| 1. |
- Frenkel, Martin, 1973-
(författare)
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Light, stress and herbivory : from photoprotection to trophic interactions using Arabidopsis thaliana as a model organism
- 2008
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Photosynthesis is the most important process for nearly all life on earth. Photosynthetic organisms capture and transfer light energy from the sun into chemical energy which in turn provides a resource base for heterotrophic organisms. Natural light regimes are irregular and vary over magnitudes. At a certain light intensity, metabolic processes cannot keep up with the electron flow produced by the primary photoreactions, and thus reactive oxygen species (ROS) are produced. ROS are highly reactive and can damage the photosynthesis apparatus and hence plants have evolved several photoprotection mechanisms to avoid the formation of ROS. The aim of this thesis was to examine the ecological effects of variations in photoprotection in plants. In particular I wanted to study the effect on fitness and the interaction with herbivorous insects of plants with different ability in photoprotection. To study this I used wild-type and transgenic Arabidopsis thaliana plants and grew them under natural conditions in field experiments in our botanical garden in Umeå, northern Sweden. For the investigation of the plant-insect interaction, a specialist on Brassicaceae (Plutella xylostella – diamondback moth) and a generalist herbivore (Spodoptera littoralis - Egyptian cotton worm) were used. Plants that are genetically deficient in one of the photoprotection mechanisms showed reduced fitness under natural conditions. I could thus show that feedback de-excitation (FDE) is the most important photoprotection mechanism, because a lack of FDE showed the highest reduction in fitness. The comparison of field grown wild-type with FDE mutant plants, using molecular biology methods, revealed large changes in gene transcription and metabolic composition. In particular, the jasmonate pathway was upregulated in light stressed plants, especially in plants lacking FDE. Jasmonate in turn is known to be a chemical compound which induces herbivore resistance genes and other stress responses. Specialist and generalist insect herbivores responded differently in feeding (dual-choice and no-choice) and oviposition experiments with field grown plants that differed in FDE. Female diamondback moths were attracted by induced defense compounds whereas the larvae avoided these plants in feeding experiments. Generalist larvae preferred, and showed a higher survival rate, on less light-stressed plants compared to more light-stressed plants. Combining molecular biology with ecological experiments is a challenging task. To summarize my experiences, I have produced a guide for experiments on transgenic plants in common gardens. In future investigations it is important to examine natural variations in photoprotection to elucidate selection pressures on specific genes.
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| 2. |
- Horstkotte, Tim, 1981-
(författare)
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Contested Landscapes : social-ecological interactions between forestry and reindeer husbandry
- 2013
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Throughout northern Fennoscandia, reindeer husbandry is a central part in the cultural heritage of the Sámi people. In its history, Sámi culture and reindeer husbandry have undergone significant adaptations to environmental, social and political challenges. Landscape changes on the winter grazing grounds were mainly driven by resource exploitation, especially by industrialized forestry. Important grazing resources were lost, i.e. terrestrial and arboreal lichens that constitute essential key elements in the herding year.In my thesis, I explore the consequences of these transformations in Swedish boreal forests for reindeer husbandry. The multi-disciplinary approach integrates interview studies, ecological fieldwork and theoretical modeling of forest development.I emphasize the understanding of landscapes as multi-dimensional concepts with ecological, social and economic components. They interact in determining the amount of landscape fragmentation in physical or administrative ways, or in enabling reindeer herders to move between different landscape elements. These elements, e.g. forest stands of different ages, can react differently to winter weather. Thus, they enable reindeer herders to adjust their grazing grounds according to the availability of forage, mediated by snow conditions. However, forestry practices have reduced the abundance of old-growth forests, and therewith the functionality of the landscape. By comparing snow conditions in different forest types, I show that multi-layered canopies can offer a more diverse pattern of snow hardness. However, the interaction between forest characteristics with snow is strongly dependent on weather conditions, e.g. the timing and intensity of warm spells. The prevalence of single-layered forest stands therefore can lead to a reduction in snow variability and potentially restricts the availability of suitable grazing grounds for reindeer. If snow conditions hinder reindeer in foraging on terrestrial lichens, old forests formerly supplied reindeer with arboreal lichens. I show how industrial forestry has reduced the availability of this emergency forage by the reduction of old forests and increased landscape fragmentation and analyze the consequences of different management strategies on future habitat availability for arboreal lichens. By integrating these results into a model of forest management, I offer insights into consequences arising from different priorities that either favor timber production or the development of lichen-rich grazing grounds.In conclusion, I emphasize the importance of landscape diversity, as well as the ability to make use of this diversity, as a source of adaptability of reindeer husbandry to changes in grazing conditions by e.g. winter weather dynamics. A shared future of reindeer husbandry and forestry could be fostered by encouraging the social-ecological co-evolution of multiple use landscapes and the enhancement of the cultural and biological significance of the Swedish boreal forests.
