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PREVIOUS RESULTS IN THE TOPIC OF ALLELOPATHY
Subalpine spruce (Picea abies L. Karsten) forests are characterised by deficient natural regeneration.
Although severe parasitism of the seeds exists, this factor cannot alone explain the regeneration failure of spruce stands in the Alps. Allelopathic phenomena inhibiting spruce natural regeneration were investigated in both in situ and in vitro studies.
Field experiment has shown that competition between two dominant understory species, Vaccinium myrtillus L. and Athyrium filix-femina L. Roth, and spruce seedlings occurs even when nutrients and light are not restrictive. Experimental seedlings indicated that humus restricts spruce germination (less than 1% germinated) and is also responsible for a substantial loss of seedlings (at least 50%) from the first year onwards.
In vitro spruce germination and mycorrhizal fungi growth tests were carried out with V. myrtillus, A. filix-femina and P. abies aqueous leaf extracts and humic solutions. Greatest inhibitions was achieved with A. filix-femina foliar extracts and its humic solution.
Analysis of foliar material identified four phenolic acids synthesised by spruce needles and leaves of the two common understory species. These compounds were also found in humic solution at 10-5 molar and were then selected for a second identical series of in vitro bioassays. This gave a specific way of determining phytotoxicity of phenolic molecules.
Interference of these phenolic acids on metabolism mechanisms was explained using a polarographically oxygen electrode : these compounds seem to act as uncouplers.
In situ experimental seedling, with and without humic solutions concluded this work. It confirmed the laboratory results.
Key words : allelopathy ecology forestry germination humus mycorrhiza phenol Picea regeneration understory.
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