Beerling D J, Royer D L
Department of Animal and Plant Sciences, University of Sheffield, Sheffield S10 2TN, UK.
Department of Geology and Geophysics, Yale University, PO Box 208109, New Haven, Connecticut 06520-8109, USA.
New Phytol. 2002 Mar;153(3):387-397. doi: 10.1046/j.0028-646X.2001.00335.x. Epub 2002 Mar 5.
The inverse relationship between atmospheric CO and the stomatal index (proportion of epidermal cells that are stomata) of vascular land plant leaves has led to the use of fossil plant cuticles for determining ancient levels of CO . In contemporary plants the stomatal index repeatedly shows a lower sensitivity atmospheric CO levels above 340 ppm in the short term. These observations demonstrate that the phenotypic response is nonlinear and may place constraints on estimating higher-than-present palaeo-CO levels in this way. We review a range of evidence to investigate the nature of this nonlinearity. Our new data, from fossil Ginkgo cuticles, suggest that the genotypic response of fossil Ginkgo closely tracks the phenotypic response seen in CO enrichment experiments. Reconstructed atmospheric CO values from fossil Ginkgo cuticles compare well with the stomatal ratio method of obtaining a quantitative CO signal from extinct fossil plants, and independent geochemical modelling studies of the long-term carbon cycle. Although there is self-consistency between palaeobiological and geochemical CO estimates, it should be recognized that the nonlinear response is a limitation of the stomatal approach to estimating high palaeo-CO levels.
大气中二氧化碳（CO）与维管陆地植物叶片气孔指数（即表皮细胞中气孔所占比例）之间的反比关系，促使人们利用化石植物角质层来测定古代的CO水平。在当代植物中，气孔指数在短期内反复显示出对高于340 ppm的大气CO水平敏感性较低。这些观察结果表明，表型反应是非线性的，这可能会限制通过这种方式估算高于当前水平的古CO水平。我们回顾了一系列证据来研究这种非线性的本质。我们从化石银杏角质层获得的新数据表明，化石银杏的基因型反应与在CO富集实验中观察到的表型反应密切相关。从化石银杏角质层重建的大气CO值，与从已灭绝化石植物中获取定量CO信号的气孔比率法，以及长期碳循环的独立地球化学模型研究结果吻合良好。尽管古生物学和地球化学对CO的估计之间存在自洽性，但应该认识到，非线性反应是气孔法估算高古CO水平的一个局限性。
