Lichens often grow in microhabitats where they are exposed to severe abiotic stresses such as desiccation and temperature extremes. They are also often exposed to levels of light that are greater than lichen photobionts can use in carbon fixation. Unless regulated, excess energy absorbed by the photobionts can convert ground state oxygen to reactive oxygen species (ROS). These ROS can attack the photosynthetic apparatus, causing photoinhibition and photo-oxidative stress, reducing the ability of the photobionts to fix carbon. Here, we outline our current understanding of the effects of high light on lichens and the mechanisms they use to mitigate or tolerate this stress in hydrated and desiccated states. Tolerance to high light can be achieved first by lowering ROS formation, via synthesizing light screening pigments or by thermally dissipating the excess light energy absorbed; second, by scavenging ROS once formed; or third, by repairing ROS-induced damage. While the primary focus of this review is tolerance to high light in lichen photobionts, our knowledge is rather fragmentary, and therefore we also include recent findings in free-living relatives to stimulate new lines of research in the study of high light tolerance in lichens.

中文翻译：

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地衣的光保护：光生物对高光的适应

地衣通常生长在微生境中，在那里它们会受到严重的非生物胁迫，例如干燥和极端温度。它们也经常暴露在比地衣光生物可以用于碳固定的光照水平下。除非受到监管，否则光生物吸收的多余能量可以将基态氧转化为活性氧 (ROS)。这些 ROS 可以攻击光合装置，引起光抑制和光氧化应激，降低光生物固碳的能力。在这里，我们概述了我们目前对高光对地衣的影响的理解，以及它们在水合和干燥状态下用来减轻或耐受这种压力的机制。首先可以通过降低 ROS 的形成来实现对强光的耐受性，通过合成遮光颜料或通过热耗散吸收的多余光能；第二，通过清除一旦形成的ROS；第三，通过修复 ROS 引起的损伤。虽然这篇综述的主要焦点是地衣光生物对强光的耐受性，但我们的知识相当零碎，因此我们还包括最近在自由生活亲属中的发现，以激发地衣高光耐受性研究的新研究方向。