Browsing by master's degree program "Magisterprogrammet i botanik"

Climate change poses an ever-increasing threat on biodiversity as the global mean temperature rises causing changes in weather patterns. Species will have to adapt to the circumstances or follow their climatic niches across space to avoid decline and extinction. Many species are already threatened by extinction due to climate change. Understanding how species are reacting to rising temperatures can help us preserve biodiversity. Genetic adaptation is a long process and takes several generations to occur. A more immediate means to cope with variation is adjusting through phenotypic plasticity, which can help species cope with environmental changes in the short-term. Plasticity can help individuals maintain fitness in different environments and with fluctuating environmental conditions. Flowering phenology is a plastic trait which can have a large impact on reproductive success. Flowering is an important part of a plant’s life cycle as it can produce offspring with new combinations of genes. In this thesis I examine how temperature affects the flowering phenology of Hypericum species and how this thermal plasticity affects fitness. Populations of Hypericum perforatum, H. maculatum and H. montanum from different parts of their distribution across Europe were studied in greenhouse experiments. The plants were grown in four different temperature treatments (16/6°C, 20/10°C, 24/14°C, 28/20°C) and the timing of first flowering was monitored. Seed mass and flower count were recorded and used as measures of fitness. In general, the plants flowered later in the colder temperature treatments. The results differed between species: in H. maculatum the leading-edge populations were less plastic while in H. perforatum differences between areas were negligible. More plastic accessions produced more flowers due to earlier flowering. There was no effect on seed mass. The possible effects of plasticity on overall fitness highlight the need for detailed information on plasticity for predicting species response to climate change.

For a better understanding of global climate change we need evidence allowing us to track changes in the environment. Pollen is geologically stable, making it a key option as a potential proxy for tracing historic environmental changes. To quantify past environmental changes, it is necessary to test proxies under today’s climate. The amount of UV-B radiation reaching the surface of the Earth has varied throughout the Earth’s history. These variations are ecologically important because changes in UV-B radiation impact plant regulation, growth, defense, and decomposition. The availability of fossil pollen and spores has resulted in significant interest in the potential of using the relationship between UV-B radiation and the accumulation of phenolic sunscreens as a proxy to trace past changes in UV-B radiation. Fossil pollen from Pinus sylvestris is readily available and proven techniques exist to quantify levels of UV-B absorbing compounds from both fossil and extant pollen. We investigated how levels of UV-B-absorbing compounds in Pinus sylvestris pollen change after strobili developed under UV attenuating filters. Fifteen Pinus sylvestris trees were selected from a seed orchard of trees in Nurmijärvi, Finland. The treatments used were Rosco 226 film – filtering solar UV-A and UV-B light, polyester film – filtering solar UV-B, polyethylene film – acting as a transparent control, and an open control condition with no filter. The filters were installed in April 2022 and 2023 and remained in place each year beyond dehiscence towards the end of May. The pollen was analysed using Fourier-transform infrared spectroscopy. Principal component analyses and linear regression models were used to simplify the multivariate data and then describe the levels of UV-B absorbing compounds in the different treatment groups. A sample of needles from underneath the filters was used to verify the effectiveness of UV treatments across the experimental design by analysing their epidermal flavonol content. Our results found no clear link between UV-B exposure and accumulation of UV-B absorbing compounds in Pinus sylvestris pollen. However, we did find statistically significant differences in concentrations of UV-B absorbing compounds in pollen between the different trees. The needle analyses verified that the experimental design had the potential to affect the biochemistry of these branches by revealing significant differences in relative absorbance by epidermal flavonols due to UV treatment type. Multifactorial drivers affect the concentrations of UV-B-absorbing compounds in plants, and viewing the response of these compounds to a single driver may be an oversimplification complicating their use as a proxy. We argue that methodologies used in previous research have inconsistencies which fail to account for environmental factors that either covary with UV radiation or diverge from it. This may explain why our results go against the trend. Finally, we examine our own research experimental design and suggest improvements and avenues by which this research can move forward.