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- Creators: Beethoven, Ludwig van, 1770-1827
Description
Nitrous oxide (N2O) is a major contributor to the greenhouse effect and to stratospheric ozone depletion. In soils, nitrogen reduction is performed by biotic and abiotic processes, including microbial denitrification and chemical denitrification. Chemical denitrification, or chemodenitrification, is the abiotic step-wise reduction of nitrate (NO3-), nitrite (NO2-), or nitric oxide (NO) to N2O in anoxic environments, with high turnover rates particularly in acidic soils. Chemodenitrification was identified in various environments, but the mechanism is still not understood. In this study, the factors influencing abiotic reduction of NO2- to N2O in acidic tropical peat soil are examined. These factors include pH, organic matter content, and dissolved ferrous iron. Anoxic peat soil from sites located in the Peruvian Amazon was used for incubations. The results show that peat soil (pH ~4.5) appears to reduce NO2- more quickly in the presence of lower pH and higher Fe(II) concentrations. NO2- is completely reduced in excess Fe(II), and Fe(II) is completely oxidized in excess NO2-, providing evidence for the proposed mechanism of chemodenitrification. In addition, first order reaction rate constants kFe(II) and kNO2- were calculated using concentration measurements over 4 hours, to test for the hypothesized reaction rate relationships kFe(II): kFe(II) kFe(II)~NO2- > kFe(II)>NO2- and kNO2-: kFe(II)NO2-. The NO2- k values followed the anticipated pattern, although the Fe(II) k value data was inconclusive. Organic material may also play a role in NO2- reduction through chemodenitrification, and future experimentation will test this possibility. How and to what extent the pH and the concentrations of organic matter and Fe(II) affect the kinetic rate of chemodenitrification will lend insight into the N2O production potential of natural tropical peatlands.
ContributorsTylor, Kaitlyn Marie (Author) / Cadillo-Quiroz, Hinsby (Thesis director) / Day, Thomas (Committee member) / School of Life Sciences (Contributor) / Barrett, The Honors College (Contributor)
Created2016-05
ContributorsBeethoven, Ludwig van, 1770-1827 (Composer)
ContributorsBeethoven, Ludwig van, 1770-1827 (Composer)
Description
Functional traits research has improved our understanding of how plants respond to their environments, identifying key trade-offs among traits. These studies primarily rely on correlative methods to infer trade-offs and often overlook traits that are difficult to measure (e.g., root traits, tissue senescence rates), limiting their predictive ability under novel conditions. I aimed to address these limitations and develop a better understanding of the trait space occupied by trees by integrating data and process models, spanning leaves to whole-trees, via modern statistical and computational methods. My first research chapter (Chapter 2) simultaneously fits a photosynthesis model to measurements of fluorescence and photosynthetic response curves, improving estimates of mesophyll conductance (gm) and other photosynthetic traits. I assessed how gm varies across environmental gradients and relates to other photosynthetic traits for 4 woody species in Arizona. I found that gm was lower at high aridity sites, varied little within a site, and is an important trait for obtaining accurate estimates of photosynthesis and related traits under dry conditions. Chapter 3 evaluates the importance of functional traits for whole-tree performance by fitting an individual-based model of tree growth and mortality to millions of measurements of tree heights and diameters to assess the theoretical trait space (TTS) of “healthy” North American trees. The TTS contained complicated, multi-variate structure indicative of potential trade-offs leading to successful growth. In Chapter 4, I applied an environmental filter (light stress) to the TTS, leading to simulated stand-level mortality rates up to 50%. Tree-level mortality was explained by 6 of the 32 traits explored, with the most important being radiation-use efficiency. The multidimentional space comprising these 6 traits differed in volume and location between trees that survived and died, indicating that selective mortality alters the TTS.
ContributorsFell, Michael (Author) / Ogle, Kiona (Thesis advisor) / Barber, Jarrett (Committee member) / Hultine, Kevin (Committee member) / Franklin, Janet (Committee member) / Day, Thomas (Committee member) / Arizona State University (Publisher)
Created2017
ContributorsBeethoven, Ludwig van, 1770-1827 (Composer)
ContributorsBeethoven, Ludwig van, 1770-1827 (Composer)
ContributorsBeethoven, Ludwig van, 1770-1827 (Composer)
ContributorsBeethoven, Ludwig van, 1770-1827 (Composer)
ContributorsBeethoven, Ludwig van, 1770-1827 (Composer)