Ruth Phoebe Tchana Wandji will defend her doctoral thesis in Natural Sciences and Environment at the Faculty of Environmental and Forest Sciences at the Agricultural University of Iceland.
Ruth Phoebe’s dissertation is entitled "Effects of soil warming on growth processes of unmanaged subarctic grasslands"
The defence will take place on 26th of June at Keldnaholt, Árleyni 22, Reykjavík, starting at 9h00 GMT. The defence will also be streamed on Teams. It will be conducted in English. Link to the Teams meeting here.
Ruth Phoebe’s supervisors are Pr. Bjarni Diðrik Sigurðsson, and co-supervisors Dr. Peter Lootens and Dr. Iolanda Filella
Her opponents are Assistant Professor, Rúna Magnússon, Wageningen University & Research, the Netherlands and Dr, Guðrún Óskarsdóttir, Náttúrustofa Austurlands, Iceland.
Abstract
High-latitude plant growth processes involve a range of physiological and biochemical mechanisms that allow plants to progress during relatively short growing seasons from unmature to fully developed organisms capable of reproducing.
During the past decades, terrestrial ecosystems have experienced a lot of alterations from climate change, and high latitude ecosystems are affected at a faster pace compared to other terrestrial ecosystems. Therefore, it is important to study how further warming is likely to affect high-latitude plant communities, including Iceland.
There are now 18 whole-soil warming experiments ongoing worldwide to increase our understanding of how plant and soil communities are likely to respond to further climate warming, and the ForHot research site is one of them. It utilises warm bedrocks below the soil profiles of known age to study the impacts of soil warming.
The ForHot contains six ecosystem-level field experiments that involve different amounts of soil warming, duration of warming and N-availability in different vegetation communities. whereof I used two grassland experiments. That is the medium-term warming (MTW) site that has been warm since 2008 and the long-term warming (LTW) site with the same type of grassland, but where the warming has been ongoing for >60 years.
To understand how subarctic grassland growth processes respond to soil warming, I looked at the first step in the plant growth processes, that is, the responses in the photosynthetic system. Secondly, I studied the duration of vegetation activity (phenology) throughout the growing season with both traditional and remote-sensing methods. Lastly, I investigated how soil warming and interannual variation affected the aboveground net primary productivity (ANPP).
The main outcomes were that even if the photosynthetic capacity remained unaltered per unit leaf area under warmer conditions, the amount of community leaf area over each m2 of surface (NDVI) increased and the duration of growth lengthened with warming. Which likely resulted together in more seasonal carbon uptake and the observed increases in ANPP under warming in both grasslands. Nevertheless, the increasing ANPP was associated with a “down-regulation” at the higher warming levels, which was possibly linked to N losses from the warmed soils. Duration of warming was generally not found to be important in plant aboveground responses.
