POSTER


VILLEGAS, JAVIER, PETER MOUTOGLIS & J. ANDRE FORTIN. Institut 
de recherche en biologie vegetale, Universite de Montreal,4101 
est rue Sherbrooke, Montreal, Quebec, Canada HIX 2B2.- 
Bacteria, mycorrhizal roots or external mycorrhizal mycelium, 
who is the best phosphorous solubilizer?

AM-mycorrhizal transformed carrot (Daucus carota) roots, mycorrhizal 
external mycelium and Pseudomonas aeruginosa and its effect, either 
alone or in interaction, on phosphorous solubilization and the pH of the 
media was studied.  A two sided Petri plate system was used.  
Mycorrhizal transformed carrot roots colonized with Glomus intraradices 
were inoculated on one side on a minimal growing medium with N in the 
form of NO3-.  The second compartment contained the same media but 
insoluble phosphorous was added.  In this compartment, mycorrhizal roots 
or just the external mycelium was allowed to be established and was 
tested alone or in combination with P. aeruginosa. In addition, P. 
aeruginosa. was tested separately in the second compartment.  The pH as 
well as the soluble phosphorous concentrations in the media were 
measured at the beginning and 13 weeks after inoculation.  An increase 
in the pH of the media was observed where external mycelium and bacteria 
were growing alone.  A decrease in the pH was observed where mycorrhizal 
carrot roots were maintained alone.  By contrast, a notorious decrease 
of the pH in the media was observed when external mycelium and bacteria 
were interacting.  Mycorrhizal carrot roots associated with bacteria 
showed a higher decrease of the surrounding pH compared to treatments 
containing mycorrhizal carrot roots alone.  Significant differences in 
the concentration of soluble phosphorous were detected in the various 
treatments.  External mycelium and bacteria, were less effective 
phosphorous solubilizers than mycorrhizal roots.  The levels of soluble 
phosphorous detected in the media were significantly higher where both 
mycorrhizal roots and external mycelium interacted with bacteria.  
However, the latter combination produced the highest concentration of 
soluble phosphorous in the media.  This study shows that the effect of 
mycorrhizal roots, external mycelium and P. aeruginosa on pH and the 
phosphorous dynamics is different if the organisms are alone or in 
direct interaction.