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The growth rate hypothesis (GRH) proposes that higher growth rate (the rate of change in biomass per unit biomass, μ) is associated with higher P concentration and lower C∶P and N∶P ratios. However, the applicability of the GRH to vascular plants is not well-studied and few studies have been done on belowground biomass. Here we showed that, for aboveground, belowground and total biomass of three study species, μ was positively correlated with N∶C under N limitation and positively correlated with P∶C under P limitation. However, the N∶P ratio was a unimodal function of μ, increasing for small values of μ, reaching a maximum, and then decreasing. The range of variations in μ was positively correlated with variation in C∶N∶P stoichiometry. Furthermore, μ and C∶N∶P ranges for aboveground biomass were negatively correlated with those for belowground. Our results confirm the well-known association of growth rate with tissue concentration of the limiting nutrient and provide empirical support for recent theoretical formulations.
ContributorsYu, Qiang (Author) / Wu, Honghui (Author) / He, Nianpeng (Author) / Lu, Xiaotao (Author) / Wang, Zhiping (Author) / Elser, James (Author) / Wu, Jianguo (Author) / Han, Xingguo (Author) / College of Liberal Arts and Sciences (Contributor) / School of Life Sciences (Contributor) / Julie Ann Wrigley Global Institute of Sustainability (Contributor) / School of Sustainability (Contributor)
Created2012-03-13
Grasshoppers Regulate N: P Stoichiometric Homeostasis by Changing Phosphorus Contents in Their Frass
Description
Nitrogen (N) and phosphorus (P) are important limiting nutrients for plant production and consumer performance in a variety of ecosystems. As a result, the N:P stoichiometry of herbivores has received increased attention in ecology. However, the mechanisms by which herbivores maintain N:P stoichiometric homeostasis are poorly understood. Here, using a field manipulation experiment we show that the grasshopper Oedaleus asiaticus maintains strong N:P stoichiometric homeostasis regardless of whether grasshoppers were reared at low or high density. Grasshoppers maintained homeostasis by increasing P excretion when eating plants with higher P contents. However, while grasshoppers also maintained constant body N contents, we found no changes in N excretion in response to changing plant N content over the range measured. These results suggest that O. asiaticus maintains P homeostasis primarily by changing P absorption and excretion rates, but that other mechanisms may be more important for regulating N homeostasis. Our findings improve our understanding of consumer-driven P recycling and may help in understanding the factors affecting plant-herbivore interactions and ecosystem processes in grasslands.
ContributorsZhang, Zijia (Author) / Elser, James (Author) / Cease, Arianne (Author) / Zhang, Ximei (Author) / Yu, Qiang (Author) / Han, Xingguo (Author) / Zhang, Guangming (Author) / College of Liberal Arts and Sciences (Contributor) / School of Life Sciences (Contributor) / Julie Ann Wrigley Global Institute of Sustainability (Contributor) / School of Sustainability (Contributor)
Created2014-08-04
Description
A large fraction of the world grasslands and savannas are undergoing a rapid shift from herbaceous to woody-plant dominance. This land-cover change is expected to lead to a loss in livestock production (LP), but the impacts of woody-plant encroachment on this crucial ecosystem service have not been assessed. We evaluate how tree cover (TC) has affected LP at large spatial scales in rangelands of contrasting social–economic characteristics in the United States and Argentina. Our models indicate that in areas of high productivity, a 1% increase in TC results in a reduction in LP ranging from 0.6 to 1.6 reproductive cows (Rc) per km[superscript 2]. Mean LP in the United States is 27 Rc per km[superscript 2], so a 1% increase in TC results in a 2.5% decrease in mean LP. This effect is large considering that woody-plant cover has been described as increasing at 0.5% to 2% per y. On the contrary, in areas of low productivity, increased TC had a positive effect on LP. Our results also show that ecological factors account for a larger fraction of LP variability in Argentinean than in US rangelands. Differences in the relative importance of ecological versus nonecological drivers of LP in Argentina and the United States suggest that the valuation of ecosystem services between these two rangelands might be different. Current management strategies in Argentina are likely designed to maximize LP for various reasons we are unable to explore in this effort, whereas land managers in the United States may be optimizing multiple ecosystem services, including conservation or recreation, alongside LP.
