New phD project

How elevated CO2 drives invertebrate interactions and community changes in grasses

This is a fully funded PhD project open to Australian and International applicants

Increases in atmospheric CO2 concentrations have the capacity to shape plant-herbivore interactions with wider impacts on other trophic groups. Previous work in a grassy woodland exposed to current and future (+150ppm) concentrations of CO2 (EucFACE in Australia) suggested that invertebrate populations had already declined by around 14% under elevated CO2 (eCO2) (Facey et al., 2017). It remains unclear, however, which species were in decline, whether significant functional groups were affected or if populations have now stabilised. Simultaneously, several grasses in the understory show altered levels of silicon defence against invertebrate herbivores under eCO2, which may explain some of the underlying changes in invertebrate communities.

Application Details

Our group is interested in the functional role of silicon in plants, particularly in terms of how it defends plants against herbivores and helps grasses cope with climate change such as drought and rising CO2 concentrations. Silicon defends plants against herbivory by toughening tissues, forming physical structures (e.g. spines or phytoliths) and influencing other chemical defences. At the same time, higher levels of CO2 cause plants to take up less silicon, which could make them more susceptible to herbivores with cascading effects on higher trophic groups (Ryalls et al. 2017; Johnson & Hartley, 2018).

Interestingly, silicon is an inducible defence so when herbivores attack, many grasses acquire more silicon from the soil and deposit it in their leaves. This is an irreversible process so the plant is subsequently defended against new herbivore attack. In a way, herbivores may therefore compete with one other even though they have never shared the plant at the same time. This phenomenon is sometimes called ‘the ghost of competition past’ but has not been investigated in the context of silicon defences.

How will the project work?

The successful candidate will design the project, but we envisage it having two approaches:

 

1. Field. Sampling invertebrates from the grassy Eucalypt woodland exposed to ambient and elevated atmosphere CO2 – EucFACE. In collaboration with NatureMetrics in the UK, invertebrates will be sent for DNA barcoding to identify changes in community composition. Changes in grass silicon will be measured simultaneously in order to explore relationships between changes in silicon defence and invertebrates (e.g. herbivores and their natural enemies).

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2. Controlled manipulative experiments. These could be based in open top chambers (field-based) or the glasshouse. Experiments will challenge grasses grown under the same CO2 conditions as EucFACE with herbivores and determine outcomes for higher trophic groups (e.g. predators) and competing herbivores. Ideally, the project would use the same invertebrate and plant species as in EucFACE to link the two components.       

 

In addition to student stipend, conference allowance and consumables the student will have access to casual assistance for conducting fieldwork. We also work closely with the lab of Professor Sue Hartley in the UK so there is an option for further collaboration with this project.

Hawkesbury Institute for the Environment (HIE) Western Sydney University

© 2019 Scott Johnson