The physiological function of the plant enzyme alternative oxidase has long been a topic of debate. The cyanide-resistant alternative oxidase (AOX), along with the cytochrome c oxidase (COX), catalyzes the reduction of oxygen to water in the electron transport chain of mitochondrial respiration. Although respiration via the alternative pathway (AP) results in approximately one third of the ATP production as respiration via the cytochrome pathway (CP), the AP is utilized by all plants and some fungi and animals. This “energy wasteful” pathway has been proposed to reduce oxidative stress in plant cells under a variety of stressful conditions. Virtually all previous work on the AP has been performed on laboratory-grown plants in controlled environment conditions; thus, there is little knowledge of how the AP responds to unstable conditions and multiple environmental stresses in the field. This thesis presents new methodology for studying AP respiration and the AOX protein in field-grown plants, and investigates how the AP responds to natural changes in environmental conditions in the field in several plant species grown in diverse ecosystem types. The experimental work presented here also investigates how AP activity is related to changes in total rates of respiration, and questions whether abundance of the AOX protein determines electron partitioning to the AP. AP partitioning (or relative changes in AP partitioning) varied over seasonal timescales in each of the experimental studies. Chapter 3 reports on two species of Chionochloa, a native New Zealand tussock grass growing along an altitudinal gradient. In Chapter 4, seasonal variation was studied in two tree types: Populus x canadensis, a deciduous angiosperm, and Pinus radiata, an evergreen gymnosperm. Quercus rubra trees were studied along an urban-rural gradient originating in New York City in Chapter 5. In a highly exposed and variable environment, relative changes in AP partitioning in two species of Chionochloa were correlated with the previous day’s integrated light. In Quercus rubra, the AP was instead related to temperature changes: relative AP partitioning increased in response to seasonally low temperature in trees grown at colder, more rural field sites, while at the warmer, urban sites, it increased in response to high summer temperatures. Each of these environmental conditions that were related to increases in the AP (high light, low temperatures, and heat) are potentially stressful to plants. Thus, it is possible that the increases in AP respiration observed in these studies served to oxidize excess reducing equivalents generated through stressful conditions. In Chapter 4, although AP partitioning in Populus x canadensis and Pinus radiata varied seasonally, these changes were not directly related to environmental parameters. However, AP partitioning in Populus x canadensis was clearly shown to be dependent on measurement temperature. In each of the studies presented here, changes in the AP were not related to abundance of the AOX protein. AOX protein abundance showed consistent seasonal patterns in the two deciduous angiosperms, Populus sp. and Quercus sp, and was correlated with seasonal changes in temperature in Chionochloa spp. However, the lack of correlation between protein abundance and AP partitioning indicates that the AP is subject to post-translational control and likely varies more rapidly than protein levels. In each of Chapters 3 – 5, there was no clear impact of changes in AP partitioning on rates of total respiration. As the AP produces less ATP than the CP, I hypothesized that increases in AP activity would lead to higher respiration rates in order to meet a plant’s energy demands. However, in Populus x canadensis and Quercus rubra, respiration rates remained stable during sharp increases in AP partitioning, indicating that, at least under certain conditions, increases in AP activity are accompanied by a decrease in the CP. In some of the first research studying AP partitioning in field-grown plants, this thesis illuminates possible mechanisms, functions, and implications of the AP. Over a range of plant taxa and environmental settings, this work shows that the AP does respond to stressful conditions in the wild, but that this does not result in increased respiration. Lastly, the methods presented here to study AP activity and AOX proteins in the field enable future studies to further probe the specific responses of AOX to natural stresses.

No description available.

京都大学 / 0048 / 新制・課程博士 / 博士(農学) / 甲第21971号 / 農博第2361号 / 新制||農||1071(附属図書館) / 学位論文||R1||N5222(農学部図書室) / 京都大学大学院農学研究科森林科学専攻 / (主査)教授 大澤 晃, 教授 髙部 圭司, 教授 小杉 緑子 / 学位規則第4条第1項該当 / Doctor of Agricultural Science / Kyoto University / DFAM

