Seed Dormancy Break, Germination, and Seedling Establishment  in the Genus Lespedeza Michx.

Hevey, Robert

doi:https://doi.org/10.21985/n2-87vw-9r80

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Seed Dormancy Break, Germination, and Seedling Establishment in the Genus Lespedeza Michx.

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Successful restoration depends on the establishment and survival of selected species, and sowing seed is the most cost-effective method to ensuring a successful restoration. Generally, a locally sourced seed is thought to be better adapted to local environmental conditions and, therefore, more likely to thrive. In addition, a local seed is more likely to be hand- or wild-collected rather than bulk produced by commercial vendors, which may or may not have production facilities within any given region. As a result, exclusively sourcing seed locally is a practical challenge for restoration practitioners as the demand for seed may exceed the available supply of locally harvested seed. Additionally, advancing climate change is challenging the “local is best” paradigm. Even without these challenges, there is limited data on how well commercially sourced seed from areas outside the local provenance will perform. This dissertation examined species within the genus Lespedeza Michx. (bush clover; Fabaceae) to test the “local is best” paradigm by documenting dormancy break, germination, seedling establishment, and survival and analyzing commercially produced seed lots sourced across a broad geographic range. The results are intended to help guide seed procurement, seed mix design, and application during the restoration process.Chapter 1 reports research results on the impact of seed pretreatment on dormancy break, as is recommended by commercial suppliers regardless of provenance. Four species of Lespedeza Michx. were used in these trials; L. capitata Michx., L. hirta (L.) Homem., L. violacea (L.) Pers., and L. virginica (L.) Britton. Treatments included scarification, stratification, cold treatment, hulling, and light exposure. Overall, the results indicate that treatment does not significantly influence dormancy break of commercially produced seeds that the vendor has hulled. There were no discernable differences in patterns of seed behavior that would influence where appropriate seed should be sourced. Chapter 2 reports the results from research on germination rates, specifically investigating the impact of two temperature treatments. Hulled Lespedeza capitata seeds were exposed to temperature treatments, using both diurnal and constant temperatures, for 28 days without any researcher applied pretreatment. Results indicate that temperature affects germination rates but not significantly past approximately 20°C, in constant or diurnal trials. Chapter 3 reports the seedling emergence, establishment, and survival results from trials conducted in the lab and the field. The laboratory setting was designed to model a single growing season simulating field temperatures in the field. The field setting spanned three seasons in three locations. Lab and field results for emergence, establishment, and survival were dissimilar. The average emergence rate in the lab was 51% compared with 3% in the field, while the survival rate in the lab averaged 93% compared with the first-year average field rate of 70%. Field trial results were significantly influenced by field location with a 5% emergence rate and 84% first-year survival rate at the Wisconsin location compared with an average emergence rate of 3% and an average first-year survival rate of 58% at the Illinois locations. Seed analysis provided by vendors includes information about the potential success of a seed lot, but those rates were not observed in the field trials. Lespedeza capitata seed varies in color ranging from green to purple. Chapter 4 explored whether seed color and seed lot color, along with seed mass, were influential to germination rates and seedling establishment. Results suggest that germination rates were significantly influenced by seed color but not by mass. Seedling establishment was significantly influenced by seed mass and seed color, although seed lot color was not practical for predicting performance. Economic metrics, calculated on a cost per gram basis, were developed using trial results to inform practitioner decisions regarding seed lot performance.

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