Adam is an ecologist interested in plant-microbe and plant-insect interactions. His research investigates plant defences against herbivores, the ecology of arbuscular mycorrhizal fungi, and everything in-between. He usually employs experimental approaches in controlled environment (glasshouse/growth chamber) and field studies to tease apart the functional ecology of the interactions between mycorrhizal fungi, plants, and herbivores. He recently took up an ongoing position at the University of Southern Queensland in Australia.

Plant-insect interactions

My research career started back in Scotland as an undergraduate at the University of St Andrews. Here I was introduced for the first time to interactions between plants and insect herbivores. I remember being struck by the vast complexity of these interactions and the endless questions that could be asked to try and understand the ecology of these relationships. I began to read around the topic of silicon-based plant resistance to insect herbivores, the different responses between insect feeding guilds and the diversity of mechanisms through which silicon can affect plant-herbivore interactions (Massey et al., 2006; Massey and Hartley, 2009). The questions answered, and new ones raised in these studies enticed me to look into some of these questions myself, specifically around how silicon defences and aphids.

Australia and mycorrhizal fungi

Moving from Scotland to Australia didn’t come without some bumps, but I found a new home in the Hawkesbury Institute for the Environment at Western Sydney University. Working under the supervision of A.Prof. Scott Johnson and Prof. Jeff Powell I was able to continue with my interests in silicon-enhanced plant defence throughout my PhD. This time I was focussed on root-herbivores, mainly Dermolepida albohirtum (a.k.a the canegrub), but also other root-feeding scarab larvae. I was able to look at a range of aspects of plant defence ecology belowground, from how soil silicon defences function under elevated atmospheric CO₂ (Frew et al., 2017a), to understanding potential trade-offs between silicon and carbon-based plant defence (Cooke and Leishman, 2012; Frew et al., 2016).

Importantly, this was where my fascination with arbuscular mycorrhizal (AM) fungi began. I was interested in understanding how the mycorrhizal symbiosis can impact the capacity of plants to defend themselves against belowground herbivory. Specifically, I evaluated how different fungal communities affect root defences, and how AM fungi can augment silicon-based defences (Frew et al., 2017b, 2017b), depending on context of course.

Post-doc and beyond

After my PhD I moved to regional Australia (Wagga Wagga) when I was awarded a Charles Sturt University Postdoctoral Research Fellowship. The fellowship allowed me to delve further into the ecology of mycorrhizal fungal-plant-herbivore interactions. The work I was able to do as a post-doc laid the foundations for one of my current lines of research investigating some of the broader questions around how AM fungal diversity shapes plant defences.

My post-doc work mainly used crop species, but I also conducted experiments on a range of Australian native grasses to investigate how inoculation with different AM fungal communities affect plant performance and defence traits (Frew, 2020, 2019), and how aboveground herbivory can impact the AM symbiosis. A component of this was also to understand how components of climate change can affect AM fungal community composition, and what this might mean for plant-herbivore interactions (Frew and Price, 2019). For some of this work I was lucky enough to travel to Estonia to collaborate with Research Prof. Maarja Öpik and members of the Plant Ecology Laboratory at the University of Tartu.

More recently I took up an ongoing position at the University of Southern Queensland as a Lecturer and as an ecologist within the Centre for Crop Health. Here I’m continuing to investigate aspects of AM fungal ecology and plant-herbivore interactions, asking questions to develop our mechanistic understanding of how AM fungal communities affect plants and their interactions with insect herbivores. As well as teaching into several courses on ecology, environmental science and sustainability, I’m looking to build my research program and would welcome potential collaborators or research students who might share my interests.

Recommended reading

Functional Ecology consistently published exciting research, so it is difficult to pick favourites. But if its AM fungal-plant-herbivore interactions you’re interested in, then there are a few of particular note I recommend you check out (although there are many more to add to these):

• “Arbuscular mycorrhizal fungi mediate below-ground plant-herbivore interactions: a phylogenetic study” by Vannette and Rasmann (2012). This paper provides insight into how AM fungi can impact belowground herbivores, where root colonisation by the fungi were stronger predictors of herbivore performance than root chemical defences.
• “Arbuscular mycorrhizal fungi and aphids interact by changing host plant quality and volatile emission” by Babikova et al. (2014). Here the authors found AM fungi increase attractiveness of the host plant to herbivores (aphids), an effect which was associated with changes in the volatile organic compound emissions of the host plant, but this effect depended on the timing of AM fungal inoculation. They also found aphid infestation suppressed mycorrhizal colonisation, which is an interesting finding that relates to some of my recent research, still to be published.
• “Aphids can acquire the nitrogen delivered to plants by arbuscular mycorrhizal fungi” by Wilkinson, Ferrari, Hartley & Hodge (2019). In keeping with the AM fungi and aphid theme, this study used a cool experimental set-up to show that AM fungi transfer nitrogen from an organic source (not available to the host plant) to the aphid herbivores.

