Cheng Kin-wing. / "May 1999." / Thesis (Ph.D.)--Chinese University of Hong Kong, 1999. / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Mode of access: World Wide Web. / Abstracts in English and Chinese.

Land-use change is prevalent across the Prairie Pothole Region (PPR) because of widespread agricultural expansion over the last century. Different land-use histories will affect the distributions of native vegetation and soil biogeochemistry of PPR wetlands. Furthermore, because native vegetation is partially required for wetland classification, supplementary methods are needed for proper wetland delineation. Accurate estimates of GHG emissions are required for correct climate change models; therefore proper investigation of contrasting land-use histories on GHG emissions is essential. This study focused on determining the effect that different land-use histories had on the expression of soil hydric features and magnetic susceptibility as well as examining interacting effects among contrasting land-use histories and biogeochemical controls of GHG emissions of PPR wetlands. To determine the differing effects of land-use histories on hydric soil indicators and magnetic susceptibility, fifteen ephemeral wetlands under differing land-uses (annually cultivated, restored grassland, seeded pasture and native grassland) were sampled to a depth of 1 m with samples collected every 10 cm. An upland pit was correspondingly sampled for each wetland. Soils were then analyzed for organic C, inorganic C, dithionite extractable Fe, particle size distributions, wet stable aggregate distributions and magnetic susceptibility at four different temperature treatments (room temperature, 100 °C, 300 °C and 500 °C). While some variables had observable difference among the land-uses (i.e. organic C, dithionite extractable Fe and magnetic susceptibility), the most pronounced differences were between the different pit positions (i.e. wetland pits vs. upland pits). The data was holistically analyzed through non-metric multidimensional scaling (NMDS) and position based differences were easily identified through this approach; however, only slight differences were present with respect to contrasting land-use histories. The controls of GHG emissions and their interactions were evaluated through two laboratory incubations (i.e. CH4 incubation and N2O incubation), with a factorial design using land-use history treatments as well as biogeochemical controls specific to each GHG (i.e. CH4: SO4- additions; N2O: water filled pore space [WFPS] treatments and NO3 - additions). Both incubations had the presence of interacting factors among the differing land-use histories. During the CH4 incubation, each land-use history responded oppositely to sulfate additions. During the N2O incubations, both WFPS treatments and NO3 - additions had additive effects on the emissions of N2O. Moreover, the presence of the interactions satisfied the objective of the incubation study. Overall it was determined that while land-use history significantly altered the response of GHG controls with respect to GHG emissions, it did not have strong effects in influencing hydric soil indicators and magnetic susceptibility values.

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The diathesis-stress model focuses on the interaction between gene polymorphisms and negative environmental conditions (i.e., stressors); however, Belsky and Pluess (2009) recently proposed an alternative to diathesis-stress: the differential susceptibility hypothesis, which states that some individuals may be predisposed to be more adversely affected by negative environments but, also, to benefit more from positive environments. Nevertheless, the differential susceptibly hypothesis has not been rigorous tested. Thus, the purpose of this study was to test the differential susceptibility hypothesis by examining individual differences in men’s testosterone, behavioral, and psychological responses to social status as a function of the serotonin transporter promoter region polymorphism (5-HTTLPR), which was cited by Belsky and Pluess as a potential “plasticity gene” because one variant – the long (l) allele – appears to be associated with lower susceptibility/plasticity and another – the short allele (s) – appears to be associated with higher susceptibility/plasticity. In this study, groups of 3-4 male participants were allowed to socialize before being told that they were part of a larger initiative to create a student-run Honor Committee. They were asked to nominate one person to be the leader and one person to not be on the committee. Then, participants were told privately that everyone voted them to either (1) be the leader or (2) not be on the committee. Salivary hormone samples were collected at baseline and 20 minutes after vote feedback. In addition, after receiving the vote feedback, participants completed a series of dating anxiety and mate preference tasks and were given the option to examine an “actual honor violation” case either alone or as part of the committee. The results support the differential susceptibility hypothesis. In terms of testosterone response, ss individuals showed both greater reactivity and differential responses to vote feedback. Furthermore, the testosterone responses of ss individuals were moderated by basal cortisol, which is associated with approach/avoidance behavior (Kagan et al., 2003; Shoal, Giancola, & Kirillova, 2003). In addition, ss individuals’ decisions to work on the committee or work alone and responses to the mating tasks were dependent upon the vote feedback, whereas l-carriers’ decisions and responses were not. / text

published_or_final_version / Anatomy / Doctoral / Doctor of Philosophy

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Hypertension is associated with a reduction in sensitivity to pain in both animals and humans. Changes in nociception pre-date elevations in blood pressure in animals genetically predisposed to hypertension, and preliminary findings with male offspring of hypertensives indicate that genetic risk for hypertension is related to decreased pain sensitivity in humans. Sensitivity to naturalistic and laboratory pain stimuli was compared in normotensive females with and without a parental history of hypertension in three studies. Genetic risk for hypertension was associated with decreased sensitivity for blood donation venipuncture pain and electric shock, but not for menstrual pain or the cold pressor test. These findings provide modest support for the notion that hypoalgesia is present in females at risk for hypertension. Issues for future research include extension of these findings to other pain stimuli, use of multiple indices of risk, assessment of the effects of cyclic hormonal changes on the relationship between pain sensitivity and risk for hypertension, and further study of the mechanisms and pathophysiological implications of this effect.

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