Short-term changes in the spatial distribution of microorganisms in soil aggregates as affected by glucose addition

We studied the location of microorganisms in soil aggregates by low temperature scanning electron microscopy and by confocal laser microscopy (direct counts of bacteria) on dissected aggregates. We compared a sandy and a clayey soil and studied the effect of adding glucose on the spatial distribution of microorganisms. In the sandy soil, pores with diameters between 6 µm and 30 µm were the most abundant. In the clayey soil, the pores were <0.2 µm in diameter. In the sandy soil, microorganisms were present both on the surface and inside aggregates, whereas they were concentrated on the surface of clayey soil aggregates. Glucose addition increased the amount of bacteria and fungi on the surface of clayey soil aggregates but not inside them. For the sandy soil, microbial numbers were increased dramatically both inside and on the surface of the aggregates after glucose additions. This study thus evidenced contrasting microbial habitats in soil aggregates.