CANCELLED - Evaluating arbuscular mycorrhizal responsiveness and fungal colonization of medicinal plants

Background/Question/Methods

Arbuscular mycorrhizal (AM) fungi form symbiotic relationships with approximately 80% of terrestrial vascular plants. However, the extent to which most herbaceous plants respond to AM fungi exists along a gradient from facultative mycotrophs (plants that receive benefits from AM fungi, but do not require the symbiosis) to obligate mycotrophs (plants that depend on AM fungi to complete their life cycle). Although AM fungal benefits have been determined for numerous native and cultivated species, remarkably little research has involved medicinal plants, although the use of plants for their medicinal properties has been recognized for centuries. Recently, World Health Organization estimated 80 percent of people worldwide rely on herbal medicines for some aspect of their health care, with approximately 21,000 plant species being used as medicinal plants. As only 50 medicinal plant species from 19 families have been tested for AM fungal responsiveness, we selected fourteen medicinal species from five families. Plants were grown in either pasteurized soil (eliminating AM fungi), or whole soil (with AM fungi). Native microbial wash was added to each pot, excluding mycorrhizal spores while adding other soil microorganisms, to accurately determine the benefits of AM fungi. Above- and belowground biomass and AM fungal root colonization were assessed.

Results/Conclusions

Species varied dramatically in their responsiveness to the symbiosis, ranging from 48-98% ([rMR = (Mmyco–Mnonmyco)/Mnonmyco)], where M is total dry mass). While most species were highly responsive ( >80%), some, such as cumin (Cuminum cyminum), marigold (Tagetes erecta), and garden sage (Salvia officinalis), were only moderately responsive, and thus classified as facultative mycotrophs. Contrary to our initial hypotheses, no clear patterns emerged when comparing rMR within and among taxonomic groups. For example, rMR of the five members of the mint family (Lamiaceae) ranged from 58-98%, greater than expected for confamilial plant species. Similarly, rMR of members of the daisy family (Asteraceae) ranged from 48-94%. However, AM fungal colonization was extremely consistent among all medicinal herbs, with a majority of the species ranging from 14-17%, regardless of plant family. Variance among rMR and consistency among the colonization may reflect that species differ in cost/benefit relationships with preferred taxa of AM fungal partners. As the need for medicinal herbs increases, over-collection is a major concern; one strategy to ensure continued availability is increasing commercial production. However, production under low-input practices is vital; if mycorrhizas can be managed in-situ as “natural biofertilizers” they could dramatically improve plant production, while reducing commercial fertilizer amendments.