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- All Subjects: Panamanian Tropical forest
- Creators: Day, Thomas
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
Description
Rising temperatures and increased droughts caused by climate change are threatening tropical forests through leaf thermal damage and subsequent thermal mortality. As temperatures are predicted to continue rising, understanding what mechanisms tropical tree species have to cool their leaves is important. Therefore, this study examines whether the rate of stem sap flow is significantly driven by changes in leaf temperature, other climate variables, and leaf size. Thermal videos of five different tropical tree species were collected at San Lorenzo National Park (Panama), alongside sap flow, weather, and leaf trait data. These data sets were used to estimate average leaf temperatures, rates of sap flow, leaf level vapor pressure deficit (VPD), and average leaf area for each tree species. In an initial analysis, average leaf temperatures and leaf level VPD were compared to rates of sap flow using nonlinear least squares regression. The greatest rate of change in the increase of the rate of sap flow as leaf temperature increased, (kTleaf), was compared to the average leaf areas in a second analysis using linear regression. For the first analysis, there was a positive correlation between the rate of sap flow and average leaf temperature, which implied that leaf temperature did partially drive changes in the rate of sap flow. The positive correlation between rates of sap flow and leaf level VPD demonstrated that VPD affected sap flow, but only up to certain values of VPD. The plateau of sap flow rates also suggested that individual root and vascular systems limited the volume of water that could be transported at once. For the second analysis, there was no correlation between leaf area and changes in rates of sap flow. These results imply that tropical tree species with the largest maximum rates of sap flow will be able to evaporatively cool in hotter climates. Furthermore, the lack of relationship between increased average leaf area and kTleaf for the analyzed species suggests that different measurements should be used to study the relationship boundary layers and the rate of sap flow in future, or that there potentially was an unidentified variable that influenced this relationship.
ContributorsRyan, Martha Ruth (Author) / Blonder, Benjamin (Thesis director) / Day, Thomas (Committee member) / Aparecido, Luiza (Committee member) / School of Life Sciences (Contributor) / School of Mathematical and Statistical Sciences (Contributor) / Watts College of Public Service & Community Solut (Contributor) / Barrett, The Honors College (Contributor)
Created2020-12