Cordell S, Goldstein G, Mueller-Dombois D, Webb D, Vitousek P M
Department of Botany, University of Hawaii, 3190 Maile Way, Honolulu, HI 96822, USA, , , , , , US.
Department of Biological Sciences, Stanford University, Stanford, CA 94305, USA, , , , , , US.
Oecologia. 1998 Jan;113(2):188-196. doi: 10.1007/s004420050367.
Metrosideros polymorpha, a dominant tree species in Hawaiian ecosystems, occupies a wide range of habitats. Complementary field and common-garden studies of M. polymorpha populations were conducted across an altitudinal gradient at two different substrate ages to ascertain if the large phenotypic variation of this species is determined by genetic differences or by phenotypic modifications resulting from environmental conditions. Several characteristics, including ecophysiological behavior and anatomical features, were largely induced by the environment. However, other characteristics, particularly leaf morphology, appeared to be mainly determined by genetic background. Common garden plants exhibited higher average rates of net assimilation (5.8 μmol CO m s) and higher average stomatal conductance (0.18 mol HO m s) than their field counterparts (3.0 μmol CO m s, and 0.13 mol HO m s respectively). Foliar δC of most common-garden plants was similar among sites of origin with an average value of -26.9‰. In contrast, mean values of foliar δC in field plants increased substantially from -29.5‰ at low elevation to -24.8‰ at high elevation. Leaf mass per unit area increased significantly as a function of elevation in both field and common garden plants; however, the range of values was much narrower in common garden plants (211-308 g m for common garden versus 107-407 g m for field plants). Nitrogen content measured on a leaf area basis in common garden plants ranged from 1.4 g m to 2.4 g m and from 0.8 g m to 2.5 g m in field plants. Photosynthetic nitrogen use efficiency (PNUE) decreased 50% with increasing elevation in field plants and only 20% in plants from young substrates in the common garden. This was a result of higher rates of net CO assimilation in the common garden plants. Leaf tissue and cell layer thickness, and degree of leaf pubescence increased significantly with elevation in field plants, whereas in common garden plants, variation with elevation of origin was much narrower, or was entirely absent. Morphological characteristics such as leaf size, petiole length, and internode length decreased with increasing elevation in the field and were retained when grown in the common garden, suggesting a potential genetic basis for these traits. The combination of environmentally induced variability in physiological and anatomical characteristics and genetically determined variation in morphological traits allows Hawaiian M. polymorpha to attain and dominate an extremely wide ecological distribution not observed in other tree species.
多花铁心木是夏威夷生态系统中的优势树种，占据了广泛的栖息地。针对多花铁心木种群，在两个不同基质年龄的海拔梯度上开展了野外和同园对照研究，以确定该物种的巨大表型变异是由遗传差异决定，还是由环境条件导致的表型修饰决定。包括生态生理行为和解剖特征在内的几个特征很大程度上是由环境诱导的。然而，其他特征，特别是叶片形态，似乎主要由遗传背景决定。同园种植的植物比它们在野外的对应植株表现出更高的平均净同化率（5.8 μmol CO₂ m⁻² s⁻¹）和更高的平均气孔导度（0.18 mol H₂O m⁻² s⁻¹）（野外对应植株分别为3.0 μmol CO₂ m⁻² s⁻¹和0.13 mol H₂O m⁻² s⁻¹）。大多数同园种植植物的叶片δ¹³C在不同起源地之间相似，平均值为 -26.9‰。相比之下，野外植株叶片δ¹³C的平均值从低海拔处的 -29.5‰大幅增加到高海拔处的 -24.8‰。单位面积叶质量在野外和同园种植的植物中均随海拔升高而显著增加；然而，同园种植植物的值范围要窄得多（同园种植植物为211 - 308 g m⁻²，野外植株为107 - 407 g m⁻²）。以叶面积为基础测量的同园种植植物的氮含量范围为1.4 g m⁻²至2.4 g m⁻²，野外植株为0.8 g m⁻²至2.5 g m⁻²。在野外植株中，光合氮利用效率（PNUE）随海拔升高下降50%，而在同园年轻基质中的植株中仅下降20%。这是同园种植植物净CO₂同化率较高的结果。野外植株的叶片组织和细胞层厚度以及叶片茸毛程度随海拔升高显著增加，而在同园种植植物中，随起源海拔的变化范围要窄得多，或者完全没有变化。叶片大小（叶长、叶柄长度和节间长度）等形态特征在野外随海拔升高而减小，在同园种植时保持不变，这表明这些性状具有潜在的遗传基础。生理和解剖特征的环境诱导变异性与形态特征的遗传决定变异性相结合，使得夏威夷的多花铁心木能够实现并占据其他树种未观察到的极其广泛的生态分布。
