Nascent aggregates in the rhizosphere of perennial ryegrass (Lolium perenne L.)

Abstract

Since there is little information on compound particles in the size range 2–20 μm, the genesis of the initial stages of soil aggregation was examined by transmission electron microscopy on ultrathin sections of the rhizospheres of Lolium perenne L. grown in attapulgite. Since attapulgite contains neither microorganisms nor organic matter, microorganisms were added as a soil suspension and all the organic matter was supplied by the ryegrass roots. Clusters were formed de novo by accumulation of attapulgite particles on root gel, on root cell fragments, and on microbial extracellular polysaccharides. Microaggregates were formed by the fusion of attapulgite-coated bacteria, colonies and cell remnants. Aggregates persisted after the death of the microorganisms. Key words: Microaggregates, clusters, soil ultrastructure, rhizosphere, extracellular polysaccharides