PARENT SESSION
Contributed Oral Session 26: Soil Fungi
Monday, August 8, 1:30 PM - 5:00 PM, Meeting Room 518 C, Level 5, Palais des congrès de Montréal

Organic acid exudation by mycorrhizal Andropogon virginicus L. (broomsedge) roots in response to aluminum.

Klugh, Katrina^*,1, Cumming, Jonathan¹, ¹ West Virginia University, Morgantown, WV, USA

ABSTRACT- High aluminum (Al) concentrations of acidic soils are detrimental to plant physiological processes. Availability of Al is exacerbated regionally due to acidic deposition and locally from activities such as coal mining and road building when acidic parent materials are disturbed. Plants exhibit a range of sensitivity to Al in the rhizosphere and organic acid exudation from plant roots is associated with Al resistance. When released by plants into the root zone, organic acids chelate Al and render it non-toxic to plants. Arbuscular mycorrhizal (AM) fungi may also confer Al resistance. Andropogon virginicus (L.) is an early successional species that colonizes disturbed areas and is able to resist Al toxicity. Al resistance in A. virginicus has been associated with colonization by AM fungi and, although mechanisms have not been elucidated, AM influence on organic acid exudation by roots may be one potential mechanism. In the present study, the extent of Al resistance conferred by several AM species was assessed and organic acid exudation was quantified to determine whether organic acid production was altered by AM fungi and Al. Andropogon virginicus plants were inoculated with several species of AM fungi (Acaulospora morrowiae, Glomus claroideum, Glomus clarum, Glomus etunicatum, Paraglomus brasilianum, Scutellospora heterogama) or a non-mycorrhizal control and grown in sand culture. Aluminum treatments of 0, 100, and 400 M Al were delivered in nutrient solutions. After eight weeks of treatment, plant biomass and root zone organic acids were measured. The production of citrate and malate, organic acids implicated in Al resistance in plants, varied by species. Patterns of growth indicated that the level of conferred Al-resistance was not uniform across AM isolates in symbiosis with A. virginicus. Arbuscular mycorrhizal species that maintain organic exudation under Al exposure are most beneficial to their hosts in promoting Al-resistance.

Key words: arbuscular mycorrhizal fungi, aluminum, organic acids