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 tempera ture scanning electron microscopy and by confocal laser microscopy (direct counts of bacteria) on dissected aggregates. We compared a sandy and a clay ey soil and studied the effect of adding glucose on the spatial distributio n of microorganisms. In the sandy soil, pores with diameters between 6 mum and 30 mum were the most abundant. In the clayey soil, the pores were <0.2 mum in diameter. In the sandy soil, microorganisms were present both on the surface and inside aggregates, whereas they were concentrated on the surfa ce of clayey soil aggregates. Glucose addition increased the amount of bact eria and fungi on the surface of clayey soil aggregates but not inside them . For the sandy soil, microbial numbers were increased dramatically both in side and on the surface of the aggregates after glucose additions. This stu dy thus evidenced contrasting microbial habitats in soil aggregates.