Variations in organic acid exudation and aluminum resistance among arbuscular mycorrhizal species colonizing Liriodendron tulipifera

Aluminum (Al) in acidic soils is toxic to plants, affecting Growth, water uptake and nutrient assimilation. Aluminum resistance in some plant species and genotypes has been ascribed to organic acid exudation from roots and arbuscular mycorrhizal (AM) fungal symbiosis. We investigated variation amona several AM species in altering Al resistance of Liriodendron tulipifera L. and evaluated AM influence on oraganic acid production as a potential A] resistance mechanism. Growth. nutritional responses and rhizosphere organic acid profiles were assessed for seedlings in association with Acaulospora morrowiae Spain & Schenck, Glonuts claroideum Schenck & Smith. G. clarum Nicol. & Schenck or Paraglomus brasilianum (Spain & Miranda) Morton & Redecker and non-nycorrhizal seedlings exposed to 0, 50 or 200 mu M Al. Plants colonized by G. clarum had the greatest biomass, least Al and most phosphorus (P) in leaf tissues and exuded rnalate and citrate into the rhizosphere at rates that complexed 99% of delivered Al in all treatments. Other AM fungi did not confer significant Al resistance on L. tutipifera and did not maintain citrate and rnalate exudation in response to Al exposure. This study illustrates functional diversity among AM fungal species ill conferred Al resistance to plants and highlights the potential importance of fungal diversity ill ecosystem responses to environmental stresses.