The influence of the microflora on the physical properties of soils. I. Effects associated with filamentous algae and fungi

Abstract

Current views that aggregation of soils results from by-products of microbial growth and that filamentous microorganisms contribute very little to physical binding are reviewed. The microscopical examination of soils and aggregates showed fungal mycelium to be persistent in well-aggregated soils, but relatively deficient in soils lacking structure. Cases are cited where physical properties of soils depend upon the presence of filamentous microorganisms: (1) Surface crusts on sands in open plant communities where algae dominate the coenoses with filamentous fungi; (2) the aggregation of deeper horizons of sands by adhesive fungal mycelium; (3) the sand capping to clay subsoils in solonetzic soils bound by abundant fungal mycelium and microbial gums; (4) the water repellence of sandy soils associated with the growth of microorganisms, particularly basidiomycete fungi; (5) the progressive improvement of crumb structure in fine-textured soils associated with increased development of persistent mycelium after several years under pasture.