ContributorsAnadon, Jose Daniel (Author) / Sala, Osvaldo (Author) / Turner II, B. L. (Author) / Bennett, Elena M. (Author) / College of Liberal Arts and Sciences (Contributor) / School of Life Sciences (Contributor) / Julie Ann Wrigley Global Institute of Sustainability (Contributor) / School of Sustainability (Contributor) / School of Geographical Sciences and Urban Planning (Contributor)
Created2014-09-02
Description
We studied the microbial community structure of pilot two-stage membrane biofilm reactors (MBfRs) designed to reduce nitrate (NO[subscript 3]–) and perchlorate (ClO[subscript 4]–) in contaminated groundwater. The groundwater also contained oxygen (O[subscript 2]) and sulfate (SO[2 over 4]–), which became important electron sinks that affected the NO[subscript 3]– and ClO[subscript 4]– removal rates. Using pyrosequencing, we elucidated how important phylotypes of each “primary” microbial group, i.e., denitrifying bacteria (DB), perchlorate-reducing bacteria (PRB), and sulfate-reducing bacteria (SRB), responded to changes in electron-acceptor loading. UniFrac, principal coordinate analysis (PCoA), and diversity analyses documented that the microbial community of biofilms sampled when the MBfRs had a high acceptor loading were phylogenetically distant from and less diverse than the microbial community of biofilm samples with lower acceptor loadings. Diminished acceptor loading led to SO[2 over 4]– reduction in the lag MBfR, which allowed Desulfovibrionales (an SRB) and Thiothrichales (sulfur-oxidizers) to thrive through S cycling. As a result of this cooperative relationship, they competed effectively with DB/PRB phylotypes such as Xanthomonadales and Rhodobacterales. Thus, pyrosequencing illustrated that while DB, PRB, and SRB responded predictably to changes in acceptor loading, a decrease in total acceptor loading led to important shifts within the “primary” groups, the onset of other members (e.g., Thiothrichales), and overall greater diversity.
ContributorsOntiveros-Valencia, Aura (Author) / Tang, Youneng (Author) / Zhao, Heping (Author) / Friese, David (Author) / Overstreet, Ryan (Author) / Smith, Jennifer (Author) / Evans, Patrick (Author) / Rittmann, Bruce (Author) / Krajmalnik-Brown, Rosa (Author) / Biodesign Institute (Contributor) / Swette Center for Environmental Biotechnology (Contributor) / Julie Ann Wrigley Global Institute of Sustainability (Contributor) / School of Sustainability (Contributor)
Created2014-07-01
Description
The importance of second language learning in today’s ever-increasing globalized world is becoming ever more paramount. Despite seeming trends which indicate aversion to globalization, the international phenomenon which describes the connection made between peoples and cultures, will only increase its influence in coming years. With the advances globalization has made, it is becoming more important to learn and study foreign languages in order to keep abreast of this trend and not be left behind by globalization. Why electronic translation is not so viable in the long run (at least currently) is that culture and syntax are not things which can be simply ascertained via mediums such as application use. Due to the fact that advanced language proficiency is considered to be an integral piece towards stronger sentiments of “integration” (i.e. Syrian refugees integrating into EU and US) it is of more importance that increasing second language proficiency receives the adequate study and implementation to reflect a more cohesive globalized world. Accompanying this necessity is the simple fact that adult second language learners often struggle to overcome difficulty to the challenging yet rewarding task of learning and eventually mastering a second language.
To truly understand the difficulty some adult second language learners have with learning a second language it can be helpful to compare second language acquisition to how one naturally, and seemingly effortlessly in many cases, acquires their native language. How can a comparative analysis of how native speakers and adult second language learners each learn their first and second language respectively be successfully converted to a specific means of assisting adult second language learners achieve the highest level of possible fluency? In order to more accurately propose a viable solution to the overarching question, the following three questions have been proposed as a means to springboard into better understanding the nature of the main topic.
The points to consider while analyzing the main question throughout this analysis are as follows: How would it be best for an adult second language learner to achieve the same level off proficiency as a native speaker of a given language whom has been exposed to all of its intricacies since birth? At what point exactly is someone considered to have the same level of proficiency which a native speaker of a given language would have and how does that differ from being a heritage speaker? With the final supporting question being: What type of learning would be best suited in helping a heritage speaker (someone who learns a language in the home by virtue of their heritage) or adult second language learner to become highly proficient in a second language?
