Data from: Cascading effects of induced terrestrial plant defenses on aquatic and terrestrial ecosystem function

Herbivores induce plants to undergo diverse processes that minimize costs to the plant, such as producing defences to deter herbivory or reallocating limited resources to inaccessible portions of the plant. Yet most plant tissue is consumed by decomposers, not herbivores, and these defensive processes aimed to deter herbivores may alter plant tissue even after detachment from the plant. All consumers value nutrients, but plants also require these nutrients for primary functions and defensive processes. We experimentally simulated herbivory with and without nutrient additions on red alder (Alnus rubra), which supplies the majority of leaf litter for many rivers in western North America. Simulated herbivory induced a defence response with cascading effects: terrestrial herbivores and aquatic decomposers fed less on leaves from stressed trees. This effect was context dependent: leaves from fertilized-only trees decomposed most rapidly while leaves from fertilized trees receiving the herbivory treatment decomposed least, suggesting plants funnelled a nutritionally valuable resource into enhanced defence. One component of the defence response was a decrease in leaf nitrogen leading to elevated carbon : nitrogen. Aquatic decomposers prefer leaves naturally low in C : N and this altered nutrient profile largely explains the lower rate of aquatic decomposition. Furthermore, terrestrial soil decomposers were unaffected by either treatment but did show a preference for local and nitrogen-rich leaves. Our study illustrates the ecological implications of terrestrial herbivory and these findings demonstrate that the effects of selection caused by terrestrial herbivory in one ecosystem can indirectly shape the structure of other ecosystems through ecological fluxes across boundaries.

植食性动物会诱导植物启动多种进程以降低自身代价，例如产生防御物质以抵御植食行为，或是将有限资源重新分配至植物难以被取食的部位。然而绝大多数植物组织并非被植食性动物取食，而是被分解者消耗；且这些旨在抵御植食行为的防御进程，甚至会在植物组织脱离植株后仍改变其特性。所有消费者（包括取食者与分解者）均依赖营养物质生存，而植物自身的基础生理功能与防御进程同样需要这些营养元素。我们以北美西部诸多河流的主要落叶凋落物来源——红桤木（Alnus rubra）为实验材料，开展了添加与不添加营养元素的植食模拟实验。模拟植食行为诱导了植物的防御响应，并产生级联效应：陆生植食性动物与水生分解者对受胁迫植株叶片的取食率均有所降低。该效应具有环境依赖性：仅施加肥料的植株叶片分解速率最快，而施加肥料并接受植食处理的植株叶片分解速率最慢，这表明植物将具有营养价值的资源调配至增强防御的进程中。防御响应的其中一项表现为叶片氮含量下降，致使碳氮比（C:N）升高。水生分解者更偏好天然碳氮比较低的叶片，而这种改变后的营养特征在很大程度上解释了水生分解速率下降的原因。此外，陆生土壤分解者未受两种实验处理的影响，但确实表现出对本地来源与高氮含量叶片的偏好。本研究阐明了陆生植食行为的生态学意义，同时证实：某一生态系统中陆生植食性动物所引发的选择效应，可通过跨生态系统边界的生态通量，间接塑造另一生态系统的结构。