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Jesse Lincoln ACF Abstract FY10

Ailanthus altissima increases nodulation in Trifolium pratense: A novel weapon for an invasive species

Conference Name: Botany & Mycology 2009 (Botanical Society of America)

Ailanthus altissima (Simaroubaceae) is an invasive tree from China that has spread over much of North America. A number of characteristics contribute to its success, notably tolerance of poor soils, rapid growth rates and production of allelopathic compounds. A mechanism increasing soil nitrogen would facilitate rapid growth on poor soils and previous studies indicate sites invaded by A. altissima have increased soil nitrogen levels. Increased soil nitrogen may be achieved through an alleochemical impact on legumes which solicit nitrogen-fixing rhizobia by emitting flavonoids into the rhizosphere under low nitrogen conditions. We investigated if and how A. altissima root exudates impact nodulation and growth in Trifolium pratense (Fabaceae). The experiment included a factorial design with the following treatments: soil leachate source (presence / absence of A. altissima), leachate source fertilization, and T. pratense fertilization. Treatment effects on T. pratense total biomass and shoot:root ratio were complex. Trifolium pratense treated withA. altissima leachates had a significantly increased nodule biomass to total biomass ratio and were twice as likely to be nodulated compared to control groups. We are currently monitoring changes in transcript abundance for T. pratense genes encoding enzymes chalcone synthase and chalcone isomerase in response to A. altissima leachates. These genes are involved in the production of the flavonoid released by T. pratense to solicit rhizobia for nodulation. Flavonoid signaling molecules are analogous to early responsive defense genes, suggesting increased nodulation results from an upregulation along a defense pathway. This previously unreported plant-plant interaction potentially facilitates rapid growth of A. altissima in poor soils via increased nitrogen fixation in neighboring legumes.