Matching Items (13)

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Physiological Response to Environmental Stress in Drylands Ecosystems: Examining Prosopis velutina Seedling Responses to Temporal Water Availability Gradients

Description

Climate change is increasing global surface temperatures, intensifying droughts and increasing rainfall variation, particularly in drylands. Understanding how dryland plant communities respond to climate change-induced rainfall changes is crucial for

Climate change is increasing global surface temperatures, intensifying droughts and increasing rainfall variation, particularly in drylands. Understanding how dryland plant communities respond to climate change-induced rainfall changes is crucial for implementing effective conservation strategies. Concurrent with climate change impacts on drylands is woody encroachment: an increase in abundance of woody plant species in areas formerly dominated by grasslands or savannahs. For example, the woody plant, Prosopis velutina (velvet mesquite), has encroached into grasslands regionally over the past century. From an agricultural perspective, P. velutina is an invasive weed that hinders cattle forage. Understanding how P. velutina will respond to climate change-induced rainfall changes can be useful for management and conservation efforts. Prosopis velutina was used to answer the following question: Is there a significant interactive effect of mean soil water moisture content and pulse frequency on woody seedling survival and growth in dryland ecosystems? There were 256 P. velutina seedlings sourced from the Santa Rita Experimental Range in southern Arizona grown under four watering treatments where mean and pulse frequency were manipulated over two months. Data were collected on mortality, stem height, number of leaves, instantaneous gas exchange, chlorophyll fluorescence, biomass, and the leaf carbon to nitrogen (C:N) ratio. Mortality was low across treatments. Pulse frequency had less impact across response variables than the mean amount of water received. This may indicate that P. velutina seedlings are relatively insensitive to rainfall timing and are more responsive to rainfall amount. Prosopis velutina in the low mean soil moisture treatments lost a majority of their leaves and had greater biomass allocation to roots. Prosopis velutina’s ability to survive in low soil moisture conditions and invest in root biomass can allow it to persist as drylands are further affected by climate change. Prosopis velutina could benefit ecosystems where native plants are at risk due to rainfall variation if P. velutina occupies a similar niche space. Due to conflicting viewpoints of P. velutina as an invasive species, it’s important to examine P. velutina from both agricultural and conservation perspectives. Further analysis on the benefits to P. velutina in these ecosystems is recommended.

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Date Created
  • 2020

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The Mineralogy and Chemical Evolution of the Earth’s Deep Mantle

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The mineralogy of the deep mantle is one of the key factors for the chemical evolution of the Earth. The constituent minerals of the mantle rock control the physical properties

The mineralogy of the deep mantle is one of the key factors for the chemical evolution of the Earth. The constituent minerals of the mantle rock control the physical properties of the mantle, which have significant impacts on the large-scale processes occurring in the Earth's interior. In my PhD research, I adopted experimental approaches to investigate the mineralogy and the physical properties of the Earth's materials in the deep mantle by using the diamond anvil cells (DACs) combined with in-situ X-ray diffraction techniques.

First, I found that Ca-bearing bridgmanite can be stable in the deeper part of the Earth's lower mantle where temperature is sufficiently high. The dissolution of calcium into bridgmanite can change the physical properties of the mantle, such as compressibility and viscosity. This study suggests a new mineralogical model for the lower mantle, which is composed of the two layers depending on whether calcium dissolves in bridgmanite or forms CaSiO3 perovskite as a separate phase.

Second, I investigated the mineralogy and density of the subducting materials in the Archean at the P-T conditions near 670 km-depth. The experiments suggest that the major phases of Archean volcanic crust is majoritic garnet and ringwoodite in the P-T conditions of the deep transition zone, which become bridgmanite with increasing pressure. The density model showed that Archean volcanic crust would have been denser than the surrounding mantle, promoting sinking into the lower mantle regardless of the style of the transportation in the Archean.

Lastly, I further investigated the mineralogies and densities of the ancient volcanic crusts for the Archean and Proterozoic at the P-T conditions of the lower mantle. The experiments suggest that the mineralogy of the ancient volcanic crusts is composed mostly of bridgmanite, which is systemically denser than the surrounding lower mantle. This implies that the ancient volcanic crusts would have accumulated at the base of the mantle because of their large density and thickness. Therefore, the distinctive chemistry of the ancient volcanic crusts from the surrounding mantle would have given a rise to the chemical heterogeneities in the region for billions of years.

