PARENT SESSION
Poster Session # 10: Soil Ecology.

Tuesday, August 5 Presentation from 5:00 PM to 6:30 PM. SITCC Exhibit Hall B.

Variation in organic acid exudates among mycorrhizal species colonizing Liriodendron tulipifera L. (yellow-poplar) in the presence of aluminum.

Klugh, Katrina ^*,1, Cumming, Jonathan¹, ¹ Department of Biology, Morgantown, WV

ABSTRACT- Acidic soils have phytotoxic levels of aluminum (Al) that have detrimental effects on numerous plant physiological processes. Aluminum availability is exacerbated by acidic deposition in the eastern United States. Liriodendron tulipifera (yellow-poplar) is an economically important tree species in this region and is sensitive to Al. Root exudation of organic acids is one mechanism of Al resistance in pants. Arbuscular mycorrhizal (AM) fungi may also confer resistance, although the mechanisms involved are not known. In the present study, the extent of Al resistance conferred by several AM species was assessed and organic acid exudation was quantified to determine if organic acid production was altered by AM fungi and Al. Liriodendron tulipifera seedlings were inoculated with one of four AM fungal species (Glomus clarum, Acaulospora morrowiae, Glomus claroideum, or Paraglomus brasilianum) or a control inoculum and grown in sand culture. Aluminum treatments of 0 and 50 M Al were delivered in solution. After eight weeks of treatment, biomass and root exudates were measured. Organic acid profiles differed among fungi highlighting interspecific variation in carbon flux to the rhizosphere. Citrate, malate, and oxalate concentrations were up to 6 times greater in the rhizospheres of plants colonized by AM fungi compared to non-mycorrhizal plants. Fungi conferring Al resistance maintained high organic acid concentrations under exposure to Al. Rhizosphere citrate concentrations in plants colonized by Al resistant G. clarum were not suppressed under Al exposure while plants colonized by Al sensitive G. claroideum exhibited 50% reductions. Similarly, G. clarum colonized plants exhibited 30% reductions in malate rhizosphere production, while plants colonized by G. claroideum had 80% reductions. Organic acid exudation differed among AM fungal species and Al resistance of AM fungi appears to be associated with maintenance of organic acid exudation.

Key words: Aluminum, Liriodendron tulipifera, Mycorrhizae, Organic acids