The following is a list of potential projects for research practicals in plant diversity, bachelor projects or master projects. However, these are only a selection of ideas and other projects are also possible, so if you have an idea for a project that addresses some aspect of biodiversity (coexistence, global change, biodiversity-functioning) then email Eric Allan to discuss it.
Research practical in plant diversity: this is worth 7.5 ECTS and is around four weeks of work. Students carry out a small research project of their own, which can involve running a greenhouse experiment, collecting data in the field (only in the spring semester), or analysing or identifying samples in the lab, e.g. insects, soil analysis. Students therefore get an overview of all stages of research, including designing a study, collecting plant ecological data, analysing data and writing a report. The report is structured like a scientific paper with introduction, methods, results and discussion. The work can be done flexibly and therefore spread out over a semester, although if you are running a greenhouse experiment you will probably have to commit to taking measurements at a certain time when plants need to be harvested.
Bachelor projects are similar to research practicals but are worth 10 ECTS and therefore constitute around 5-6 weeks of work. This allows a larger project to be carried out.
PaNDiv Experiment: direct and indirect effects of N enrichment on ecosystem functioning and pathogen communities
Who: Research practical, master student or bachelor student
With: Eric Allan and PhD students, depending on the project
Start: Spring or summer, most field work runs from beginning of May to end of August
Background: Humans are causing a range of environmental changes that threaten biodiversity and alter the services provided by ecosystems. Nitrogen (N) enrichment, from agricultural runoff or atmospheric deposition, is one of the most important environmental changes in European grasslands and it has many effects on the ecosystem. It changes soil chemistry and directly increases plant growth. At the same time, it causes loss of biodiversity, a shift towards faster growing plant species and often an increase in the abundance of herbivores and foliar fungal pathogens. Foliar fungal pathogens are abundant in grasslands, and they can reduce biomass, but we know very little about their effects on ecosystem services. All of the changes which occur with N enrichment might affect the services provided by grasslands but we still don’t know how important the different effects are and how they might interact with each other.
The study: To answer these questions, we established a large grassland field experiment to test which mechanisms explain the effect of N enrichment on ecosystem function. The experiment manipulates N addition (0, 100kg N ha-1, y-1), species richness (1, 4, 8, 20 species), functional composition (only fast growing, only slow growing or a mix of species) and fungal pathogens (foliar fungicide or not). Many ecosystem functions and services have been measured including biomass production (above and belowground), pathogen infection and herbivory, soil carbon, soil nutrients, soil respiration and litter decomposition.
Potential projects: There are many options for student projects in the experiment. For instance projects could:
- Measure root production and respiration using ingrowth cores. These can also be used to exclude mycorrhizae to measure mycorrhizal respiration
- Measure different fractions of soil carbon to assess effects on short and long term carbon storage
- Use molecular methods to characterise the pathogen community and identify fungal pathogens in leaves
- Assess functional diversity of soil microbial communities using BIOLOG plates
- Use soils from the experiment to conduct feedback experiments in the greenhouse
- Many other options
The direct and indirect effects of nitrogen enrichment on arthropod predators in grassland ecosystems
Who: Research practical, Bachelor student or Masters student
What: Insect identification and analyses of samples collected in the PaNDiv Experiment
Start: From Autumn 2019
Background: Nitrogen enrichment in grasslands often results in a reduction in plant species richness and shifts the functional composition of plant communities from slow growing to those dominated by fast growing species. These shifts in plant communities affect natural enemy populations such as fungal pathogens and insect herbivores, but also cascade up to affect higher tropic levels such as arthropod predators. Predators play a critical role in grasslands from being important links in the food chain to reducing the potential impact herbivores have on productivity. The abundance and diversity of arthropod predators likely reflects the quantity and quality of available prey and niche space. For example, an increase in plant species richness often positively correlates with insect herbivore diversity, which could in turn increase the diversity of predators. Additionally, an increase in plant species richness and/or a change in plant functional composition could increase the structural complexity of a plant community, which can provide more diverse refuges and oviposition sites for predator species. However, our current knowledge on how global change will directly and indirectly impact arthropod predators is incomplete. By factorially manipulating these plant community characteristics we can attempt to disentangle the relative impact nitrogen, plant species diversity and functional composition will have on predator communities.
The project: Insect communities have already been collected from the PaNDiv experiment using a suction sampling method. The proposed research project will involve sorting and identifying these insect samples in the lab, with a particular focus on identifying predator groups. The student will obtain measures of predator abundance, diversity and biomass, and in turn link these to plant community and herbivore data.
