Department of Ecology and Forest Genetics, Instituto de Ciencias Forestales (ICIFOR-INIA), Consejo Superior de Investigaciones Científicas (CSIC), Carretera La Coruña Km 7.5, E-28040 Madrid, Spain.
Tree Physiol. 2024 Sep 3;44(9). doi: 10.1093/treephys/tpae107.
Understanding covariation patterns of drought resistance, post-drought recovery and phenotypic plasticity, and their variability at the intra-population level are crucial for predicting forest vulnerability to increasing aridity. This knowledge is particularly urgent at the trailing range edge since, in these areas, tree species are proximal to their ecological niche boundaries. While this proximity increases their susceptibility, these populations are recognized as valuable genetic reservoirs against environmental stressors. The conservation of this genetic variability is critical for the adaptive capacity of the species in the current context of climate change. Here we examined intra-population patterns of stem basal growth, gas exchange and other leaf functional traits in response to an experimental drought in seedlings of 16 open-pollinated families within a marginal population of European beech (Fagus sylvatica L.) from its southern range edge. We found a high degree of intra-population variation in leaf functional traits, photosynthetic performance, growth patterns and phenotypic plasticity in response to water availability. Low phenotypic plasticity was associated with higher resistance to drought. Both drought resistance and post-drought recovery of photosynthetic performance varied between maternal lines. However, drought resistance and post-drought recovery exhibited independent variation. We also found intra-population variation in stomatal sensitivity to soil drying, but it was not associated with either drought resistance or post-drought recovery. We conclude that an inverse relationship between phenotypic plasticity and drought resistance is not necessarily a sign of maladaptive plasticity, but rather it may reflect stability of functional performance and hence adaptation to withstand drought. The independent variation found between drought resistance and post-drought recovery should facilitate to some extent microevolution and adaption to increasing aridity. The observed variability in stomatal sensitivity to soil drying was consistent with previous findings at other scales (e.g., inter-specific variation, inter-population variation) that challenge the iso-anisohydric concept as a reliable surrogate of drought tolerance.
了解抗旱性、旱后恢复和表型可塑性的协同变化模式及其在种群内水平的变异性对于预测森林对日益干旱的脆弱性至关重要。在尾缘范围内，这种知识尤为紧迫，因为在这些地区，树种接近其生态位边界。虽然这种接近增加了它们的易感性，但这些种群被认为是对环境胁迫的有价值的遗传储备。在当前气候变化背景下，这种遗传变异性的保护对于物种的适应能力至关重要。在这里，我们研究了 16 个开放授粉家系的幼苗在实验干旱条件下的茎基部生长、气体交换和其他叶片功能性状的种群内模式，这些家系来自其南部范围边缘的欧洲山毛榉（Fagus sylvatica L.）的边缘种群。我们发现，在对水分可用性的反应中，叶片功能性状、光合性能、生长模式和表型可塑性在种群内具有高度的变异性。低表型可塑性与对干旱的更高抗性相关。抗旱性和光合性能的旱后恢复在母系之间存在差异。然而，抗旱性和旱后恢复表现出独立的变化。我们还发现种群内对土壤干燥的气孔敏感性存在变异性，但它与抗旱性或旱后恢复无关。我们的结论是，表型可塑性和抗旱性之间的反比关系不一定是适应不良可塑性的标志，而是可能反映了功能性能的稳定性，从而适应了耐旱性。抗旱性和旱后恢复之间发现的独立变化在某种程度上应该有助于微进化和适应日益干旱的环境。对土壤干燥的气孔敏感性的观察到的变异性与以前在其他尺度上的发现一致（例如，种间变异、种群间变异），这挑战了等渗透假说作为耐旱性可靠替代物的概念。
