Southeastern wildrye (Elymus glabriflorus (Vasey ex L.H. Dewey) Scrib & C.R. Ball) is a relatively new perennial cool-season grass that has shown potential as a forage crop in the Southeastern United States. However, there is a lack of research on this species assessing its agronomic performance. To assess the agronomic performance and it’s tolerance to imazapic field trials were established in Newton and Starkville, MS. A forage production trial included five nitrogen (N) 0, 56, 112, 168, and 224 kg N ha -1 (high input) and five annual clover (low input) treatments. Tolerance to imazapic was assessed with applications of four pre- and early post-emergent applications applied at 0.0, 0.35, 0.7, 0.105, and 0.14 kg ai ha -1. Results from both field trials combine to validate southeastern wildrye as a potential forage crop and continued research and development of agronomic traits in this species.

The hippocampus is a brain region that can undergo tremendous plasticity in adulthood. The hippocampus is related to the formation of spatial memories in birds and mammals. In birds, plasticity in the hippocampus occurs when formation of such memories is directly relevant to survival or reproduction, such as for breeding or food caching. In reptiles, the homologues to the hippocampus are the dorsal and medial cortices (DC and MC). In several lizard, snake and turtle species, these structures have been related to spatial memory. Experimental investigations indicate that differences in DC volume are related to space use associated with differing foraging ecologies. Differences in MC volume have been associated with territory size-based mate acquisition strategies. Furthermore, territory size has previously been correlated with plasma testosterone (T) levels. Therefore, I hypothesized that neuroplasticity within the MC/DC is controlled by demands on spatial navigation and seasonal differences and that these changes may involve the action of T. During two experimental trials, male Western Fence Lizards (Sceloporus occidentalis) were placed into either large or small semi-natural enclosures and allowed to interact with a female and intruder males over the span of seven weeks. One trial was performed during the spring breeding season and the other during the summer non breeding season, to examine seasonal differences in plasticity. Blood samples were collected at initial time of capture and before sacrifice to measure plasma T. Immunostaining for doublecortin was used to determine the density of immature neurons in each region, and cresyl violet staining allowed for volume measurements of specific regions. MC cell layer neurogenesis was higher in lizards placed in large enclosures than those in small enclosures and higher in the summer than in the spring. DC volume was smaller in lizards held in large enclosures than those in small enclosures. The decreased DC volume seen lizards held in large enclosures may indicate a cost to the increased neurogenesis in the MC of lizards in the same enclosures. These results indicate a possible trade-off between DC volume and MC neurogenesis that allows for switching between the ability to solve novel spatial tasks using the DC while storing a cognitive map in the MC. During the spring, T had no relationship with MC volume, while during the summer this was negative, so effects of T on the MC may be seasonal.

No description available.

No description available.

A more thorough knowledge of rooting behavior of transplanted trees is needed to better understand plant establishment. The objectives of this research were to: 1) determine if transplant timing affected root system regeneration of northern red oak (Quercus rubra L.) and willow oak (Q. phellos L.), 2) determine the effect of transplant timing and nursery production system on root, shoot, and trunk growth periodicity of balled-and-burlapped (B&B) and pot-in-pot (PIP) sugar maple (Acer saccharum Marsh.), and 3) characterize seasonal patterns of root production and mortality of transplanted sugar maple. No new root growth occurred outside or within the root balls of red or willow oak between November transplanting and January excavation. However, new root growth was observed when November- and March-transplanted oaks were excavated in April, indicating that new root growth occurs primarily in late winter and/or early. Transplanted and non-transplanted sugar maples exhibited a pattern of maximum rates of shoot extension in early May, root length accumulation in late May, and trunk expansion in mid June. Rate of root length accumulation was less in summer and fall. Transplanting did not appear to disrupt the normal growth periodicity of sugar maple, except when transplanted in July. Abundant root length accumulation occurred in the July transplants at a time when root length accumulation had slowed in all other treatments, resulting in the July transplants having similar standing root lengths as the other transplants by fall. Standing root length of non-transplanted PIP sugar maple declined dramatically in spring. While root production in sugar maple was limited to the growing season, root mortality occurred at a steadier rate throughout the year. Most root mortality occurred in winter in transplanted trees and spring and summer in non-transplanted trees. Non-transplanted PIP trees had greater standing root length, production, and mortality than the other treatments. Indices of root activity (analogous to turnover rates) and production:mortality ratios illustrated the dominant role that root production plays relative to mortality in recently transplanted trees. These data indicate that transplanting and the PIP production system disrupt typical patterns of root production and mortality in sugar maple. / Ph. D.

