BACKGROUND AND AIMS Crassulacean Acid Metabolism (CAM) is an adaptation to increase water use efficiency in dry environments. Similar biochemical patterns occur in the aquatic lycophyte genus Isoëtes. It has long been assumed and accepted that CAM-like behavior in aquatic plants is an adaptation to low daytime carbon levels in aquatic ecosystems, but this has never been directly tested. METHODS To test this hypothesis, populations of Isoëtes engelmannii and I. tuckermanii were grown in climate-controlled chambers and starved of atmospheric CO2 during the day while pH was measured for 24-hours. KEY RESULTS We demonstrate that terrestrial plants exposed to low atmospheric CO2 display diel acidity cycles similar to those in both xerophytic CAM plants and submerged Isoëtes. CONCLUSIONS We determine that daytime CO2 starvation induces CAM-like nocturnal acid accumulation in terrestrial Isoëtes, substantiating the hypothesis that carbon starvation is a selective pressure for this physiological behavior.

中文翻译：

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二氧化碳饥饿实验为 Isoëtes 类 CAM 行为进化的碳限制假说提供支持

背景和目的 景天酸代谢 (CAM) 是一种在干燥环境中提高用水效率的适应性方法。类似的生化模式发生在水生石松属 Isoëtes 中。长期以来，人们一直假设并接受水生植物中的类似 CAM 的行为是对水生生态系统中白天低碳水平的适应，但这从未被直接测试过。方法 为了验证这一假设，Isoëtes engelmannii 和 I. tuckermanii 种群在气候控制的房间中生长，白天缺乏大气 CO2，同时测量 pH 值 24 小时。主要结果 我们证明，暴露于低大气 CO2 的陆生植物显示出与旱生 CAM 植物和水下等离子植物相似的酸性循环。