Short-Term Versus Long-Term Effects Of Nitrogen Addition And Warming On Ecosystem N Dynamics In A Grass-Dominated Temperate Old Field, Benjamin F. A. Souriol

Electronic Thesis and Dissertation Repository

Increased atmospheric nitrogen (N) deposition and climate warming are both anticipated to influence the ecosystem N dynamics of northern temperate ecosystems substantially over the next century. Nevertheless, in field experiments with N addition and warming treatments, temporal scale can play an important role in determining the extent of treatment effects on N dynamics, and it is unclear to what extent the results of short-term studies can be extrapolated to responses over longer time scales. I compared the short-term versus long-term effects of N addition and warming on net N mineralization, N leaching, and N retention in a grass-dominated old field. …

Nitrogen Transfer From Cover Crops To The Subsequent Grain Crop And The Influence Of Variability In Winter Conditions, Spencer Heuchan

Electronic Thesis and Dissertation Repository

Cover crops, which are used to provide ground cover after the harvest of the grain crop, can potentially improve the sustainability of agroecosystems by reducing nutrient losses. However, few data are available to document the extent to which cover crops improve both the retention of soil nitrogen (N) and the transfer of this N to the grain crop. The efficiency of this N transfer may be further influenced by variation in winter soil temperature; for example, reduced snow cover can increase the frequency and intensity of soil freezing, which can affect the survival of cover crops and the timing of …

The Effects Of Silver Nanoparticles On Soybean (Glycine Max) Growth And Nodulation, Paul J. Boersma

Electronic Thesis and Dissertation Repository

Due to their antimicrobial properties, silver nanoparticles (AgNPs) have become more popular in consumer and industrial products, leading to increasing agricultural and environmental concentrations. Exposure to AgNPs could be detrimental to plants, microbes, and their symbiotic relationships. When subjected to 10 µg/mL AgNPs in a 96-well plate, growth of Bradyrhizobium japonicum USDA 110 was halted. In hydroponic culture with 2.5 µg/mL AgNPs, biomass of inoculated Glycine max (L.) Merr. was 50% of control. Axenic plants were unaffected by this dose, but growth was inhibited at higher doses, indicating that AgNPs inhibit both nodulation and growth. Nodules treated with 2.5 µg/mL …

Spatial And Temporal Variation Of Nutrients In The Great Lakes-St. Lawrence Basin: Implications For Primary Production In Stream Ecosystems, Nolan Pearce

Electronic Thesis and Dissertation Repository

Growing human populations and associated land use activities has increased the amount of nutrients delivered to surface waters. Eutrophication from the over-enrichment of nitrogen and phosphorus has degraded ecosystem conditions in streams, lakes, and coastal areas worldwide. Thus, the management of anthropogenic nutrient loading is a global concern. This thesis employed a combination of field and experimental research to provide watershed managers with information on the spatial and temporal patterns in stream nutrient enrichment, and the associated ecological effects of anthropogenic nutrient loading in the Great Lakes-St. Lawrence basin. Four studies were completed to address this research goal. First, I …

Urea As An Effective Nitrogen Source For Cyanobacteria, Kevin J. Erratt

Electronic Thesis and Dissertation Repository

Urea use has grown substantially in the past half-century, with urea now accounting for > 50% of nitrogen fertilizer applications worldwide. The shift from inorganic nitrogen fertilizers to urea-based sources has coincided with the reappearance of cyanobacteria blooms in freshwaters. Here, we examined urea as a nitrogen source for three bloom-forming cyanobacteria species. We found that (1) urea was consumed more rapidly relative to inorganic nitrogen substrates, suggesting that cyanobacteria exhibit a preference for urea; (2) urea was consumed in excess of cellular requirements; and (3) urea may offer cyanobacteria a competitive edge over eukaryotic algae by enhancing light absorption capabilities. …

Molybdenum And Iron Interactions As Micronutrients For Growth Of A Freshwater Cyanobacterium, Microcystis Aeruginosa, Yan Xu

Electronic Thesis and Dissertation Repository

The cyanobacterium M. aeruginosa is an important bloom former in freshwater environments. We investigated the growth, photosynthesis and toxin contents of two toxic strains of M. aeruginosa, CPCC 299 and CPCC 300, under a combination of nitrogen supply (nitrate or ammonium) and depleted or replete Molybdenum (Mo) and/or Iron (Fe) concentrations. When Mo and Fe were supplied at growth-replete levels, M. aeruginosa grew equally well on nitrate and ammonium. Reducing Fe dramatically reduced growth rate efficiency when the cells were supplied with nitrate, but not with ammonium. In contrast, the removal of Mo from the medium did not impair …

Iron-Regulated Cyanobacterial Predominance And Siderophore Production In Oligotrophic Freshwater Lakes, Ryan J. Sorichetti

Electronic Thesis and Dissertation Repository

The frequency and intensity of cyanobacterial blooms (cyanoblooms) is increasing globally. Contrary to existing phosphorus (P) and nitrogen (N) paradigms describing cyanobloom proliferation in eutrophic (nutrient-rich) freshwater lakes, many of the recent cyanobloom reports pertain to oligotrophic (nutrient-poor) freshwater lakes with no prior history of cyanobloom occurrence. There exists a critical research need to re-visit existing conceptual models, identify regulating factors currently unaccounted for and improve our ability to effectively detect and measure cyanobacterial toxins (cyanotoxins) in lakes. Iron (Fe) is required in nearly all pathways of cyanobacterial macronutrient use, though its direct role in regulating cyanobacterial biomass is not …

Tree Seedling Establishment In Response To Warming And Nitrogen Addition In A Temperate Old Field, Bryana D. Mcwhirter

Electronic Thesis and Dissertation Repository

Climate change and increased atmospheric nitrogen deposition over the next century may alter the ability of woody species to germinate and compete with grasses and forbs in temperate old fields. To investigate the responses of seed germination and seedling growth to warming and nitrogen addition, I transplanted seeds and seedlings into plots of a field experiment and conducted a greenhouse experiment. The combination of warming and nitrogen allowed seeds to germinate earlier, although there was no effect on final germination. In the greenhouse nitrogen increased seedling growth, and warming had little effect. However, in the field, warming significantly decreased the …

Overwintering Diet Quality And Timing Of Initiation Of Breeding In The Deer Mouse (Peromyscus Maniculatus), Lindsey Valliant

Electronic Thesis and Dissertation Repository

Timing of breeding in seasonal environments is important in population dynamics, but it is not always known what cues animals use to time breeding. In northern deer mice (Peromyscus maniculatus) at Kananaskis, Alberta, Canada, early seasonal births are related to overwinter protein supplementation. It is not however known if natural variation in diet quality has the same effect. I hypothesized that yearly winter arthropod availability would influence yearly spring breeding. I predicted that the mean date of initiation of breeding in the population would be related to overwinter diet quality, indicated by ¹⁵N enrichment of hair of …