Introduction

Our knowledge of the condition and behaviour of ectomycorrhiza in their natural surroundings is very limited, both in terms of physiology and morphology. Studies on the decline of forests in particular have revealed how ljttle we really know in this field. We cannot even define the threshold above which fine roots and mycorrhiza should be classified as "damaged", because we do not know what their "normal" state is. We know practically nothing about the range of morphological characteristics of any one particular mycorrhizal type, its growth dynamics, seasonal variation, or life-span. The main reason for this lack of knowledge is that the observation of mycorrhiza in their natural surroundings is very difficult.

METHODS IN MICROBIOLOGY VOLUME 23 ISBN 0-12-521523-1

Copyright © 1991 by Academic Press Limited All rights of reproduction in any form reserved

Soil core sampling, the most common method for studying root systems and mycorrhiza, is certainly useful for observing conditions at any given time, but has the great disadvantage of being destructive and thus precluding continuous observation of particular microsites, so that it does not allow conclusions about developments or changes in the mycorrhiza. These problems can be largely overcome through the installation of root windows, which allow continuous, long-term observation with minimum disturbance. Photographs can be used to register morphological changes.

The root window is not a new concept. As early as the beginning of the 1950s, glass plates laid flat on the soil were employed to observe root growth in forest trees (Orlov, 1957, 1960). At East Mailing Research Station (Maidstone, Kent, UK), underground tunnels were installed in the mid-1960s for the observation of the root system of fruit trees under natural and experimental conditions. Gottsche (1972) and Turner and Streule (1983) used vertical root windows to measure root growth and growth periodicity. It is surprising that such methods have practically never been employed in the study of mycorrhiza.

In developing the method described in this paper, special emphasis was laid on using basic laboratory equipment so as to keep the method as simple as possible.

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