Extreme climate events, such as drought, are becoming increasingly important drivers of plant community change, yet little is known about their impacts on invasive plants. Further, drought impacts may be altered by other anthropogenic stressors, such as eutrophication. We found drought dramatically reduced density of invasive Lepidium latifolium in salt marshes, and this die-back was mitigated by nutrient addition. In a 3-year field experiment (2014-2016) conducted during an unprecedented drought (2012-2015), we tracked the effects of drought and nutrient addition on the plant community. We conducted this research at four salt marshes across a salinity gradient in the San Francisco Bay, CA, USA. We manipulated paired native and invaded plots, half of which were treated monthly with N and P for 1.5 years during the most intense period of the drought and one subsequent wet winter. In addition, we monitored unmanipulated L. latifolium-invaded transects within our freshest and most saline sites throughout the three years of our manipulative experiment and one additional wet winter. We documented a dramatic die-back of invasive L. latifolium during extreme drought, with reductions in stem density (52%-100%) and height (17%-47%) that were more severe at low salinity sites than high salinity sites. We found nutrient application lessened the effect of drought on L. latifolium stem density, but not height. In native plots, extreme drought reduced native plant cover (4%-24%), but nutrient addition mitigated this impact. Interestingly, native plants in invaded plots did not suffer reductions in cover due to drought, perhaps because they were simultaneously benefiting from the die-back of the invader. Our results show drought negatively impacted both native and invasive plants and this impact was stronger on the invader, which experienced persistent declines two years after the end of the drought. However, by mitigating the effect of drought on invasive plants, nutrient addition potentially erased the advantage drought provided native plants over invasive plants under ambient nutrient conditions.

中文翻译：

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营养素减轻极端干旱对植物入侵的影响

干旱等极端气候事件正成为植物群落变化越来越重要的驱动因素，但人们对其对入侵植物的影响知之甚少。此外，干旱影响可能会被其他人为压力因素改变，例如富营养化。我们发现干旱显着降低了盐沼中侵入性阔叶兰的密度，并且通过添加营养物减轻了这种枯死。在史无前例的干旱（2012-2015）期间进行的为期 3 年的田间试验（2014-2016）中，我们追踪了干旱和养分添加对植物群落的影响。我们在美国加利福尼亚州旧金山湾盐度梯度的四个盐沼中进行了这项研究。我们操纵成对的原生地块和入侵地块，其中一半每月用 N 和 P 处理 1 次。5 年是干旱最严重的时期，随后是一个潮湿的冬天。此外，我们在三年的操纵实验和一个额外的潮湿冬季期间，在我们最新鲜和盐分最多的地点监测了未经操纵的阔叶林入侵横断面。我们记录了极端干旱期间入侵 L. latifolium 的戏剧性枯萎，茎密度 (52%-100%) 和高度 (17%-47%) 的降低在低盐度地点比高盐度地点更为严重。我们发现施肥减少了干旱对阔叶树茎密度的影响，但没有减少对高度的影响。在原生地块中，极端干旱减少了原生植物覆盖率 (4%-24%)，但添加养分减轻了这种影响。有趣的是，入侵地块中的本地植物并未因干旱而减少覆盖，也许是因为他们同时受益于入侵者的消亡。我们的结果表明干旱对本地植物和入侵植物都产生了负面影响，这种影响对入侵者的影响更大，在干旱结束两年后，入侵者经历了持续下降。然而，通过减轻干旱对入侵植物的影响，在环境营养条件下，营养添加可能消除了干旱为本地植物提供的优于入侵植物的优势。