The objective was to evaluate the insulin-leptin interactions in grazing mares and their impact on aspects of reproductive function using a series of four studies. Fourteen mares were first examined, 10 grazing and 4 confined to stalls in four 22-h studies in April, August, October (2005) and January (2006). There was a positive relationship between insulin and leptin concentrations (r = 0.50; P < 0.001). The second study used 24 mares maintained at pasture and fed supplements rich in either FF, or SS, or pasture forage. Nonstructural carbohydrate (NSC) content of forage was correlated to insulin concentration (r = 0.55; P < 0.01). Insulin was associated with leptin (r = 0.55; P < 0.001) and progesterone (r = 0.48; P < 0.001). In the third study nine mares adapted to FF, SS or forage only underwent two FSIGT tests; once during the luteal phase and again during the follicular phase of the estrous cycle. Minimal model analysis was used to describe insulin sensitivity (SI), glucose effectiveness (Sg), acute insulin response to glucose (AIRg) and the disposition index (DI). SI was lower (P < 0.001) in the luteal phase (3.1 ± 0.6) compared to the follicular phase (5.0 ± 0.6). In the fourth study 15 mares had their follicular fluid collected during the luteal and follicular phase of the estrous cycle. Insulin concentration (ln (x+1)) was 52% higher (P < 0.01) in large (> 25 mm) follicles (1.4 ± 0.1 mIU/L) than either medium (16 to 25 mm) or small (le; 15 mm) follicles (0.9 ± 0.1; 0.9 ± 0.1 mIU/L, respectively) irrespective of estrous cycle phase. A correlation was observed between follicular fluid (FFL) leptin and plasma leptin (r = 0.30; P < 0.001). A similar relationship was observed between FFL insulin and plasma insulin (r = 0.25; P < 0.001). Plasma insulin and leptin were positively associated (r = 0.45, P < 0.0001), along with FFL insulin and FFL leptin (r = 0.46, P < 0.0001). Both leptin and insulin were affected by season and this observation contradicts the use of single sample analysis for determining detrimental concentrations of these hormones. / Ph. D.

Monitoring and understanding plant phenology is becoming an increasingly important way to identify and model global changes in vegetation life cycle events. Although numerous studies have used synoptically sensed data to study phenological patterns at the continental and global scale, relatively few have focused on characterizing the land surface phenology of specific ecosystems. Mountain environments provide excellent examples of how variations in topography, elevation, solar radiation, temperature, and spatial location affect vegetation phenology. High elevation biomes cover twenty percent of the Earth's land surface and provide essential resources to both the human and non-human population. These areas experience limited resource availability for plant growth, development, and reproduction, and are one of the first ecosystems to reflect the harmful impact of climate change. Despite this, the phenology of mountain ecosystems has historically been understudied due to the rough and variable terrain and inaccessibility of the area. Here, we use two MODIS/Terra satellite 16-day products, Vegetation Index and Nadir BRDF Adjusted Reflectance, to assess start of season (SOS) for the 2007 calendar year. Independent data for elevation, slope, aspect, solar radiation, and temperature as well as longitude and latitude were then related to the SOS output. Based on the results of these analyses, we found that SOS can be predicted with a significant R² (0.55-0.64) for each individual zone as well as the entire western mountain range. While both elevation and latitude have significant influences on the timing of SOS for all six study areas. When examined at the regional scale and accounting for aspect, SOS follows closely with Hopkins' findings in regard to both elevation and latitude. / Master of Science

Spectral reflectance-based, remote sensing technology has been used to adjust in-season nitrogen (N) fertilizer rates for wheat to account for spatial variability in grain yield potential at a sub-meter resolution. The objective of this study was to examine the relationships among spectral reflectance indices, corn tissue N content, chlorophyll measurements, plant size and spacing measurements, and grain yield to develop a similar strategy for variable-rate N management in corn. Irrigated and non-irrigated studies were conducted during the 2002 and 2003 growing seasons in eastern Virginia. Plots were treated with various rates of preplant, starter, and sidedress N fertilizer to establish a wide range of grain yield potential. Spectral measurements, tissue N, chlorophyll measurements, and plant physical measurements were collected at growth stages V6, V8, and V10. At maturity, grain yield was determined and correlated with in-season data and optimum N rate to calibrate in-season, variable-rate N fertilization strategies. Results from these studies indicate that spectral reflectance is well correlated with plant N uptake and chlorophyll meter readings and can also be correlated with final grain yield. These relationships may be used to develop a model to predict in-season, variable N application rates for corn production at a sub-meter resolution. / Master of Science