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Date Created
  • 2020

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Analysis of Genetic Diversity and Clarification of Species Boundaries in Echinomastus erectocentrus var. acunensis and Close Relatives

Description

Echinomastus erectocentrus (J.M. Coulter) Britton & Rose var. acunensis (W.T. Marshall) Bravo, the Acuña cactus, is a small, single-stemmed spherical cactus with a restricted distribution across the Sonoran Desert in

Echinomastus erectocentrus (J.M. Coulter) Britton & Rose var. acunensis (W.T. Marshall) Bravo, the Acuña cactus, is a small, single-stemmed spherical cactus with a restricted distribution across the Sonoran Desert in southern Arizona and into northern Sonora, Mexico. Populations of E. erectocentrus var. acunensis are threatened by loss of habitat, climate change, predation, and border related impacts. Due to the severity of these threats and shrinking population sizes, E. erectocentrus var. acunensis was federally listed as endangered by the United States Fish and Wildlife Service in 2013. The varieties of Echinomastus erectocentrus, E. erectocentrus var. acunensis and E. erectocentrus var. erectocentrus (J.M. Coulter) Britton & Rose, share many morphological characteristics that make them difficult to distinguish from one another. Echinomastus johnsonii (Parry ex Engelm.) E.M. Baxter, a presumed closely related species, also has a high level of morphological overlap that further complicates our understanding of species boundaries and detailed morphological data for these three taxa indicate a geographical cline. The goal of this project is to document the genetic diversity within and among populations of E. erectocentrus var. acunensis, and its close relatives E. erectocentrus var. erectocentrus and E. johnsonii. To accomplish this, populations of E. erectocentrus var. acunensis, E. erectocentrus var. erectocentrus, E. johnsonii and the outgroup Echinomastus intertextus (Engelm.) Britton & Rose were sampled. Deoxyribonucleic acid (DNA) was extracted, and data were collected for nine microsatellite regions developed specifically for these taxa, and two microsatellite regions developed for Sclerocactus, a closely related genus. Standard population genetic measures were used to determine genetic variation and structure, and this observed genetic differentiation was then compared to the current morphological understanding of the group. These analyses help improve the knowledge of the genetic structure of E. erectocentrus var. acunensis and inform the understanding of species boundaries and evolutionary relationships within the group by revealing genetic distinctiveness between all four taxa and hybrid populations between the two varieties. This information also reveals patterns of gene flow and population locations that have the highest conservation priority, which can be incorporated into efforts to conserve and protect this endangered species.

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Date Created
  • 2020

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A Preliminary Flora for Las Cienegas National Conservation Area and Studies on the Life History of the Endangered Huachuca Water Umbel

Description

Las Cienegas National Conservation Area (LCNCA), located in southeastern Arizona, is a place of ecological and historical value. It is host to rare native, threatened and endangered fauna and flora.

Las Cienegas National Conservation Area (LCNCA), located in southeastern Arizona, is a place of ecological and historical value. It is host to rare native, threatened and endangered fauna and flora. as well as the site of the oldest operating ranch in the state. The first chapter of this thesis provides a preliminary flora of vascular plants at LCNCA assembled from field collections, photographs and herbarium specimens, and published through the online database SEINet. This preliminary flora of LCNCA identified 403 species in 76 families. Less than 6% of the flora is non-native, perennial forbs and grasses are the most abundant groups, and over a third of species in the checklist are associated with wetlands. LCNCA has been the target of adaptive management and conservation strategies to preserve its biotic diversity, and results from this study will help inform actions to preserve its rare habitats including cottonwood willow forests, mesquite bosques, sacaton grasslands, and cienegas. The second chapter investigates poorly understood aspects of the life history of the endangered Huachuca Water Umbel (Lilaeopsis schaffneriana subsp. recurva. Apiaceae) (hereafter HWU). This wetland species occurs in scattered cienegas and streams in southeastern Arizona and northern Sonora, Mexico. Three studies were conducted in a greenhouse to investigate seed bank establishment, seed longevity, and drought tolerance. A fourth study compared the reproductive phenology of populations transplanted at LCNCA to populations transplanted at urban sites like the Phoenix Zoo Conservation Center and the Desert Botanical Garden (DBG). Results from the greenhouse studies showed that HWU seeds were capable of germinating 15 years in a dormant state and that HWU seeds are present in the seed banks at sites where populations have been transplanted. Also, greenhouse experiments indicated that colonies of HWU can tolerate up to 3 weeks without flowing water, and up to 2 weeks in dry substrate. Transplanted populations at LCNCA monitored in the fourth study produced a higher abundance of flowers and fruit relative to urban sites (i.e. DBG) suggesting that in-situ conservation efforts may be more favorable for the recovery of HWU populations. Findings from these studies aim to inform gaps in knowledge highlighted in USFWS recovery plan for this species.

