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Root productivity likely has consequences for the composition, activity, and recovery of soil microbial populations and the belowground processes mediated by these organisms. In tallgrass prairie, ecotypic variation potentially exists in response to a strong precipitation gradient across the Great Plains. Thus, ecotypic variation within a species may differentially affect belowground net primary productivity (BNPP), the associated soil microbial community, and may scale up to affect ecosystem processes. The goals of this study were to elucidate: (1) whether ecotype, environment, or an ecotype by environment interaction regulate BNPP of a dominant species (Andropogon gerardii) collected from and reciprocally planted in common gardens across a precipitation gradient, and (2) whether variation in BNPP scales to affect microbial biomass and ecosystem processes. I quantified root biomass, BNPP (using root ingrowth bags), soil microbial biomass, and nutrient mineralization rates in root-ingrowth cores below six population sources of A. gerardii (2 Illinois, 2 eastern Kansas, and 2 central Kansas) established in southern Illinois, eastern Kansas, and central Kansas. An ecotype effect was found on above and belowground net primary productivity, but these findings did not translate to soil response variables. Microbial populations themselves may affect the productivity and composition of prairie species. In a second study, soil ecological knowledge (SEK) was tested by applying a native prairie soil slurry amendment to restoration plots to determine efficacy of this method as a restoration practice. The goals of this two year study were to elucidate: (1) whether a slurry amendment of prairie soil would increase above and belowground productivity and belowground ecosystem processes in a prairie restoration, and (2) to evaluate whether differences in plant diversity will scale to affect belowground productivity and ecosystem processes. I quantified aboveground net primary productivity (ANPP) and species composition, as well as root biomass, belowground net primary productivity (BNPP), soil microbial biomass, and nutrient mineralization rates in root-ingrowth cores installed in treated and control plots. A treatment effect was noted on root biomass and total PLFA biomass; however, there was no treatment effect on cover, ANPP, or soil microbial processes. Though the soil microbial community did represent native prairie soil, there was poor establishment of prairie plant species. These factors may be due to the limited time available for data collection and the lack of precipitation in the second growing season. Longer studies may be necessary to fully examine the effects of soil slurry amendments as restoration tools.

The relative competitive abilities of Agropyron desertorum and Agropyron spicatum were compared using Artemisia tridentata transplants as indicator plants. Although these two tussock grasses have similar shoot growth forms and shoot physiological characteristics, they have substantial differences in their competitive abilities. Artemisia had lower survival, growth, reproduction, and water potential when transplanted into neighborhoods of A. desertorum than in neighborhoods of A. spicatum. Plant attributes associated with the differences in competitive ability were explored. Agropyron desertorum and~ spicatum have remarkably similar potential growth rates at warm soil temperatures. In a prolonged cold soil temperature treatment in the greenhouse, A. desertorum had a 66% greater aboveground relative growth rate than A. spicatum. These differences, however, were not apparent for early spring tiller growth rates in the field. Distinct differences in timing of root growth were found between the two tussock grasses. Aqropyron desertorum exhibited greater root growth during winter and early spring and invaded disturbed soil space more rapidly than A. spicatum, especially if the disturbance occurred soon after the snow had melted. Similarly, A. desertorum proliferated its roots in zones of nutrient enrichment created early in the spring sooner than A. spicatum. No differences in root growth were found between species in zones of nutrient enrichment that were created later in the growing season. Despite differences in early spring root growth, water extraction and radiophosphorus acquisition early in the spring were similar for the two grass species. Later in the spring, A. desertorum extracted more water and radiophosphorus than A. spicatum. Differences in resource extraction between the two species in a specific soil layer occurred weeks before A. spicatum, but not A. desertorurn, had obtained maximum root length. Early root growth probably provides A. desertorum an important head start over A. spicatum in soil exploration each growing season. Differences in resource extraction, however, do not become apparent between the two species of Agropyron until plant demand exceeds soil supply rate to the roots.

Field studies were conducted over two growing seasons to evaluate the effect of different levels of third instar European corn borer, Ostrinia nubilalis Hübner (Lepidoptera: Crambidae), on whole-plant dry matter in corn grown for silage. Mean (± SEM) whole-plant dry matter was significantly greater by 18.8% in uninfested control plants than in plants with an infestation level of 6 larvae/plant in 2004. Whole-plant dry matter in 2005 was significantly greater by 10.5% in control plants than in plants with an infestation level of 5 larvae/plant. Economic injury levels were calculated for each year using regression equations between whole-plant dry matter and European corn borer infestation level. Plant growth stage and infestation level had no effect on percent acid detergent fiber, neutral detergent fiber, and crude protein values for either year. Greenhouse studies were conducted to examine the relationship between aboveground herbivory by European corn borer and belowground herbivory by root knot nematode, Meloidogyne incognita Chitwood (Tylenchida: Heteroderidae), in corn. Two experiments were conducted to measure belowground herbivory by M. incognita in juvenile penetrations and eggs/root system. In the first experiment, the main effects interaction was not significant for either M. incognita juvenile penetrations or eggs/root system. Overall mean juvenile penetrations/root system across all three growth stages, at infestation levels of 1 and 3 larvae/plant were significantly less than in the non-infested control. In addition, overall mean eggs/root system at an infestation level of 3 larvae/plant were significantly less than in the control. In the second experiment, the main effects interaction was significant for both juvenile penetrations and eggs/root system. At the 8 and 10 leaf growth stages, juvenile penetrations/root system at infestation levels of 1 and 3 larvae/plant were significantly less than in the control. In addition, eggs/root system at an infestation level of 3 larvae/plant were significantly less than in the control, at all growth stages. In the reciprocal study, which examined the effect of different M. incognita inoculation levels on European corn borer stalk tunneling, no significant effect of inoculation level on European corn borer stalk tunneling was found. / Ph. D.

