31.08.2021 - 14:15
On 31 August at 14:15 Thomas Schindler will defend his doctoral thesis “Tree stem CH4 and N2O fluxes in various forest ecosystems” in Environmental Technology.
Professor Ülo Mander, University of Tartu
Associate Professor Kaido Soosaar, University of Tartu, Global Change Research Institute CAS (Czech Republic)
Associate Professor Katerina Machacova, University of Tartu, Global Change Research Institute CAS (Czech Republic)
Research Fellow Sunitha Pangala, Lancaster University (United Kingdom)
Terrestrial ecosystems like forests play an essential role in the global carbon cycle, regulating climate and climate change by contributing to the methane (CH4) and nitrous oxide (N2O) exchange with the atmosphere. However, the complexity of various climatic zones, forest ecosystem types, tree species and their physiological dynamics cause a challenge to identify and quantify the processes and pathways behind the fluxes. This thesis investigates the specific role of CH4 and N2O fluxes from tree stems in two temperate riparian forests in Estonia and the Danube River basin (Austria), a tropical palm swamp forest in Amazonian Peru, and a tropical rain forest at the volcanic island of La Reunion. Further, their temporal dynamics and the impact of altering water tables on these fluxes are examined. Enhanced CH4 and N2O emissions at higher soil water content were found in temperate forests, especially at the lower segments of the tree stems. The investigated species (grey alder, poplar, ash) demand stable hydrological regimes to form and maintain aerenchyma to exchange gas between the tree above the water and the submerged tissues. Consequently, seasonal adaptations were identified, but diurnal changes of CH4 and N2O fluxes were not found. Observations in the tropics revealed the relevance of specific physiological and morphological parameters in trees' role as a source or sink. Amazonian palm stems formed pseudobark in the lower stem zones, likely inhibiting the radial gas exchange. The observed net uptake of CH4 and N2O by tree stems at La Reunion was less linked to adjunct soils, instead, cryptogamic covers likely play a dominating role. A limited number of studies in different forest ecosystem show high variability of CH4 and N2O exchange between tree stems and atmosphere. In some forests, tree stem fluxes can even dominate in budgets of these gases. Therefore, further complex interdisciplinary investigations are required to better understanding these relationships. Identifying microorganisms and biochemical pathways is evident for reliable estimation and further modelling of the gas exchange dynamics.
Senate Hall (Ülikooli 18–204) and via video bridge