And if it’s silicon you’re interested in, there are many of these, but certainly check out the special issue on The Functional Role of Silicon in Plant Biology, in particular I recommend the review:

• “The ecology of herbivore-induced silicon defences in grasses” by Hartley and DeGabriel (2016), where the authors take a look at the induction of silicon-based plant defences and also consider the role of these defences in regulating populations of grazing herbivores. 

Finally, also relating to functional ecology silicon, I suggest the recent Perspective:

• “Is it time to include legumes in plant silicon research?” by Putra, Powell, Hartley & Johnson (2020). Most work on plant silicon is biased towards using grass species. This perspective highlights the important effects of silicon in Fabaceae species (legumes) and presents a model of how silicon may affect legume-rhizobia symbiotic interactions. Worth a read!

References

Babikova, Z., Gilbert, L., Bruce, T., Dewhirst, S.Y., Pickett, J.A., Johnson, D., 2014. Arbuscular mycorrhizal fungi and aphids interact by changing host plant quality and volatile emission. Functional Ecology 28, 375–385. doi:10.1111/1365-2435.12181

Cooke, J., Leishman, M.R., 2012. Tradeoffs between foliar silicon and carbon-based defences: evidence from vegetation communities of contrasting soil types. Oikos 121, 2052–2060.

Frew, A., 2020. Contrasting effects of commercial and native arbuscular mycorrhizal fungal inoculants on plant biomass allocation, nutrients and phenolics. Plants, People, Planet doi:10.1002/ppp3.10128.

Frew, A., 2019. Arbuscular mycorrhizal fungal diversity increases growth and phosphorus uptake in C₃ and C₄ crop plants. Soil Biology and Biochemistry 135, 248–250. doi:10.1016/j.soilbio.2019.05.015

Frew, A., Allsopp, P.G., Gherlenda, A.N., Johnson, S.N., 2017a. Increased root herbivory under elevated atmospheric carbon dioxide concentrations is reversed by silicon-based plant defences. Journal of Applied Ecology 54, 1310–1319.

Frew, A., Powell, J.R., Allsopp, P.G., Sallam, N., Johnson, S.N., 2017b. Arbuscular mycorrhizal fungi promote silicon accumulation in plant roots, reducing the impacts of root herbivory. Plant and Soil 419, 423–433. doi:10.1007/s11104-017-3357-z

Frew, A., Powell, J.R., Sallam, N., Allsopp, P.G., Johnson, S.N., 2016. Trade-offs between silicon and phenolic defenses may explain enhanced performance of root herbivores on phenolic-rich plants. Journal of Chemical Ecology 42, 768–771.

Frew, A., Price, J.N., 2019. Mycorrhizal-mediated plant-herbivore interactions in a high CO₂ world. Functional Ecology 33, 1376–1385. doi:10.1111/1365-2435.13347

Hartley, S.E., DeGabriel, J.L., 2016. The ecology of herbivore-induced silicon defences in grasses. Functional Ecology 30, 1311–1322.

Massey, F.P., Ennos, A.R., Hartley, S.E., 2006. Silica in grasses as a defence against insect herbivores: contrasting effects on folivores and a phloem feeder. Journal of Animal Ecology 75, 595–603.

Massey, F.P., Hartley, S.E., 2009. Physical defences wear you down: progressive and irreversible impacts of silica on insect herbivores. Journal of Animal Ecology 78, 281–291.

Putra, R., Powell, J.R., Hartley, S.E., Johnson, S.N., 2020. Is it time to include legumes in plant silicon research? Functional Ecology 34, 1142–1157. doi:https://doi.org/10.1111/1365-2435.13565

Vannette, R.L., Rasmann, S., 2012. Arbuscular mycorrhizal fungi mediate below‐ground plant–herbivore interactions: a phylogenetic study. Functional Ecology 26, 1033–1042. doi:10.1111/j.1365-2435.2012.02046.x

Wilkinson, T.D.J., Ferrari, J., Hartley, S.E., Hodge, A., 2019. Aphids can acquire the nitrogen delivered to plants by arbuscular mycorrhizal fungi. Functional Ecology 33, 576–586. doi:https://doi.org/10.1111/1365-2435.13283