Environmental factors affecting woodland legume restoration
Past efforts to reintroduce the native legume species Desmodium glutinosum and Lespedeza violacea into restored woodlands have not produced self-sustaining populations. Proposed factors preventing reintroduction include herbivory, persistent environmental effects of invasive shrubs, poor performance of commercial Rhizobium inoculants, and competitive displacement associated with elevated nitrogen availability. To address these factors, we conducted field experiments to determine how restoration
... ine how restoration maturity and six environmental conditions: light availability, soil moisture, soil pH, ammonium (NH 4 ), nitrate plus nitrite (NO x ), and phosphate (PO 4 ), affected survival and productivity of transplanted legume seedlings. Legume vegetative growth was not affected by environmental variables, but D. glutinosum survival was negatively correlated with soil moisture (p = 0.034) and NO x (p = 0.017) and L. violacea fruit set increased with higher pH (p = 0.023) and more light (p = 0.026). Older restoration sites were correlated with lower NO x (p = 0.028) and reduced light availability (p < 0.009). Controlled greenhouse experiments tested inoculant specificity and the effects of nitrogen addition and plant competition with neighboring grasses on seedling growth and productivity. Neither species-specific nor nonspecific commercial inoculants yielded viable root nodules. Competition did not affect D. glutinosum performance, while L. violacea aboveground biomass was reduced under competition with Elymus villosus (p = 0.045). High nitrogen addition caused reduced biomass in both species under all competition treatments, but this effect was likely due to direct toxicity of urea fertilizer. Data collected from these experiments will help develop protocol revisions and best practices for the reintroduction of woodland legumes in sites where previous restoration attempts have failed. -iv - Acknowledgements To the following, I would like to express my gratitude: Sonia Doshi for her assistance in the field and at the bench; to Elizabeth Winkowski, Ben McKinney, Erin Spear, and Erin Watson for their help planting seedlings and for their tolerance of my terribly stinky herbivore repellant; to Lindsay Darling, Emily Hansen, Josh Drizin, and Wes Glisson for their help in the greenhouse; to Brian Clark and the friendly people of Chicago Botanic Garden's "production head house" for their help with growing seedlings and their guidance with greenhouse logistics; to members of the Larkin and Wagenius lab groups for their helpful suggestions and willingness to water plants when I wasn't around; to Emily Yates and Chris Clary for their help unlocking the mysteries of GIS; to Jim Steffen for his sage advice regarding the particulars of working in McDonald Woods; to Krissa Skogen, an ever-flowing font of enthusiasm and knowledge on all things leguminous and nodulating; to my advisor Dan Larkin for being a benevolent proofreader and overall rock-star mentor. I would also like to thank Nyree Zerega for maintaining the PBC program in shipshape and Bristol fashion, and Robert and Charlene Shaw for their generous support of PBC students through their Shaw Fellowship program. Without all your help, this project would not have gotten off the ground, much less succeeded. Thanks to you all.