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+...

生态学家日益认识到，植物对硅的吸收——尤其是禾本科（Poaceae）植物——可同时对植物生长及植食性动物防御产生有益效应。硅对其他植物功能群（如固氮豆科植物）的影响则鲜有研究。但若已有研究表明，固氮作用的增强可提升植食性动物的寄主植物品质，那么硅可能会间接促进该类植物功能群中植食性动物的生存表现。
本研究以豆科植物紫花苜蓿（Medicago sativa）为对象，探究了硅补充处理对其生长速率、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。
经硅补充处理的植株（Si+）生长速率是未处理对照组（Si-）的三倍，其生长优势几乎完全体现在地上部生物量上。尽管根系生长不受硅吸收的影响，但携带固氮细菌的根瘤在Si+植株上的丰度提升了44%。Si+植株上的蚜虫丰度则是对照组的两倍……