Precipitation, more than any other environmental factor, controls patterns of ecosystem production and biogeochemical cycling in arid and semiarid environments. Growing-season rains in these regions are highly unpredictable as they come in intermittent pulses varying in size, frequency and spatial extent, thereby producing unique hydrological patterns that constrain the location and residence time of soil water available for biological activity. In order to understand how arid and semiarid ecosystems respond to inputs of precipitation within the context of ecosystem science and global change studies, knowledge is needed on how plants and other organisms respond as an integrated system to such environmental control. The focus of my research was to understand how the distribution of precipitation events influences the dynamics of carbon cycling in semiarid ecosystems. At a semiarid riparian woodland, measurements of CO2 exchange and evapotranspiration revealed that following precipitation events occurring soon after prolonged dry periods the efficiency of rain-use (amount of carbon gain per unit of precipitation over a specific period time) was low. Precipitation did not readily stimulate primary productivity, water was mainly lost as soil evaporation and large respiratory CO2 effluxes were observed. This commonly observed features in seasonally dry ecosystems might have profound consequences for the seasonal and annual carbon balance. In this woodland, 47% of the precipitation within a single growing season (May-October) was returned to atmosphere as soil evaporation and the CO2 efflux observed just during the first rainy month (July) was equivalent to almost 50% of the net carbon gain observed over the six-month growing season. Results from experimental irrigations in understory plots of riparian mesquite woodland revealed that the magnitude and duration of the large CO2 fluxes occurring soon after rainfall was higher in plots located under tree canopies where, relative to intercanopy plots, the amount of plant litter was higher, soil evaporation and plant photosynthetic rates were lower. Efficiency of rain-use in semiarid ecosystems during the growing season apparently was determined by the degree of coupling between gross photosynthesis and ecosystem respiration, by the fraction of precipitation lost as soil evaporation and by the water-use efficiency of the component vegetation.

In this project I have tried to obtain stable transformants of Drosophila melanogaster flies using electroporation. I have completed approximately 200 tests using different DNA concentrations, voltages and cuvettes, including a novel Petri dish cuvette which I developed and manufactured myself. I also developed new and more efficient procedures of egg collection and egg dechorionation. Although I was not  successful in obtaining true stable transformants, control experiments indicate that electroporation of DNA into embryos could be accomplished under the conditions used. The lack of stable transformants was probably due to failure of the electroporated DNA to integrate into the host genome. The reasons for why the DNA did not integrate was not further investigated in this study.

The max-stable Paretian distribution is analyzed in this Master’s work.

Understanding wolf (Canis lupus) food habits provides critical information for boreal woodland caribou (Rangifer tarandus caribou; forest-dwelling ecotype) recovery strategies. By incorporating the stable isotope ratios of different caribou ecotypes into a stable isotope mixing model, I determined the relative importance of boreal woodland caribou in the summer diet of wolves in northern Manitoba, Canada. Boreal woodland caribou were primary summer prey for wolves collected in winter in registered trapline (RTL) districts where these caribou are considered rare, suggesting migratory behaviour in some wolves. Moose were primary prey in other RTL districts, followed by boreal woodland caribou, with beaver providing important contributions. Recovery strategies for woodland caribou should investigate annual wolf, caribou, and moose movement in the region to complement these findings and gain a better insight into this complex ecosystem.

Afforestation and reforestation programs utilizing available fields for biofuel production, carbon sequestration, and other uses linked to climate change are looking to tree physiologists to identify species and genotypes best-suited to their purposes. The ideal poplar genotype for use in Canadian programs would be drought-resistant, cold-climate adapted, and fast-growing, thus requiring an understanding of links between a variety of physiological traits linked to growth and productivity. This study examined the basis for variations in water-use efficiency within four selected populations of Populus trichocarpa and Populus balsamifera (2 provenances each). Each species included both a northern and a southern provenance. Correlations between water-use efficiency, nitrogen-use efficiency, ¹³C/¹²C isotope ratio, stomatal conductance, and overall productivity were evaluated. Gas exchange variables measured included net photosynthesis, transpiration rate, stomatal conductance, and intercellular CO₂ content. Water-use efficiency and ¹³C content across all genotypes were highly correlated. Results suggested that variation in water-use efficiency was primarily related to variation in stomatal conductance across all genotypes. Whereas differences in net photosynthesis in this study were not significant between species, P. balsamifera did reveal a higher average stem volume overall. Although variation in stomatal conductance was the major determinant of differences in water-use efficiency, positive correlations were found between ¹³C isotope abundance and net photosynthesis in both P. balsamifera provenances. In this regard, results for the northern P. balsamifera provenance are the most consistent across all gas-exchange and growth trait correlations, in terms of meeting expectations for sink-driven water-use efficiency. The findings in this study suggest the possibility of identifying poplar genotypes with an absence of trade-off between water-use efficiency and nitrogen-use efficiency, notably among genotypes from the northern P. balsamifera provenance, near Gillam.

