Plant silicon defences suppress herbivore performance, but mode of feeding is key

The performance of herbivorous animals depends on the nutritional and defensive traits of the plants they consume. The uptake and deposition of biogenic silicon in plant tissues is arguably the most basic and ubiquitous anti-herbivore defence used by plants, especially the grasses. We conducted meta-analyses of 150 studies reporting how vertebrate and invertebrate herbivores performed when feeding on silicon-rich plants relative to those feeding on low silicon plants. Silicon levels were 52% higher and 32% more variable in silicon-rich plants compared to plants with low silicon, which resulted in an overall 33% decline in herbivore performance. Fluid-feeding herbivore performance was less adversely impacted (–14%) than tissue-chewing herbivores, including mammals (–45%), chewing arthropods (–33%) and plant-boring arthropods (–39%). Fluid-feeding arthropods with a wide diet breadth or those feeding on perennial plant species were mostly unaffected by silicon defences. Unlike many other plant defences, where diet specialisation often helps herbivores overcome their effects, silicon negatively impacted herbivores regardless of diet breath. We conclude that silicon defences primarily target chewing herbivores and impact vertebrate and invertebrate herbivores to a similar degree.

植食性动物的生存表现，取决于其所取食植物的营养特性与防御性状。植物组织中生物源硅（biogenic silicon）的吸收与沉积，堪称植物（尤其是禾本科植物）所采用的最基础、最普遍的抗植食性防御（anti-herbivore defence）手段。我们针对150项相关研究开展了荟萃分析（meta-analyses），这些研究对比了脊椎动物与无脊椎动物植食者在取食富硅植物与低硅植物时的生存表现差异。与低硅植物相比，富硅植物的硅含量平均高出52%，且变异程度高32%，这一差异整体导致植食性动物的生存表现下降了33%。取食汁液的植食性动物所受的负面影响（下降14%）弱于组织咀嚼型植食性动物，其中包括哺乳类（下降45%）、咀嚼式节肢动物（arthropods）（下降33%）以及钻蛀植物的节肢动物（下降39%）。食性范围较广的汁液取食节肢动物，或是取食多年生植物的类群，基本不受硅基防御的影响。与多数其他植物防御机制不同——后者通常可通过食性特化帮助植食性动物克服其防御效果——硅基防御会对植食性动物产生负面影响，且不受其食性宽度的影响。我们的研究结论表明，硅基防御主要针对咀嚼型植食性动物，且对脊椎动物与无脊椎动物植食者的影响程度相近。