Geographic range limits of species are often a reflection of their ecological niche limits. In many organisms, important niche limits that coincide with distribution limits are warm and warm-dry conditions. We investigated the effects of heat and drought, as they can occur at the warm end of distribution. In a greenhouse experiment, we raised North American Arabidopsis lyrata from the centre of its distribution as well as from low- and high-latitude limits under average and extreme conditions. We assessed plant growth and development, as well as leaf and root functional traits, and tested for a decline in performance and selection acting on growth, leaf, and root traits. Drought and heat, when applied alone, lowered plant performance, while combined stress caused synergistically negative effects. Plants from high latitudes did not survive under combined stress, whereas plants originating from central and low latitudes had low to moderate survival, indicating divergent adaptation. Traits positively associated with survival under drought, with or without heat, were delayed and slowed growth, though plastic responses in these traits were generally antagonistic to the direction of selection. In line, higher tolerance of stress in southern populations did not involve aspects of growth but rather a higher root-to-shoot ratio and thinner leaves. In conclusion, combined heat and drought, as can occur at southern range edges and presumably more so under global change, seriously impede the long-term persistence of A. lyrata, even though they impose selection and populations may adapt, though under likely interference by considerable maladaptive plasticity.

物种的地理范围限制通常反映了其生态位限制。在许多生物体中，与分布限制相一致的重要生态位限制是温暖和暖干条件。我们研究了高温和干旱的影响，因为它们可能发生在分布的温暖端。在温室实验中，我们在平均和极端条件下从其分布中心以及低纬度和高纬度范围种植北美拟南芥。我们评估了植物的生长和发育，以及叶和根的功能性状，并测试了对生长、叶和根性状的性能和选择的下降。干旱和高温单独施用时会降低植物性能，而联合胁迫则会产生协同负面影响。来自高纬度地区的植物在联合胁迫下无法存活，而来自中纬度和低纬度地区的植物则具有低至中等的存活率，表明适应能力存在差异。与干旱条件下生存呈正相关的性状，无论有没有高温，都会延迟并减慢生长，尽管这些性状的可塑性反应通常与选择方向相反。同样，南方种群对压力的更高耐受性并不涉及生长方面，而是涉及更高的根冠比和更薄的叶子。总之，炎热和干旱的结合，正如南部山脉边缘可能发生的那样，在全球变化下可能更是如此，严重阻碍了琴弦琴的长期存在，尽管它们强加了选择，并且种群可能会适应，尽管可能会受到以下因素的干扰：相当大的适应不良可塑性。