Data from: 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 diameter were negatively correlated with material toughness and lamina density, but were independent of structural toughness and cell wall fiber contents. Leaf toughness traits were uncorrelated with relative growth rates. These results imply that material toughness enhances resistance to natural enemies, which increases survival and offsets the biomass allocation cost of producing tough leaves in the shaded understory.

耐荫植物物种的生长缓慢幼株，据推测具备坚硬叶片——这是因为在荫蔽环境下，相较于潜在碳收益，叶片替换的成本显著更高。本研究针对巴拿马巴罗科罗拉多岛50公顷森林动态监测样地林下的197种乔木与灌木物种，评估了与叶片硬度相关的8个性状间的相关演化程度，以及这些性状与物种生长速率、死亡率的关联。基于系统发育独立对比的路径分析结果显示，植物叶片可通过提升组织密度、单位干重纤维素占比以及叶脉抗断裂性，获得材料硬度（即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，二者分别代表了通向材料硬度的不同演化路径。结构硬度（即单位断裂长度的抗断裂能力）则由材料硬度与叶身厚度共同决定。茎直径处于1-10cm区间的个体死亡率，与材料硬度、叶身密度呈显著负相关，但与结构硬度及细胞壁纤维含量无显著关联。叶片硬度相关性状与相对生长速率无显著关联。上述研究结果表明，材料硬度可提升植物对天敌的抗性，进而提高植株存活率，并抵消在荫蔽林下构建坚硬叶片所需的生物量分配成本。