This thesis investigates how variations in the oxygen isotopic composition of lake waters in northern Fennoscandia are recorded in lake sediment archives, especially diatoms, and how these variations can be used to infer past changes in climate and atmospheric circulation. Results from analyses of the oxygen isotopic composition of lake water samples (δ18Olakew) collected between 2001 and 2006 show that δ18O of northern Fennoscandian lakes is mainly controlled by the isotopic composition of the precipitation (δ18Op). Changes in local δ18Op depend on variations in ambient air temperature and changes in atmospheric circulation that lead to changes in moisture source, vapour transport efficiency, or winter to summer precipitation distribution. This study demonstrates that the amount of isotopic variation in lake water δ18O is determined by a combination of the original δ18Olakew, the amount and timing of the snowmelt, the amount of seasonally specific precipitation and groundwater, any evaporation effects, and lake water residence time. The fact that the same isotope shifts have been detected in various δ18Olakew proxies, derived from hydrologically different lakes, suggests that these records reflect regional atmospheric circulation changes. The results indicate that diatom biogenic silica isotope (δ18Odiatom) records can provide important information about changes in atmospheric circulation that can help explain temperature and precipitation changes during the Holocene. The reconstructed long-term Holocene decreasing δ18Op trend was likely forced by a shift from strong zonal westerly airflow (relatively high δ18Op) in the early Holocene to a more meridional flow pattern (relatively low δ18Op). The large δ18Olakew depletion recorded in the δ18O records around ca. 500 cal yr BP (AD 1450) may be due to a shift to more intense meridional airflow over northern Fennoscandia resulting in an increasing proportion of winter precipitation from the north or southeast. This climate shift probably marks the onset of the so-called Little Ice Age in this region. / At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 1: In press. Paper 2: Submitted. Paper 5: In progress.

<p>The rationale of this study is to apply light stable isotope chemistry towards investigations that require temporally high-resolution data. High-resolution (or high sampling frequency) data sets, are critical for testing environmental and/or paleoenvironmental hypotheses that seek to explain processes occurring over rapid or short time intervals. The investigation of climate variation (e.g., seasonality, El Niño, deglaciation), animal migration and physiology, and disturbance ecology (e.g., fire, flooding) benefits from the recovery of proxy information at decadal to subannual resolutions. The type of material used also dictates a spatial scale. Herein are presented four studies that utilize high-resolution light stable isotope profiles with contrasting temporal and spatial scales. The first study employs advances in three-dimensional computer-controlled micromilling to recover ~daily to weekly deposited carbonate from small (~1 cm) mollusc shells. Stable oxygen isotope values from freshwater mollusc shells are predictably related to the local environment of growth using previously published temperature-fractionation relationships, providing a paleoclimate record of temperature and precipitation. The second study investigates variation in stable carbon isotope values from Aplodinotus grunniens otoliths, for which high-resolution patterns were critical in assessing metabolic rate as the governing control. The third study employs high-resolution stable oxygen and carbon isotope values to determine chinook salmon (Oncorhynchus tshawytscha) seasonal and ontogenetic migration in Lake Ontario and its tributaries. Lastly, high-resolution stable hydrogen and carbon isotope values of chitin derived from Mexican free-tailed bat (Tadarida brasiliensis) guano are presented, providing a record of abrupt climate change. Thus, this thesis reports on promising new research avenues for paleoclimatology, paleoecology, and modern ecology.

<p>The rationale of this study is to apply light stable isotope chemistry towards investigations that require temporally high-resolution data. High-resolution (or high sampling frequency) data sets, are critical for testing environmental and/or paleoenvironmental hypotheses that seek to explain processes occurring over rapid or short time intervals. The investigation of climate variation (e.g., seasonality, El Niño, deglaciation), animal migration and physiology, and disturbance ecology (e.g., fire, flooding) benefits from the recovery of proxy information at decadal to subannual resolutions. The type of material used also dictates a spatial scale. Herein are presented four studies that utilize high-resolution light stable isotope profiles with contrasting temporal and spatial scales. The first study employs advances in three-dimensional computer-controlled micromilling to recover ~daily to weekly deposited carbonate from small (~1 cm) mollusc shells. Stable oxygen isotope values from freshwater mollusc shells are predictably related to the local environment of growth using previously published temperature-fractionation relationships, providing a paleoclimate record of temperature and precipitation. The second study investigates variation in stable carbon isotope values from Aplodinotus grunniens otoliths, for which high-resolution patterns were critical in assessing metabolic rate as the governing control. The third study employs high-resolution stable oxygen and carbon isotope values to determine chinook salmon (Oncorhynchus tshawytscha) seasonal and ontogenetic migration in Lake Ontario and its tributaries. Lastly, high-resolution stable hydrogen and carbon isotope values of chitin derived from Mexican free-tailed bat (Tadarida brasiliensis) guano are presented, providing a record of abrupt climate change. Thus, this thesis reports on promising new research avenues for paleoclimatology, paleoecology, and modern ecology.

