Graduate Program

Biological Sciences

Degree Name

Master of Science (MS)

Semester of Degree Completion

2009

Thesis Director

Janice Coons

Thesis Committee Member

Henry Owen

Thesis Committee Member

Karen Gaines

Thesis Committee Member

Barbara Carlsward

Abstract

Physaria ludoviciana (Nuttal) O'Kane and Al-Shehbaz is an endangered species in Illinois and Minnesota sand prairies, but has many individual populations in western states. Areas where P. ludoviciana occurs have high summer temperatures, a sandy soil with low water holding capacity and high drainage, the frequent disturbance of blowing sand and little canopy vegetation, giving it a full sun environment. This habitat is where few other plants are able to establish, providing P. ludoviciana with little competition. Physaria ludoviciana exists in a niche where it is adapted and able to establish and persist. The focus of this study was to investigate survival strategies of P. ludoviciana. The objectives were to understand P. ludoviciana with regards to: 1) seed biology, 2) growth and development with different light conditions and with root competition, 3) structural and physiological adaptations, and 4) a survey of soils and associated species that occur with P. ludoviciana. Seed biology was studied at the Henry Allan Gleason Nature Preserve (HAGNP) in Mason County, Illinois from 1999-2008. Beneficial aspects of seed biology include high seed production averaging 192 to 55 5 seeds per plant, an afterripening response that staggers seed germination, high germination percentages (around 70%), and maintained viability of seeds at least for 6.5 years when collected mature and stored at 4 °C with less than 50% relative humidity. Detrimental aspects of seed biology include no apparent mechanism for seed dispersal as evidenced by seeds not being dispersed farther than 1 meter from mother plant and limited persistence of seeds in the seed bank with only 4% of seeds in June still being found in November of same year. These seed conditions create variable establishment of seedlings from year to year at HA GNP with O to 11 seedlings per m2. Growth and development with different light intensities or photoperiods and with root competition were studied to simulate effects of encroaching vegetation that was observed in areas with P. ludoviciana at HAGNP. Flowers developed when plants were transferred to both long (16 hr light/8 hr dark) and short (8 hr light/16 hr dark) day photoperiods after being grown in long days for 4 months. Flowers likely were initiated in long days. Plants grown at higher light intensity (584 μmol/m2/sec) had significantly greater leaf areas, leaf numbers, fresh and dry masses, and root development than those grown at lower light (174 μmol/nl/sec). Container size affected both vegetative and reproductive development of plants when 4 months old plants were transferred to larger containers (control 20 cm X 4 cm, 2 depths: 22 cm=short and 36 cm=tall and 2 widths: 12 cm=narrow and 23 cm=wide) and then harvested at 4 and 5 weeks. Both light and root competition affected the development of P. ludoviciana stressing the importance of little or minimal competition of other species for optimal growth. Physaria ludoviciana possesses many structural and physiological adaptations for sand prairie conditions. A long taproot extending to 46 cm can help anchor the plant and help attain ground water. Early in development, plants put more energy into roots than shoots corresponding to a larger root to shoot ratio for younger plants (0.5) than for older plants (0.3). This root to shoot ratio also corresponds to more secondary growth present in roots than in stems. Physaria ludoviciana is an evergreen herbaceous perennial so it does not need to regenerate all of its leaves each spring in its water and nutrient limited environment. Plants have C3 photosynthesis based on anatomy and an isotope analysis, allowing it to photosynthesize during cooler times of the year. A palisade layer occurs on both the top and bottom of the leaf to maximize light collection. Plants also have dense stomates (329 to 698/mni2) and trichomes (31 to 48/mm.2) which allow for transpirational cooling while still minimizing water loss. Plants have a lower water potential in June and September compared to March and May, allowing them to absorb water from the soil even in dry conditions. No water storage tissues were present in plants. Surveys of soil and associated species were compared in areas where P. ludoviciana was present or absent in three states including Illinois, Minnesota and Nebraska. Associated plant species were consistent throughout the range of P. ludoviciana being typical grassland and dry sand prairie forbs and grasses with no apparent differences between areas were P. ludoviciana was present or absent. Substantial differences in soil characteristics were not found between sites with P. ludoviciana present or absent. Seed production per plant for P. ludoviciana was high in all sites, 234 to 305; however seedling establishment was low. This study suggests that the ability of P. ludoviciana to survive depends more on its ability to arrive and establish in an area than it does on the associated plant species and soil characteristics. Disjunct populations could be a result of poor seed dispersal and limited persistence in the seed bank. So rather than soil characteristics being the limiting factor, establishment and seed dispersal could be the limiting factors. Our understanding of adaptations and requirements for P. ludoviciana can aid management decisions for sand prairie species, especially for P. ludoviciana.

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