Predicting vegetation responses to increased future drought is challenging, owing to the complex interaction of multiple factors influencing both plant drought resistance and local climatic conditions, each of which may be subject to spatial and temporal heterogeneity. We conducted a detailed study of potential mechanisms underlying an elevational gradient in mortality that has characterized recent population declines of a threatened alpine plant, the Haleakalā silversword (Argyroxiphium sandwicense subsp. macrocephalum). We used a pair of greenhouse experiments staged at high and low elevations to test the influences of plasticity (to contrasting soil water availability and atmospheric conditions) and heredity (different seed source elevations) on the development of functional traits associated with drought resistance and on performance in a terminal drought. We then out‐planted a subset of plants into three common‐garden plots near the bottom, middle, and top of the silversword elevational range, and tracked growth and survival over 3.5 yr. A range of morphological traits (root and leaf mass fractions, specific leaf area, leaf area ratio, and root length per shoot mass) exhibited either heritable variation or plasticity or both. Among physiological traits measured, only water use efficiency exhibited a plastic treatment response. Survival of out‐plants was influenced during the first year by a home site advantage, and by the water treatment imposed in the greenhouses, with high water plants dying more often than low water plants. These effects subsequently dissipated, being replaced over the final 1.5 yr by a strengthening out‐plant site effect: survival was positively associated with site elevation, matching the pattern of mortality observed in the wild population. The balance of information suggests this pattern stems from lower elevation plants being less drought resistant than higher elevation plants, owing principally to plasticity, and thus suffering greater mortality during recent dry seasons. The pattern may be enhanced by stronger deviations from typical climatic conditions at lower elevations. Our findings suggest that future management should focus on climatically suitable habitat rather than advantageous genetic ecotypes. More broadly, they provide evidence that clinal variation can be important to consider when modeling future vegetation responses to climate change.

中文翻译：

---

抗旱性的最终变化塑造了过去人口的减少以及受威胁植物的未来管理

由于影响植物抗旱性和当地气候条件的多种因素之间的复杂相互作用，预测植被对未来干旱加剧的反应具有挑战性，而每种因素都可能受到时空异质性的影响。我们进行的潜在机制基本死亡率的海拔梯度进行详细的研究已经表征近期人口威胁的高山植物的下降，在哈雷阿卡拉silversword（Argyroxiphium sandwicense亚种。macrocephalum）。我们使用了在高海拔和低海拔上进行的一对温室实验，以测试可塑性（与对比的土壤水分和大气条件）和遗传（不同的种子源高度）对与抗旱性相关的功能性状发展和性能的影响。在极端干旱中。然后，我们在银剑海拔范围的底部，中部和顶部附近，将一部分植物移植到三个常见的花园地块中，并跟踪了3.5年以上的生长和存活情况。一系列形态特征（根和叶的质量分数，比叶面积，叶面积比和每枝茎的根长）表现出可遗传的变异或可塑性，或两者兼而有之。在测量的生理特征中，仅水分利用效率表现出可塑性处理响应。外来植物的生存在第一年受到家庭所在地优势以及温室中水处理的影响，高水生植物比低水生植物更容易死亡。这些作用随后消失，在最后的1.5年中被增强的厂外部位效应所代替：存活与部位升高成正相关，与在野生种群中观察到的死亡率模式相符。信息的平衡表明，这种模式是由于海拔较低的植物比海拔较高的植物抗旱性较低，主要是由于可塑性，因此在最近的旱季死亡率更高。可以通过与较低海拔处的典型气候条件之间更大的偏差来增强样式。我们的发现表明，未来的管理应着眼于气候适宜的栖息地，而不是有利的遗传生态型。从更广泛的意义上讲，它们提供了证据，说明在模拟未来植被对气候变化的响应时，考虑斜面变化可能很重要。