During environmental change, invasive species may be favored by increased resource input or reduced resource use of the resident community. Plasticity in certain plant traits of invasive species may be one possible mechanism behind their ability to quickly exploit unused resources. We tested whether rainfall manipulations (severe drought, moderate drought, watering) alter the growth and reproductive success of the invasive annual Conyza canadensis, and if it translates into a change in the abundance of the species in a semiarid perennial grassland in Central Hungary. Overall, C. canadensis exhibited greater individual performance and higher abundance in drought plots than in control and watered plots. At individual level, plants showed the strongest response to moderate drought: they grew 2.5-times taller than in control and watered plots, and produced twice and 2.5-times more seeds than in watered and control plots, respectively. Reproductive phenology was advanced in response to rain exclusions. Although severe drought caused 40% mortality, the cumulative performance of C. canadensis, expressed as plot-level aboveground biomass, was consistently greater in severe drought plots than in control and watered plots throughout the 3 years of the study. The higher performance of C. canadensis in drought plots is most likely due to the decreased abundance and, thus, decreased competitive effect of previously dominant perennial grasses caused by the rain exclusions. We conclude that drier summers that suppress perennial grasses will favor this alien annual forb, and phenotypic plasticity in growth and reproduction may contribute to its invasion success.

在环境变化期间，增加资源投入或减少居民社区对资源的使用可能会有利于入侵物种。入侵物种某些植物性状的可塑性可能是其迅速开发未利用资源的能力背后的一种可能机制。我们测试了降雨的操作（严重干旱，中度干旱，浇水）是否会改变入侵的一年生加拿大康乃滋的生长和繁殖成功，以及是否转化为匈牙利中部半干旱多年生草地物种的丰度变化。总体而言，加拿大念珠菌与对照和浇水样地相比，干旱地块表现出更好的个体表现和更高的丰度。在个体水平上，植物对中度干旱表现出最强的响应：它们的生长比对照和浇水地高2.5倍，种子产量分别比浇水和对照地高两倍和2.5倍。对雨水的排斥反应使生殖物候发展。尽管严重干旱导致40％的死亡率，但在整个研究的3年中，严重干旱区的加拿大油菜累积表现（以地块级地上生物量表示）始终高于对照区和浇水区。加拿大念珠菌的更高性能干旱地区的干旱很可能是由于丰度的下降，以及由雨水排斥引起的以前占优势的多年生草的竞争效应下降。我们得出的结论是，抑制多年生草的较干燥的夏季将有利于这种外来的一年生杂草，生长和繁殖的表型可塑性可能有助于其入侵成功。