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.
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
What root traits are important for ecosystem functioning?
Who: Research practical or bachelor student
Start: February/March 2019 (most of the trait measures will be done in late March)
Background The field of functional trait ecology has developed dramatically in the last 10-15 years. Many studies have shown that functional trait diversity is a better predictor of ecosystem functioning than species diversity and functional traits can be used to better understand the mechanisms by which diversity affects function. Most of the work on functional traits has focused on easy to measure leaf traits. However, these may not correlate with root traits and measuring root traits is therefore important to better characterize functional diversity.
The study: we will grow 20-30 grassland species in sand for a few weeks, with and without an N-addition treatment, and will measure their root traits. Roots will be washed and then scanned using “WinRHIZO”. The scanned images will be analysed to derive root traits like root diameter and specific root length. These data can then be compared with data on leaf traits which we have previously measured in the same species. They can also be combined with data from a large biodiversity experiment (PaNDiv) which contains communities with different combinations of these species, crossed with addition of nitrogen and removal of fungal pathogens. This would allow us to calculate functional composition (community weighted means) and diversity based on root traits and to relate these to the ecosystem functioning (root and shoot biomass) measured in the experimental plots.
- Are leaf and root traits correlated with each other, or do roots represent different axes of strategy variation?
- How does functional diversity and functional composition of root traits affect ecosystem functioning?
- Does nitrogen or pathogen abundance modify the effects of root traits on functioning?
Is there selection for increased plant defense in species poor plant communities?
When: spring 2019 (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.
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.