Leaf fossil record suggests limited influence of atmospheric CO2 on terrestrial productivity prior to angiosperm evolution
Leaf fossil record suggests limited influence of atmospheric CO2 on terrestrial productivity prior to angiosperm evolution
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DOI：
10.1073/pnas.1203769109
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发表时间：
2012-06-26
影响因子：
11.1
通讯作者：
Zwieniecki, Maciej A.
中科院分区：
文献类型：
--
作者：
Boyce, C. Kevin;Zwieniecki, Maciej A.
白垩纪的CO2下降被认为是高叶脉密度（7-28 mm mm（-2））的进化驱动力，这是整个地球历史上被子植物所独有的。光合作用模型表明，高静脉密度和生产力之间的联系记录在现代低CO2制度将失去CO2浓度的增加，但也意味着植物非常低的静脉密度（小于3 mm mm（-2））应经历大量的高CO2的不利条件。因此，二氧化碳和植物进化之间的假设关系可以通过分析替代谱系的并行历史来测试，因为像大气中的二氧化碳这样的外在驱动因素应该会影响所有植物，而不仅仅是开花植物。没有看到这种关系。无论二氧化碳浓度如何，低静脉密度在整个历史上的非被子植物中同样常见，并且普遍到足以包括森林冠层，而不仅仅是生产力有限的专性遮荫物种。建模结果可以调和与化石记录，如果最大同化率的nonflowering植物的上限远低于开花植物，捕获生化和生理差异，将与现存的植物，但以前未被识别的化石记录。虽然以前的光合作用模型表明，生产力将增加一倍或三倍，从低到高CO2的每一个中生代的过渡，生产力的变化很可能是有限的，伴随着显花植物的进化大幅增加之前。
Declining CO2 over the Cretaceous has been suggested as an evolutionary driver of the high leaf vein densities (7-28 mm mm(-2)) that are unique to the angiosperms throughout all of Earth history. Photosynthetic modeling indicated the link between high vein density and productivity documented in the modern low-CO2 regime would be lost as CO2 concentrations increased but also implied that plants with very low vein densities (less than 3 mm mm(-2)) should experience substantial disadvantages with high CO2. Thus, the hypothesized relationship between CO2 and plant evolution can be tested through analysis of the concurrent histories of alternative lineages, because an extrinsic driver like atmospheric CO2 should affect all plants and not just the flowering plants. No such relationship is seen. Regardless of CO2 concentrations, low vein densities are equally common among nonangiosperms throughout history and common enough to include forest canopies and not just obligate shade species that will always be of limited productivity. Modeling results can be reconciled with the fossil record if maximum assimilation rates of nonflowering plants are capped well below those of flowering plants, capturing biochemical and physiological differences that would be consistent with extant plants but previously unrecognized in the fossil record. Although previous photosynthetic modeling suggested that productivity would double or triple with each Phanerozoic transition from low to high CO2, productivity changes are likely to have been limited before a substantial increase accompanying the evolution of flowering plants.