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  1. Wheat and rice produce nutritious grains that provide 32% of the protein in the human diet globally. Here, we examine how genetic modifications to improve assimilation of the inorganic nitrogen forms ammonium and nitrate into protein influence grain yield of these crops. Successful breeding for modified nitrogen metabolism has focused on genes that coordinate nitrogen and carbon metabolism, including those that regulate tillering, heading date, and ammonium assimilation. Gaps in our current understanding include (1) species differences among candidate genes in nitrogen metabolism pathways, (2) the extent to which relative abundance of these nitrogen forms across natural soil environments shape crop responses, and (3) natural variation and genetic architecture of nitrogen-mediated yield improvement. Despite extensive research on the genetics of nitrogen metabolism since the rise of synthetic fertilizers, only a few projects targeting nitrogen pathways have resulted in development of cultivars with higher yields. To continue improving grain yield and quality, breeding strategies need to focus concurrently on both carbon and nitrogen assimilation and consider manipulating genes with smaller effects or that underlie regulatory networks as well as genes directly associated with nitrogen metabolism.
    Free, publicly-accessible full text available January 1, 2024
  2. Abstract Premise: The agar‐based culture of Arabidopsis seedlings is widely used for quantifying root traits. Shoot traits are generally overlooked in these studies, probably because the rosettes are often askew. A technique to assess the shoot surface area of seedlings grown inside agar culture dishes would facilitate simultaneous root and shoot phenotyping. Methods: We developed an image processing workflow in Python that estimates rosette area of Arabidopsis seedlings on agar culture dishes. We validated this method by comparing its output with other metrics of seedling growth. As part of a larger study on genetic variation in plant responses to nitrogen form and concentration, we measured the rosette areas from more than 2000 plate images. Results: The rosette area measured from plate images was strongly correlated with the rosette area measured from directly overhead and moderately correlated with seedling mass. Rosette area in the large image set was significantly influenced by genotype and nitrogen treatment. The broad‐sense heritability of leaf area measured using this method was 0.28. Discussion: These results indicated that this approach for estimating rosette area produces accurate shoot phenotype data. It can be used with image sets for which other methods of leaf area quantification prove unsuitable.
    Free, publicly-accessible full text available December 1, 2023
  3. Abstract

    Public understanding about complex issues such as climate change relies heavily on online resources. Yet the role that online instruction should assume in post-secondary science education remains contentious despite its near ubiquity during the COVID-19 pandemic. The objective here was to compare the performance of 1790 undergraduates taking either an online or face-to-face version of an introductory course on climate change. Both versions were taught by a single instructor, thus, minimizing instructor bias. Women, seniors, English language learners, and humanities majors disproportionately chose to enroll in the online version because of its ease of scheduling and accessibility. After correcting for performance-gaps among different demographic groups, the COVID-19 pandemic had no significant effect on online student performance and students in the online version scored 2% lower (on a scale of 0–100) than those in the face-to-face version, a penalty that may be a reasonable tradeoff for the ease of scheduling and accessibility that these students desire.

  4. Abstract Nitrogen is an essential element required for plant growth and productivity. Understanding the mechanisms and natural genetic variation underlying nitrogen use in plants will facilitate the engineering of plant nitrogen use to maximize crop productivity while minimizing environmental costs. To understand the scope of natural variation that may influence nitrogen use, we grew 1135 Arabidopsis thaliana natural genotypes on two nitrogen sources, nitrate and ammonium, and measured both developmental and defense metabolite traits. By using different environments and focusing on multiple traits, we identified a wide array of different nitrogen responses. These responses are associated with numerous genes, most of which were not previously associated with nitrogen responses. Only a small portion of these genes appear to be shared between environments or traits, while most are predominantly specific to a developmental or defense trait under a specific nitrogen source. Finally, by using a large population, we were able to identify unique nitrogen responses, such as preferring ammonium or nitrate, that appear to be generated by combinations of loci rather than a few large-effect loci. This suggests that it may be possible to obtain novel phenotypes in complex nitrogen responses by manipulating sets of genes with small effects rather thanmore »solely focusing on large-effect single gene manipulations.« less
    Free, publicly-accessible full text available September 20, 2023
  5. Free, publicly-accessible full text available May 1, 2023
  6. Visual discomfort is related to the statistical regularity of visual images. The contribution of luminance contrast to visual discomfort is well understood and can be framed in terms of a theory of efficient coding of natural stimuli, and linked to metabolic demand. While color is important in our interaction with nature, the effect of color on visual discomfort has received less attention. In this study, we build on the established association between visual discomfort and differences in chromaticity across space. We average the local differences in chromaticity in an image and show that this average is a good predictor of visual discomfort from the image. It accounts for part of the variance left unexplained by variations in luminance. We show that the local chromaticity difference in uncomfortable stimuli is high compared to that typical in natural scenes, except in particular infrequent conditions such as the arrangement of colorful fruits against foliage. Overall, our study discloses a new link between visual ecology and discomfort whereby discomfort arises when adaptive perceptual mechanisms are overstimulated by specific classes of stimuli rarely found in nature.
  7. The extent to which rising atmospheric CO2 concentration has already influenced food production and quality is uncertain. Here, we analyzed annual field trials of fall-planted common wheat in California from 1985 to 2019, a period during which global atmospheric CO2 concentration increased 19%. Even after accounting for other major factors (cultivar, location, degree-days, soil temperature, total water applied, nitrogen fertilization, and pathogen infestation), wheat grain yield and protein yield declined 13% over this period, but grain protein content did not change. These results suggest that exposure to gradual CO2 enrichment over the past 35 years has adversely affected wheat grain and protein yield, but not grain protein content.
  8. Jain, A. ; Fostvedt, J. I. ; Kriegel, B. M. ; Grant, L. N. ; Small, D. W. ; Bergman, R. G. ; Arnold, J (Ed.)
  9. Arnold, J. E., & Zerkle, S. A. (2021). Additional Methods and Analyses for “Who gets mentioned next? The answer depends on the experimental task.” Technical Report #5. UNC Language Processing Lab, Department of Psychology & Neuroscience, University of North Carolina – Chapel Hill, Chapel Hill, North Carolina.