Department of Phytology, Technical University, 960 53 Zvolen, Slovakia.
Am J Bot. 2012 Sep;99(9):1489-500. doi: 10.3732/ajb.1100593. Epub 2012 Aug 24.
Knowledge of functional leaf traits can provide important insights into the processes structuring plant communities. In the genus Sorbus, the generation of taxonomic novelty through reticulate evolution that gives rise to new microspecies is believed to be driven primarily by a series of interspecific hybridizations among closely related taxa. We tested hypotheses for dispersion of intermediacy across the leaf traits in Sorbus hybrids and for trait linkages with leaf area and specific leaf area.
Here, we measured and compared the whole complex of growth, vascular, and ecophysiological leaf traits among parental (Sorbus aria, Sorbus aucuparia, Sorbus chamaemespilus) and natural hybrid (Sorbus montisalpae, Sorbus zuzanae) species growing under field conditions. A recently developed atomic force microscopy technique, PeakForce quantitative nanomechanical mapping, was used to characterize the topography of cell wall surfaces of tracheary elements and to map the reduced Young's modulus of elasticity.
Intermediacy was associated predominantly with leaf growth traits, whereas vascular and ecophysiological traits were mainly parental-like and transgressive phenotypes. Larger-leaf species tended to have lower modulus of elasticity values for midrib tracheary element cell walls. Leaves with a biomass investment related to a higher specific leaf area had a lower density. Leaf area- and length-normalized theoretical hydraulic conductivity was related to leaf thickness.
For the whole complex of examined leaf traits, hybrid microspecies were mosaics of parental-like, intermediate, and transgressive phenotypes. The high proportion of transgressive character expressions found in Sorbus hybrids implies that generation of extreme traits through transgressive segregation played a key role in the speciation process.
功能叶性状的知识可以为理解植物群落结构过程提供重要的见解。在花楸属中，通过种间杂交产生的新微种的分类学新颖性被认为主要是由一系列密切相关的类群之间的种间杂交驱动的。我们检验了花楸属杂种中中间性状在叶片性状中的扩散假说，以及与叶面积和比叶面积的性状联系。
在这里，我们在野外条件下测量和比较了亲代（花楸、花楸、茶镳子）和天然杂种（蒙山花楸、祖扎纳花楸）的生长、维管束和生理叶性状的整个复合体。最近开发的原子力显微镜技术，即 PeakForce 定量纳米力学映射，用于表征导管元素细胞壁的表面形貌，并绘制弹性模量的降低。
中间性状主要与叶片生长性状有关，而维管束和生理性状主要是亲代样和超越性表型。较大叶的物种倾向于具有较低的中脉导管细胞壁的弹性模量值。与较高比叶面积相关的生物量投资的叶片具有较低的密度。叶面积和长度归一化理论水力传导率与叶片厚度有关。
对于所检查的叶片性状的整个复合体，杂种微种是亲代样、中间和超越性表型的镶嵌体。在花楸属杂种中发现的大量超越性特征表达表明，通过超越性分离产生的极端特征在物种形成过程中发挥了关键作用。
