Royer Dana L, Wilf Peter, Janesko David A, Kowalski Elizabeth A, Dilcher David L
Department of Geosciences, Pennsylvania State University, University Park, Pennsylvania, 16802 USA;
Am J Bot. 2005 Jul;92(7):1141-51. doi: 10.3732/ajb.92.7.1141.
The sizes and shapes (physiognomy) of fossil leaves are widely applied as proxies for paleoclimatic and paleoecological variables. However, significant improvements to leaf-margin analysis, used for nearly a century to reconstruct mean annual temperature (MAT), have been elusive; also, relationships between physiognomy and many leaf ecological variables have not been quantified. Using the recently developed technique of digital leaf physiognomy, correlations of leaf physiognomy to MAT, leaf mass per area, and nitrogen content are quantified for a set of test sites from North and Central America. Many physiognomic variables correlate significantly with MAT, indicating a coordinated, convergent evolutionary response of fewer teeth, smaller tooth area, and lower degree of blade dissection in warmer environments. In addition, tooth area correlates negatively with leaf mass per area and positively with nitrogen content. Multiple linear regressions based on a subset of variables produce more accurate MAT estimates than leaf-margin analysis (standard errors of ±2 vs. ±3°C); improvements are greatest at sites with shallow water tables that are analogous to many fossil sites. The multivariate regressions remain robust even when based on one leaf per species, and the model most applicable to fossils shows no more signal degradation from leaf fragmentation than leaf-margin analysis.
化石叶片的大小和形状（形态特征）被广泛用作古气候和古生态变量的代理指标。然而，用于重建年均温度（MAT）近一个世纪的叶缘分析虽有显著改进，但仍难以捉摸；此外，形态特征与许多叶片生态变量之间的关系尚未得到量化。利用最近开发的数字叶片形态特征技术，对北美和中美洲一组测试地点的叶片形态特征与MAT、单位面积叶质量和氮含量之间的相关性进行了量化。许多形态特征变量与MAT显著相关，表明在温暖环境中，叶片齿数量减少、齿面积变小和叶片分裂程度降低是一种协调一致的趋同进化反应。此外，齿面积与单位面积叶质量呈负相关，与氮含量呈正相关。基于部分变量的多元线性回归比叶缘分析能产生更准确的MAT估计值（标准误差分别为±2°C和±3°C）；在地下水位浅的地点（类似于许多化石地点）改进最为显著。即使基于每个物种一片叶子进行多元回归，其稳健性依然良好，并且最适用于化石的模型在叶片破碎时信号退化程度并不比叶缘分析更大。
