Soil hypha-mediated movement of allelochemicals: arbuscular mycorrhizae extend the bioactive zone of juglone

Summary Allelopathy is a phenomenon where plants have deleterious effects on growth of surrounding plants through the production of chemical substances. Soil hyphae of arbuscular mycorrhizal fungi may enhance transport processes of allelochemicals by providing ‘highways’ connecting plants below-ground. In three studies ranging from high ecological realism to experimental control, we showed that the presence of mycorrhizal hyphae may strongly contribute to the transport of allelochemicals. We analysed the accumulation of naturally released juglone in the field in intact or disrupted hyphal connections and determined its growth reducing effects on sensitive target plants in a bioassay. Secondly, we tested the effects of Juglans regia leaf litter addition in the presence or absence of the mycorrhizal fungus Rhizophagus irregularis on target plants, and finally, we added pure juglone to Lycopersicon lycopersicum plants in the presence or absence of Rhizophagus. Throughout, we found increased juglone transfer if mycorrhizal hyphae were present, resulting in reduced growth of target plants. Our results point to mycorrhizal hyphae playing an important role in extending the bioactive zone of allelochemicals. We suggest that hyphal networks increase the effectiveness of allelochemicals in natural systems and play a crucial role in chemical interaction processes and hence influence plant community structure.