Prairies once constituted a large portion of midwestern ecosystems and the North American landscape in general, until European settlers altered the land use. Now, 99% of prairies east of the Missouri River have been lost. Prairie restorations often produce more complex ecosystems than the sites they began on, but they lack the plant diversity found in remnant prairies, possibly due to missing mutualists. In mutualisms, both partners benefit from resource exchange; two soil mutualists found in remnant prairies but often lacking in restored ones, are arbuscular mycorrhizal fungi (AMF) and rhizobia. They exchange phosphorus and nitrogen, respectively, for carbon with their plant partners. The additional nutrients provided by these soil microbes may increase plant productivity, but how they interact to influence plant reproduction is unknown. Furthermore, how the mutualism-reproduction relationship changes in response to plant competition is also unknown. To address these knowledge gaps, we grew Chamaecrista fasciculata, an early-successional prairie legume that forms mutualisms with both rhizobia and AMF, in greenhouse mesocosms and individual pots inoculated with AMF, rhizobia, both, or neither. We then recorded biomass, the time to first flower, and the number of fruits and seeds. AMF increased the number of fruits and total seed production and decreased the time to first flower in mesocosms, but these effects were not present in the individual pots. Unexpectedly, rhizobia and the interaction between AMF and rhizobia both had no detectable effects in either experiment. Our results suggest that competition may increase the benefits of AMF, but rhizobia has a negligible effect across the board. This implies that to jumpstart restoration, this pioneer species and perhaps others could reproduce more and sooner with the addition of AMF.
Author(s): Adela Wilson, Isabelle Turner, Biology
Advisor(s): Jonathan Bauer, Biology
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