College of Agriculture & Natural Resources
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The collections in this community comprise faculty research works, as well as graduate theses and dissertations.
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Item THE INFLUENCE OF LAND-USE, ENVIRONMENT, AND SOCIOECONOMIC FACTORS ON TREE SPECIES DISTRIBUTION IN BALTIMORE, MARYLAND.(2009) Mead, Kimberley Ellen; Sullivan, Joseph H.; Plant Science and Landscape Architecture (PSLA); Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)With the exponential growth in human population and rapid increase in global urbanization, understanding changes in community dynamics and structure in human dominated landscapes is essential, yet, rarely studied. To determine what factors account for tree species composition and distribution in an urban setting, data from the 1999 UFORE Model vegetation survey of Baltimore, Maryland was analyzed. There was a diverse arboreal population found, comprised primarily of species native to the area. Detrended correspondence analysis did not show a clear pattern of species assemblages based on land-use, possibly indicating a homogenization of conditions across the urban environment. In canonical correspondence analyses, species distribution could not be explained by socioeconomic factors, however, there was a significant relationship of tree species assemblages and the physical environment, specifically with percent impervious surface cover. The amount of variance accounted for was small indicating that other factors may be involved in determining tree species distribution.Item Pedogenesis in Rain Gardens: The Role of Earthworms and Other Organisms in Long-Term Soil Development(2009) Ayers, Emily Mitchell; Kangas, Patrick; Biological Resources Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)As bioretention comes into widespread use, it has become increasingly important to understand the development of bioretention soils over time. The objective of this research is to investigate the development of bioretention soils and the importance of ecological processes in the performance of rain gardens. The research includes descriptive studies of pre-existing rain garden soil profiles, laboratory experiments quantifying the effect of earthworms on infiltration rates, and a simulation model describing the influence of earthworms and soil organic matter on infiltration. Surveys of several different rain gardens of various ages provide the first detailed descriptions of rain garden soil profiles. The study revealed a great deal of biological activity in rain gardens, and evidence of pedogenesis even in very young sites. The uppermost soil layers were found to be enriched with organic matter, plant roots, and soil organisms. The field sites surveyed showed no signs of clogging due to the trapping of suspended solids carried in stormwater runoff. Some evidence was found of higher than expected infiltration rates at the field sites, which may be attributable to the effects of bioturbation by living organisms. The ability of earthworms to mitigate the effects of trapped suspended solids on bioretention soils was assessed in the laboratory. Results show that earthworms are capable of maintaining the infiltration rate of bioretention soils, but that their effects have a high degree of variability. This variability is attributed to soil aggregate instability caused by the oversimplification of the ecosystem. Other organisms play a significant role in stabilizing earthworm burrows and casts, and may be essential ingredients in a self-maintaining bioretention ecosystem. A simulation model of the action of earthworms on soil infiltration rates was developed in order to illustrate the physical processes taking place as a result of earthworm activity. The model was calibrated using data from the field study and microcosm experiment. This research is intended to provide a first glimpse into the biological processes at work in rain garden soils. The research shows that soil organisms are present in rain gardens, and suggests that their impact on bioretention performance may be significant.Item Post-bottleneck inbreeding accumulation reduces fitness in laboratory populations of Tribolium castaneum under environmental stress(2008) Choiniere, Ashley Danielle; Siewerdt, Frank; Animal Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Populations are often driven to extinction due to low genetic diversity. One major cause for loss of genetic diversity in a population is a demographic bottleneck. A demographic bottleneck was imposed on twenty-one populations of Tribolium castaneum using multiple strategies. After recovering to original census numbers, the populations were subjected to stressful environments, and fitness was quantified. There was a significant decrease in additive genetic variance in all populations as a result of the bottleneck event (P<0.05). As estimated inbreeding accumulation increased, there was a decrease in the mean of fitness related traits, such as adult weight, total progeny, fecundity and survivorship. This relationship was best explained using quadratic models and became even more significant when the populations were under stress. This suggests that both dominance and epistatic gene effects are playing a role in phenotypic expression of traits and that expression may be flexible, supporting survival and fitness.Item Effects of nitrogen and calcium on photosynthesis and metabolic activity in Acer saccharum in the Catskill Mountains(2008-03-31) Behling, Shawna