The Role of Microorganisms in Aggregate Formation and Soil Stabilization: Types of Aggregation

Soil biota and the presence of organic matter are the major factors for developing soil structure in sandy soils. Three types of aggregates were observed in sand dunes: ( 1) microbial aggregates, 1-12 mm in diameter, formed by the action of bacteria, actinomycetes, and fungi, ( 2) root-microbial aggregates, formed by microorganisms in conjunction with root exudates and root structural components, and ( 3) debris-microbial aggregates, up to 6 mm in diameter, formed during decomposition of macroscopic plant debris. In maritime sand dunes the aggregates contributed up to 0.4% of total bulk soil weight. The VAM fungal hyphae participated in aggregate formation, and the presence of cyanobacteria in aggregates indicated their contribution to nitrogen cycling. Inocculation of dune sand with fungi and bacteria in addition to soluble organic matter improved soil structure and plant growth. The results indicated that soil microflora could be used as a tool for improving soil structure with a subsequently improved plant growth in sandy desert soils.