Allelopathic effects of humus phenolics on growth and respiration of mycorrhizal fungi

Allelopathy due to humus phenolics is a cause of natural regeneration defic iency in subalpine Norway spruce (Picea abies) forests. If inhibition of sp ruce germination and seedling growth due to allelochemicals is generally ac cepted, in contrast there is a lack of knowledge about phenolic effects on mycorrhizal fungi. Thus, this work tested effects of a humic solution and i ts naturally occurring phenolics on the growth and respiration of two mycor rhizal fungi: Hymenoscyphus ericae (symbiont of Vaccinium myrtillus, the ma in allelochemical-producing plant) and Hebeloma crustuliniforme (symbiont o f P. abies, the target plant). Growth and respiration of H. crustuliniforme were inhibited by growth medium with the original humic solution (-6% and -30%), respectively, whereas the same humic solution did not affect growth but decreased respiration of H. ericae (-55%). When naturally occurring phe nolics (same chemicals and concentrations in the original humic solution) w ere added to the growth medium, growth of H. crustuliniforme was not affect ed, whereas that of H. ericae significantly increased (+10%). We conclude t hat H. ericae is better adapted to the allelopathic constraints of this for est soil than H. crustuliniforme and that the dominance of V myrtillus amon g understory species could be explained in this way.