Investigating the relative mycorrhizal responsiveness of common medicinal herbs

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Lauren Murray, Environmental Science, Oklahoma State University, Stillwater, OK, Eric Duell and Gail Wilson, Natural Resource Ecology and Management, Oklahoma State University, Stillwater, OK

Background/Question/Methods
Arbuscular mycorrhizal (AM) fungi form symbiotic relationships with approximately 80% of terrestrial vascular plants. The extent to which plants depend on AM fungi exists along a gradient from non-mycorrhiza to plants that depend on AM fungi to complete their life cycle. Obligate mycotrophs include perennial C4 native grasses and several agriculturally important crops; facultative mycotrophs are also common. Although AM fungal benefits have been well studied 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. To date, only 50 medicinal plant species from 19 families have been tested for dependency on AM fungi. Interestingly, many common medicinal plants are absent from this list, including several species native to North American prairies and woodlands. Seedlings of fourteen species from five families were grown in either pasteurized soil (eliminating AM fungi), or whole soil (with AM fungi). Nonsterile soil sievate was added to all pots, which excludes mycorrhizal spores, but contains other soil microorganisms, to accurately determine the benefits of AM fungi. End of season biomass of mycorrhizal and non-mycorrhizal plants was assessed, relative mycorrhizal responsiveness calculated, and roots assessed for AM fungal colonization.
Results/Conclusions
Selected plant species varied dramatically in their responses to AM fungal inoculation, ranging from 48-98%. Some, such as cumin (Cuminum cyminum), marigold (Tagetes erecta), and garden sage (Salvia officinalis) were determined to be only moderately responsive, and thus classified as facultative mycotrophs. Most other species were highly responsive (>80%). Interestingly, and contrary to initial hypotheses, no clear patterns emerged when comparing rMR within and among taxonomic groups. Specifically, rMR of the five members of the mint family (Lamiaceae) ranged from 58-98%, greater than what could be expected for confamilial plant species. Similarly, the range of rMR for members of the daisy family (Asteraceae) was 48-94%. Colonization by AM fungal colonization levels varied greatly among selected medicinal herbs, with no clear patterns emerging. With a growing interest in the properties of medicinal herbs, this research provides much-needed insight into the ecological relationship between these plants and AM fungi. Symbioses with AM fungi can potentially enhance host-plant health and production even in low-input conditions. Globally, the costs of N-fertilizers and dwindling P reserves are looming crises. If AM fungi can be managed in-situ as “natural biofertilizers” they could dramatically improve plant production of many of these species, while reducing commercial fertilizer amendments.