Data from: Silicon-induced root nodulation and synthesis of essential amino acids in a legume is associated with higher herbivore abundance

Ecologists have become increasingly aware that silicon uptake by plants, especially the Poaceae, can have beneficial effects on both plant growth and herbivore defence. The effects of silicon on other plant functional groups, such as nitrogen-fixing legumes, have been less well studied. Silicon could, however, indirectly promote herbivore performance in this group if reported increases in N2-fixation caused improvements in host plant quality for herbivores.
We tested how silicon supplementation in the legume Medico sativa affected plant growth rates, root nodulation and foliage quality (silicon content and amino acid profiles) for an insect herbivore (Acyrthosiphon pisum).
Plants supplemented with silicon (Si+) grew three times as quickly as those without supplementation (Si-), almost entirely in shoot mass. While root growth was unaffected by silicon uptake, root nodules containing nitrogen-fixing bacteria were 44% more abundant on Si+ plants. Aphid abundance was twice as high on Si+ plants compared to Si- plants and was positively correlated with silicon-stimulated plant growth.
Si+ plants accumulated more than twice as much silicon as Si- plants, but did not have higher silicon concentrations because of dilution effects linked to the rapid growth of Si+ plants. Si+ plants showed a 65% increase in synthesis of essential foliar amino acids, probably due to increased levels of root nodulation.
These results suggest that increased silicon supply makes M. sativa more susceptible to A. pisum, mainly because of increased plant growth and resource availability (i.e. essential amino acids). While silicon augmentation of the Poaceae frequently improves herbivore defence, the current study illustrates that this cannot be assumed for other plant families where the beneficial effects of silicon on plant growth and nutrition may promote herbivore performance in some instances.

生态学家愈发意识到，植物（尤其是禾本科（Poaceae））对硅的吸收，可同时对植物生长与植食性防御产生有益作用。而硅对其他植物功能群（如固氮豆科植物（nitrogen-fixing legumes））的影响则较少得到深入研究。不过，若已有研究显示固氮作用增强可提升植食性动物宿主植物的品质，那么硅可能会通过间接途径促进该类群植食性动物的生存表现。

本研究以固氮豆科植物紫花苜蓿（Medicago sativa）为对象，通过施加硅肥处理，探究其对植物生长速率、根瘤形成，以及为昆虫植食者豌豆蚜（Acyrthosiphon pisum）提供的叶片品质（硅含量与氨基酸谱）的影响。

施加硅肥的植株（Si+）生长速率是未施加硅肥植株（Si-）的三倍，其生物量增长几乎全部体现在地上部分。尽管硅吸收未对根系生长产生影响，但携带固氮细菌的根瘤在Si+植株上的丰度提升了44%。Si+植株上的豌豆蚜丰度是Si-植株的两倍，且与硅素刺激的植物生长呈正相关。

Si+植株的硅积累量是Si-植株的两倍以上，但由于其快速生长带来的稀释效应，Si+植株的硅浓度并未升高。Si+植株的叶片必需氨基酸合成量提升了65%，这可能与根瘤丰度增加有关。

本研究结果表明，硅素供应增加会使紫花苜蓿更易受豌豆蚜侵害，这主要源于植物生长与资源可获得性（即必需氨基酸）的提升。尽管对禾本科植物施加硅肥通常可增强其植食性防御能力，但本研究表明，这一结论无法推广至其他植物类群：硅对植物生长与营养的有益作用，在部分场景下可能反而会促进植食性动物的生存表现。