Root-feeding insects can have top-down influence on vegetative composition and ecosystem processes; however, they may respond to bottom-up factors such as soil resources, site productivity, and disturbance.  My research addressed the following questions: (1) Do disturbance (fire), vegetative composition, soil resources, and fine root standing mass influence the structure of root-feeding insect assemblages? (2) What types of roots do root-feeding insects eat, and do they forage selectively?  (3) Do root-feeding insects influence fine root productivity?  To address these questions, I studied root-feeding insect assemblages in longleaf pine wiregrass (Pinus palustris-Aristida stricta) ecosystems of southwestern Georgia, U.S.A.  On a random basis, study sites were burned at least every other year (B), or left unburned (UB) for about 9 years.  Fine root productivity and root-feeding insect abundances were sampled repeatedly across 54 random plots in UB and B sites.  In Chapter 2, I characterized spatial and temporal patterns of root-feeding insect abundance, understory plant composition, soil resource availability, and fine root standing mass within each plot.  Insect population densities were low overall, but abundance, patchiness, and diversity were greater in UB sites.  Abundance patterns were significantly related to vegetative composition.  In Chapter 3, I quantified the diet of root-feeding insects by measuring the natural abundance of carbon (C) and nitrogen (N) stable isotopes in insects and fine roots.  Using 13C abundance, I examined the contribution of warm season grass roots to insect diet, relative to the proportion of warm season grass roots within adjacent root standing crop samples; 15N abundance was used to detect omnivory.  Overall, insects appeared to be non-selective herbivores and omnivores that may alter foraging behavior to maintain a mixed diet (i.e. reducing or increasing warm season grass consumption when its abundance was high or low, respectively).  The extent of omnivory varied within and among taxa.  In Chapter 4, I estimated the top-down influence of root-feeding insects on fine root productivity by comparison of ingrowth cores with or without an insecticide treatment.  I detected a weak positive effect of herbivores on the productivity of non-grass fine roots (< 10% of fine root productivity). / Ph. D.

Due to the paucity of long-term harvest impact data, the primary goals of this study were to quantify the long-term effects of different harvest disturbances twenty-four years after harvest on two major wetland functions: stand productivity and C storage. This study evaluated the effects of three harvest types that were originally applied in 1986 to a tupelo (Nyssa aquatic)-cypress (Taxodium distichum) forested wetland in the Mobile-Tensaw River Delta of southwestern Alabama. Treatments were: 1. Helicopter harvest (HELI), 2. Skidder simulation where 50% of the site was rutted to a depth of 30 cm (SKID), and 3. Helicopter harvest followed by glyphosate herbicide removal of all sprouts and seedbank regeneration for two years following harvest (GLYPH). An adjacent mature stand (94 years old) within the same original composition represented mature forest or pre-harvest reference conditions (REF). Above- and belowground plant biomass, belowground woody debris, soil C, and soil CO2 efflux were measured. Twenty-four years after treatments were applied, forest C levels were higher in SKID treatments (206.1 Mg C ha-1) than in HELI treatments (168.7 Mg C ha-1). GLYPH treatments are holding less (144.2 Mg C ha-1) while REF areas hold 332.6 Mg C ha-1. SKID treatments are also holding the most biomass of all treatments with 243.2 Mg ha-1 of overstory biomass. Ecosystem C and biomass patterns indicate HELI and SKID are becoming similar to the original site conditions represented by the REF areas. The resiliency of these highly disturbed stands are explained by the frequent inputs of non-compacted sediments, presence of species well adapted to very poorly drained and aerated conditions, high rates of coppice regeneration, shrink-swell ameliorative properties of the soil and creation of more complex microtopography within SKID treatments. / Master of Science

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Within the last two decades substantial progress has been made in understanding seed bank dynamics and the contribution of the soil seed bank to a post-disturbance plant community. There has been relatively little progress, however, in understanding perennial bud bank dynamics and the contribution of the soil bud bank to secondary succession. This lack of information is due primarily to the inability to reliably identify roots, rhizomes, and lignotubers that lie dormant beneath the soil surface. This scientific investigation, therefore, addressed the issue of identification of belowground woody structures. The first objective was to develop a methodology that utilizes molecular tools to reliably identify woody plant species from subsoil tissue samples. The second objective was to create a key in which molecular markers serve as criteria for identification and differentiation of selected tree and shrub species common to the mountains of northeast Oregon and southeast Washington. Application of restricted fragment length polymorphism (RFLP) analysis on polymerase chain reaction (PCR)-amplified rbcL gene products proved to be a reliable method to identify and differentiate 15 plants to the genus level. Two restriction enzymes, DPN II and Hha I, cut (or do not cut) the PCR-rbcL product into one to six fragments. Fragment number and length are used to develop an identification key. Plants not analyzed in this key may share the same banding patterns , resulting in a false-positive identification of unknowns. Future research needs and management implications are discussed.

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