Forest Ecosystems and Society, College of Forestry, Oregon State University, 321 Richardson Hall, Corvallis, OR 97331, USA.
Rocky Mountain Biological Laboratory, PO Box 519, Crested Butte, CO 81224, USA.
Tree Physiol. 2018 Apr 1;38(4):630-640. doi: 10.1093/treephys/tpx120.
Quaking aspen (Populus tremuloides Michx.), a widespread and keystone tree species in North America, experienced heat and drought stress in the years 2002 and 2003 in the southwestern United States. This led to widespread aspen mortality that has altered the composition of forests, and is expected to occur again if climate change continues. Understanding interactions between aspen and its environments is essential to understanding future mortality risk in forests. Polyploidy, which is common in aspen, can modify plant structure and function and therefore plant-environment interactions, but the influence of polyploidy on aspen physiology is still not well understood. Furthermore, the ploidy types of aspen have different biogeographies, with triploids being most frequent at lower latitudes in generally warmer and drier climates, while the northerly populations are virtually 100% diploid. This suggests that ploidy-environment interactions differ, and could mean that the ploidy types have different vulnerabilities to environmental stress. In this study, to understand aspen ploidy-environment interactions, we measured 38 different traits important to carbon uptake, water loss and water-use efficiency in diploid and triploid aspen in Colorado. We found that triploid aspen had lower stand density, and greater leaf area, leaf mass, leaf mass per area, percent nitrogen content, chlorophyll content and stomatal size. These differences corresponded to greater potential net carbon assimilation (A, measured using A/Ci curves, and chlorophyll fluorescence) and stomatal conductance (gs) in triploids than diploids. While triploid aspen had higher intrinsic water-use efficiency (iWUE, calculated from measurements of δ13C in leaf tissue), they also had greater potential water loss from higher measured gs and lower stomatal sensitivity to increasing vapor pressure deficit. Therefore, despite greater iWUE, triploids may have lower resilience to climate-induced stress. We conclude that ploidy type strongly influences physiological traits and function, and mediates drought stress responses in quaking aspen.
颤杨（Populus tremuloides Michx.）是北美广泛分布的关键树种，在美国西南部的 2002 年和 2003 年经历了热和干旱胁迫。这导致了广泛的颤杨死亡，改变了森林的组成，如果气候变化继续下去，预计这种情况还会再次发生。了解颤杨与其环境之间的相互作用对于了解森林未来的死亡率风险至关重要。多倍体，在颤杨中很常见，可以改变植物的结构和功能，从而改变植物与环境的相互作用，但多倍体对颤杨生理学的影响仍不为人知。此外，颤杨的倍性类型具有不同的生物地理分布，三倍体在通常更温暖和干燥的低纬度地区最为常见，而北方种群几乎 100%为二倍体。这表明倍性与环境的相互作用不同，这可能意味着倍性类型对环境胁迫的脆弱性不同。在这项研究中，为了了解颤杨的倍性与环境的相互作用，我们在科罗拉多州测量了 38 种不同的与碳吸收、水分损失和水分利用效率有关的重要性状，这些性状在二倍体和三倍体颤杨中都有。我们发现三倍体颤杨的林分密度较低，叶面积、叶质量、叶质量/面积、氮含量、叶绿素含量和气孔大小较大。这些差异对应于三倍体比二倍体具有更大的净碳同化潜力（通过 A/Ci 曲线和叶绿素荧光测量）和气孔导度（gs）。虽然三倍体颤杨具有更高的内在水分利用效率（从叶片组织的δ13C 测量中计算得出），但由于较高的 gs 和较低的气孔对蒸气压亏缺增加的敏感性，它们也具有更大的潜在水分损失。因此，尽管三倍体具有更高的 iWUE，但它们对气候引起的胁迫的恢复能力可能较低。我们得出的结论是，倍性类型强烈影响生理性状和功能，并介导了颤杨对干旱胁迫的反应。
