Botany Department, School of Natural Sciences, Trinity College, Dublin 2, Ireland
Botany Department, School of Natural Sciences, Trinity College, Dublin 2, Ireland.
Plant Physiol. 2019 Nov;181(3):1148-1162. doi: 10.1104/pp.19.00749. Epub 2019 Sep 4.
The fossil record and models of atmospheric concentrations of O and CO suggest that past shifts in plant ecological dominance often coincided with dramatic changes in Earth's atmospheric composition. This study tested the effects of past changes in atmospheric composition on the photosynthetic physiology of a limited range of early-diverging angiosperms (eight), gymnosperms (three), and ferns (two). We performed physiological measurements on all species and used the results to parameterize simulations of their photosynthetic paleophysiology using three independent modeling approaches. Unique physiological attributes were identified for the three evolutionary groups: angiosperm taxa displayed significantly higher mesophyll conductance ( ), yet their stomatal conductance ( ) was lower than that of ferns. Gymnosperm taxa displayed low and , but they partially offset their significant diffusional limitations on photosynthesis through their higher maximum Rubisco carboxylation rate. Despite their high total conductance to CO, fern taxa lacked an optimized control of , which was reflected in their low intrinsic water use efficiency. Simulations of the photosynthetic physiology of ferns, angiosperms, and gymnosperms through Earth's history demonstrated that past fluctuations in O and CO concentrations may have resulted in significant shifts in the relative competitiveness of the three evolutionary groups. Although preliminary because of limited species sampling, these findings hint at a potential mechanistic basis for the observed broad temporal correlation between atmospheric change and shifts in plant evolutionary group-level richness observed in the fossil record and are presented as a framework to be tested with paleophotosynthetic proxies and through increased species sampling.
化石记录和大气中 O 和 CO 浓度模型表明，过去植物生态优势的转变往往与地球大气成分的剧烈变化同时发生。本研究测试了过去大气成分变化对有限范围的早期分化被子植物（8 种）、裸子植物（3 种）和蕨类植物（2 种）光合作用生理的影响。我们对所有物种进行了生理测量，并使用结果使用三种独立的建模方法对其光合作用古生理进行模拟参数化。为三个进化组确定了独特的生理特征：被子植物类群的叶肉导度（ ）显著较高，但它们的气孔导度（ ）低于蕨类植物。裸子植物类群的 和 较低，但它们通过较高的最大 RuBP 羧化率部分抵消了光合作用的显著扩散限制。尽管它们对 CO 的总导度较高，但蕨类植物类群缺乏对 的优化控制，这反映在它们较低的内在水分利用效率上。通过地球历史对蕨类植物、被子植物和裸子植物光合作用的模拟表明，过去 O 和 CO 浓度的波动可能导致这三个进化组的相对竞争力发生显著变化。尽管由于物种采样有限，这些发现还只是初步的，但它们暗示了在化石记录中观察到的大气变化与植物进化组水平丰富度之间广泛的时间相关性的潜在机制基础，并提出了一个框架，该框架将通过古光合作用示踪剂和增加物种采样来进行测试。
