Abschlussarbeiten betreut in der Vegetationsökologie
Contact Katja Tielbörger Email
A) Evolution of heterocarpic plants
Many composites produce two or more types of seeds which differ in dispersal and germination characteristics. This heterocarpy is considered a type of bet-hedging strategy whereby different seed morphs are produced in environments which are spatially and/or temporally variable.
A1) Along a gradient of environmental unpredictability (i.e. an aridity gradient in Israel), the ratio of far vs. short dispersing seeds should change: more seeds with high dormancy should be produced towards the arid. There should be a trade-off with dispersal, i.e. dispersal distance and seed dormancy should be inversely related. This hypothesis will be tested using a collection seeds from of annual heterocarpic species. They will be grown in Winter 2020/21. Start: Sept-Nov 2020 (preparation), peak work March-May 2021 (i.e. between Nov and March there is time for taking courses).
A2) Plasticity should be more pronounced for plants coming from more variable (i.e. arid environments). Thus, we assume that plants will plastically change the ratio between the two seed morphs more when coming from arid sites. This hypothesis will be tested with growing several species of annual plants from an aridity gradient under drought and well-watered conditions. Start: Sept-Nov 2020 (preparation), peak work March-May 2021 (i.e. between Nov and March there is time for taking courses)
B) Can plants tell each other about their flowering time?
Plant can benefit from the presence of neighbours if they are rare and their neighbours attract pollinators. In that case, having more neighbours will increase pollination services. Vice-versa, very abundant plants will rather compete for pollinators, i.e. there will be negative density-dependence related to pollination services. If it would be possible for plants to detect in situ whether or not their (conspecific) neighbours flower, it would be advantageous if they adjust their flowering time accordingly. Namely, rare plants that should benefit from neighbours should be stimulated by flowering neighbours while abundant plants should retard flowering to spread flowering across a longer time and thus avoid competition for pollinators. These (somewhat crazy) hypotheses will be tested with Israeli annuals grown in a greenhouse. The experiments could be combined with active manipulation of pollinator presence or absence and by manipulating the degree to which plants can sense their neighbours.
C) Competition intensity and relatedness
In an equilibrium world, coexistence requires that plants differ from each other. Therefore, competition should be stronger between plants that are very similar. Thus, competition intensity should increase along a gradient of relatedness, ranging from between regions, between family within a region, between species within a family, between individuals within a species from different climates, between individuals from same climate and species, between sibling plants. relatedness should also affect symmetry of interactions and should be more symmetric on an intraspecific level.
This topic is more relevant for an MSc level and will be tested with the collection of Israeli annuals, i.e. this is again a winter topic.
D) Allocation of root and shoot biomass under varying levels of stress in adult plants and seedlings of lowland and alpine plants
What effects does climatic stress have on the resource allocation of mountain and lowland plants? Climate change will modify the distribution range of plant species. At the same time, it is not necessarily the macroclimate that plants experience. If protected by surrounding vegetation, the microclimate they experience can be milder. Mechanical disturbances of the vegetation cover in the mountains can be both positive for plants - they experience less competition - and negative - the absence of neighbouring increases thermal stress. The balance between these processes has the potential to change the distribution range of distribution of mountain and lowland plants.
To study the effects of disturbances, climate, and neighbouring plants, we have set up an experiment in the Norwegian Scandes in Dovrefjell, which includes different disturbance intensities and climatic conditions. We are looking for a dedicated student in biology or geoecology, with previous knowledge in plant ecology and motivation to work in the mountains under adverse climatic conditions, to complete a Master Thesis between August 2021 and March 2022. Fieldwork phase is August 2021. The Master Thesis uses the experiment to investigate the allocation of biomass to roots and aboveground organs. In addition to the fieldwork, there is a phase with work in the plant laboratory.
Prof. Dr. Katja Tielbörger is supervising the project in Tübingen in cooperation with Ronja Wedegärtner at the NTNU in Trondheim, Norway.
E) The role of beta-diversity for ecosystem function
Myriads of studies have been published on the role of alpha diversity (i.e. species richness) on ecosystem functions, with the general result that ecosystem function (mostly: productivity) increases in an asymptotic manner with increasing species richness- albeit only at low richness. Nothing is known about how beta-diversity, e.g. the number of different habitat types or species turnover affects ecosystem function. Here, we can utilize a large experiment in which we experimentally manipulated habitat diversity to test this. The experiment is located at our common garden, the first work for Theses can start in the growing season of 2021.
F) Can we see climate change and land use change effects in the plant microbiome?
Looking at and describing plant microbiomes has become very popular. However, due to the very small scale at which microorganisms vary (e.g. sometimes across centimeters on a single plant), we know virtually nothing about larger scale environmental effects on the organisms that live on an inside a plant. In this topic, we attempt to utilize two long-term experiments to test whether effects we can see on entire plant and plant communities are also reflected in the abundance, composition and diversity of plant-associated microorganisms (bacteria and fungi). These pioneering projects are conducted in collaboration with the group of Prof. Eric Kemen at the ZMBP.
In one set of possible Theses, we want to study the microbiome of plants growing under various levels of drought. To that end, we have harvested plots in meadows and forests within a large 4-year study in the field (Swabian Alb) where we imposed different drought treatments on natural communities. The material is readily available, and some pilot analyses could start in winter 2020.
In a second set of analyses, we will harvest plants from experimental plots where land use and habitat heterogeneity was manipulated (see topic F). Here, some pilot projects (i.e. MSc Theses) can start in summer 2021.