Joy; Sullivan, Joseph H; Plant Science and Landscape Architecture (PSLA); Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The Catskill Mountains in southern New York have received some of the most acidic rainfall in the country for the past 50 years. Acid deposition on these thin soils may deplete the concentration of calcium and other essential ions in the soil solution and mobilize other ions that can be harmful to sugar maple (Acer saccharum) rooting systems. The effects of fertilizers on the metabolism and photosynthesis rates of sugar maple are of great interest to both farmers and ecologists. In this study, 12 plots in a 60-year-old sugar maple dominated forest were treated with no fertilizer, nitrogen, calcium, or nitrogen and calcium together. Photosynthesis was measured with a LiCor 6400. Metabolic heat rate was measured with a MC-DSC calorimeter. While some sampling periods showed significant responses to some treatments, the study as a whole suggests the addition of calcium and/or nitrogen had minimal effects on photosynthesis or metabolism.Item Soil Nematode Communities as Influenced by Cover Crops, with a Focus on Brassicaceae(2007-06-11) Gruver, Lisa Stocking; Weil, Ray R.; Plant Science and Landscape Architecture (PSLA); Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The effect of brassicaceous cover crops (Brassica juncea/Sinapis alba, B. napus, and Raphanus sativus) on plant-parasitic and free-living soil nematode communities, in grain agroecosystems, was evaluated in three experiments, at two sites in Maryland. Brassicaceous cover crops alone did not suppress plant-parasitic nematodes, however when combined with rye (Secale cereale) or clover (Trifolium incarnatum), juvenile (J2) Heterodera glycines populations were lower in June, soybean yields were higher, or free-living nematode abundance was higher. Indices of free-living nematode community structure suggested that winter-kill of N-rich radishes activated the bacterivore community in early spring resulting in high populations of bacterivore dauer larvae and high community structure by summer. In contrast, nematode communities in spring-terminated rapeseed and rye plots had high abundances of fungivore nematodes and a plant associate/fungal feeder, Coslenchus. Brassicaceous cover crops in Maryland grain rotations may be more useful for managing soil ecology than for biofumigation of plant-parasitic nematodes.Item Assessment of nitrogen status and vegetation composition in tidal freshwater marshes using partial least squares regression models of hyperspectral canopy reflectance(2006-04-28) Jenkins, Emily Poynter; Tilley, David R; Biological Resources Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Hyperspectral canopy reflectance was used to predict sub-surface water nutrients, vegetation composition, and canopy nutrients, which could lead to more useful means for assessing the status of wetlands. Thirty field quadrats at two tidal freshwater marsh sites on the Nanticoke River (Maryland) were treated with five nitrogen levels. During the 2004-05 growing seasons, hyperspectral canopy reflectance was measured using a spectroradiometer with 1nm resolution across the visible and near - infrared spectrum (350-1075 nm), water samples were collected using lysimeters, species cover was quantified, and biomass was collected and analyzed for canopy nutrients. ANOVA was used to determine whether nitrogen affected reflectance, species composition, canopy N and P, and partial least squares regression was used to develop reflectance models predictive of these ecosystem properties. Results indicated that hyperspectral radiometry could be used as a remote sensing tool for quantifying sub-surface water nitrogen, vegetation composition, and canopy nutrients in tidal freshwater marshes.Item GRAPH THEORETIC CONNECTIVITY ANALYSIS OF THE MID-ATLANTIC REGION OF THE UNITED STATES(2005-12-13) Ferrari, Joseph Robert; Neel, Maile C; Plant Science and Landscape Architecture (PSLA); Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Connectivity is critical for persistence of species in the face of anthropogenic habitat destruction and fragmentation. Graph theory is a relatively new method for quantifying connectivity that has tremendous potential, but landscape graph applications to date are limited to specific conservation situations with static proportions of habitat (P). This study provides a uniform evaluation of graph metrics across wide gradients in P in both random neutral landscapes and real, forested landscapes from the Mid-Atlantic region of the United States. Such an analysis provides a background that will be valuable for future interpretation of graph metrics. Results indicate that graph metrics have characteristic forms when plotted against P that can be exploited for conservation management.Item EPIDEMIOLOGIC ANALYSIS OF RISK FACTORS FOR LOCAL DISAPPEARANCES OF NATIVE RANID FROGS IN ARIZONA(2005-08-11) Witte, Carmel Lee; Kane, Andrew S.; Animal Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)This study used epidemiologic case-control methodology to examine habitat and environmental factors contributing to amphibian declines in Arizona. Risk factors were compared between sites where frogs disappeared (cases) and persisted (controls) using univariate and multivariable logistic regression analyses. Thirty-six percent (117/324) of all sites became cases during the study period. Elevation, non-native predators, hydrologic characteristics, aspect, and effects of nearby sites were significantly