Mutualistic associations facilitate swainsonine production in species of Oxytropis from North America and China

Mutualistic associations can provide beneficial feedbacks between a host plant and its microbial symbionts, give the host plant a competitive advantage over neighboring species, and increase tolerance to environmental stresses. Species of Oxytropis and Astragalus are capable of hosting endophytic fungi and dinitrogen fixing bacteria.  Oxytropis and Astragalus species from Eurasia and North America have also one of the greatest rates of speciation and parallel biochemical and morphological adaptations to extreme environments. As a result of this tripartite microbial-plant association, Oxytropis host plants are capable of growing in soils with low nitrogen and contain the indolizidine alkaloid, swainsonine, which is toxic to most mammalian herbivores.  Our study hypothesized that the mutualistic associations in some Oxytropis species growing in arid and semi-arid ecosystems of China will be similar to those from North America. To test this hypothesis we studied five plant populations of Oxytropis glabra from Inner Mongolia, China, to determine 1) if the alkaloid swainsonine was present, 2) if a swainsonine producing fungal endophyte was present, and 3) the presence of symbiotic dinitrogen fixing bacteria. The results for Oxytropis glabra were compared with previous studies from Oxytropis sericea populations from North America. Oxytropis glabra from Inner Mongolia produce the same alkaloid (0.04-0.14 % of swainsonine), contained endophytic fungi from the same genus, and produced dinitrogen fixing nodules similar to those found in Oxytropis sericea from North America.  Both species grow in similar ecosystems, and are associated with similar intoxication problems with domesticated livestock.