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Date Created
  • 2020

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A Seed Bank Study of Southwestern Riparian Areas: Temperature Effects and Diversity

Description

Throughout the Southwest, complex geology and physiography concomitant with climatic variability contribute to diverse stream hydrogeomorphologies. Many riparian plant species store their seeds in soil seed banks, and germinate

Throughout the Southwest, complex geology and physiography concomitant with climatic variability contribute to diverse stream hydrogeomorphologies. Many riparian plant species store their seeds in soil seed banks, and germinate in response to moisture pulses, but the climatic controls of this response are poorly understood. To better understand the ecological implications of a changing climate on riparian plant communities, I investigated seed bank responses to seasonal temperature patterns and to stream hydrogeomorphic type. I asked the following questions: Are there distinct suites of warm and cool temperature germinating species associated with Southwestern streams; how do they differ between riparian and terrestrial zones, and between ephemeral and perennial streams? How does alpha diversity of the soil seed bank differ between streams with ephemeral, intermittent, and perennial flow, and between montane and basin streams? Do streams with greater elevational change have higher riparian zone seed bank beta-diversity? Does nestedness or turnover contribute more to within stream beta-diversity?

I collected soil samples from the riparian and terrestrial zones of 21 sites, placing them in growth chambers at one of two temperature regimes, and monitoring emergence of seedlings for 12 weeks. Results showed an approximately equal number of warm and cool specialists in both riparian and terrestrials zones; generalists also were abundant, particularly in the riparian zone. The number of temperature specialists and generalists in the riparian zones did not differ significantly between perennial headwater and ephemeral stream types. In montane streams, alpha diversity of the soil seed bank was highest for ephemeral reaches; in basin streams the intermittent and perennial reaches had higher diversity. Spatial turnover was primarily responsible for within stream beta-diversity—reaches had different species assemblages. The large portion of temperature specialists found in riparian seed banks indicates that even with available moisture riparian zone plant community composition will likely be impacted by changing temperatures. However, the presence of so many temperature generalists in the riparian zones suggests that some component of the seed bank is adapted to variable conditions and might offer resilience in a changing climate. Study results confirm the importance of conserving multiple hydrogeomorphic reach types because they support unique species assemblages.

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Date Created
  • 2016

Membrane specificity of proton pyrophosphatase and plasmodesmata ultrastructure provide the structural basis for sugar loading in Oryza sativa and Physcomitrella patens

Description

The remarkable conservation of molecular and intra-/inter-cellular pathways underpinning the fundamental aspects of sugar partitioning in two evolutionarily divergent organisms – a non-vascular moss Physcomitrella patens and a vascular cereal

The remarkable conservation of molecular and intra-/inter-cellular pathways underpinning the fundamental aspects of sugar partitioning in two evolutionarily divergent organisms – a non-vascular moss Physcomitrella patens and a vascular cereal crop Oryza sativa (rice) – forms the basis of this manuscript. Much of our current knowledge pertaining to sugar partitioning in plants mainly comes from studies in thale cress, Arabidopsis thaliana, but how photosynthetic sugar is loaded into the phloem in a crop as important as rice is still debated. Even less is known about the mechanistic aspects of sugar movement in mosses. In plants, sugar either moves passively via intercellular channels called plasmodesmata, or through the cell wall spaces in an energy-consuming process. As such, I first investigated the structure of plasmodesmata in rice leaf minor vein using electron tomography to create as of yet unreported 3D models of these channels in both simple and branched conformations. Contrary to generally held belief, I report two different 3D morphotypes of simple plasmodesmata in rice. Furthermore, the complementary body of evidence in arabidopsis implicates plasma membrane localized Proton Pyrophosphatase (H+-PPase) in the energy-dependent movement of sugar. Within this wider purview, I studied the in situ ultrastructural localization patterns of H+-PPase orthologs in high-pressure frozen tissues of rice and physcomitrella. Were H+-PPases neo-functionalized in the vascular tissues of higher plants? Or are there evolutionarily conserved roles of this protein that transcend the phylogenetic diversity of land plants? I show that H+-PPases are distinctly expressed in the actively growing regions of both rice and physcomitrella. As expected, H+-PPases were also localized in the vascular tissues of rice. But surprisingly, H+-PPase orthologs were also prominently expressed at the gametophyte-sporophyte junction of physcomitrella. Upon immunogold labeling, H+-PPases were found to be predominantly localized at the plasma membrane of the phloem complexes of rice source leaves, and both the vacuoles and plasma membrane of the transfer cells in the physcomitrella haustorium, linking H+-PPases in active sucrose loading in both plants. As such, these findings suggest that the localization and presumably the function of H+-PPases are conserved throughout the evolutionary history of land plants.