associated with frog persistence or disappearance. In the final multivariable model, risk for disappearance increased with increasing elevation (OR=2.7 for every 500 meters, P<0.01). Sites where disappearances occurred were 4.3 times more likely to have other nearby sites that also experienced disappearances (P<0.01), while having an extant population nearby decreased risk of disappearance by 85% (OR=0.15, P<0.01). Sites experiencing disappearances were 2.6 times more likely to have crayfish than control sites (P=0.04). Identification of risk factors associated with frog disappearances will guide future research and conservation efforts.Item Effects of embryonic exposure to androgen-active endocrine disrupting chemicals in Japanese quail(2005-04-18) Quinn, Jr., Michael James; Ottinger, Mary Ann; Animal Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Endocrine disrupting chemicals (EDCs) are compounds that alter the production, secretion, action, and elimination of endogenous hormones. EDCs have been shown to be responsible for disrupting development, reproduction, immune function, behavior, and all other life functions mediated by hormones. In the environment, organisms are exposed to many different types of EDCs at any one time, each with different mechanisms of action, many of which are not fully understood at present. Most research done with EDCs has focused on the effects of these chemicals on the estrogen and thyroid systems, however, many of these same chemicals also exert strong effects on the androgen system. Also, many studies assessing the effects of EDCs on wildlife have focused on reproductive measures of exposure, often overlooking potential effects on the immune system. We have demonstrated that embryonic exposure to androgen-active EDCs, anti-androgenic DDE and androgenic trenbolone acetate, impairs development of the bursa of Fabricius in Japanese quail, providing a possible mechanism for EDC-induced immunosuppression. The bursa is a primary immune organ responsible for development of the humoral part of the immune system. We have also demonstrated that the bursa can be resilient to embryonic exposure to EDCs, if post-hatch exposure to these chemicals is prevented. Measures of reproduction, behavior, growth, and developmental stability were also taken in this study. Male and female rates to sexual maturity were altered by the one-time in ovo exposure to DDE and trenbolone. Male reproductive behavior, as measured by attempts to mount and successful cloacal contacts achieved, was suppressed by both chemicals. Vocalization was abolished in one and two week old chicks from the highest trenbolone acetate treatment levels. Although environmentally relevant, the levels of DDE used in this study were below those reported to affects avian reproduction. Environmental levels of trenbolone acetate are unknown, however, previous studies have concluded trenbolone acetate to be safe to wildlife and non-teratogenic. The myriad of endpoints used in this study has been compiled to provide toxicologists with a list of sensitive and persistent measures that can be used as reliable biomarkers of exposure to androgen-active EDCs in birds.Item Efficiency and Ecological Risks of Reducing Soil pH during Thlaspi caerulescens Phytoextraction of Cadmium and Zinc(2004-11-29) Wang, Shengchun; Angle, Jay S; Plant Science and Landscape Architecture (PSLA); Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The major aims of this research were to determine whether reducing soil pH can enhance phytoextraction and to examine the ecological risks of reducing pH. Two soils differing in Cd and Zn concentrations were used and adjusted to 5 or 6 different pH levels ranging from 7.27 to 4.74 and seeded with a hyperaccumulator of Cd and Zn, Thlaspi caerulescens. Plants were harvested after six months, the pH were restored to above 6.5, incubated for 6 months. Soils were analyzed for biological activities and microbial population changes after both pH adjustments. Reducing pH significantly (p=0.05) enhanced plant metal uptake. For the high metal soil, plant grew best at the lowest pH treatment (4.74) and the highest metal concentration was at the second lowest pH treatment (5.27). For the low metal soil, due to low pH induced Al and Mn toxicity, plant growth and metal uptake were highest at the intermediate pH level (6.07). Metal sequential extraction results further verified that reducing pH redistributed Cd and Zn among five fractions. The most soluble metal form (F1) was greatly increased. In addition, T. caerulescens was able to differentially utilize Cd in all 5 fractions while it could only access Zn from the F1 and F2 pools. Reducing soil pH significantly reduced a number of soil biological activities and shifted the community structure at different levels. Generally, soil biological activities were more sensitive than soil microbial populations to pH change. Good indicators of soil pH status were acid phosphatase activity, alkaline phosphatase activity, acid to alkaline phosphatase activity ratio, arylsulphatase, nitrification potential, soil microbial biomass C and N, and population of rhizobium. After raising pH to > 6.5, negatively impacted soil parameters were partially restored to original levels. Soil biological activities showed lower recovery than soil microbial populations. The threshold pHs were 6.1 and 5.3 for low and high metal soils, respectively. Above this value, most soil biological activities and all microbial populations returned to background levels within a short period.