In urban areas, stormwater management ponds (SWPs) are built to mitigate polluted runoff. Although these ponds are increasing in numbers, their ecology is not well understood. Physical and chemical characteristics of 17 SWPs in the City of Ottawa were measured to determine the drivers of phytoplankton biomass (Chl. a) and primary production (PP). While total phosphorus was the best predictor of algal biomass in the ponds (as in lakes), the imperviousness of the catchment could also predict Chl. a. Planktonic PP in two ponds measured seasonally was more closely related to water residence time than to nutrient concentrations with rates approaching at times the theoretical maximum for aquatic systems. In one pond, whole ecosystem metabolism, estimated using diel changes in dissolved oxygen and δ18O-O2, suggested that these hypereutrophic systems were net sinks for carbon in the summer but likely sources to the atmosphere at other times of the year.

In urban areas, stormwater management ponds (SWPs) are built to mitigate polluted runoff. Although these ponds are increasing in numbers, their ecology is not well understood. Physical and chemical characteristics of 17 SWPs in the City of Ottawa were measured to determine the drivers of phytoplankton biomass (Chl. a) and primary production (PP). While total phosphorus was the best predictor of algal biomass in the ponds (as in lakes), the imperviousness of the catchment could also predict Chl. a. Planktonic PP in two ponds measured seasonally was more closely related to water residence time than to nutrient concentrations with rates approaching at times the theoretical maximum for aquatic systems. In one pond, whole ecosystem metabolism, estimated using diel changes in dissolved oxygen and δ18O-O2, suggested that these hypereutrophic systems were net sinks for carbon in the summer but likely sources to the atmosphere at other times of the year.

This thesis investigates the relationship between climate, agriculture and social change in South Asia’s Bronze Age urban Indus Civilisation. Specifically, my research tests the hypothesis that an abrupt weakening of the Indian Summer Monsoon ca 2100 cal BC led to increasing crop water stress, and hence potentially contributed to the Civilisation’s decline by reducing food supply. This hypothesis is frequently invoked in discussions of the Civilisation’s end, yet until now, has not been empirically tested. Using material excavated from several Indus settlements, this study uses a novel combination of isotopic techniques to directly test the connection between climate change and agricultural stress. These techniques are first, oxygen isotope analysis of faunal bones and teeth; and second, stable carbon isotope analysis of crop remains. The oxygen analyses provide detailed records of monsoon intensity at a local, human scale, while the carbon analyses provide an empirical test of whether crop water stress increased. Applied in parallel across a diverse suite of Indus sites, these techniques together provide an archaeologically and ecologically-nuanced analysis of climatic impacts. The archaeological analyses are supported by a methodological study, which investigates how water status relates to the stable carbon isotope signature in barley (Hordeum vulgare) and the Indian jujube (Ziziphus mauritiana) along a climatic transect in north-western India today. Overall, the isotopic results suggest that at the sites sampled here, climate change probably had minimal impacts on crop water availability. This does not necessarily mean that climate change had no impacts on agriculture across the greater Indus sphere, and indeed there are hints that there may have been climatic stress in more vulnerable settings. However, at the sites studied here, any hydrological consequences of climate change—including the 4.2 ka event—appear to have had neither a lasting nor a pervasive impact on the adequacy of crop water supply. This is an important finding, and necessitates a clear refinement of how we think about climatic sensitivity, climatic vulnerability, and climatic impacts across—and indeed beyond—the greater Indus.

In urban areas, stormwater management ponds (SWPs) are built to mitigate polluted runoff. Although these ponds are increasing in numbers, their ecology is not well understood. Physical and chemical characteristics of 17 SWPs in the City of Ottawa were measured to determine the drivers of phytoplankton biomass (Chl. a) and primary production (PP). While total phosphorus was the best predictor of algal biomass in the ponds (as in lakes), the imperviousness of the catchment could also predict Chl. a. Planktonic PP in two ponds measured seasonally was more closely related to water residence time than to nutrient concentrations with rates approaching at times the theoretical maximum for aquatic systems. In one pond, whole ecosystem metabolism, estimated using diel changes in dissolved oxygen and δ18O-O2, suggested that these hypereutrophic systems were net sinks for carbon in the summer but likely sources to the atmosphere at other times of the year.