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| 3. |
- Jonsson Čabrajić, Anna V, 1978-
(författare)
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Modeling lichen performance in relation to climate : scaling from thalli to landscapes
- 2009
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Lichens can colonize nearly all terrestrial habitats on earth and are functionally important in many ecosystems. Being poikilohydric, their active growth periods are restricted to periods when the thallus is hydrated from atmospheric water sources, such as rain, fog and high relative humidity. Since lichen hydration varies greatly over time lichen growth is therefore more difficult to model compared with, for example vascular plants with more even water supply. I developed two models to predict lichen hydration under field conditions that incorporates the atmospheric water potential (Ψair), derived from air temperature and humidity, only or in combination with species-specific rehydration and desiccation rates. Using Ψair allows the prediction of hydration induced by several water sources. These models were very accurate for epiphytic lichens with a close coupling to atmospheric conditions, but they were less accurate for mat-forming lichens with substantial aerodynamic boundary layers. The hydration model was further developed to include photosynthetic activation for different species, in order to compare their performance under different micro-climatic scenarios. Water balance and activation rate had large effects on lichen activity and were positively related to habitats providing long hydration periods, for example close to streams. To study effects of climate change, a complete model for net carbon gain (photosynthesis minus respiratory losses) was developed for an epiphytic lichen with intricate responses to light, hydration and temperature. Simulation responses in different climate scenarios revealed that projected climate change on a regional scale resulted in varied local scale responses. At the lighter, exposed sites of a forest, the growth responses were positive, but were potentially negative at darker sites with closed canopy. At the local scale, fluctuating hydration, summed irradiance when wet and Chlorophyll a are variables that predict lichen growth. However, at a landscape scale, these variables may be too detailed. We tested this for two terrestrial, mat-forming lichens and developed statistical models for lichen growth in the widest possible climatic gradient in northern Scandinavia, varying in light, temperature and precipitation. Light was the most important factor for high growth at the landscape scale, reaching saturation at a site openness of 40 %, equivalent to a basal tree area of 15 m2 ha -1 in this study. Thereafter, hydration was the next limiting factor, which could be well described by precipitation for one of the species. The simplest predictor was the normal temperature in July, which was negatively correlated with growth. It was apparent that the predictive variables and their power varied at different scales. However, light and hydration are limiting at all scales, particularly by light conditions when lichens are wet. This implies that ensuring that there is sufficient light below the forest canopy is crucial for lichen growth, especially for mat-forming lichens. Hydrophilic lichens may be better preserved in open habitats with long hydration periods. It was shown that models can be powerful and “easy to use” tools to predict lichen responses in various habitats and under different climate scenarios. Models can therefore help to identify suitable habitats with optimal growth conditions, which is very important for the conservation and management of lichens and their habitats.
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| 4. |
- Kaarlejärvi, Elina, 1980-
(författare)
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The role of herbivores in mediating responses of tundra ecosystems to climate change
- 2014
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The Arctic areas are warming more rapidly than other parts of the world. Increasing temperatures are predicted to result in shrubification, higher productivity, declining species diversity and new species invasions to the tundra. Changes in species diversity and plant community composition are likely to alter ecosystem functions with potential consequences for human population also at lower latitudes. Thus, in order to better predict the effects of the rapid arctic warming, we need knowledge on how plant communities respond to a warmer climate. Here, I investigate the effects of climate warming on tundra plant communities and focus on the role of mammalian herbivores in mediating these responses. I examined the role of herbivores by incorporating herbivore manipulations to short- and long-term warming experiments as well as along altitudinal gradients. I measured how individual plants and plant communities respond to warming with and without herbivores.Results of my PhD Thesis illustrate several ways how herbivores modify the responses of plants to warming. I found that herbivores (reindeer, hare, voles, lemmings) may prevent lowland forbs from invading open tundra. Herbivores might also protect small tundra forbs from being outcompeted by taller and denser vegetation under climate warming. Thus, different herbivore pressures may lead to differing plant abundances and distribution shifts in different areas. Furthermore, my results show that high herbivore pressure can reverse the effects of long-term climate warming very rapidly, even in one year. This finding suggests that well-planned targeted reindeer grazing episodes could potentially be used as a conservation tool to keep selected tundra habitats open. Sudden cessation of grazing may initiate rapid changes in plant community, especially if it coincides with warm temperatures. Taken together, I show that herbivores counteract the effects of climate warming by slowing down or preventing vegetation changes in tundra. Therefore, it is important to consider mammalian herbivores when predicting tundra plant community responses to changing climate.
