Data from: Biomechanical and leaf-climate relationships: a comparison of ferns and seed plants

Premise of the study: Relationships of leaf size and shape (physiognomy) with climate have been well characterized for woody non-monocotyledonous angiosperms (dicots), allowing the development of models for estimating paleoclimate from fossil leaves. More recently, petiole width of seed plants has been shown to scale closely with leaf mass. By measuring petiole width and leaf area in fossils, leaf mass per area (MA) can be estimated and an approximate leaf life span inferred. However, little is known about these relationships in ferns, a clade with a deep fossil record and with the potential to greatly expand the applicability of these proxies. Methods: We measured the petiole width, MA, and leaf physiognomic characters of 179 fern species from 188 locations across six continents. We applied biomechanical models and assessed the relationship between leaf physiognomy and climate using correlational approaches. Key results: The scaling relationship between area-normalized petiole width and MA differs between fern fronds and pinnae. The scaling relationship is best modeled as an end-loaded cantilevered beam, which is different from the best-fit biomechanical model for seed plants. Fern leaf physiognomy is not influenced by climatic conditions. Conclusions: The cantilever beam model can be applied to fossil ferns. The lack of sensitivity of leaf physiognomy to climate in ferns argues against their use to reconstruct paleoclimate. Differences in climate sensitivity and biomechanical relationships between ferns and seed plants may be driven by differences in their hydraulic conductivity and/or their differing evolutionary histories of vein architecture and leaf morphology.

研究背景：目前针对木本非单子叶被子植物（双子叶植物），其叶片大小、形状与叶相（leaf physiognomy）的关联已得到充分表征，由此得以建立基于化石叶片估算古气候的模型。近期已有研究证实，种子植物的叶柄宽度与叶片质量呈紧密的缩放关系。通过测量化石中的叶柄宽度与叶面积，可估算比叶质量（leaf mass per area，MA）并推导出近似的叶片寿命。然而，对于蕨类植物而言，这类关联的相关研究仍较为匮乏。蕨类植物作为拥有悠久化石记录的演化支，有望极大拓展上述气候替代指标的应用范围。
方法：我们对采自六大洲188个样点的179种蕨类植物的叶柄宽度、比叶质量以及叶相性状进行了测量。我们运用生物力学模型，并通过相关分析方法探究叶相与气候之间的关联。
主要结果：面积归一化叶柄宽度与比叶质量之间的缩放关系，在蕨类叶状体（fronds）与羽片（pinnae）之间存在显著差异。该缩放关系的最优拟合模型为末端负载悬臂梁模型，这与种子植物的最优生物力学拟合模型截然不同。此外，蕨类的叶相性状不受气候条件的影响。
结论：末端负载悬臂梁模型可应用于化石蕨类的相关研究。蕨类叶相性状对气候缺乏敏感性，这意味着无法利用蕨类叶片来重建古气候。蕨类植物与种子植物在气候敏感性及生物力学关联上的差异，可能源于二者导水率的不同，以及二者在叶脉结构和叶片形态演化历史上的差异。