Over the past several decades, native and managed bee populations have decreased in the United States and worldwide. Although bee decline is attributable to several factors, habitat loss is the primary driver. Simultaneously, cattle producers in the eastern U.S. rely primarily on cool-season forages that peak in biomass production in late spring, leading to a lack of forage in the summer months and increasing the costs of cattle production. Seeding pastures with a mix of native warm-season grasses and native wildflowers could increase forage availability while also increasing available resources for bees. In this study, a mix of three native warm-season grasses (NWSGs) and 15 wildflower species was planted at the Virginia Tech Shenandoah Valley Agricultural Research and Extension Center (SVAREC). The objectives of this project were to document the establishment and species composition of NWSG + wildflower pasture mixtures, compare the attractiveness of wildflowers and weedy species to bees, and compare the bee community between NWSG + wildflower pastures and more typical cool-season grass pastures. The wildflowers in the NWSG + wildflower pastures dominated over grasses. All wildflower species that established were attractive to bees, as were some weedy species. The NWSG + wildflower treatments had the highest abundance of bees collected, with an average of 14.8 bees collected per pasture per sampling date in 2018, and an average of 12.4 bees collected per pasture per sampling date in 2019. These results indicate that with modification of establishment methods so that more grasses are present, this pasture system could be beneficial from both a cattle production and bee conservation standpoint. / Master of Science in Life Sciences / Over the past several decades, there has been a decline in bee populations in the U.S. and around the world. Bees play an important role in pollinating many food crops, including most fruits and vegetables. Habitat loss is the biggest contributor to their decline. There are also issues with cattle production in the eastern U.S. Most farmers rely on grasses that are the most productive in the late spring and early summer, meaning that by mid- and late summer, there is little grass available for cattle. Planting pastures with native grasses designed to be the most productive in the late summer and native wildflowers could increase food available for cattle as well as provide more pollen and nectar for bees. In this experiment, we planted a mix of three grasses and 15 wildflowers. We documented how well the grasses and wildflowers established. We also examined how attractive wildflowers and weeds were to bees and compared the number and types of bees collected between the new pastures and traditional pastures. We found that the wildflowers, instead of the grasses, dominated the pastures. All wildflowers that established, as well as some weeds, attracted bees and provided resources. Higher numbers of bees were collected in the pastures with wildflowers than standard grass pastures, but there were not necessarily more bee species present. These results suggest that, with some modifications, planting native grasses and wildflowers in pastures could help conserve bees as well as benefit cattle farmers.

Insulin-like growth factor binding proteins (IGFBP) are modulators of insulin-like growth factor I (IGF-I), which functions as a regulator of cartilage and bone development. Rapid growth and high starch diets have been associated with increased circulating concentrations of IGF-I, which lead to developmental orthopedic disorders in foals. The objective of this study was to assess the effects of age, diet, growth and season on plasma IGFBP and IGF-I concentrations from birth to 16 mo of age in Thoroughbred foals. Twenty-two mares maintained on mixed grass/legume pasture were randomly divided into two dietary groups and fed either a high starch and sugar supplement (SS) or a starch-restricted fiber and fat supplement (FF) for 3 mo prior to and after foaling. Monthly blood samples were obtained from SS and FF foals up to 16 mo of age and analyzed for IGF-I using an RIA and IGFBP using western ligand blot analysis. Auxilogical measurements of foals were also obtained each month. The effect of diet, month, and diet*month interactions upon the subject horse (diet) were analyzed using a mixed model with repeated measures, and correlations of normally distributed data were calculated using Pearson's correlation. Six IGFBP bands of molecular weights 109, 39, 36, 35, 34, and 33 kDa were identified in foal plasma. Doublet bands were recognized at 109, 39, and 35 kDa, however they were not all believed to be singular pure IGFBP. A band with a molecular weight of 213 kDa was observed and presumed to be a ternary complex of IGFBP-3, IGF-I, and an acid labile subunit. The IGFBP 109 kDa has been previously recognized as a band unique to the equine, it was not a singular pure IGFBP because of its high molecular weight. No effect of diet on plasma IGFBP was found in individual sampling of yearlings, but an effect of month was noted when testing May - August 2001 against May - August 2002 in pooled plasma samples with concentrations of the IGFBP 39 kDa increasing (P < 0.0003). In contrast, concentrations of the IGFBP's 33, 34 and 36 kDa decreased (P < 0.003, P < 0.0002, and P < 0.0003 respectively). Environmental effects were noted upon IGFBP's 33, 36, 39, and 109 kDa (P < 0.003, P < 0.001, P < 0.04, and P < 0.01) with a temperature*daylength interaction. Correlations existed between ADG and IGFBP 33 (r = 0.64; P < 0.0001), 34 (r = 0.40; P < 0.0001), 35 (r = 0.33; P < 0.0006), 36 (r = 0.47; P < 0.0001), and 39 kDa (r = - 0.18, P < 0.02). A correlation was also found between IGF-I and ADG (r = 0.11; P < 0.04), confirming the previously reported relationship of IGF-I in growth rate of foals. These results underline the importance of characterizing the activity of IGFBP's in relation to growth, age and season when interpreting changes of the somatotropic axis. Further, the increase in certain IGFBP's and simultaneous decrease in others stress the need for further research on the tissue specific modulating effects that IGFBP's have on IGF-I. / Master of Science