In order to propose a wide variety of integration between these questions with the conjoined purpose of answering the inquiry of this thesis, many different sources supporting each of the above questions will contain certain overlap, providing a clear basis for constructing a tri-fold argument in answering the thesis question as acutely as possible. In regards to the first question, the question of “proficiency” will be a subsection committed to understanding the nature of how language proficiency works and at what point (if ever) one can ever be considered “highly proficient” in a second language.
All three exploratory questions are compatible with a theory known as Critical Period Theory, a theory in linguistics proposed by Montreal neurologist Wilder Penfield, which states, “There is a critical age, before puberty, that one must learn language. If one has not learned to speak before puberty it is much more difficult, and sometimes impossible, to learn language and speak in a meaningful way.” The overlap which this method binds to Universal Grammar is a rather close-knit relationship. Research composed by certain linguists suggest that “children are born with a certain universal grammar wired into their brains.” This will be compared and cross-examined to a higher degree in a later section of the paper.
The importance of Universal Grammar in relation to Critical Period Theory cannot be overstated. Universal Grammar in relation to the second language Critical Period Theory will help explain at which point, someone is considered to be a “native speaker” of a given language. The third question posed of how would it be best for heritage and second language learners to increase their proficiency in a second language really touches on both of these theories in regards to at which age someone is exposed to a specific language in addition to how Universal Grammar affects the development of second language acquisition. In the realm of perpetually working towards mitigating an answer to this analysis’s thesis, the connecting thread or “roter Faden”, as it is said in German, will be the integrative domain the above questions will have on arriving to a clearer understanding of the nature of how a comparative analysis of second language learners and mother-tongue speakers can expedite the language learning process of second language learners, using techniques of native speakers which they inherently pick-up.
To truly understand the difficulty some adult second language learners have with learning a second language it can be helpful to compare second language acquisition to how one naturally, and seemingly effortlessly in many cases, acquires their native language. How can a comparative analysis of how native speakers and adult second language learners each learn their first and second language respectively be successfully converted to a specific means of assisting adult second language learners achieve the highest level of possible fluency? In order to more accurately propose a viable solution to the overarching question, the following three questions have been proposed as a means to springboard into better understanding the nature of the main topic.
The points to consider while analyzing the main question throughout this analysis are as follows: How would it be best for an adult second language learner to achieve the same level off proficiency as a native speaker of a given language whom has been exposed to all of its intricacies since birth? At what point exactly is someone considered to have the same level of proficiency which a native speaker of a given language would have and how does that differ from being a heritage speaker? With the final supporting question being: What type of learning would be best suited in helping a heritage speaker (someone who learns a language in the home by virtue of their heritage) or adult second language learner to become highly proficient in a second language?
In order to propose a wide variety of integration between these questions with the conjoined purpose of answering the inquiry of this thesis, many different sources supporting each of the above questions will contain certain overlap, providing a clear basis for constructing a tri-fold argument in answering the thesis question as acutely as possible. In regards to the first question, the question of “proficiency” will be a subsection committed to understanding the nature of how language proficiency works and at what point (if ever) one can ever be considered “highly proficient” in a second language.
All three exploratory questions are compatible with a theory known as Critical Period Theory, a theory in linguistics proposed by Montreal neurologist Wilder Penfield, which states, “There is a critical age, before puberty, that one must learn language. If one has not learned to speak before puberty it is much more difficult, and sometimes impossible, to learn language and speak in a meaningful way.” The overlap which this method binds to Universal Grammar is a rather close-knit relationship. Research composed by certain linguists suggest that “children are born with a certain universal grammar wired into their brains.” This will be compared and cross-examined to a higher degree in a later section of the paper.
The importance of Universal Grammar in relation to Critical Period Theory cannot be overstated. Universal Grammar in relation to the second language Critical Period Theory will help explain at which point, someone is considered to be a “native speaker” of a given language. The third question posed of how would it be best for heritage and second language learners to increase their proficiency in a second language really touches on both of these theories in regards to at which age someone is exposed to a specific language in addition to how Universal Grammar affects the development of second language acquisition. In the realm of perpetually working towards mitigating an answer to this analysis’s thesis, the connecting thread or “roter Faden”, as it is said in German, will be the integrative domain the above questions will have on arriving to a clearer understanding of the nature of how a comparative analysis of second language learners and mother-tongue speakers can expedite the language learning process of second language learners, using techniques of native speakers which they inherently pick-up.