G) How plants affect soils and rock: Nutrient dynamics along a steep climatic gradient in Chile (additional contact: Liesbeth van den Brink: firstname.lastname@example.org - projects are embedded in the project EarthShape)
G1) Effect of herbivory on litter decomposition: Greenhouse experiment with seeds of Chilean plants to be grown in the greenhouse and clipped to simulate herbivory. The response of the litter quality to clipping and subsequent decomposition rates will be tested. We hypothesize, that herbivory may induce the production of defense compounds which reduce litter quality and thus impede litter decomposition.
G2) Nutrient limitation of plants along a climate gradient
Nutrient limitation can have drastic effects on the way in which plants take up and recycle nutrients. This in turn affects the rate at which bedrock is weathered by biota (plants and microorganisms). Thus, understanding nutrient limitation- especially of rock-borne nutrients such as P and K, can help us understand the rate of biogenic vs. abiotic weathering of rocks. Within this overarching topic, we will utilize soil sampled in Chile along a steep climatic gradient to test various hypotheses about the nature of nutrient limitation along climatic gradients. We conduct a series of experiments with plants collected in Chile and grown on natural soil, where we add (resp. not add) nutrients to see which type of limitation dominates on which type of soil.
This topic is still hampered by a limitation of seeds, i.e. we could not collect many seeds in 2020, which was a drought year, and by the fact that our soil is still stuck in Chile (due to Corona). However, once the soil arrives at Tübingen, we could start with a pilot study (e.g. BSc Thesis). The main study is then anticipated starting from mid- to end 2021.
Contact Maria Majekova Email
A) Asynchrony and stability of winter annual communities along a steep environmental gradient in the Eastern Mediterranean Basin
Master project; start any time, no field work involved, good command of R required
Background: What determines stability of populations and communities remains one of the most debated questions in both theoretical and applied ecology. An important factor affecting the stability of communities over time is the degree of synchrony in fluctuations of individual species populations that coexist within a community.
Aim and Methods: Here we will investigate the crucial question whether deviations from perfect synchrony (asynchrony) lead to more stable communities. For this, we will use a long-term dataset on winter annuals assembled along a steep gradient of aridity and intensity of environmental fluctuations in the Eastern Mediterranean Basin in Israel. The dataset encompasses four sites (arid, semi-arid, Mediterranean and mesic-Mediterranean) and climate change manipulations (increased drought and increased precipitation) within two of them.
What you should know: You should have a good command of R to handle the big dataset (packages tidyr, dplyr, ggplot2). You can start any time, and duration will depend on your speed in handling the data. There is no field work involved, but as a member of our Plant Ecology group, you are welcome to sniff into empirical projects, too.
Contact Anubhav Mohiley Email
A) Can metal hyperaccumulation increase drought tolerance?
Metal hyperaccumulation is an intriguing trait found in very few plant species. Hyperaccumulation has been hypothesized to perform several functions in hyperaccumulator species. We did in previous studies show that this trait is likely related to defence against herbivores and competitors. Another hypothesis suggested in the literature is that plants hyperaccumulate heavy metal to withstand drought. Evidence bearing on this hypothesis is scarce. Hence in this study we hypothesize that metal hyperaccumulation (e.g. Cadmium, Zinc) will enhance drought tolerance of metal hyperaccumulating plant Arabidopsis halleri. Does this response differ between plants from metalliferous and non-metalliferous origin of A. halleri. The experiment will be performed in the green house. We will combine drought and metal in a full factorial experiment.
Starting Flexible, 3 – 4 months of experiment approximately (BSc or MSc; in English)
Contact Sara Tomiolo Email
A) Can microplastic buffer the effects of drought?
Microplastic is a common novel pollutant in the environment and its effect on the environment and plants or animals are poorly understood. It is generated from various sources and contains fibers of various size. Due to its ubiquity, its environmental implications have been discussed a lot in the past few years, and the general assumption is, that microplastic is ‘bad’ for the environment. However, studies have also shown that microplastic generated from plastic used in agriculture may have positive effects on soil water retention capacity, though this also depends on the type of soil considered. Therefore, it is perceivable that microplastic may have positive effects on plant growth, especially in dry areas and/or dry years.
Unfortunately, nothing is known about such effects, and we are planning a bigger research project addressing this question. To that end, we would like to start a pilot project (MSc or BSc) as a proof-of-principle for the effect of microplastic on soil water and on plants. The experiment could be done in winter (with Israeli winter annuals) or in summer, i.e. it can start either around October or April.
Contact Sara Heshmati Email
Land degradation assessment using residual trend analysis in Namibia
Dryland ecosystems cover a large share of the world’s terrestrial surface. Deficiency and spatio-temporal variability of precipitation as well as low vegetation growth rates make dry rangelands prone to degradation, especially under changing climate and intensified land use. Drivers of aboveground net primary productivity (ANPP) in drylands are manifold but it is generally believed that precipitation is the main factor. The best correlation between ANPP and precipitation ascends to ANPP and lagging precipitation. Precipitation is not directly available to plants but is partitioned into run off, evapotranspiration, soil moisture and ground water recharge. Therefore, soil moisture might be a better indicator of the increased ANPP. Within this study we want to find which factor is more correlated with ANPP, precipitation or soil moisture? RESTREND method give us an opportunity to reveals the proportion of ANPP change is not due to climate variability by analysing the residuals from ANPP-precipitation or ANPP-soil moisture regression model over time. To do this study you need to have a good command of R and ArcGIS or QGIS.
(Starting day is flexible, MSC thesis in English.)
If you are interested in a topic and you don’t have a knowledge of ArcGIS or QGIS, I could teach you ArcGIS to the point to be able to do this project.