Plant Science & Landscape Architecture Theses and Dissertations
Permanent URI for this collectionhttp://hdl.handle.net/1903/2797
Browse
Search Results
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.Item FACTORS AFFECTING MEDIA pH AND NUTRIENT UPTAKE IN GERANIUMS(2004-08-30) Raymond, Carinne A.; MCINTOSH, MARLA S; Plant Science and Landscape Architecture (PSLA); Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Consumer demand has prompted an increase in geranium breeding efforts to produce new cultivars each season. It is hypothesized that the breeding for unique morphological traits has inadvertently resulted in changing the plant's ability to competitively take up nutrients. Under certain conditions, nutrient uptake of these novelty cultivars is less efficient, possibly caused by the influence of the geranium itself. Information collected from the container media is a good indicator of the container nutritional status and can be used as a diagnostic tool for early identification of nutritional problems and prevent plant loss. Severe nutrient deficiencies and toxicities have been associated with plants fertigated with low alkalinity water, suggesting that an unsteady pH in the rhizosphere coupled with low buffering capacity of irrigation water may cause preferential nutrient uptake. Maintaining a media pH that optimizes nutrient solubility while preventing interactions or precipitation is the goal for ensuring proper plant nutrition. Three experiments were performed to address the following objectives: 1.) Evaluate the effects of the geranium cultivar and class on the container media. 2.) Determine if media type affects nutrient availability and uptake by geraniums. 3.) Identify if preferential nutrient uptake occurs in response to changing pH and water alkalinity levels in the container media. Results indicate that a significant reduction in media pH occurs for zonal and ivy geraniums during a specific stage of growth and that the effects of pH and water alkalinity on nutrient uptake and are highly specific to the nutrient tested and the media type. Significant interactions between water alkalinity and pH contributed to preferential uptake of several of the tested nutrients especially at low water alkalinities. Overall, the differences in uptake were in most cases specific to cultivar, the stage of growth and nutrient tested and should be considered when determining optimal fertility requirements for specific geranium cultivars.