ContributorsRoselius, Thomas Jacob (Author) / Lee, Sara (Thesis director) / Reves, Christiane (Committee member) / College of Public Service and Community Solutions (Contributor) / College of Integrative Sciences and Arts (Contributor) / School of International Letters and Cultures (Contributor) / Barrett, The Honors College (Contributor)
Created2018-12
Description
The gastrointestinal (GI) tract is home to a complex and diverse microbial ecosystem that contributes to health or disease in many aspects. While bacterial species are the majority in the GI tract, their cohabitants, fungal species, should not be forgotten. Children with autism spectrum disorder (ASD) often suffer from GI disorders and associated symptoms, implying a role the bacterial and fungal gut microbiota play in maintaining human health. The irregularities in GI symptoms can negatively affect the overall quality of life or even worsen behavioral symptoms the children present. Even with the increase in the availability of next-generation sequencing technologies, the composition and diversities of fungal microbiotas are understudied, especially in the context of ASD. We therefore aimed to investigate the gut mycobiota of 36 neurotypical children and 38 children with ASD. We obtained stool samples from all participants, as well as autism severity and GI symptom scores to help us understand the effect the mycobiome has on these symptoms. By targeting the fungal internal transcribed spacer (ITS) and bacterial 16S rRNA V4 regions, we obtained fungal and bacterial amplicon sequences, from which we investigated the diversities, composition, and potential link between two different ecological clades. From fungal amplicon sequencing results, we observed a significant decrease in the observed fungal OTUs in children with ASD, implying a lack of potentially beneficial fungi in ASD subjects. We performed Bray-Curtis principal coordinates analysis and observed significant differences in fungal microbiota composition between the two groups. Taxonomic analysis showed higher relative abundances of Candida , Pichia, Penicillium , and Exophiala in ASD subjects, yet due to a large dispersion of data, the differences were not statistically significant. Interestingly, we observed a bimodal distribution of Candida abundances within children with ASD. Candida's relative abundance was not significantly correlated with GI scores, but children with high Candida relative abundances presented significantly higher Autism Treatment Evaluation Checklist (ATEC) scores, suggesting a role of Candida on ASD behavioral symptoms. Regarding the bacterial gut microbiota, we found marginally lower observed OTUs and significantly lower relative abundance of Prevotella in the ASD group, which was consistent with previous studies. Taken together, we demonstrated that autism is closely linked with a distinct gut mycobiota, characterized by a loss of fungal and bacterial diversity and an altered fungal and bacterial composition.
ContributorsPatel, Jigar (Author) / Krajmalnik-Brown, Rosa (Thesis director) / Kang, Dae Wook (Committee member) / Adams, James (Committee member) / School of Molecular Sciences (Contributor) / Barrett, The Honors College (Contributor)
Created2018-05
Description
The effect of an anaerobic reductive environment produced by the oxidation of zero valent iron (ZVI) on the microbial reductive dechlorination of trichloroethylene and its applicability to in-situ bioremediation processes was investigated using microcosms and soil column studies. I learned that microbial dechlorination requires a highly reductive environment, as represented by negative values for oxidation-reduction potential (ORP), which can be maintained through the addition of reducing agents such as ZVI, or to a lesser extent, the fermentation of added substrates such as lactate. Microcosm conditions represented distance from an in-situ treatment injection well and contained different types of iron species and dechlorinating bioaugmentation cultures. Diminishing efficacy of microbial reductive dechlorination along a gradient away from the injection zone was observed, characterized by increasing ORP and decreasing pH. Results also suggested that the use of particular biostimulation substrates is key to prioritizing the dechlorination reaction against competing microbial and abiotic processes by supplying electrons needed for microbial dechlorination.
