Scott N. Johnson, James M.W. Ryalls, Craig V.M. Barton, Mark G. Tjoelker, Ian J. Wright & Ben D. Moore

Grass roots
Grass roots

Traditionally not seen as an essential plant nutrient, silicon (Si) has been revealed to have numerous functional roles in plants – especially grasses. It’s particularly useful for relieving the adverse effects of stress, including drought, pathogens and insect attackers. The mechanisms remain controversial, but Si is known to strengthen plant tissues which can makes them harder to eat – particularly for insects that chew on plant tissues. Grasses get Si exclusively from the soil via their roots using passive (e.g. transpiration stream) and, in many cases, active uptake. In this field study, we established that Si was associated with increased biomechanical properties of grass (Phalaris aquatica) leaves and reduced growth rates (–56%) of a global pest (the cotton bollworm, Helicoverpa armigera). Si addition also promoted growth in shoots (+48%) and roots (+61%). However, environmental conditions such as warmer temperatures might impact Si accumulation and consequently resistance to herbivores. We tested this by warming half of our field plots by around 3°C. We saw a 17% decrease in Si uptake compared to grasses growing under ambient temperatures. But adding Si to the plots increased Si uptake in warmed plots to levels seen under ambient temperatures. Beneficial effects of Si addition on plant growth and reduced herbivore performance, however, were stronger under ambient temperatures than warmed conditions. In conclusion, Si uptake under warmer conditions can be restored with Si supplementation but Si-enhanced biomechanical defences against a global pest might not be fully restored.

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