Browsing by Author "Fruhauf, Yasmin"

Increasing atmospheric CO2 concentrations due to anthropogenic activity is resulting in climatic changes. Cities are major emitters of CO2 and are therefore interested in the possibilities of urban vegetation to sequester carbon in order to mitigate climate change. The city of Helsinki aims to become carbon neutral by 2035; subsequently, there is interest to understand the sink capacity of its urban vegetation. Current existing carbon cycle models are based on natural ecosystems and there is a need for carbon cycle models based on vegetation in an urban setting. Photosynthetic potential provides a base for understanding the carbon cycle in an ecosystem, which is calculated using a light response curve. Chlorophyll fluorescence measurements provide information about the general status of photosystem II and are commonly used as indication of the leaf photosynthetic potential, general health status and the leaf’s response to environmental conditions. Photosynthetic potential is also depended on illumination conditions around the canopy; leaves located in the sun will generally be more productive than those in shade. In this study, three tree species were selected for photosynthesis potential measurements: Tilia cordata, Tilia x europaea and Betula pendula. In Helsinki, Tilias are usually planted in managed areas while B. pendula is naturally regenerating. Data collection was conducted during May-September 2020 around Kumpula, Helsinki. Trees were located in three different urban settings: urban forest (B. pendula), built garden (T. cordata) and roadside (T. x europaea). Photosynthetic potential and chlorophyll fluorescence yield were measured four times during the summer at different canopy heights. Results show that B.pendula had higher photosynthetic potential than the Tilias, with no differences between the canopy heights. T. cordata showed differences in the photosynthetic potential and chlorophyll fluorescence between the canopy heights in July and August, with higher values at the bottom canopy. T. cordata also showed a seasonal cycle, with low photosynthetic potential values in the beginning and end of the season and high values in July. B. pendula demonstrated a similar seasonal cycle. Lastly, T. x europaea showed higher photosynthetic potential values at the top canopy compared to the bottom. Overall, chlorophyll fluorescence mirrored photosynthetic potential especially in the case of seasonal dynamics, rather than canopy heights. The high photosynthesis potential observed with B. pendula allows greater amount of carbon to enter the urban ecosystem and could be since the trees are naturally growing in the forest patch. The Tilia trees were transplanted as saplings, which could have caused damage to their roots in excess soil moisture conditions and cause growth inhibition. A better understanding of the urban managed vegetation is needed, as well as the urban stress factors. Nevertheless, based on these findings, I would recommend conserving the natural unmanaged urban forests patches, as they seem to have an important role in urban carbon cycle.