Restoring legumes and their mycorrhizal and rhizobia symbioses

Jonathan Bauer, Miami University, Oxford, OH, Paul A. Price, Biology, Eastern Michigan University, Ypsilanti, MI and Emily Grman, Biology Department, Eastern Michigan University, Ypsilanti, MI

Background/Question/Methods
Re-establishing the full biodiversity of degraded landscapes is a persistent challenge in ecological restoration. Establishment limitation of rare species arises in part due to land-use legacies, where the effects of previous land-use have long-lasting effects on soil microbial communities and soil resources. These land-use legacies may limit re-establishment of legumes (Fabaceae) because most species in this family rely on two soil microbial symbionts, mycorrhizae and rhizobia, and because legumes are often adapted to low-nutrient environments. Limited re-establishment of legumes is a problem because legumes are a diverse family in our study system, tallgrass prairie, and because legumes and their associated symbionts play an important role in soil ecosystem services. Here, we test if legumes experience strong establishment limitation relative to other restored tallgrass prairies species. Then, we test the availability and quality of microbial symbionts in post-agricultural soils. Finally, we report preliminary results on how legacies of soil fertilization in post-agricultural fields may alter interactions among plants, mycorrhizae, and rhizobia.
Results/Conclusions
We found high variability in establishment rates among legumes in prairie restorations. In surveys of over 100 restored prairies, we found that establishment rates for legumes varied from over 90% to complete failure to establish within restorations, and there was a trend for legumes to experience stronger establishment limitation than other species. Establishment limitation may be partially explained by a lack of suitable rhizobia in post-agricultural soils. Two species, Amorpha canescens and Lespedeza capitata, experience greater nodulation in remnant prairie soils than soils from restored prairies (p<0.05), and we found no evidence that rhizobia abundance recovers in post-agricultural soils with time since restoration. In contrast, mycorrhizal colonization of our study species was similar in remnant and restored sites, even in the most recently restored prairies. This suggests that the abundance of mycorrhizae is not limiting to legume establishment in restorations. However, for both mycorrhizae and rhizobia, the quality of symbiotic partners in post-agricultural soils may present further challenges to establishment. The complex legacies of post-agricultural soils that could limit the establishment of some legumes, potentially encompassing changes in soil fertility and the abundance and quality of multiple microbial mutualists, calls for ongoing research with the promise of enhanced restoration outcomes.