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.

生态学家日益意识到，植物（尤其是禾本科（Poaceae））对硅的吸收，可同时促进植物生长并增强其抵御植食性昆虫的能力。但学界对硅在其他植物功能群（如固氮豆科植物）上的效应研究尚不充分。不过，若固氮作用增强可提升寄主植物的品质，进而改善植食性昆虫的寄主适宜性，那么硅或可间接促进该类植物上植食性昆虫的种群表现。
本研究以固氮豆科植物紫花苜蓿（Medicago sativa）为研究对象，探究硅肥施用对其生长速率、根瘤形成，以及作为昆虫植食者豌豆蚜（Acyrthosiphon pisum）寄主的叶片品质（硅含量与氨基酸谱）的影响。
施用硅肥的植株（Si+组）生长速率为未施用组（Si-组）的3倍，该生长优势几乎完全体现在地上部生物量上。尽管硅吸收未对根系生长产生显著影响，但携带固氮细菌的根瘤数量在Si+组植株上增加了44%。Si+组植株上的豌豆蚜种群数量为Si-组的2倍，且与硅诱导的植物生长呈显著正相关。
Si+组植株的硅积累量是Si-组的2倍以上，但由于快速生长带来的稀释效应，其硅浓度并未显著升高。此外，Si+组植株的叶片必需氨基酸合成量提升了65%，这可能与其根瘤形成水平升高密切相关。
上述结果表明，硅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提升与资源可获得性（即必需氨基酸）的增加。尽管对禾本科植物施用硅通常可增强其植食性防御能力，但本研究显示，这一结论无法推广至其他植物类群——在这些类群中，硅对植物生长与营养的有益作用，在部分情境下反而会促进植食性昆虫的种群表现。