Microbial and biogeochemical responses to changing precipitation patterns in grassland ecosystems

2012 Summer.Includes bibliographical references.Global circulation models predict that precipitation patterns in grasslands will both intensify and be characterized by more severe drought in the future. In these systems, the availability of water strongly controls ecosystem function, so changes in precipitation are likely to significantly alter biological communities and biogeochemical dynamics. Since these biogeochemical changes could feed back on climate drivers by influencing regional to global scale energy and water balance, predicted changes in grassland precipitation call for a better understanding of relationships between water availability and grassland biogeochemical dynamics. My dissertation aimed to address how changing rainfall patterns affect biogeochemical cycling and soil microbial communities in grasslands. I first tested the generality of controls over soil organic matter storage in temperate grasslands by studying existing spatial gradients in soil carbon and nitrogen, as they relate to the spatial variation in average precipitation and temperature, and soil texture. I found that statistical models developed in US grasslands overestimated soil organic carbon and underestimated soil organic nitrogen in Chinese grasslands. However, when I incorporated nitrogen deposition and historical land use using a simulation model, it resulted in more accurate model estimates for this region. This work suggests that nitrogen deposition and historical land use legacies may need to be considered to accurately describe biogeochemical dynamics in Chinese grasslands and better predict the vulnerability of global carbon stocks to loss. Responses of ecosystems to changes through time are often somewhat different than relationships gleaned from large-scale spatial gradients. At the local scale, I found that an 11-year drought can significantly alter biogeochemical and ecosystem dynamics in the highly drought-resistant shortgrass steppe. Here, soil inorganic nitrogen availability increased up to 4-fold in plots receiving 25% of summer precipitation. This accumulation of nitrogen under drought may explain the higher plant tissue nitrogen and N2 flux observed under recovery. A more "open" nitrogen cycle that I observed following severe drought could affect the impact of drought on grassland ecosystems, as well as the timescale of recovery. Soil microbial community composition was also altered by this 11-year drought manipulation in the shortgrass steppe, and these differences persisted even after communities were subject to the same moisture conditions for 36 hours in the lab. In this lab experiment, I also identified specific microbial groups that grew under a certain moisture levels, presenting evidence of moisture niche partitioning in microbial communities. However, this niche differentiation wasn't realized in the field; communities that grew under dry conditions in the lab were not similar to those that emerged under long-term drought plots. Overall, this work suggests that contrary to previous assumptions, microbial communities display legacies from long-term field treatments, and that although soil moisture has the potential to drive microbial community composition through niche partitioning, this factor may not always be the primary driver of long-term community composition. Microbial communities were also sensitive to altered precipitation timing in the tallgrass prairie. In addition, communities that were subject to intensified precipitation patterns in the field respired less than control soils after laboratory rewetting events, but respiration rates of the different field treatments converged after 100 days under the same conditions. Surprisingly, species composition of these communities was more sensitive to drying and rewetting pulses in the lab than those from the control. Together, these results show that microbial communities display legacies to altered precipitation timing, in addition to drought, but community composition is not necessarily tightly linked to respiration. Overall, my dissertation work suggests that grasslands will be sensitive to extreme shifts in precipitation, and that biogeochemical and microbial responses could influence how grasslands are altered under future precipitation regimes. However, my work also shows that precipitation is not the only factor controlling biogeochemical and microbial community dynamics in grasslands, even under rainfall manipulations and across precipitation gradients. Therefore, the response of grasslands to other environmental factors - that shift with precipitation changes or are predicted to change independently - should not be overlooked

In situ apparatus for the study of clathrate hydrates relevant to solar system bodies using synchrotron X-ray diffraction and Raman spectroscopy

Clathrate hydrates are believed to play a significant role in various solar system environments, e.g. comets, and the surfaces and interiors of icy satellites, however the structural factors governing their formation and dissociation are poorly understood. We demonstrate the use of a high pressure gas cell, combined with variable temperature cooling and time-resolved data collection, to the in situ study of clathrate hydrates under conditions relevant to solar system environments. Clathrates formed and processed within the cell are monitored in situ using synchrotron X-ray powder diffraction and Raman spectroscopy. X-ray diffraction allows the formation of clathrate hydrates to be observed as CO2 gas is applied to ice formed within the cell. Complete conversion is obtained by annealing at temperatures just below the ice melting point. A subsequent rise in the quantity of clathrate is observed as the cell is thermally cycled. Four regions between 100-5000cm-1 are present in the Raman spectra that carry features characteristic of both ice and clathrate formation. This novel experimental arrangement is well suited to studying clathrate hydrates over a range of temperature (80-500K) and pressure (1-100bar) conditions and can be used with a variety of different gases and starting aqueous compositions. We propose the increase in clathrate formation observed during thermal cycling may be due to the formation of a quasi liquid-like phase that forms at temperatures below the ice melting point, but which allows easier formation of new clathrate cages, or the retention and delocalisation of previously formed clathrate structures, possibly as amorphous clathrate. The structural similarities between hexagonal ice, the quasi liquid-like phase, and crystalline CO2 hydrate mean that differences in the Raman spectrum are subtle; however, all features out to 5000cm-1 are diagnostic of clathrate structure.Comment: Astronomy & Astrophysics, in press. 6 page

