Plant functioning and survival in drylands are affected by the combination of high solar radiation, high temperatures, low relative humidity, and the scarcity of available water. Many ecophysiological studies have dealt with the adaptation of plants to cope with these stresses in hot deserts, which are the territories that have better evoked the idea of a dryland. Nevertheless, drylands can also be found in some other areas of the Earth that are under the Mediterranean-type climates, which imposes a strong aridity during summer. In this review, plant species from hot deserts and Mediterranean-type climates serve as examples for describing and analyzing the different responses of trees and shrubs to aridity in drylands, with special emphasis on the structural and functional adaptations of plants to avoid the negative effects of high temperatures under drought conditions. First, we analyze the adaptations of plants to reduce the input of energy by diminishing the absorbed solar radiation through (i) modifications of leaf angle and (ii) changes in leaf optical properties. Afterwards, we analyze several strategies that enhance the ability for heat dissipation through (i) leaf size reduction and changes in leaf shape (e.g., through lobed leaves), and (ii) increased transpiration rates (i.e., water-spender strategy), with negative consequences in terms of photosynthetic capacity and water consumption, respectively. Finally, we also discuss the alternative strategy showed by water-saver plants, a common drought resistance strategy in hot and dry environments that reduces water consumption at the expense of diminishing the ability for leaf cooling. In conclusion, trees and shrubs living in drylands have developed effective functional adaptations to cope with the combination of high temperature and water scarcity, all of them with clear benefits for plant functioning and survival, but also with different costs concerning water use, carbon gain, and/or leaf cooling.

中文翻译：

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生活在旱地：树木和灌木的功能适应以应对高温和缺水

高太阳辐射，高温，低相对湿度和可用水的缺乏共同影响着干旱地区的植物功能和生存。许多生态生理学研究涉及植物的适应以应对炎热沙漠中的这些压力，而沙漠是最能唤起干旱地区思想的领域。尽管如此，在地中海型气候下的地球上其他一些地区也可以找到干旱地区，这在夏季造成了强烈的干旱。在这篇评论中，来自炎热沙漠和地中海型气候的植物物种可作为示例，描述和分析树木和灌木对干旱地区干旱的不同反应，特别强调植物的结构和功能适应性，以避免干旱条件下高温的负面影响。首先，我们通过（i）改变叶片角度和（ii）改变叶片的光学特性，通过减少吸收的太阳辐射来分析植物的适应性，以减少能量的输入。之后，我们分析了几种通过以下方式增强散热能力的策略：（i）减小叶片尺寸和改变叶片形状（例如，通过浅叶叶片），以及（ii）提高蒸腾速率（即节水策略），分别对光合能力和耗水量有负面影响。最后，我们还讨论了节水植物展示的替代策略，一种在炎热和干燥环境中的常见抗旱策略，它以减少叶片冷却能力为代价的方式减少了用水量。总之，生活在干旱地区的树木和灌木丛已开发出有效的功能适应措施，以应对高温和缺水的综合影响，它们对植物的功能和生存都有明显的好处，但在用水，碳增加，和/或叶片冷却。