used 16S rRNA gene-based terminal restriction fragment polymorphism (T-RFLP) analyses to examine bacterial communities associated with different the aggregate size fractions (macroaggregates, microaggregates-within-macroaggregates and inner-microaggregates-within-macroaggregates) of soils incubated for 28 days with and without earthworms. We hypothesized that bacterial communities in different soil aggregate size fractions are differentially influenced by earthworm activities. Our results indicate significantly enhanced aggregate formation (both macroaggregates and microaggregates within macroaggregates) in earthworm-worked soils relative to soils receiving only plant litter. Although significant differences were found between bacterial communities of earthworm and litter-only treatments for all soil fractions, communities associated with earthworm-worked macroaggregate fractions exhibited the least similarity to all other soil fractions regardless of treatment. In addition differences in terminal restriction fragment (T-RF) size distributions, T-RFLP profiles of earthworm-worked soil macroaggregates had significantly fewer T-RF sizes, further suggesting less species evenness and more extensive alteration of bacterial communities within this fraction. These findings suggest that, due to rapid occlusion of organic materials, microbioal communities associated with microaggregates-within-macroaggregates formed during or shortly after passage through the earthworm gut are relatively inactive, and therefore change relatively little over time compared to macroaggregates populations as a whole.