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 five and half 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 7 and a half weeks of work. This allows a larger project to be carried out.

Master projects last about one year and therefore constitute a substantial research project. We welcome students following the master in ecology and evolution and the masters in climate science.

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

Bug-Network: A global collaborative research network that aims to better understand the impact of invertebrate herbivores and pathogenic fungi on plant communities and ecosystems

Background: Invertebrate herbivores and fungal pathogens can strongly affect the diversity, structure and functioning of plant communities. However, we still have a limited idea of how generally important they are. One reason for our lack of knowledge is that the impact of consumers is likely to vary across environmental gradients. Lots of ecological theories have suggested that enemy impact depends on abiotic conditions at large spatial scales such as climate (latitude, altitude) and plant productivity, but also on abiotic and biotic drivers operating at smaller spatial scales, such as plant diversity and soil fertility (bottom-up) and predator abundance (top-down).
Our understanding of how consumer communities and their impact varies across environmental gradients is surprisingly limited. Existing studies differ substantially in methodology, making generalities across large scales difficult, which calls for comparative approaches that implement standardised protocols across sites. This is particularly important if we are to understand how global change drivers, such as climate and land use change, will alter consumer communities and their functioning.

The study: A powerful tool to quantify the variation in plant consumer communities and their impact are globally coordinated experiments, using standardized measurements and replicated experiments across ecological gradients. The “Bug-Network” will be such a project and aims to explore the general effects and context dependency of biotic interactions within a coordinated research network comprised of many grassland and shrubland sites worldwide. The BugNet has just started!
BugNet consists of a comparative part and an experimental part. For the comparative part we will characterize different plant communities and at the same time sample their invertebrate communities in different grasslands in Switzerland and elsewhere in Europe. We aim to test whether changes in the structure of invertebrate communities are driven by climatic factors or via changes in the plant community. For the experimental approach we will install a field experiment where we will exclude insects, fungal pathogens and molluscs using pesticides. We will observe how the plant community changes in response to enemy removal. The comparative part and the experimental parts will be replicated in many parts of the world – which offers exciting possibilities to answer pressing questions in community ecology.

You can find more information on the BugNet project on the website: bug-net.org

Potential projects: There are also numerous options for student projects in the Bug-Network. For instance projects could:

• Characterisation and sequencing of the global soil phyllosphere microbiome or soil microbial community using Bug-Network soil samples and determining the key environmental and biological effects that create variability in this system
• Determining the direct and indirect effects of broad scale envrionmental conditions on plant nutrient and fibre contents using globally collect plant material

To find out more about available student projects in the Bug-Network, contact Dr. Suz Everingham or Prof. Eric Allan.

 

Getting to the roots I: Belowground traits and plant fungal interactions to better understand plant-plant interactions and BEF relationships?

With: Gemma Rutten

Who: Bachelor/Master student

What: Experiments in the greenhouse or garden with a focus on belowground root traits and soil microbial communities.

Start: from Sept 2021 onwards

Background: Biodiversity ecosystem functioning research experimentally modifies the diversity of plant species in a community, many of these studies found that functioning (e.g. productivity) increases with diversity. Accordingly, ongoing biodiversity loss presents a major threat to ecosystem functioning and is an important driver of environmental change. A central mechanism for this effect of biodiversity is resource partitioning, which occurs when plants grown in mixtures have diverse traits that lead to a greater resource capture than in any that of any of the single species in monoculture. Yet, resource partitioning does not fully explain BEF-relationships. Besides partitioning, also facilitation might be an important mechanism driving BEF relationships.

To better understand the mechanisms underlying BEF relationships, we need to get to the roots of belowground plant-plant interactions but generally roots remain understudied -possibly because they are quite challenging to work with-. Recent evidence suggests that roots have more complex resource acquisition strategies than leaves. Even though both leaf and root traits span a conservation gradient from “live fast and die young” to “slow and steady”, most of the variation in root traits is actually explained by an orthogonal “collaboration” gradient, ranging from “do-it-yourself” resource uptake by fine roots to “outsourcing” of resource uptake to symbiotic mycorrhizal fungi. In this project, we ask if this two-dimensional root economics space can help predict the outcome of plant-plant interactions.

The study:  Plant species that range in functional root traits will be grown in monocultures and mixtures in a greenhouse or common garden. Depending on the students’ interest, the project can for example focus on disentangling direct plant-plant interactions from indirect effects of belowground microbes like mycorrhiza or quantify root plasticity along diversity gradient. Just contact me for more information or if you would like to discuss the possibilities.

Getting to the roots II: How mutualists and pathogens maintain tree diversity in a changing world?

With: Gemma Rutten

Who: Bachelor/Master student

What: Plant-soil feedback experiments with woody species in the field or garden.

