Plant Science & Landscape Architecture Theses and Dissertations
Permanent URI for this collectionhttp://hdl.handle.net/1903/2797
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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 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 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 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.