Constraining conifer physiological parameters in leaf gas-exchange models for ancient CO2 reconstruction
Constraining conifer physiological parameters in leaf gas-exchange models for ancient CO2 reconstruction
复制标题
约束古代二氧化碳重建的叶片气体交换模型中的针叶树生理参数
DOI：
10.1016/j.gloplacha.2022.103737
复制
发表时间：
2022-01-21
影响因子：
3.9
通讯作者：
Yang, Hong
中科院分区：
文献类型：
--
作者：
Liang, Jia-Qi;Leng, Qin;Yang, Hong
树叶气体交换模型越来越多地被用于重建古代大气中二氧化碳(CO2)的浓度。这些广泛使用的模型之一，Franks模型，需要植物化石的气孔大小(保卫细胞宽度和保卫细胞长度或孔长)、全叶气孔密度和散叶碳同位素组成(增量C-13)。然而，这些参数在植物叶片内部和之间的自然变化还没有得到密切的评估，这阻碍了该模型的应用及其相关不确定性的评估。在这里，我们调查了这些参数的变化范围，并评估了它们对三种针叶树(水杉、红杉和杉木)Franks模型产量的影响。我们介绍了一种改进的清叶法，它可以准确地测量气孔大小。结果表明，在气孔大小参数中，气孔长度变化最大。整个叶片的气孔密度可以在叶片中部的代表性区域准确估计。在水杉叶片组织腐烂早期，Delta C-13值的变化仅略高于分析误差，但在水杉叶片组织的早期腐烂过程中，Delta C-13值的负移接近千分之1。我们测量的孔长和全叶气孔密度的范围对模型估计的二氧化碳影响最大。为了改进模型的性能，我们建议(1)使用我们改进的清叶法，从位于小枝中间部分的叶片的中间部分获得准确的气孔大小和全叶气孔密度测量；(2)根据保卫细胞长度来衡量气孔长度；以及(3)如果有关于组织腐烂和化石保存的信息，则可以对碳同位素分馏进行系统的校正。我们通过从现有材料和化石材料中重建二氧化碳来检验我们的建议。根据2004年和2020年收集的现代叶片(346和416ppm)建立的Franks模型得出的二氧化碳接近目标(378和414ppm)，而气孔频率法大大低估了(285ppm和341ppm)。从中新世中期克拉基亚矿床中恢复的二氧化碳(水杉和红豆杉分别为505ppm和507ppm)与公布的结果相当。我们的结论是，改进的精确测量关键气孔参数的透明叶方法和具有统计信息的气孔计数策略将改进Franks模型的性能，以利用这些自白垩纪以来在北半球广泛分布的化石记录的针叶树重建CO2。
Leaf gas-exchange models are increasingly used to reconstruct ancient atmospheric carbon dioxide (CO2) concentrations. One of these widely used models, the Franks model, requires stomatal size (guard cell width and either guard cell length or pore length), whole-leaf stomatal density, and bulk-leaf carbon isotope composition (delta C-13) from plant fossils. However, natural variations of these parameters within and across plant leaves have not been assessed closely, hindering the application of this model and the evaluation of its associated uncertainties. Here we investigate the range of variations of these parameters, and evaluate their impact on the output of the Franks model in three conifers (Metasequoia, Sequoia, and Taxodium). We introduce a modified cleared leaf method that allows accurate measurements of stomatal size. We show that among the stomatal size parameters, pore length is the most variable. Whole-leaf stomatal density can be accurately estimated in a representative area in the middle portion of a leaf. Variations of delta C-13 values are only slightly above analytical errors within a leaf and between leaves from a branchlet, but a similar to 1 parts per thousand negative shift of delta C-13 during early decay of Metasequoia leaf tissues was observed. Our measured ranges in pore length and whole-leaf stomatal density have the biggest influence on model estimated CO2. To improve model performance, we recommend (1) the use of our modified cleared leaf method to acquire accurate stomatal size and whole-leaf stomatal density measurements from the middle portion of a leaf located at the middle portion of a branchlet; (2) scaling pore length from guard cell length; and (3) a systematic correction of carbon isotope fractionation may be applicable if information regarding tissue decay and fossil preservation is available. We tested our recommendations by reconstructing CO2 from both extant and fossil materials. Franks model-derived CO2 based upon modern leaves collected in 2004 and 2020 (346 and 416 ppm) are close to their targets (378 and 414 ppm) whereas stomatal frequency methods substantially underestimate (285 and 341 ppm). Reconstructed CO2 from the middle Miocene Clarkia deposit (505 and 507 ppm for Metasequoia and Taxodium) are comparable with published results. We conclude that an improved cleared leaf method for accurate measurements of key stomatal parameters and a statistically-informed stomatal counting strategy will improve the performance of the Franks model for reconstructing CO2 using these conifers with wide distributions of fossil records in the Northern Hemisphere since the Cretaceous.