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Material and Methods
Preparation of the soil:
The soil samples were prepared according to JENSEN & LYSEK (1991): the soil samples were moistened (if necessary) to enhance the adhesive contact of the
soil, which allowed putting it on a cover slide and turning it upside down to obtain a hanging drop. To keep the soil in its native structure, further manipulations were
strictly avoided.
Fluorochroming:
The fluorescein di-acetate (FDA) was obtained from Sigma (F-7378). A stock solution (0.05 Z in acetone) was kept dark and cool; from it the working solution
was prepared by adding 100 µl to 5 ml buffer solution. This working solution could be used for 20 min at the most, since it degraded rapidly. For details see JENSEN (1994)
For other fluorochromes see results.
Microscopic equipment:
Microscope A Leitz Dialux 20 was used for these investigations, completed with a Pleomopak 2.4 fluorescence unit equipped with a mercury arc lamp HBO 50 W
(Osram). Filter units: The filter units A, E3, 13 and N2 were used to get an optimal fluorescence from the various fluorochromes. Photographic equipment: The Dialux 20
microscope was additionally equipped with a Wild photo-tube and camera MPS 11; connected to a Wild MPS 15 semiphotomat for semi-automatic regulation of the exposures.
Several normal speed Kodak Ektachrome 100 and Ilford Delta 400 & 100 negative and slide films were used.
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