ICIFOR-INIA, CSIC. Ctra La Coruña km 7.5, 28040 Madrid, Spain.
Department of Biology and Geology, Physics and Inorganic Chemistry Rey Juan Carlos University, c/Tulipán s/n, 28933 Móstoles, Spain.
Tree Physiol. 2023 Jun 7;43(6):909-924. doi: 10.1093/treephys/tpad021.
Forests are threatened globally by increased recurrence and intensity of hot droughts. Functionally close coexisting species may exhibit differences in drought vulnerability large enough to cause niche differentiation and affect forest dynamics. The effect of rising atmospheric [CO2], which could partly alleviate the negative effects of drought, may also differ between species. We analysed functional plasticity in seedlings of two taxonomically close pine species (Pinus pinaster Ait., Pinus pinea L.) under different [CO2] and water stress levels. The multidimensional functional trait variability was more influenced by water stress (preferentially xylem traits) and [CO2] (mostly leaf traits) than by differences between species. However, we observed differences between species in the strategies followed to coordinate their hydraulic and structural traits under stress. Leaf 13C discrimination decreased with water stress and increased under elevated [CO2]. Under water stress both species increased their sapwood area to leaf area ratios, tracheid density and xylem cavitation, whereas they reduced tracheid lumen area and xylem conductivity. Pinus pinea was more anisohydric than P. pinaster. Pinus pinaster produced larger conduits under well-watered conditions than P. pinea. Pinus pinea was more tolerant to water stress and more resistant to xylem cavitation under low water potentials. The higher xylem plasticity in P. pinea, particularly in tracheid lumen area, expressed a higher capacity of acclimation to water stress than P. pinaster. In contrast, P. pinaster coped with water stress comparatively more by increasing plasticity of leaf hydraulic traits. Despite the small differences observed in the functional response to water stress and drought tolerance between species, these interspecific differences agreed with ongoing substitution of P. pinaster by P. pinea in forests where both species co-occur. Increased [CO2] had little effect on the species-specific relative performance. Thus, a competitive advantage under moderate water stress of P. pinea compared with P. pinaster is expected to continue in the future.
森林受到全球范围内炎热干旱频率和强度增加的威胁。功能上接近的共存物种可能表现出足够大的干旱脆弱性差异，从而导致生态位分化并影响森林动态。大气中[CO2]的升高可能部分缓解干旱的负面影响，但这种影响也可能在物种之间有所不同。我们分析了在不同[CO2]和水分胁迫水平下两种亲缘关系密切的松树（Pinuspinea L.）幼苗的功能可塑性。多维功能性状变异性更多地受到水分胁迫（优先影响木质部性状）和[CO2]（主要影响叶片性状）的影响，而不是物种间差异的影响。然而，我们观察到在胁迫下，物种之间在协调其水力和结构特征方面存在差异。叶片 13C 分馏随水分胁迫的增加而降低，随[CO2]的升高而增加。在水分胁迫下，两种物种都增加了边材面积与叶面积比、导管密度和木质部空穴化，而减少了导管腔面积和木质部传导性。Pinus pinea 比 Pinus pinaster 更具有等水合性。在水分充足的条件下，Pinus pinea 产生的导管比 Pinus pinea 大。Pinus pinea 对水分胁迫更耐受，在低水分势下对木质部空穴化更具抵抗力。Pinus pinea 的木质部可塑性较高，特别是在导管腔面积方面，表现出比 Pinus pinaster 更高的适应水分胁迫的能力。相比之下，Pinus pinaster 通过增加叶片水力性状的可塑性来应对水分胁迫。尽管在物种对水分胁迫的功能反应和耐旱性方面观察到的差异很小，但这些种间差异与这两个物种在共同发生的森林中正在发生的 Pinus pinaster 被 Pinus pinea 取代的情况相吻合。增加的[CO2]对物种特异性相对表现几乎没有影响。因此，与 Pinus pinaster 相比，Pinus pinea 在中度水分胁迫下的竞争优势预计将在未来继续存在。
