A comparative analysis of the photoprotection hypothesis for the evolution of autumn colors

The adaptive value of autumn colors – the seasonal production of red anthocyanins observed in many species of trees and shrubs – is still debated. According to the photoprotection hypothesis, anthocyanins protect leaves from photoinhibition and photooxidation at low temperatures, enabling the tree to reabsorb nutrients more efficiently before leaf fall. Hence, the hypothesis predicts that autumn colors are more likely to evolve in species growing in colder environments. We tested this prediction by comparing the climatic parameters of 237 North American tree species. We found that, while species with yellow autumn leaves grow under lower minimum temperatures than species with green leaves, there is no significant difference in temperaturebetween species with red autumn leaves and species with green or yellow autumn leaves. We conclude that, while reabsorbing chlorophyll in autumn, and the consequent unmasking of yellow carotenoids, may be an adaptation to cold temperatures, the producti...秋季叶色的适应值——即诸多乔木与灌木物种中观测到的季节性红色花青素（anthocyanins）合成现象——至今仍存在争议。根据光保护假说（photoprotection hypothesis），花青素可在低温环境下保护叶片免受光抑制与光氧化损伤，使树木能够在落叶前更高效地重新吸收营养物质。因此该假说预测，在低温环境中生长的物种更易演化出秋季叶色。本研究通过对比237种北美乔木的气候参数，对该预测进行了验证。研究结果显示：尽管秋季叶色为黄色的物种相比绿叶物种所处的最低温度更低，但秋季叶色为红色的物种与绿叶或黄叶物种之间的温度条件并无显著差异。本研究最终认为，尽管秋季叶绿素（chlorophyll）的重吸收以及由此显现的黄色类胡萝卜素（carotenoids）可能是对低温环境的适应，但红色素的生成...