A new invader, Potentilla recta, and its effect on the native mycorrhizal symbiosis

Background/Question/Methods

Invasive species pose a serious threat to ecosystems by altering not only plant community composition, but also ecosystem processes.  Arbuscular mycorrhizae, which can mediate plant-plant interactions through host-specific benefits, are an important factor in the success of at least some, if not all, invasive plants.  One well-studied invasive, Centraurea stoebe, is more competitive with native plants when it participates in the mycorrhizal symbiosis.  A physiologically similar invader, Potentilla recta, is spreading rapidly in Montana by creating monocultures that exclude all native vegetation.  We sampled native forbs and P. recta at 3 sites; Camera Ridge, Woodchuck Creek, and Wailey Draw in the Bitterroot Valley of Montana, across an invasion gradient broken into 3 zones: P. recta monocultures, native communities, and transition zones. We measured percent cover, aboveground biomass, seedling emergence and mycorrhizal colonization to characterize P. recta invasions and determine if these invasions are altering the mycorrhizal symbiosis in native plants.

Results/Conclusions

Potentilla recta was present in higher densities at Wailey Draw and Woodchuck Creek but spreading more rapidly at Camera Ridge.  The increased expansion was observed in the transition zones where Camera Ridge had greater numbers of P. recta despite similar coverage of mature P. recta.  This may in part be due to a more robust native community, as the aboveground biomass in native areas was equal to that of P. recta in invaded zones at Camera Ridge, while native biomass much less than P. recta biomass at the other sites.  Despite invasion differences, mycorrhizal colonization levels were consistently high at all sites. Colonization levels differed between host plants (native forbs vs P. recta) but not across the invasion gradient, even when different host plants were sampled side by side. Native plants had lower colonization (73% vs 86%) but higher density of arbuscules (32% vs 22%) than P. recta.  The consistency of colonization in native species and the P. recta plants across invasion zones and invasion types indicate that P. recta invasions are not altering the mycorrhizal symbiosis in native plants.  However, further work will elucidate any shifts in the mycorrhizal fungal communities of native plants.