Aphid evolution in response to plant diversity and fertilization (PaNDiv Experiment)
With: Anne Kempel
Start: Late summer 2019
Duration: 2-3 month, followed by data analysis and writing
What: Greenhouse experiment with material from the PaNDiv Field Experiment
When plants occur at high density this is often related to a larger pathogen and insect pest infestation, likely because enemies are more likely to find and stay longer in larger patches of host plants. This higher exposure to enemies might lead to different selection pressures of plants growing in monoculture vs mixtures. Concordantly, in biodiversity experiments it has been shown that monoculture-plants differ from mixture-plants in their metabolic profile – monoculture-plants might have selected for more defended plant genotypes. At the same time, insects might also adapt to differences in host plant chemical and nutritional quality and insect populations might differ from each other depending on whether they evolved on host plants growing in monoculture or mixtures. However, much less is known on the evolutionary changes in insects due to plant diversity or fertilization. Aphids are a perfect model system to test these ideas – aphids usually hatch in spring and colonize their host plants to start new populations. These initial populations are genetically very diverse but genetic diversity has been shown to quickly decline after a while. Because of their ability to rapidly increase in numbers by asexual reproduction, different selection pressures could potentially be observed within one season.
In addition to differences in host plant quality, we would also expect that the initial larger population size of aphids colonizing host plants growing at high density, and thus a higher initial genetic diversity, might lead to a higher potential of evolution (selection) of aphids colonizing dense host plant patches, compared to aphids colonizing host plants growing at low density.
In this project we would like to explore these ideas experimentally. The PaNDiv Experiment, which factorially manipulates plant species diversity, functional composition (fast vs. slow growing species), nitrogen addition and fungicide application, offers a great possibility to select plant and aphid material originating from different backgrounds. By using aphids from different plots in the field experiment and transferring them to plants in the greenhouse we will be able to test for evolution in aphids in response to diversity and nitrogen addition.
Impacts of nitrogen addition and plant diversity on soil fauna in grassland ecosystems
With: Nadia Maaroufi
Who: Research practical or bachelor student
What: soil fauna identification using samples collected in the PaNDiv Experiment
Start: To be determined
Background: Nitrogen addition together with plant biodiversity loss and changes in plant functional composition are global changes that are known to impact ecosystem functions and services in grasslands. These global change drivers can directly affect soil properties by for instance, affecting soil nutrient balances or indirectly by impacting plant litter quantity and quality; and thus the primary resources fuelling soil organisms. Soil fauna play a critical role in regulating ecosystem processes involved in plant litter decomposition, soil organic matter turnover and associated nutrient mineralization. In the soil food web, micro-arthropods also enhance nutrient cycling through plant litter and organic matter comminution and by grazing microbial biomass. However, most studies have focused on global change effects on soil microbes, while neglecting other soil organisms at higher trophic levels. This has led to an incomplete understanding of how the entire soil food web drives ecosystem processes involved in organic matter turnover and nutrient cycling.
The study: The PaNDiv Experiment, which factorially manipulates nitrogen addition, plant species diversity, functional composition (fast vs. slow growing species) offers a great opportunity to study the impact of these global change drivers on soil micro-arthropods in grasslands. Soil micro-arthropods have been already collected and extracted by PhD student Thu Zar Nwe. The proposed research project will consist of lab work using a binocular microscope, where the student will identify soil mites at the order level: Oribatida (mainly fungivores), Mesostigmata (predators) and Astigmata-prostigmata combined. This will allow us to assess the impact of global change drivers on soil mite abundances at different trophic levels.
Is there selection for increased plant defense in species poor plant communities?
When: autumn 2019 with cuttings, spring 2020 (with seeds)
We can find plant fungal pathogens almost everywhere in the environment. They can have large effects on their hosts and as well on the whole plant community. Because of the big impacts they can have on plant communities and therefore most likely also on ecosystem services it is interesting to understand the mechanisms in plant-pathogen interactions.
For plants it is crucial to defend themselves against the pathogens. Since defense is considered to be costly, it makes sense to be well defended only when pathogen pressure is high. Mainly from agricultural studies we know, that when plants are grown at high densities the disease pressure increases due to increased encounter rates between pathogens and host (host concentration hypothesis). Also when plants grow in monocultures they suffer from more disease pressure than when they grow in polycultures. This is due to the fact that plant fungal pathogens are usually restricted to only one or a few closely related host species. Therefore it is harder for the pathogens to “find” the right host in species rich plant communities.
In the PaNDiv Experiment we have observed such density dependent pattern in infection levels. The more ground a species covers the higher it is infected by pathogens. This relationship gets steeper when the plants grow in species richer communities. We assume that this is because of selection for better defended plants in monocultures than in polycultures. This is in line with findings for plants of the long term Jena experiment. Plants with a history of growing in monoculture suffered from more infection than plants with a polyculture background under standardized greenhouse conditions. This could be explained with underlying genetic differences.
The aim of this project is to test if the monoculture plants of the PaNDiv Experiment are less susceptible to pathogens than plants from polycultures under standardized conditions.
Small project: For this you will produce clones of plants growing in communities with different species diversity (1, 4, 8, 20 species), put them in pots outside of the PaNDiv field in the grassland and observe infection levels of the plants.
Bigger project: Alternatively you can take these plants into the greenhouse and do a crossed infection study, where you try to infect the plants with infected leaf material from the field.
Instead of producing clones you can also collect seeds from the plants in the field.