The doctoral dissertation in the field of Environmental Science will be examined at the Faculty of Science, Forestry and Technology, Kuopio campus and online.
What is the topic of your doctoral research? Why is it important to study the topic?
My doctoral research aimed to advance knowledge of the role of climate change in shaping biogeochemical and ecophysiological processes in northern high-latitude ecosystems. Warming trends are predicted to be strongest in the Arctic and subarctic regions, accompanied by increased nutrient availability and cloudiness. This study investigated effects of the climate change variables, i.e. increased temperature, nutrient availability, and cloudiness, on vegetation and the ecosystem-atmosphere exchange of greenhouse gases (GHGs) and other atmospheric reactive gases (ARGs) in the subarctic. Additionally, the study explored relationships between vegetation and ecosystem-atmosphere gas exchanges in the subarctic.
We have an inadequate understanding of how vegetation and the exchange of trace gases between ecosystems and the atmosphere in northern high latitudes are affected by the rapidly changing climate. Furthermore, comprehensive reports on the fluxes of GHGs and ARGs in concert in northern ecosystems are currently lacking. Simultaneous quantification of GHGs and ARGs represents a novel approach to studying the role of vulnerable northern ecosystems in climate change and enhances our understanding of climate change effects in these regions.
What are the key findings or observations of your doctoral research?
The research indicates that subarctic palsa mires and upland tundra ecosystems are significant sinks of methane and sources of carbon dioxide, nitrous oxide, and biogenic volatile organic compounds (BVOCs). The thesis shows that future warming will enhance the methane sink and BVOC source strength of these ecosystems, contributing to negative climate feedback while future warming and enhanced nutrient availability will enhance the carbon dioxide and nitrous oxide source strength, contributing to positive climate feedback. The research also shows that the methane sink and BVOC source strength of these ecosystems would decrease under future conditions of warming and more cloudiness, which could feedback positively to climate. Based on the findings, the climate change effects would be generally stronger in subarctic palsa mires than in upland tundra heaths.
The research further indicates that future warming, increased nutrients, and increased cloudiness conditions in the subarctic (as simulated) will alter vegetation composition, mainly dominated by plant functional types such as graminoids and forbs, and structure (i.e. vegetation cover, greenness, leaf anatomical and biochemical traits) which have important implications for carbon gain and abiotic and biotic stress tolerance of subarctic plant species. Prevailing vegetation and soil characteristics could explain some changes in gas fluxes, highlighting the role of northern vegetation and soils in controlling ecosystem gas fluxes. In this thesis, I identified surface cover (vegetated vs bare surface) and soil type (mineral vs organic) as important factors controlling the ecosystem gas fluxes. Vegetation composition and biomass were important factors controlling the fluxes of carbon dioxide, nitrous oxide and BVOCs. Soil moisture was an important factor controlling methane flux while the availability of mineral nitrogen was essential in controlling the fluxes of nitrous oxide and other nitrogen-based gases, such as nitric oxide and nitrous acid.
How can the results of your doctoral research be utilised in practice?
For the scientific community, the research and findings represent a significant contribution to the field of biosphere-atmosphere interactions, highlighting the role of vulnerable northern ecosystems in climate change. It provides a substantial basis for new perspectives and directions for future research on climate change impacts in northern ecosystems. The research and findings are expected to drive future studies aimed at modelling climate change and feedback responses for a better understanding of climate change and feedback effects in the inadequately studied, vulnerable northern ecosystems. The findings are also relevant for local stakeholders, inhabitants, and indigenous communities of the northern regions in developing strategies for climate change mitigation and environmental monitoring, as well as adapting to ecosystem service changes associated with the changing environmental conditions.
What are the key research methods and materials used in your doctoral research?
The study involved both laboratory and field experiments. The laboratory experiment was conducted at the University of Eastern Finland, where sample mesocosms collected from a subarctic tundra heath in Northern Sweden and Finland were exposed to individual and combined effects of warming and increased cloudiness in a climate chamber setup. The field experiment was conducted at a long-term climate-change-manipulation site in a tundra heath in Abisko, Northern Sweden. In both the mesocosms and the long-term experimental tundra heath, the fluxes of GHGs and ARGs were quantified, and vegetation composition and leaf traits were analyzed. The measurements and analyses were performed using state-of-the-art instruments and statistical approaches.
The doctoral dissertation of Flobert Andongah Ndah, MSc, entitled Subarctic ecosystems under climate change: carbon and nitrogen-based gas fluxes and vegetation change will be examined at the Faculty of Science, Forestry and Technology, Kuopio Campus and online. The opponent will be Professor Anne Tolvanen, Natural Resources Institute Finland and the custos will be Professor Marja Maljanen, University of Eastern Finland. Language of the public defence is English.
For more information, please contact:
Flobert Andongah Ndah, flobert.ndah@uef.fi