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| 5. |
- Lindgren, Åsa, 1973-
(författare)
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Effects of herbivory on arctic and alpine vegetation
- 2007
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The distribution of plant species and functional traits in alpine and arctic environments are determined by abiotic conditions, but also by biotic interactions. In this thesis, I investigate interactions among plants and herbivory effects on plant community composition and plant functional traits in three different regions: Swedish Lapland, Beringia (USA/Russia) and Finnmark (Norway). Reindeer grazing was found to be extensive in southern Lapland and had limited effects on plant community composition and seedling germination. However, reindeer presence was found to influence plant functional traits, particularly in the subalpine birch forest. Tall herbs were lower and had lower SLA when reindeer were present, while small herbs showed an opposite pattern. The contrasting effects on the two herb groups are probably explained by a competitive release for small herbs when the tall herbs are suppressed by reindeer. Rodents had the largest relative impact on plant community composition in southern Lapland and this is consistent with the study from Finnmark, where rodents heavily affected dwarf shrubs on predator-free islands. With no predators present, vole densities increased profoundly and almost depleted some dwarf shrub species. These results support the idea that small mammals in arctic and alpine tundra are controlled by predators (i.e. top-down). However, a decrease in the nutritional quality in a sedge after defoliation gives support for the idea that small mammals are regulated by plant quality (i.e. bottom-up). In Beringia, small and large herbivores differed in the relation to plant community composition, since large herbivores were related to species richness and small herbivores were related to plant abundance. Plant functional traits were related only to large herbivores and standing crop of vascular plants.
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| 6. |
- Moen, Jon, 1960-
(författare)
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Herbivory and plant community structure in a subarctic altitudinal gradient
- 1993
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The object of this thesis was to study plant community structure, especially in relation to vertebrate herbivory, in an altitudinal gradient in the Fennoscandian mountain chain.A sowing experiment in a high alpine Ranunculus glacialis population showed that seeds germinated better in cleared microsites than under established individuals. This is contrasted with a hypothesis that predicts positive plant-plant interactions in high alpine environments. It was concluded that plant-plant interactions in die studied population varied from neutral to negative, whereas no indications for positive interactions were found.An exclosure experiment in a snow-bed showed that a lemming population consumed 33 % of the available graminoids and 66 % of the mosses from August to June during a population peak. The results shows that grazing needs to be considered as a structuring factor in snow-bed vegetation.The vegetation in exclosures in another snow-bed changed from a graminoid-dominated to a herb-dominated plant community during a long-term (six years) experiment No changes of the same magnitude were seen in a tall herb meadow on a lower altitude. Survival of transplanted adult shoots from the tall herb meadow was equally high in the snow-bed as on the meadow, and germination was also high on bare ground in the snow-bed. Grazing seemed to be a more important structuring factor in the snow-bed than in the more productive tall herb meadow.Raising the grazing pressure during one growing season by introducing microtine rodents into enclosures did not cause any large short-term effects on plant community structure in a tall hob meadow or in a snow-bed. Marked shoots showed that some preferred plant species had a high shoot mortality, but biomass for pooled categories of plants was not significantly affected. It was predicted that the tall herb meadow would be more grazing sensitive than die snow-bed, but productivity on the meadow seemed to be sufficiently high for the plants to compensate for the grazing during the growing season.A greenhouse experiment showed that voles, when grazing freely, have the potential to deplete productive field layer vegetation contrary to predictions from plant defence theories. A nitrogen-based defence did not prevent heavy shoot mortality for toxic tall herbs.
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| 7. |
- Össbo, Åsa, 1971-
(författare)
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Nya vatten, dunkla speglingar : industriell kolonialism genom svensk vattenkraftutbyggnad i renskötselområdet 1910-1968
- 2014
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Hydropower development was one of the first systematic large-scale exploitations in the reindeer herding areas within Swedish borders. Therefore, this thesis departs from postcolonial approaches wherein the Swedish state policy and practice towards Sami, reindeer herders and Sápmi, the Sami homeland, is analysed as colonialism in relation to hydropower development.The study spans over the first large-scale hydropower projects in the reindeer herding area during the 1910’s and 1920’s, continuing with the decreased legal security during the second world war, and finally the opposition and opinion in the 1950’s and 1960’s, enabled by the establishment of a national association for Swedish Sami, SSR. The industrialisation of watercourses in the reindeer herding areas were brought about by the works of an institutional framework consisting of the Water Act and the Reindeer Grazing Act together with the tutelage of a Lapp Administration. These institutions made invisible both reindeer herding as an industry and the herders rights. Authorities as well as hydropower companies acted and argued within an industrial colonial discourse. One technique was the re-writing of history and of the herders’ rights in favour of power developers. The Swedish hydropower system was built up based on cheap energy from the North, at the expense of stakeholders’ rights. This was made possible by arguing that exploitation was for the sake of ”the common good”. When reindeer herders eventually were noted in the process, reindeer herding was regarded as a vested interest and reindeer herding rights as a privilege given to the Sami by the state. In this system reindeer herders were given a more vulnerable legal position than farmers, in addition non-reindeer herding Sami were in some aspects even more affected by discriminating structures. By damming the watercourses, the grazing lands were reduced which affected the amount of herders that could practice reindeer husbandry and thereby also the amount of individuals holding Sami rights. During the 1950’s and 1960’s the self-evidenced hydropower development was questioned by a Sami struggle for justice. With regards to Sami rights, the situation was more stagnant due to the state avoiding official investigation of certain legal issues that were object for trial. However, the industrial colonial discourse and the governing of hydropower politics were challenged and the authorities changed some of their notions of reindeer herders. Nevertheless, the Sami were denied representation and involvement in governing the finances that were aimed at alleviation of the consequences of various interferences in the herding area.
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