Mycorrhizal Association in Dwarf Shrub Species Growing in Soft Cretaceous Rocks

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Abstract
The dwarf shrubs Poterium spinosum, Cistus villosus and Thymus capitatus which are common in Israel on exposed soft chalk or on the overlying calcareous rendzina, were grown under glasshouse conditions within split blocks of the same chalk and in rendzina soil. Growth and survival were very poor in the chalk blocks in spite of the addition of a nutrient solution. A striking improvement in growth was observed, however, when nutrient application was accompanied by the insertion into the stone blocks of a small quantity of root fragments which had been taken out of rock interstices in the field. These root fragments proved to be densely permeated by a septate mycelium. Intercellular hyphae were likewise found within the cortex of young roots in the field, as well as in the experimentally inoculated plants. No mycorrhizas were observed in plants of the same species growing in more favorable substrates. It is suggested that a mycorrhizal fungus in the above calcareous habitat has a comparable function to that of forest tree mycorrhizas in the strongly leached acid soils of the temperate region.