Nicole Cavender | Dissertation Conclusions

I. RAPD (Randomly Amplified Polymorphic DNA) analysis was used to investigate the genetic diversity of big bluestem in Ohio populations as well as in other populations further west in the Prairie Peninsula. A summary of the observations and conclusions are listed below.

Individuals of big bluestem have maintained high levels of genetic diversity in remnant prairies of Ohio and in other populations of the Prairie Peninsula.
Most of the genetic variation resides among individuals within populations relative to the amount of variation among populations or among regions. This is consistent with other studies of outcrossing grasses.
UPGMA and PCA analysis showed some differentiation and clustering among populations and regions. The more eastern states (OH, IN, IL,WI) were grouped together, while KS and MO were separated.
Although there is notable genetic distinction between the Adams County populations and the more central populations of Darby Plains and Marion County, Ohio's populations, as a whole, are generally more genetically similar to each other than to prairie regions sampled further west.
No correspondence between genetic and geographic distances were found when data from all remnant populations were considered, but those populations located on the geographic edge (OH & IN) showed significant correlation between genetic and geographic distance from other populations. These results along with other results obtained from UPGMA and PCA indicate that these marginal populations are the most genetically differentiated as compared to those more centrally located.

II. Implications for prairie restoration and reintroduction

Although this study has shown that genetic variation in big bluestem populations is high, it is important to minimize future genetic erosion caused by genetic drift. Because prairie habitats have been diminished, pollen movement between individuals may be greatly restricted, which could effect viable seed set.
Management should aim to increase the number of plants in small remnant populations, but artificial seed dispersal should be applied with caution.
Populations that are on the geographical edge of the Prairie Peninsula are likely to be more specifically adapted to their local environmental conditions. Therefore, the introduction of propagules from regions geographically far may have negative effects on fitness and adaptation.

III. The second part of this research involved the association of big bluestem with arbuscular mycorrhizal (AM) fungi. Trap cultures were made from soil samples collected from Ohio prairie remnants in order to identify the indigenous AM species that associate with big bluestem. Two inoculum studies were performed in the greenhouse in order to investigate the effects of a commercial inoculum and indigenous prairie inoculum on root colonization and growth of big bluestem collected from different sites in the Prairie Peninsula.

Five species of arbuscular mycorrhizal fungi, which associate with big bluestem in prairie remnants of Ohio were identified. They included Archaeospora leptoticha, Archaeospora trappei, Glomus aggregatum, Glomus claroideum, and Glomus mosseae. A. leptoticha appeared to be regionally specific and only occurred in Adams County. A. trappei was most ubiquitous occurring in eight out of the nine Ohio sites. The occurrence of the other species appeared to be random.
The commercially available arbuscular mycorrhizal inoculum from Bio-Organics was found to infect big bluestem plants growing in a mineral soil-sand substrate, but its effect on growth was generally neutral.
In the final study, there was a significant degree of variability in big bluestem plant growth relative to plant origin, mycorrhizal treatment, as well as soil type.
Big bluestem plants that received either the prairie mycorrhizal inoculum or the commercial inoculum had a higher survivor rate and generally grew better than plants without inoculum added to the non-sterile soil. Plants from Madison Co., OH and Franklin Co., MO generally benefited the most from added mycorrhizal inoculum.
Statistically, there was no difference in plant growth between the prairie and commercial mycorrhizal treatments, however, there were some isolated instances, ( i.e. Madison Co., OH plants) in which mycorrhizal preference was apparent.
The degree to which plant roots were colonized significantly varied between big bluestem sites and mycorrhizal treatment, and there was an interaction between these two effects. The prairie inoculum was generally more effective in promoting infection than either the commercial inoculum or the inoculum indigenous to the soil. The two Ohio sites, Madison Co. and Adams Co., showed the highest percentage of infection.
Regression analysis showed a positive correlation between the percentage of roots colonized and total dry weight of plants as well as the percentage of roots colonized and plant height.
Plant growth and % colonization were not associated with the enrichment of shoot or root P concentration (ľg/g), or any other nutrient concentration analyzed in this experiment. When considered on the basis of total uptake per plant (mg/plant), however, both total dry weight and % colonization were correlated with P. Percent colonization was also associated with the total uptake of Ca. Total dry weight was correlated with the total uptake of most other nutrients including K and Ca.
It is likely that genetic variation in plants, soil environment, as well as specific AM fungi play a large part in determining whether the symbiosis is effective and beneficial to the plant.

IV. Implications for prairie restoration and introduction

Results from the inoculum studies indicate that the behavior of big bluestem is very dependent upon its origin. These studies therefore confirm that big bluestem exhibits a high degree of genetic variability
In soils with high fertility, adding a commercial AM inoculum may not be cost effective or beneficial to plant growth.
In soils with low fertility the incorporation of an AM inoculum to prairie reintroduction projects may be appropriate and may greatly enhance its success, but plant genotype and inoculum type should first be considered.

V. Future Studies

Geographic distance may partially explain the genetic distance between the marginal populations of the east and the more western prairie populations. Further studies, however, should investigate the relationship between genetic distance and other factors such as environmental conditions (i.e. precipitation, temperature, and soil fertility).
Studies comparing AM fungi diversity of big bluestem in Ohio prairies with other prairies in the Prairie Peninsula may help elucidate the question of mycorrhizal preference or host specificity. It would also be useful to do similar investigations with other common prairie species.
Future AM inoculum studies should include long-term field trials of big bluestem genotypes and possibly other prairie species inoculated with indigenous and non-indigenous inoculum types.

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