The top trumps of time:Factors motivating the resolution of temporal ambiguity

What factors motivate our understanding of metaphoric statements about time? English exhibits two deictic space–time metaphors: the Moving Ego metaphor conceptualizes the ego as moving forward through time, while the Moving Time metaphor conceptualizes time as moving forward towards the ego (Clark, 1973). In addition to earlier research investigating spatial influences on temporal reasoning (e.g., Boroditsky & Ramscar, 2002), recent lines of research have provided evidence that a complex of factors, such as personality differences, event valence, lifestyle, and emotional experiences, may also influence people’s perspectives on the movement of events in time – providing new insights on metaphor and its ability to reflect thought and feeling (e.g., Duffy & Feist, 2014; Duffy, Feist, & McCarthy, 2014; Margolies & Crawford, 2008; Richmond, Wilson, & Zinken, 2012). Probing these findings further, two studies were conducted to investigate whether the interpretation of a temporally ambiguous question may arise from an interaction between the valence of the event and aspects of the personality (Experiment 1) and lifestyle (Experiment 2) of the comprehender. The findings we report on shed further light on the complex nature of temporal reasoning. While this involves conceptual metaphor, it also invokes more complex temporal frames of reference (t-FoRs) (Evans, 2013), which are only partially subserved by space-to-time conceptual metaphors

Cyclic hydrostatic pressure and cotton particles stimulate synthesis by human lung macrophages of cytokines in vitro

<p>Abstract</p> <p>Background</p> <p>Inhalation of particulates is a leading cause of the development of lung diseases and current understanding of the complex relationship between lung metabolism and airborne particulates is incomplete. It is well established that mechanical load is important in the development of the lung and in lung cell differentiation. The interaction between particle exposure and physical forces on alveolar macrophages is a physiologically relevant issue, but as yet understudied. This study examines the effect of cyclic hydrostatic pressure and cotton particles on synthesis of cytokines by human alveolar macrophages.</p> <p>Methods</p> <p>Alveolar macrophages were obtained from patients with lung disease, either from lavage samples or from lung tissue resection. The commonly used cell line THP-1 was included in the experiments. Cell cultures were exposed to cotton particles and/cyclic hydrostatic pressure (3 or 5 psi); control cultures were exposed to medium only. TNFα, IL-1β and IL-6 were assayed in the culture media using specific ELISAs. Cells were characterized using morphology and markers specific for macrophages (Jenner/Giemsa staining, CD14 and CD68).</p> <p>Results</p> <p>Exposure to cotton particles stimulated cytokine synthesis by macrophages from all three sources; exposure to cyclic hydrostatic pressure alone did not stimulate cytokine synthesis significantly. However, the combination of both particles and cyclic hydrostatic pressure increased the simulation of cytokine synthesis still further. Cell characterization demonstrated that the large majority of cells had a macrophage morphology and were positive for CD14 and CD68.</p> <p>Conclusion</p> <p>These data suggest an interaction between cyclic hydrostatic pressure and particulate exposure, which increases alveolar macrophage cytokine production. This interaction was only observed at the higher cyclic hydrostatic pressure. However, in patient samples, there was considerable variation in the amount by which secretion of an individual cytokine increased and there was also variation in the mechanosensitivity of cells from the three different sources. Cyclic hydrostatic pressure, therefore, may be an important modulator of the response of alveolar macrophages to cotton particles, but the source of the cells may be a confounding factor which demands further investigation.</p

Making Leaders: Examining How Elementary School Students Develop an Understanding of Leadership and Show Emerging Leadership Tendencies

Abstract MAKING LEADERS: EXAMINING HOW ELEMENTARY SCHOOL STUDENTS DEVELOP AN UNDERSTANDING OF LEADERSHIP AND SHOW EMERGING LEADERSHIP TENDENCIES By Sarah E. Evans, Ph.D. A dissertation submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at Virginia Commonwealth University. Virginia Commonwealth University, 2014 Director: Whitney Sherman Newcomb, Ph.D. Professor, Educational Leadership The purpose of this study was to understand how young children develop skills and concepts of leadership, when nurtured in a developmentally appropriate manner. Leadership was defined as a process that people use to bring out the best in themselves and others, while working towards a common purpose. This study examined a leadership curriculum, The Leader in Me, as it was being taught in an elementary school, grades K-5. The researcher used a qualitative lens to understand parents’ and teachers’ perceptions of the program, and the study findings indicated that The Leader in Me was used as both a way to teach leadership and for behavior modification. Teachers reported teaching leadership through direct instruction, informal instruction, curriculum materials, and practice. In addition, the children’s leadership behaviors were analyzed through the transformational leadership model to find The Leader in Me resulted in attempting to make transformational leaders. The children showed signs of transformational leadership through the behaviors of the 4 I’s: idealized influence, inspirational motivation, intellectual stimulation, and individualized consideration. The data further showed positive gains in school culture, leadership development, and personal growth. Standardized testing pass rates were examined, but the researcher found the leadership program had no discernable impact on student achievement. This study found that there is merit in looking to our nation’s educational system to support the intentional process of developing leaders in schools. Keywords: leaders, leadership, leadership development in children, The Leader in Me, 7 Habits, transformational leadershi