Start: from sept 2021 onwards (field experiment march 2021)

Background: Over the last 20 years, plant-soil feedback research has become a prominent and fast advancing ecological discipline. However, within this discipline, forest studies are strongly underrepresented. However, trees are particularly interesting to look at in the context of PSFs as they vary in mycorrhizal type, unlike grassland species that have been the focus of many PSF studies so far. Most tree species associate with either arbuscular mycorrhiza (AMF) or ectomycorrhiza (EMF). In contrast to AMF, EMF form a Hartig net and mantle around the root, which provides a physical barrier between the plant tissue and the soil. This distinct morphology of the mycorrhizal type might affect a tree’s resistance to soil pathogens. First observational studies have pinpointed the contrasting effects of mycorrhizal type on PSF and negative density dependence, but validating experiments remain rare.

This study focuses on the interactions between tree species, fungal pathogens and mycorrhiza to reveal their role in future forest dynamics under climate change. Field observations will be used to study how the negative density dependence of temperate tree species varies along environmental gradients. To validate the causality of these observations and to reveal the underlying mechanisms, we use field manipulations and common garden experiments. Reciprocal sowing experiments in the field will allow us to test plant-soil feedbacks under natural conditions and soil inoculation experiments in a common garden help to isolate the role of mutualists and fungal pathogens in pairwise tree interactions.

The study:  Tree species that range in functional root traits will be selected grown in monocultures and mixtures in a greenhouse or common garden. Depending on the students’ interest, the project can focus on disentangling positive and negative PSFs of host and neighbouring in the field or common garden. Strength and direction of PSFs can be linked to recruitment patterns in the field or root traits and mycorrhizal colonization of the roots. Just contact me for more information or if you would like to discuss the possibilities.

Keywords: recruitment dynamics, belowground ecology; Tree-tree interactions; plant-fungal interactions, plant-soil feedbacks, root traits, mycorrhiza.

Biodiversity effects on ecosystem functioning: what roles do soil microorganisms play?

With: Eric Allan, Dr. Gemma Rutten, Maddy Thakur (IEE)

Start: Flexible

Background:

Many studies have shown that diverse communities have higher levels of ecosystem functioning than less diverse communities. There are many possible mechanisms that can explain this pattern. Among them, differences in soil communities between low- and high diversity plant communities are likely to be important in driving positive effects of plant diversity on ecosystem function. For instance, low diversity plant communities often accumulate specialist pathogens which reduces their performance over time, this is a phenomenon that is well known in agriculture and is one of the reasons that crop rotation is practiced (negative soil legacy effects). In contrast, the accumulation of specialist pathogens is generally lower in high diversity communities due to dilution effects (as many host plant species are available). Moreover, some studies suggest that diverse plant communities may even build up higher populations of mutualistic microbes such as mycorrhizae or beneficial bacteria.  Diverse plant communities may further function better because different plant species use soil nutrients differently and therefore a diverse plant community has more efficient resource use overall. These effects might also interact so that functioning (e.g., plant biomass) is enhanced most when diverse plant communities grow on soil coming from diverse plant communities (positive soil legacy effects), and soils from low diversity and monocultures inhibit their growth (negative soil legacy effects). This could explain the frequent observation that ecosystem functioning increases with plant diversity and that these effects become more positive over time due to increase of legacy effects. However, the interactions between changes in soil (microbial) communities and plant diversity in driving diversity functioning effects have rarely been tested.

In addition, land use might affect the build-up of legacy effects in soils. Positive effects of soils from diverse plant communities (positive soil legacy effects) might be reduced in fertilized conditions. This would be expected if nitrogen fertilization reduces the buildup of mutualist microorganisms (e.g., rhizobacteria or mycorrhizal fungi) at high diversity, or if it leads to an overall increase in pathogens (e.g., pathogenic fungi, oomycetes). Similarly, positive soil legacy effects might be reduced if diverse plant communities are made up of fast-growing plant species. Fast growing plant species typically accumulate more pathogens than slow growing ones due to lesser defense in fast growing plants, and therefore pathogens may not be diluted in communities containing a high diversity of fast-growing plant species.

Methods: To test the importance of soil legacy effects and plant diversity in driving ecosystem functioning, we will sample soils from a large diversity experiment in Münchenbuchsee. Experimental plant communities with 1, 4, 8 or 20 species were established in 2015 and have been maintained since then. We will sample soils from communities differing in plant diversity and establish a greenhouse experiment using these soils. We will then grow 1, 4 and 8 species communities on each of the soils, to generate a full cross of soil diversity legacy and current plant diversity. This will allow us to test whether soil legacy or current diversity has a larger effect on functioning and also whether they interact, e.g., whether current diverse plant communities perform the best on soils from diverse communities. We will also sample soil from plots that have been treated with Nitrogen and from two different diversity gradients. Plots with 1, 4 and 8 species can contain either only slow or only fast-growing species and we will test whether assembling communities with these different types of plants leads to different soil history and diversity effects. We will measure above- and belowground biomass production as ecosystem functions. We could also measure additional functions such as soil enzymatic activities or decomposition. We will further quantify soil microbial communities using the molecular methods.

Possible questions to test for this project:

• How important are soil history and current diversity in affecting ecosystem functioning?
• Do negative soil legacy effects on soils collected from monocultures switch to positive legacy effects when soils are collected from more diverse plant communities?
• Does nitrogen reduce the positive effects of soil legacy on ecosystem function?
• Are positive soil legacy effects reduced when fast growing species are present in diverse plant communities?