PDF(Pubmed)
Abstract：
Species mixture is promoted as a crucial management option to adapt forests to climate change. However, there is little consensus on how tree diversity affects tree water stress, and the underlying mechanisms remain elusive. By using a greenhouse experiment and a soil-plant-atmosphere hydraulic model, we explored whether and why mixing the isohydric Aleppo pine (Pinus halepensis, drought avoidant) and the anisohydric holm oak (Quercus ilex, drought tolerant) affects tree water stress during extreme drought. Our experiment showed that the intimate mixture strongly alleviated Q. ilex water stress while it marginally impacted P. halepensis water stress. Three mechanistic explanations for this pattern are supported by our modeling analysis. First, the difference in stomatal regulation between species allowed Q. ilex trees to benefit from additional soil water in mixture, thereby maintaining higher water potentials and sustaining gas exchange. By contrast, P. halepensis exhibited earlier water stress and stomatal regulation. Second, P. halepensis trees showed stable water potential during drought, although soil water potential strongly decreased, even when grown in a mixture. Model simulations suggested that hydraulic isolation of the root from the soil associated with decreased leaf cuticular conductance was a plausible explanation for this pattern. Third, the higher predawn water potentials for a given soil water potential observed for Q. ilex in mixture can-according to model simulations-be explained by increased soil-to-root conductance, resulting from higher fine root length. This study brings insights into the mechanisms involved in improved drought resistance of mixed species forests.
摘要：
物种混合被推广为使森林适应气候变化的重要管理选择。然而,关于树木多样性如何影响树木水分胁迫几乎没有共识，潜在的机制仍然难以捉摸。通过使用温室实验和土壤-植物-大气水力模型，我们探索了是否以及为什么混合等氢阿勒颇松(Pinushalepensis，避免干旱)和无等元霍姆橡树(Quercusilex，耐旱性）影响极端干旱期间的树木水分胁迫。我们的实验表明，紧密混合物强烈缓解了Q.Ilex水胁迫，而对P.halepensis水胁迫有一定的影响。我们的建模分析支持了对这种模式的三种机械解释。首先,物种之间气孔调节的差异使Q.Ilex树可以从混合物中额外的土壤水中受益，从而保持较高的水势和维持气体交换。相比之下,哈雷普表现出早期的水分胁迫和气孔调节。第二,P.halepensis树在干旱期间显示出稳定的水势，尽管土壤水势大幅下降，即使在混合物中生长。模型模拟表明，与叶片角质层电导率降低相关的土壤中根部的水力隔离是这种模式的合理解释。第三，根据模型模拟，对于Q.Ilex在混合物中观察到的给定土壤水势的较高黎明前水势可以通过增加的土壤-根电导来解释，由于较高的细根长度。这项研究为提高混交林的抗旱性提供了见解。