ContributorsMouti, Aatikah (Author) / Krajmalnik-Brown, Rosa (Thesis director) / Delgado, Anca (Committee member) / School of Life Sciences (Contributor) / Barrett, The Honors College (Contributor)
Created2017-12
Description
This study examined the type and frequency of questions asked by attorneys in cases of children alleging sexual abuse. Of interest was whether child age would affect the questions asked. The participants included 25 child witnesses testifying in criminal trials in Maricopa County over a recent ten-year period. Children were placed into two groups: younger (five to seven-year-olds) and older (eight to nine-year-olds). Every question asked, and answer provided, during children's testimony, was systematically and reliably coded for the content of the interaction. Attorneys exhibited developmental sensitivity, varying the amount of question they asked across content areas by the age of the child. In addition, attorneys varied in what they asked about: the prosecution focused more on the plausibility of abuse, whereas the defense focused more on how others may have suggestively influenced the child's report. Both attorneys were equally concerned about the consistency of narratives. The findings from the present study have direct policy implications for how attorneys structure their arguments, both in an attempt to establish, and question, children's credibility in these important cases. Keywords: children, age, suggestibility, consistency, inconsistency, plausibility
ContributorsHogan, Caitlyn Rose (Author) / Stolzenberg, Stacia (Thesis director) / Fradella, Hank (Committee member) / College of Public Service and Community Solutions (Contributor) / School of Criminology and Criminal Justice (Contributor) / Barrett, The Honors College (Contributor)
Created2018-05
Description
Throughout history, terrorism has had major effects on tourists and tourism destinations that are targeted. When terrorists execute an attack in order to communicate a message, resulting impacts go far beyond lives lost. Included in these impacts is the fear that terror attacks leave on tourists, sometimes creating such an impression that tourists change travel plans as a result. Although there are many studies on destination image, risk perception, and decision-making, very few focus specifically on the millennial generation. Because millennials are changing the travel and tourism scene - as they now make up the largest percentage of the population \u2014 it is important for stakeholders in the tourism industry and DMOs to understand this shift and the implications that come with these changes. This study provides a qualitative analysis of millennials' views, attitudes, and beliefs regarding terror impacted tourist destinations. Specifically, it will explore how millennials develop their destination images, if millennials view international travel to be risky, and if millennials are willing to travel to terror impacted tourist destinations. Using focus group methodology, this study gathered data from students from a number of disciplines, genders, and travel experience, in order to understand the themes listed above. Analysis of the findings and implications for officials and DMOs follow, as well as a conclusion including limitations and recommendations for future studies.
ContributorsBacon, Laura Elizabeth (Author) / Buzinde, Christine (Thesis director) / Nyaupane, Gyan (Committee member) / Department of Management and Entrepreneurship (Contributor) / W. P. Carey School of Business (Contributor) / College of Public Service and Community Solutions (Contributor) / Barrett, The Honors College (Contributor)
Created2017-05
Description
Hydrogen is a key indicator of microbial activity in soils/sediments and groundwater because of its role as an electron donor for reducing sulfate and nitrate and carrying out other metabolic processes. The goal of this study was to quantitatively measure the total biological hydrogen demand (TBHD) of soils and sediments in anaerobic environments. We define the total biological hydrogen demand as the sum of all electron acceptors that can be used by hydrogen-oxidizing microorganisms. Three sets of anaerobic microcosms were set up with different soils/sediments, named Carolina, Garden, and ASM. The microcosms included 25g of soil/sediment and 75 mL of anaerobic medium. 10 mL of hydrogen were pulse-fed for 100 days. Hydrogen consumption and methane production were tracked using gas chromatography. Chemical analysis of each soil was performed at the beginning of the experiment to determine the concentration of electron acceptors in the soils/sediments, including nitrate, sulfate, iron and bicarbonate. An analysis of the microbial community was done at t = 0 and at the end of the 100 days to examine changes in the microbial community due to the metabolic processes occurring as hydrogen was consumed. Carolina consumed 9810 43 mol of hydrogen and produced 19,572 2075 mol of methane. Garden consumed 4006 33 mol of hydrogen and produced 7,239 543 mol of methane. Lastly, ASM consumed 1557 84 mol of hydrogen and produced 1,325 715 mol of methane. I conclude that the concentration of bicarbonate initially present in the soil had the most influence over the hydrogen demand and microbial community enrichment. To improve this research, I recommend that future studies include a chemical analysis of final soil geochemistry conditions, as this will provide with a better idea of what pathway the hydrogen is taking in each soil.
ContributorsLuna Aguero, Marisol (Author) / Krajmalnik-Brown, Rosa (Thesis director) / Delgado, Anca (Committee member) / Civil, Environmental and Sustainable Engineering Programs (Contributor) / School of Sustainability (Contributor) / Barrett, The Honors College (Contributor)
Created2017-05