ABSTRACT

To understand Earth´s climate variability and improve predictions of future climate change, studying past climates is an important avenue to explore. A previously published record of pCO₂, across the Triassic–Jurassic boundary (TJB, ~201 Ma) of East Greenland, showed that Bennettitales (Anamozamites and Pterophyllum) responded in parallel to the empirically proven pCO₂-responders Ginkgoales, reducing their stomatal densities by half across the TJB, indicating a transient doubling of pCO₂. The abundance of fossil Bennettitales in Mesozoic strata and natural history museum collections worldwide offers enormous potential for further stomatal proxy pCO₂ reconstructions, but a suitable nearest living equivalent (NLE) should ideally first be identified for this extinct plant group. Using specimens from herbarium collections, three species of cycads, historically considered the best NLE, were tested for pCO₂ response, as well as two species of tree ferns, grown in experimental growth chambers. None responded to changes in pCO₂, and were consequently rejected as NLEs. Finally, two species of ferns were selected from the literature, and produced very similar pCO₂ compared to Ginkgoales. However, these understory ferns are not appropriate NLEs for Bennettitales due to differences in habitat and a distant evolutionary relationship. Future work should test additional plant groups, in particular seed plants such as basal angiosperms and Gnetales, for suitability as NLE for Bennettitales in pCO₂ reconstructions, for example through biogeochemical fingerprinting using infrared microspectroscopy. Until an appropriate NLE is identified, Bennettitales pCO₂ can be reconstructed based on cross-calibration of stomatal densities with those of co-occurring pCO₂ responders, such as Ginkgoales.

摘要

要了解地球的气候变化并改进对未来气候变化的预测，研究过去的气候是一个重要的探索途径。先前发表的跨越东格陵兰三叠纪-侏罗纪边界（TJB，~201 Ma）的p CO ₂记录表明，Bennettitales（Anamozamites和Pterophyllum）与经验证明的p CO ₂反应物银杏类平行反应，减少了它们的TJB 中气孔密度减半，表明p CO ₂的瞬时加倍. 世界范围内中生代地层和自然历史博物馆收藏的丰富的 Bennettitales 化石为进一步气孔替代p CO ₂重建提供了巨大的潜力，但理想情况下，应该首先为这个已灭绝的植物群确定合适的最近生物等效物 (NLE)。使用植物标本馆收集的标本，测试了三种历来被认为是最佳 NLE 的苏铁，以及两种生长在实验生长室中的树蕨类植物的p CO ₂响应。没有人对p CO _{2 的}变化做出反应，因此作为 NLE 被拒绝。最后，从文献中选出了两种蕨类植物，并产生了非常相似的pCO ₂与银杏树相比。然而，由于栖息地的差异和遥远的进化关系，这些林下蕨类植物不适合 Bennettitales。未来的工作应该测试其他植物群，特别是种子植物，如基础被子植物和 Gnetales，在p CO ₂重建中作为 Bennettitales 的 NLE 的适用性，例如通过使用红外显微光谱进行生物地球化学指纹识别。在确定合适的 NLE 之前，可以基于气孔密度与同时发生的p CO ₂响应者（例如银杏树）的气孔密度的交叉校准来重建Bennettitales p CO ₂。