Organic acids produced by mycorrhizal <em>Pinus sylvestris</em> exposed to elevated aluminum and heavy metal concentrations.

A cultivation method was developed to enable exposure of ectomycorrhizal plants with intact extramatrical mycelium to solution containing different concentration of aluminium or heavy metals. Pinus sylvestris seedlings. Colonized by Suillus variegatus (two isolates), Rhizopogan roseolus or Paxillus involutus (tow isolates) were used. Seedling were transferred to Petri dishes containing glass beads and exposed to elevated concentrations of Al, Cd Cu, or Ni in two ways: immediately following transfer, and after allowing mycorrhizal seedlings to develop an extraradical mycelium that colonized the interface between the upper surface of the beads and the metal-containing solution. Production of organic acids in mycorrhizal and non-mycorrhizal systems was measured by with drawing samples from the solution and analyzing by HPLC. In most experiments, levels of oxalic acid were significantly higher in mycorrhizal treatments than in non-mycorrhizal controls. The measured levels of organic acids were variable, but the result obtained suggest that production of oxalic acid in stimulated by exposure to elevaled Al in mycorrhizal seedlings colonized by S. variegatus and R. roseolus. Elevated Al concentrations also increased oxalic acid production by non-mycorrhizal seedling significantly in two or four Al experiment performed, but the measured concentrations were significantly lower than in corresponding mycorrhizal treatments in both cases. Malonic acid was found in the culture solution of non-mycorrhizal and P. involutus-colonized seedlings, but only trace amounts were found in S. variegates or R. roseolus-infected seedlings. Citric shikimic, lactic, acetic, propionic, fumaric, formic, iso-butyric and butyric acid were found in variable concentrations. Production of oxalic acid by seedlings colonized by S. variegates BL or P. involutus was not stimulated by exposure to 0.44 μM Cd or 17 μM Ni. Exposure to 0.157 mM Cu two separate experiments using P. involutus 87.017 and two strains of S. variegates (BL and 159) appeared to simulate production of oxalic acid irrespective of mycorrhizal status of species. [ABSTRACT FROM AUTHOR]