Martínez-Sancho Elisabet, Dorado-Liñán Isabel, Hacke Uwe G, Seidel Hannes, Menzel Annette
Ecoclimatology, Department of Ecology and Ecosystem Management, Technische Universität MünchenFreising, Germany.
Departamento de Silvicultura y Gestión de los Sistemas Forestales, Centro de Investigación Forestal-Instituto Nacional de Investigación y Tecnología Agraria y AlimentariaMadrid, Spain.
Front Plant Sci. 2017 Apr 20;8:598. doi: 10.3389/fpls.2017.00598. eCollection 2017.
Many temperate European tree species have their southernmost distribution limits in the Mediterranean Basin. The projected climatic conditions, particularly an increase in dryness, might induce an altitudinal and latitudinal retreat at their southernmost distribution limit. Therefore, characterizing the morphological and physiological variability of temperate tree species under dry conditions is essential to understand species' responses to expected climate change. In this study, we compared branch-level hydraulic traits of four Scots pine and four sessile oak natural stands located at the western and central Mediterranean Basin to assess their adjustment to water limiting conditions. Hydraulic traits such as xylem- and leaf-specific maximum hydraulic conductivity ( and ), leaf-to-xylem area ratio (:) and functional xylem fraction (FX) were measured in July 2015 during a long and exceptionally dry summer. Additionally, xylem-specific native hydraulic conductivity () and native percentage of loss of hydraulic conductivity (PLC) were measured for Scots pine. Interspecific differences in these hydraulic traits as well as intraspecific variability between sites were assessed. The influence of annual, summer and growing season site climatic aridity (P/PET) on intraspecific variability was investigated. Sessile oak displayed higher values of , , : but a smaller percentage of FX than Scots pines. Scots pine did not vary in any of the measured hydraulic traits across the sites, and PLC values were low for all sites, even during one of the warmest summers in the region. In contrast, sessile oak showed significant differences in , , and FX across sites, which were significantly related to site aridity. The striking similarity in the hydraulic traits across Scots pine sites suggests that no adjustment in hydraulic architecture was needed, likely as a consequence of a drought-avoidance strategy. In contrast, sessile oak displayed adjustments in the hydraulic architecture along an aridity gradient, pointing to a drought-tolerance strategy.
许多温带欧洲树种在地中海盆地拥有其最南端的分布界限。预计的气候条件，尤其是干燥程度的增加，可能会导致它们在最南端分布界限处出现海拔和纬度上的退缩。因此，了解温带树种在干旱条件下的形态和生理变异性对于理解物种对预期气候变化的反应至关重要。在本研究中，我们比较了位于地中海盆地西部和中部的四个苏格兰松和四个无梗花栎天然林分的树枝水平水力特征，以评估它们对水分限制条件的适应性。在2015年7月一个漫长且异常干燥的夏季期间，测量了诸如木质部和叶片比最大水力传导率（ 和 ）、叶与木质部面积比（:）以及功能性木质部比例（FX）等水力特征。此外，还测量了苏格兰松的木质部比原生水力传导率（ ）和原生水力传导率损失百分比（PLC）。评估了这些水力特征的种间差异以及不同地点间的种内变异性。研究了年、夏季和生长季地点气候干旱度（P/PET）对种内变异性的影响。无梗花栎的 、 、: 值较高，但FX比例比苏格兰松小。苏格兰松在所测量的任何水力特征上在各地点间均无变化，并且所有地点的PLC值都很低，即使在该地区最温暖的夏季之一期间也是如此。相比之下，无梗花栎在 、 和FX方面在各地点间表现出显著差异，且这些差异与地点干旱度显著相关。苏格兰松各地点水力特征的显著相似性表明不需要对水力结构进行调整，这可能是避旱策略的结果。相比之下，无梗花栎沿干旱梯度在水力结构上表现出调整，这表明其具有耐旱策略。
