Data from: The effects of insects, nutrients, and plant invasion on community structure and function above- and belowground

Soil nutrient availability, invasive plants, and insect presence can directly alter ecosystem structure and function, but less is known about how these factors may interact. In this 6-year study in an old-field ecosystem, we manipulated insect abundance (reduced and control), the propagule pressure of an invasive nitrogen-fixing plant (propagules added and control), and soil nutrient availability (nitrogen added, nitrogen reduced and control) in a fully crossed, completely randomized plot design. We found that nutrient amendment and, occasionally, insect abundance interacted with the propagule pressure of an invasive plant to alter above- and belowground structure and function at our site. Not surprisingly, nutrient amendment had a direct effect on aboveground biomass and soil nutrient mineralization. The introduction of invasive nitrogen-fixing plant propagules interacted with nutrient amendment and insect presence to alter soil bacterial abundance and the activity of the microbial community. While the larger-scale, longer-term bulk measurements such as biomass production and nutrient mineralization responded to the direct effects of our treatments, the shorter-term and dynamic microbial communities tended to respond to interactions among our treatments. Our results indicate that soil nutrients, invasive plants, and insect herbivores determine both above- and belowground responses, but whether such effects are independent versus interdependent varies with scale.

土壤养分有效性、入侵植物与昆虫种群丰度可直接改变生态系统结构与功能，但学界对这些因子间的交互作用机制仍知之甚少。
本研究在弃耕地生态系统中开展了为期6年的野外实验，采用全因子交叉完全随机样地设计，对三项因子进行实验调控：昆虫丰度（降丰组与对照组）、入侵固氮植物的繁殖体压力（添加繁殖体组与对照组），以及土壤养分有效性（施氮组、减氮组与对照组）。

本研究发现，养分添加处理与昆虫丰度（在部分情境下）可与入侵植物的繁殖体压力产生交互作用，进而改变实验样地的地上与地下生态系统结构与功能。不出所料，养分添加处理对地上生物量与土壤养分矿化过程具有直接调控效应。入侵固氮植物繁殖体的引入可与养分添加处理及昆虫活动产生交互作用，进而改变土壤细菌丰度与微生物群落活性。

相较于生物量生产、养分矿化这类大尺度、长期的整体测量指标可响应实验处理的直接效应，短期且动态的微生物群落则更倾向于响应实验处理间的交互作用。本研究结果表明，土壤养分、入侵植物与昆虫植食者共同调控地上与地下生态系统的响应过程，但这类效应是独立还是相互依赖，会随观测尺度发生变化。