González-Carrera Santiago, Escudero Alfonso, Martín Ignacio, Martínez-Ortega Montserrat, Mediavilla Sonia
Department of Ecology, Faculty of Biology, University of Salamanca, c/ Licenciado Méndez Nieto, s/n, Salamanca 37071, Spain.
Department of Botany and Plant Physiology, Faculty of Biology, University of Salamanca, c/ Licenciado Méndez Nieto, s/n, Salamanca 37071, Spain.
Tree Physiol. 2025 Jun 2;45(6). doi: 10.1093/treephys/tpaf070.
Oaks are known for their frequent hybridization, a trend that generates a wide phenotypic spectrum and produces taxonomic confusion within the genus. Different approaches are needed for hybrids characterization, such as a combination of leaf morphological and anatomical traits supported by molecular data. Here, we characterized some morphological and anatomical (veins and stomata) leaf traits and their changes across a temperature gradient of two closely related Mediterranean Quercus species (Q. faginea Lam. and Q. pyrenaica Willd.) and their hybrids, preliminarily identified from molecular markers. Quercus faginea tended to exhibit more drought-adapted traits (smaller leaf size, larger vein and stomatal density, but lower stomatal index) than Q. pyrenaica. Quercus faginea also tended to exhibit stronger responses to environmental changes between the climatic zones. Hybrids possessed intermediate stomatal and vein traits between the two parent species but they were similar to Q. faginea for most morphological traits. For a few leaf shape parameters, such as the length/maximum width ratio, hybrids tended to exhibit larger values than both parent species. Whether this transgressive character of the hybrids affects their fitness in the contact zones between the two parent species needs to be better investigated. For the three genetic groups there were consistent changes in morphological traits across the climatic gradient. By contrast, stomatal and vein traits did not show significant within-species changes across the gradient. Leaf size decreased with decreasing temperatures, mainly due to a strong reduction of maximum leaf width. It is known that a reduced leaf size leads to the reduction of the thickness of the air boundary layer at the leaf surface. We suggest that the smaller leaf sizes at the colder sites would constitute an adaptation to avoid frost damage, given the trend of large leaves with thick boundary layers to develop nighttime temperatures lower than air temperatures.
橡树以其频繁的杂交而闻名，这种趋势产生了广泛的表型谱，并在该属内造成了分类学上的混乱。杂种鉴定需要不同的方法，例如结合叶片形态和解剖特征并辅以分子数据。在这里，我们对两种密切相关的地中海栎属物种（欧洲水青冈Quercus faginea Lam.和比利牛斯栎Quercus pyrenaica Willd.）及其杂种的一些形态和解剖（叶脉和气孔）叶片特征及其在温度梯度上的变化进行了表征，这些杂种是通过分子标记初步鉴定出来的。与比利牛斯栎相比，欧洲水青冈倾向于表现出更多适应干旱的特征（叶片尺寸较小、叶脉和气孔密度较大，但气孔指数较低）。欧洲水青冈对气候带之间的环境变化也倾向于表现出更强的响应。杂种在两个亲本物种之间具有中间的气孔和叶脉特征，但在大多数形态特征上与欧洲水青冈相似。对于一些叶片形状参数，例如长度/最大宽度比，杂种倾向于表现出比两个亲本物种更大的值。杂种的这种超亲性状是否会影响它们在两个亲本物种接触区域的适合度，还有待进一步研究。对于这三个遗传组，形态特征在气候梯度上存在一致的变化。相比之下，气孔和叶脉特征在整个梯度上没有显示出显著的种内变化。叶片尺寸随着温度降低而减小，主要是由于最大叶片宽度的强烈减小。众所周知，叶片尺寸减小会导致叶片表面空气边界层厚度减小。我们认为，鉴于具有厚边界层的大叶片在夜间温度低于气温的趋势，较冷地点较小的叶片尺寸将构成一种避免冻害的适应机制。