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Date Created
  • 2016

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Bispecific antibodies for the treatment of co-circulating flaviviruses and antibody derivatives for diagnostics in checkpoint immunotherapy

Description

Flaviviruses (FVs) are among the most medically important arboviruses of the world with the Dengue virus (DENV) accounting for a large percentage of infections observed in tropical and subtropical regions

Flaviviruses (FVs) are among the most medically important arboviruses of the world with the Dengue virus (DENV) accounting for a large percentage of infections observed in tropical and subtropical regions of the world. Globalization, travel, and the expanding range of mosquito vectors, such as Aedes aegypti, have increased the potential of infection rates and illnesses associated with FVs.

The DENV and the Zika (ZIKV) FVs frequently co-circulate and generally cause mild self-liming febrile illnesses. However, a secondary infection with a heterologous DENV serotype may lead to life threatening dengue hemorrhagic fever (DHF) and dengue shock syndrome (DSS). DHF/DSS have been linked to antibody dependent enhancement of infection (ADE), a phenomenon that occurs when antibodies (Abs) formed against an initial infection with one serotype of DENV cross-reacts but does not neutralize a heterologous DENV serotype in a secondary infection. Furthermore, Abs raised against the ZIKV have been observed to cross-react with the DENV and vice versa, which can potentially cause ADE and lead to severe DENV disease. The ZIKV can be transmitted vertically and has been linked to devastating congenital defects such as microcephaly in newborns. FDA approved treatments do not exist for DENV and ZIKV illnesses. Thus, there is a need for safe and effective treatments for these co-circulating viruses. Here, a tetravalent bispecific antibody (bsAb) targeting the ZIKV and all four serotypes of the DENV was expressed in the Nicotiana benthamiana (N. benthamiana) plant. Functional assays of the DENV/ZIKV bsAb demonstrated binding, neutralization, and a significant reduction in ADE activity against both the DENV and the ZIKV.

A single chain variable fragment (scFv) and a diabody based on an antibody directed against the immune checkpoint inhibitor PD-L1, were also expressed in N. benthamiana leaves. The smaller sizes of the scFv and diabody confers them with the ability to penetrate deeper tissues making them beneficial in diagnostics, imaging, and possibly cancer therapy. The past few decades has seen long strives in recombinant protein production in plants with significant improvements in production, safety, and efficacy. These characteristics make plants an attractive platform for the production of recombinant proteins, biologics, and therapeutics.

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Date Created
  • 2019

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The Vegetation and Flora of the Lower Verde River, Arizona

Description

For this study, the flora of the northern section of the Lower Verde River, within the Tonto National Forest in Yavapai and Gila Counties, Arizona was documented and analyzed. The

For this study, the flora of the northern section of the Lower Verde River, within the Tonto National Forest in Yavapai and Gila Counties, Arizona was documented and analyzed. The study site, part of the northern leading edge of the Sonoran Desert, encompasses about 16,000 hectares and is located approximately 45 miles north-northeast of Phoenix. The area, extends roughly 28 river miles from the East Verde River in the north to Chalk Mountain in the south and is largely only accessible by foot, or by boat, and as a result was previously extremely under-collected. Over a three-year study period, from August, 2017 to May, 2020, 835 plant specimens were collected and identified, representing 360 species which, combined with earlier herbarium specimens collected by others, resulted in 427 plant species found in the study area. The plant diversity of this remote region reflects three distinct vegetation communities: upland Sonoran Desert, perennial riparian corridor, and semi-desert grasslands. Together, these communities act as an important transition zone between the Sonoran Desert and higher elevation habitats. Perennial streams are biodiversity hotspots within the study area. For example, the 400 hectares of Red Creek that falls within the study boundaries contain 28% of the total species. The study site contains several plants of conservation importance including 12 species endemic to Arizona, 22 vulnerable or imperiled species, five US Forest Service sensitive species, and one Federally Endangered species. In order to compare the diversity of the Lower Verde River Flora to nine other similar/related floras in Arizona, a species-area curve using five different models was generated. The resulting models showed the Lower Verde River flora to be very close to, although slightly below, the species-accumulation curve which may indicate that roughly 50-100 species may yet be added to the flora. This prediction seems realistic, as there were several locations that could not be collected due to remoteness and excessive heat.

