What makes a leaf tough? Patterns of correlated evolution between leaf toughness traits and demographic rates among 197 shade-tolerant woody species in a neotropical forest

Slow-growing juveniles of shade-tolerant plant species are predicted to have tough leaves because of the high cost of leaf replacement in shade relative to potential carbon gain. We assessed the degree of correlated evolution among eight traits associated with leaf toughness and their relationships with growth and mortality rates of 197 tree and shrub species from the understory of the 50-hectare forest dynamics plot on Barro Colorado Island, Panama. Path analysis with phylogenetically independent contrasts revealed that leaves attained material toughness (resistance to fracture per unit fracture area) through increases in tissue density, percent cellulose per unit dry mass, and vein fracture toughness. Lamina density and cellulose content evolved independently, and thus represent different paths to material toughness. Structural toughness (resistance to fracture per unit fracture length) depended on material toughness and lamina thickness. Mortality rates of individuals 1-10 cm in stem...

据推测，耐阴植物物种的生长缓慢幼株会拥有韧性更强的叶片，这是因为在遮阴环境下，相较于潜在碳收益，叶片更替的成本更高。本研究针对巴拿马巴罗科罗拉多岛50公顷森林动态样地林下的197种乔木与灌木物种，评估了与叶片韧性相关的8个性状的协同演化程度，以及这些性状与物种生长、死亡率的关联。采用系统发育独立对比（phylogenetically independent contrasts）的通径分析显示，植物叶片通过提升组织密度、单位干重纤维素占比以及叶脉断裂韧性，获得材料韧性（单位断裂面积的抗断裂能力）。叶身密度与纤维素含量的演化相互独立，因此二者是实现材料韧性的不同路径。结构韧性（单位断裂长度的抗断裂能力）则取决于材料韧性与叶身厚度。茎径1-10厘米的个体死亡率……