KOHLER, M. und HILDEBRAND, E.E. (2000): Micro pedological investigations for the opening up of the soil by mycorrhizal fungi with special consideration of the skeleton fraction on a Black-Forest gneiss site.

The settling of soil by mycorrhiza is nutritionally and physiologically significant for most of our forest-tree species. In soils with a strongly heterogeneous nutrient element distribution, the supply of nutrient elements depends decisively on the extent to which fine roots and fungal hyphae open up soil compartments. A skeleton-rich gneiss site (ecosystem case study “Conventwald”) with an inhomogeneous nutrient element distribution investigated the question at issue. The investigation tested to what extent the observed plausibility deficit in the Conventwald between alarming soil chemical parameters in fine soil (base-saturation beneath the Ah horizon > 5%) and good stand growth with normal nutrient contents in the leaves can be explained by short-term mobilisable ion pools within the soil skeleton opened up by fungal hyphae and fine roots for nutrient uptake. For this purpose, resin-soaked soil preparation slides were produced and, with the use of fluorescence microscopy, distribution patterns of hyphae in their natural micro-pedological environments were taken. The first qualitative results show that the occurrence of hyphae in soil at the Conventwald site is not limited to macro-pore spaces. Rather, hyphae also extend into the fine soil matrix as well as into the soil skeleton. In stones, hyphae were found within a network of weathered zones (micro gaps), partly filled with fine substance. Hyphae were also found growing inside stones without the existence of any recognisable weathered zones. Furthermore, hyphae clusters were noticeable in the transitional area between the soil skeleton and the bordering soil matrix, and macro-pore spaces respectively.