Introduced garden plants are strong competitors of native and alien residents under simulated climate change

1) Most invasive plants have been originally introduced for horticultural purposes. Still, most alien garden plants have not naturalized yet, probably due in part to inadequate climatic conditions. Climate change may alter this, but few experimental studies have addressed this for non-naturalized alien garden plants, and those that have, addressed only singular aspects of climate change.
2) In a greenhouse experiment, we examined the performance of nine non-naturalized alien herbaceous garden plants of varying climatic origins in response to simulated climate warming and reduced water availability, in a factorial design, as projected for southern Germany. To assess their invasion potential, we grew the species in competition with resident native and already-naturalized alien species.
3) Reduced watering negatively affected non-naturalized garden plants, as well as the native and naturalized competitors, particularly at higher temperatures. However, non-naturalized aliens performed better relative to competitors when temperatures increased. Naturalized and native resident competitor responses to climate change were both negative, but across climate treatments, non-naturalized aliens, irrespective of their climatic origins, performed better against native than against naturalized competitors.
4) Synthesis. We conclude that relative performance compared to resident species may increase for non-naturalized alien garden plants under climate change, as resident species become less competitive. Ongoing climate change is therefore likely to promote naturalization of commonly-planted alien herbaceous species.

1) 多数入侵植物最初均以园艺用途引入。然而，多数外来园艺植物尚未完成归化，这在一定程度上可能源于不适宜的气候条件。气候变化或可改变这一现状，但针对未归化外来园艺植物的相关实验研究仍较为匮乏，且已有的相关研究仅关注气候变化的单一维度。
2) 本研究依托温室实验，采用针对德国南部未来气候情景设计的析因设计，模拟气候增温与水分有效性降低的双重胁迫，探究9种来源气候各异的未归化外来草本园艺植物的生长表现。为评估其入侵潜力，我们将供试物种与本土常驻物种及已归化外来物种进行混栽培养。
3) 水分减少对未归化园艺植物、本土及已归化竞争者均产生负面影响，且该效应在高温环境下尤为显著。但当温度升高时，未归化外来植物相较于竞争者的表现更为优异。已归化与本土常驻竞争者对气候变化的响应均为负面，但在所有气候处理组中，无论来源气候类型如何，未归化外来植物与本土竞争者的适配性均优于其与已归化竞争者的适配性。
4) 综合分析。本研究结论如下：气候变化背景下，未归化外来园艺植物相较于常驻物种的相对表现或可提升，因常驻物种的竞争能力会有所下降。因此，持续发生的气候变化或可推动广泛种植的外来草本园艺植物完成归化。