Grassroots Support for a Threatened Habitat

Ecologists go underground to investigate how grass roots bear up against bugs.

Pests that feast on plant roots are a significant threat to Australia’s vulnerable grassland habitats.
Researchers have been investigating the ways grasses defend themselves against these insidious attacks. 

Root-eating herbivores, including beetles, can reduce plant productivity by up to 25%, slashing crop yields and threatening food production. Roots suck up nutrients and moisture from the soil to ensure plant re-growth and stability, so the whole plant suffers when its roots are ravaged. Remarkably, the combined mass of root herbivores can exceed that of sheep grazing on Australian pastures, yet as most research focuses on above-ground defences, little was known about how roots protect themselves. 

Scott Johnson, an associate professor at Western Sydney University, leads a multi-pronged project that adopts an innovative and holistic approach to investigate plant self-defence. “Beetle larvae have a below-ground phase that can last up to two years” explains Johnson. “They chew away at plant roots until the root loses all anchorage. This is a big problem during droughts”.

 In 2014, Johnson and fellow ecologist, Dr Ben Moore, tested the way in which grasses responded to attacks from root herbivores, including the greyback cane grub, a member of the scarab family. “Our early studies revealed how much silicon was in the roots. Silicon strengthens plants and helps them retain water, and we found that plants under attack took up extra silicon from the soil to defend themselves.”

Need to know

  • The combined weight of root-eating insects exceeds that of sheep on some pastures    
  • Root-munching herbivores can reduce plant productivity by up to 25%     
  • Research shows plants take strength from silicon to brace them-selves against attacks    

Johnson and his team of postdoctoral scientists and PhD students at the Hawkesbury Institute for the Environment are now investigating how they can exploit silicon to protect plants. One way is to increase silicon in the soil, as it can be rapidly depleted by nutrient-hungry crops. “We are working with Australian Steel Mill Services to see if we can reuse the by-product of steel production, calcium silicate, by adding it to soils. But first we have to test how ecosystems respond to such an intervention.” 

Climate change is at the forefront of this work. “We may see more pest outbreaks as the climate warms” said Johnson, “and droughts have highlighted the need for resilient crops”. Recent studies from Johnson’s team suggested that higher levels of carbon dioxide in the air reduces silicon uptake by plants, further weakening their defences. One solution may be to breed grasses to absorb more silicon.

The future of staple food crops could depend upon such research. “Root feeding grubs are the biggest threat to the sugarcane industry” says Kevin Powell from Sugar Research Australia. “They affect nearly every grower. If we don’t find a way to protect plants against pests — and there will be more of them as the climate warms — farmers will lose crops and money.”

The direction of Johnson’s research continues to respond to developments in the field of ecology. “We are now starting to look at the soil microbiome,” he says, “and how symbiotic microbes affect nutrient uptake.” 

Harnessing natural processes to help crops defend themselves could help sustainably safeguard the future of food. 

Meet the Academic | Associate Professor Scott Johnson

Scott is a community ecologist working on insect–plant interactions, particularly on pest species.

He gained his PhD from the University of York in the UK in 2002 and held a number of positions in the UK, including at the University of Reading and the Scottish Crop Research Institute (now The James Hutton Institute), before moving to Australia in 2011 to take up the position of Senior Lecturer.

His research group aims to identify novel approaches for managing pest species and preserving ecosystem services, based on a better understanding of how organisms within ecosystems interact.

This includes exploiting chemical signals used by insects to locate resources, enhancing biological control by increasing searching efficiency of the herbivores' natural enemies and using plant-microbes to help plants resist herbivore attack.Their principal work is on root-feeding and sap-sucking (e.g. aphid) herbivores, but within a community level context.

A major theme of the research involves understanding how atmospheric and climate change affects insect herbivores, especially in terms of ecosystem resilience, resistance breakdown in crops and disruption of behavioural interactions (e.g. predator-prey interactions, insect mutualisms).

In addition to his research, Scott is Unit Coordinator for Invertebrate Biology, the largest teaching unit administered through the Hawkesbury Institute for the Environment.


This research was supported by the Australian Government through the Australian Research Council.

© Dr James Ryalls/ Getty Images
Future-Makers is published for Western Sydney University by Nature Research Custom Media, part of Springer Nature.