Darbe taikyta Norvaišos ir Salopk (2002) metodologija funkcijos šiurkštumui nagrinėti remiantis modifikuotu funkcijos grafiko dėžučių skaičiaus indeksu. Funkcijos šiurkštumas nusakomas p-variacijos indeksu, kuris prie tam tikrų sąlygų lygus fraktalo dimensijai. Darbe ištirtos tiesinės regresijos, kuri vertina p-variacijos indeksą, liekanos ir pasiūlytas būdas kaip išpildyti balto triukšmo prielaidas. Rezultatai apibendrinti Monte Carlo procedūra. Sukonstruoti p-variacijos indekso pasikliautinieji intevalai -stabiliam ir trupmeniniam Brauno judesio procesams. Ištirtas p-variacijos indekso kintamumas laike „Vallourec” akcijų kainos procesui. / To estimate the roughness of the sample function the methodology introdused in Norvaiša and Salopek (2002) was applied. The roughness is defined as p-variation index of the sample function graph. Methodology is based on linear regression of the oscilation index. This master thesis tests the assumptions of linear regression residuals and constructs estimator which fulfill these assumptions. The model was used for the generated α-stable process and fractional Brownian motion. Conclusions are generalized using Monte-Carlo procedure. The confidence intervals for the p-variation index was constructed making assumption that the process is the realisation of -stable or fractional Brownian motion. The p-variation index was estimated for the „Vallourec” stock price data, sampled at irregular time. In addidion the variability in time of p-variation index was studied for different segments of intervals.

Chlorine stable isotope analysis (?37Cl ) means of stream water (- 0.95 ‰, n = 22), rainwater (- 1.51 ‰, n = 12), fog water (- 1.08 ‰, n = 7) and silicate mineral bound chloride (+ 0.13 ‰, n = 3) are used in an isotope mass balance approach to estimate sources of stream chloride. During summer-baseflow conditions, the chloride budget of two catchments in southwestern Nova Scotia is approximately 39 % from rainfall, 37 % from fog water and 24 % from rock/water interactions. The results of a significant source of geological chloride suggest the use of chloride in stream water as a proxy for marine derived sulphate may not be valid. This conclusion implies that anthropogenic sources of sulphate to acid sensitive ecosystems of southwestern Nova Scotia have been underestimated when chloride is assumed to be a conservative ion in the hydrological cycle.

For a hypergraph H=(V,E) and a field F, a weighting of H is a map f:V ?F. A weighting is called stable if there is some k ? F such that the sum of the weights on each edge of H is equal to k. The set of all stable weightings of H forms a vector space over F. This vector space is termed the uniformity space of H over F, denoted U(H,F), and its dimension is called the uniformity dimension of H over F. This thesis is concerned with several problems relating to the uniformity space of hypergraphs. For several families of hypergraphs, simple ways of computing their uniformity dimension are found. Also, the uniformity dimension of random l-uniform hypergraphs is investigated. The stable weightings of the spanning trees of a graph are determined, and lastly, a notion of critical uniformity dimension is introduced and explored.

This study used the isotope pool dilution method to estimate gross rates of mineralization, nitrification, NH4+ and NO3- consumption, and denitrification emissions over two growing seasons within a conventional barley-red clover-potato crop rotation on Prince Edward Island. Gross rates within the 2010 season were, in most cases, not significant across crop species or sampling date. In comparison, gross nitrification, NH4+ consumption, and NO3- consumption rates in 2011 were greatest within the potato crop following planting and hilling. However, rates were highly variable within both seasons. Error analysis indicated that variation in soil mineral nitrogen concentrations between duplicate cores was the greatest source of error. The use of the isotope pool dilution method to estimate gross nitrogen transformation rates using intact cores was not viable within this production system due to high and variable soil mineral nitrogen concentrations, particularly following fertilizer application.

This thesis attempted to determine whether precipitation at CFB Borden, Ontario Canada is derived from recycled or marine source water using δ18O and to explore the enrichment of leaf water in three temperate forest trees. The d-excess values and rainfall intensity were used as indicators of recycled water and were found to suggest that precipitation at Borden is not derived from recycled water. The leaves of ash, aspen and maple showed significant enrichment in δ18O over xylem water. Maple leaves were significantly more enriched over the leaves of ash and aspen (p-value = 0.0019), despite source water not being significantly different (p-value = 0.1782). Modelling leaf water demonstrated the need for the inclusion of the Peclet effect in the steady state model for ash and aspen leaves, however for maple, the Peclet effect is insignificant. The non-steady state model used measured values of δET, which were uncertain and lead to poor model predictions. / NSERC Strategic Project #351040