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Physiological and morphological responses of grass species to drought
Get PDFMaster of ScienceDepartment of BiologyJesse B. NippertThe impacts of climate change over the next 100 years on North American grasslands are unknown. Climate change is projected to increase rainfall and seasonal temperature variability, leading to increased frequency of drought and decreased rainfall amounts for many grassland locations in the central Great Plains of North America. To increase our ability to predict the effects of a changing climate, I measured multiple morphological and physiological responses from a diverse suite of C3 and C4 grasses. Due to varying characteristics associated with the different photosynthetic pathways, these grass species respond differently to altered temperature and precipitation. I monitored grass physiology and microanatomy in conjunction with varying watered availability to replicate drought. In the second chapter, I observed leaf-level physiology and root level morphology of C3 and C4 grasses when exposed to 100% water reduction. Results indicated that response to water reduction are not always dependent on the photosynthetic pathway. Root-level morphological measurements were found to vary significantly between species in the same genus; F. ovina had the highest specific root length (SRL), which is an indicator of tolerance to environmental variability. Results also indicated that grasses of interest have thresholds that when passed result in a photosynthetically inactive plant; however it was shown that they are able to recover to near pre-drought gas exchange rates when water is re-applied. The third chapter investigated both leaf-level physiology and morphology in dominant C4¬ grasses across Kansas’ rainfall gradient over the growing season. I hypothesized that variation within a species’ physiology would be greater than its’ morphology. I also hypothesized that morphology would predict variability in a species physiological response to changes in climate. This research discovered within a location and species, leaf morphology is fixed across the growing season. Strong correlations between leaf physiology and morphology were observed, however, the strength and relationship changed among the species compared. A. gerardii and P. virgatum exhibited opposing relationships when comparing their photosynthetic rates to the amount of bundle sheath cells. This result highlights strong species-specific relationship between physiology and morphology. My results illustrate the importance of utilizing plant physiology and morphology to understand how grasses may respond to future climate change scenarios
Anatomical constraints on grass physiological responses depend on water availability
Get PDFDoctor of PhilosophyDepartment of BiologyJesse B. NippertGrasslands occupy more of Earth’s terrestrial surface than any other biome and are characterized by the dominance of grasses (Poaceae), fire, grazing, and an inherently variable climate. Future climate projections forecast dramatic shifts in precipitation within the next 100 years for grassland systems, negatively impacting most native grassland species. Over the past 30 years, a substantial focus has been placed on understanding the ecological consequences of grassland responses to drought. During this period, most research has focused on identifying changes in productivity and species diversity and the larger scale consequences of drought on carbon, nutrient, and water cycling. While this ecosystem and community focus has been foundational for forecasting future scenarios, it typically lacks detailed mechanistic investigation of leaf physiological and anatomical responses to drought. For this reason, research focused on the physiological responses of dominant grassland species to changes in water availability provide a missing perspective for WHY and HOW drought impacts grassland function. Prior research on a dominant grass species, Andropogon gerardii, has illustrated that leaf-level physiological responses were constrained by anatomical traits that dictate carbon assimilation and water-use strategies (Bachle & Nippert, 2018 – Acta Oecologica). In this dissertation, I used both naturally occurring climate gradients and rainfall manipulation experiments to explore responses of a dominant grass species and provide a detailed perspective of differences in grass anatomy and physiology in response to water limitations across the climate gradients of the Great Plains.
During a greenhouse dry down experiment I imposed an extreme drought by withholding water from 12 species of grasses from 6 tribes that are known to vary in drought tolerance (Bachle et al.- In Prep). I analyzed physiological responses at three stages: prior to drought (“Initial”), when samples reached stomatal closure (“Stressed”), and two days after re-watering (“Recovery”). I paired this physiological data with measurements of above- and belowground productivity, leaf and root economic traits, and leaf – level microanatomy. Results from this experiment revealed species response to drought were similar within tribe, while recovery from drought was highly variable across species. In addition, drought responses were framed by phylogenetic relatedness, physiology, morphology and microanatomical traits while drought recovery was influenced by one primary trait: the number of stomata. These data show the diverse physiological responses and variability of microanatomical traits across and within tribes. Furthermore, these results suggest that the biogeographic histories frame a species’ ability to respond to changes in low soil moisture.
To investigate trait variability, I performed a literature search to assess intraspecific variability in commonly measured traits (such as specific leaf area - SLA) in A. gerardii from 13 climatically-distinct grasslands. Results indicated that SLA varied widely between locations, but with no discernable trends with climate parameters (Bachle et al., 2018 Frontiers in Ecology and Evolution). Ecologists commonly measure SLA because differences in this trait reflect growth strategies and leaf carbon investment, and because it’s a relatively easy trait to measure. However, the investment strategies inferred from SLA result from a suite of underlying anatomical tissues (bundle sheath, mesophyll, xylem) that are seldom measured. To understand how physiology/anatomy varies across latitudinal population gradients, I collected A. gerardii leaf tissues from locations varying in temperature and precipitation (KS, NE, SD, MN). I analyzed the relationship between SLA and internal leaf anatomical traits (Bachle & Nippert, 2020 – Annals of Botany). SLA was statistically similar in A. gerardii across locations, while anatomical traits related to carbon assimilation (mesophyll area, bundle sheath thickness) varied by mean annual temperature. Anatomical traits connected with water transport and storage (xylem area, cavitation resistance) exhibited 3 – 4 times the coefficient of variation than did carbon-related traits. Results from this chapter illustrate that variation in anatomical traits, influenced by climate, may underlie patterns of growth and productivity in this species at larger ecological scales.
For my final chapter, I collected physiological and microanatomical data from A. gerardii in Kansas and Nebraska prairies managed with or without cattle in 2018 and 2019 (Bachle & Nippert – In Prep). The precipitation differences between successive years at each location had a larger impact on physiological and anatomical differences among sites compared to the grazing treatments. In addition, photosynthetic rates increased with leaf – level nitrogen content, while cavitation resistance increased with higher C:N ratios. Microanatomical traits, such as bundle sheath tissue area, were found to correlate with photosynthetic rates; however, the direction of this relationship was dependent on the year sampled. These results indicate that leaf-level nutrient content can influence microanatomical leaf structures and physiological responses to changes in climate.
Overall, the results from my dissertation highlight the integral role of leaf anatomical traits in contextualizing our interpretation of physiological responses to drought, and across regional gradients in climate. My data clearly show that commonly used whole-leaf traits (e.g., SLA), unlike leaf microanatomy, typically don’t vary predictably with leaf physiology or climate gradients. Moving forward, the research framework I have organized can be applied to other species. The increased anatomical trait representation of other native species will help elucidate leaf form and function while also adding beneficial data that may be useful for forecasting future grassland responses in this era of global change
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
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