BayCEER Workshop 2023

High Silicon Accumulation in Forbs: an Adaptation to Herbivore Pressure?

P 4.4 in Thinking sharp: Insights from inbetween

Silicon (Si) is recognized as a quasi-essential plant nutrient. However, details about specific functions and adaptations concerning Si in plants remain to be uncovered, especially in forbs. Many crop species and grasses have been shown to accumulate Si to deter herbivores. At the same time, forbs that show very high Si concentrations predominantly occur in environments considered to impose strong herbivore pressures. Here, I evaluate if high Si deposition evolved in forbs as an adaptation to herbivores. I integrated several experimental and observational approaches including the use of controlled, as well as natural growth- and feeding-conditions to test the overall hypothesis that herbivory in forbs is lower in plants with higher Si concentrations. Across approaches and across several pairs of closely related species ranging multiple angiosperm orders, no consistent decrease in herbivore preference was found with increasing leaf Si concentrations. However, in all species pairs with statistically significant preferences, higher herbivory occurred in the species with lower leaf Si concentrations. The results indicate that active Si accumulation cannot generally be considered an adaptation to herbivores in forbs but may play a role in smaller species subsets. Other selection factors like Carbon-limitation of growth are potentially more relevant for Si accumulation but remain to be investigated.

Keywords: Herbivore defense, Phytolith, wild plants, cafeteria experiment, feeding preference, plant-animal interactions, beneficial element