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  • 2020

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Evaluation of potential agricultural applications of the microalga Scenedesmus dimorphus

Description

Microalgae represent a potential sustainable alternative for the enhancement and protection of agricultural crops. The dry biomass and cellular extracts of Scenedesmus dimorphus were applied as a biofertilizer, a foliar

Microalgae represent a potential sustainable alternative for the enhancement and protection of agricultural crops. The dry biomass and cellular extracts of Scenedesmus dimorphus were applied as a biofertilizer, a foliar spray, and a seed primer to evaluate seed germination, plant growth, and crop yield of Roma tomato plants. The dry biomass was applied as a biofertilizer at 50 g and 100 g per plant, to evaluate its effects on plant development and crop yield. Biofertilizer treatments enhanced plant growth and led to greater crop (fruit) production. Timing of biofertilizer application proved to be of importance - earlier 50 g biofertilizer application resulted in greater plant growth. Scenedesmus dimorphus culture, growth medium, and different concentrations (1%, 5%, 10%, 25%, 50%, 75%, 100%) of aqueous cell extracts were used as seed primers to determine effects on germination. Seeds treated with Scenedesmus dimorphus culture and with extract concentrations higher than 50 % (0.75 g ml-1) triggered faster germination - 2 days earlier than the control group. Extract foliar sprays of 50 ml and 100 ml, were obtained and applied to tomato plants at various extract concentrations (10%, 25%, 50%, 75% and 100%). Plant height, flower development and number of branches were significantly enhanced with 50 % (7.5 g ml-1) extracts. Higher concentration sprays led to a decrease in growth. The extracts were further screened to assess potential antimicrobial activity against the bacterium Escherichia coli ATCC 25922, the fungi Candida albicans ATCC 90028 and Aspergillus brasiliensis ATCC 16404. No antimicrobial activity was observed from the microalga extracts on the selected microorganisms.

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Date Created
  • 2014

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Screwbean mesquite (Prosopis pubescens) die-off: population status at restored and unrestored sites in the lower Colorado River Watershed

Description

Die-off of screwbean mesquite (Prosopis pubescens), a species native to the American Southwest, has been documented regionally within the last decade. Historical causes for episodic mortality of the more widely

Die-off of screwbean mesquite (Prosopis pubescens), a species native to the American Southwest, has been documented regionally within the last decade. Historical causes for episodic mortality of the more widely distributed velvet mesquite (Prosopis velutina) and honey mesquite (Prosopis glandulosa) include water table declines and flood scour. Causes of the recent die-offs of P. pubescens have received little study. Numerous riparian restoration projects have been implemented regionally that include screwbean mesquite. Restoration propagules from foreign sources can introduce diseases, and low genetic diversity plantings may allow for disease irruptions. I asked: 1) Are die-offs associated with a particular age class, 2) Is die-off suggestive of a pathogen or related to specific environmental stressors, 3) Are mortality influences and outcomes the same between restoration and local populations, 4) Are particular land uses and management associated with die-off, and 5) Are populations rebounding or keeping pace with mortality?

I documented the screwbean mesquite population status at rivers and wetlands in Arizona with varying levels of restoration. I used logistic regression and Pearson correlation analysis to explore mortality response to site factors and disease related variables. I compared mortality response and disease severity between local and restoration populations.

Biotic damage surfaced as the most important factor in statistical analyses, suggesting that mortality was caused by a pathogen. Mortality was greatest for young size classes (3 to 14 cm), and biotic damage was higher for individuals at infrequently flooded areas. Strong differences were not found between local and restoration populations – however restoration populations were less stressed and had lower biotic damage. Novel urban and restored sites may provide refuge as site conditions at other locations deteriorate. A culmination of past water diversion, development and land use may be surfacing, rendering riparian species vulnerable to diseases and triggering such events as region-wide die-off.

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Date Created
  • 2016