Department of Ecology and Evolutionary Biology, Yale University, New Haven, CT, USA.
Department of Biology, University of Oxford, Oxford, UK.
Ann Bot. 2023 Nov 25;132(4):627-654. doi: 10.1093/aob/mcad135.
The growth of experimental studies of crassulacean acid metabolism (CAM) in diverse plant clades, coupled with recent advances in molecular systematics, presents an opportunity to re-assess the phylogenetic distribution and diversity of species capable of CAM. It has been more than two decades since the last comprehensive lists of CAM taxa were published, and an updated survey of the occurrence and distribution of CAM taxa is needed to facilitate and guide future CAM research. We aimed to survey the phylogenetic distribution of these taxa, their diverse morphology, physiology and ecology, and the likely number of evolutionary origins of CAM based on currently known lineages.
We found direct evidence (in the form of experimental or field observations of gas exchange, day-night fluctuations in organic acids, carbon isotope ratios and enzymatic activity) for CAM in 370 genera of vascular plants, representing 38 families. Further assumptions about the frequency of CAM species in CAM clades and the distribution of CAM in the Cactaceae and Crassulaceae bring the currently estimated number of CAM-capable species to nearly 7 % of all vascular plants. The phylogenetic distribution of these taxa suggests a minimum of 66 independent origins of CAM in vascular plants, possibly with dozens more. To achieve further insight into CAM origins, there is a need for more extensive and systematic surveys of previously unstudied lineages, particularly in living material to identify low-level CAM activity, and for denser sampling to increase phylogenetic resolution in CAM-evolving clades. This should allow further progress in understanding the functional significance of this pathway by integration with studies on the evolution and genomics of CAM in its many forms.
随着实验研究中景天酸代谢（CAM）在不同植物类群中的发展，以及分子系统发育学的最新进展，为重新评估具有 CAM 能力的物种的系统发育分布和多样性提供了机会。自最后一次发表全面的 CAM 分类群清单以来已经过去了二十多年，因此需要对 CAM 分类群的发生和分布进行更新调查，以促进和指导未来的 CAM 研究。我们旨在调查这些分类群的系统发育分布、它们多样的形态、生理学和生态学，以及基于现有谱系的 CAM 可能的起源数量。
我们在 38 个科的 370 个维管植物属中发现了 CAM 的直接证据（以气体交换、有机酸昼夜波动、碳同位素比值和酶活性的实验或野外观察的形式）。进一步假设 CAM 类群中 CAM 种的频率以及仙人掌科和景天科中 CAM 的分布，将目前估计的具有 CAM 能力的物种数量提高到近 7%的所有维管植物。这些分类群的系统发育分布表明，CAM 在维管植物中至少有 66 个独立的起源，可能还有几十个。为了进一步深入了解 CAM 的起源，需要对以前未研究的谱系进行更广泛和系统的调查，特别是在活体材料中以识别低水平的 CAM 活性，并进行更密集的采样以提高 CAM 进化类群中的系统发育分辨率。这应该允许通过与 CAM 及其多种形式的进化和基因组学研究相结合，进一步深入了解该途径的功能意义。
