Wood density predicts mortality threshold for diverse trees
Wood density predicts mortality threshold for diverse trees
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木材密度预测不同树木的死亡率阈值
DOI：
10.1111/nph.17117
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发表时间：
2020-12-19
期刊：
影响因子：
9.4
通讯作者：
Brodribb, Timothy J.
中科院分区：
文献类型：
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作者：
Liang, Xingyun;Ye, Qing;Brodribb, Timothy J.
在过去的几十年里，每个森林生物群系都记录了干旱导致的森林死亡，对生物多样性和生态系统功能产生了巨大影响（Allen et al., 2010; Hartmann et al., 2018; Brodribb et al., 2020）。由于我们对树木的致命水势（Ψlethal）的变化了解有限，因此缺乏对森林易受气候破坏的一般了解。实现这一关键目标需要一个可靠的Ψlethal代理，可以用来描述森林群落中许多物种的特征。树木水势（Ψ）决定了树木的水力导度和从土壤中吸收的水分，是生理应激的一个强大而直接的指标（Steppe, 2018）。Ψlethal是一个临界阈值Ψ，超过这个阈值，树木即使在补水一年之后也无法从干旱中恢复过来（Brodribb & Cochard, 2009; Choat, 2013）。面对干旱，随着土壤水分有效性的降低，树木Ψ逐渐下降（即变得更加负），导致木质部空化和木质部电导率的丧失（Sperry et al., 2002）。当树木Ψ低于Ψlethal时，空化现象在木质部导管内广泛传播，最终树木因细胞过度脱水而死亡（McDowellet等，2008;Körner, 2019）。最近的一项数据综合显示，脱水至Ψlethal的树木木质部电导率损失高达60%，这表明干旱导致的树木死亡普遍存在水力失效（Adams等人，2017）。然而，由于在遭受致命组织损伤的植物中测量树木Ψ存在技术问题，导致树木死亡的Ψlethal尚未在物种间广泛量化，尽管它对理解和预测植被对干旱的反应很重要（Choat等人，2018；Blackman等人，2019；McDowell等人，2019）。测定树木的Ψlethal特别费时费力。Ψlethal的量化通常是通过监测盆栽植物在暴露于不同程度的水分胁迫后的恢复情况来完成的。这种方法可能需要几个月到几年的盆栽实验（Brodribb和Cochard, 2009； Kursar等人，2009），甚至几年到几十年的研究自然干旱事件（Breshears等人，2009；McDowell等人，2016）。此外，与季节性或短暂干旱引起的落叶期相比，识别水分胁迫期间树木死亡的挑战更大（Wolfe et al., 2016）。因此，我们需要探索Ψlethal的可靠代理，以了解森林对干旱的脆弱性。
In the past decades, drought-induced forest die-off has been recorded on every forested biome, exerting great effects on biodiversity and ecosystem functions (Allen et al., 2010; Hartmann et al., 2018; Brodribb et al., 2020). A general understanding of forest vulnerability to damage due to climate is lacking, because of our limited understanding of the variation in lethal water potential (Ψlethal) of trees. Achieving this critical goal requires a reliable proxy for Ψlethal that can be used to characterize many species in a forest community.Tree water potential (Ψ), which shapes tree hydraulic conductance and water uptake from the soil, is a robust and direct indicator of physiological stress (Steppe, 2018). The Ψlethal is a critical threshold of Ψ beyond which trees are unable to recover from drought, even after a year of rewatering (Brodribb & Cochard, 2009; Choat, 2013). In the face of drought, along with decreasing soil water availability, tree Ψ gradually drops (ie becomes more negative), inducing xylem cavitation and loss of xylem conductivity (Sperry et al., 2002). When tree Ψ falls below the Ψlethal, cavitation spreads widely within xylem conduits, and eventually, trees die from excessive dehydration of cells (McDowellet al., 2008; Körner, 2019). A recent data synthesis showed that trees dehydrated to Ψlethal experienced a> 60% loss of xylem conductivity, suggesting a ubiquitous hydraulic failure in drought-induced tree mortality (Adams et al., 2017). However, due to technical problems associated with measuring tree Ψ in plants undergoing lethal tissue damage, the Ψlethal leading to tree mortality has not been quantified widely across species, despite its importance in understanding and predicting the response of vegetation to drought (Choat et al., 2018; Blackman et al., 2019; McDowell et al., 2019). The determination of the Ψlethal of trees is particularly time-and labor-consuming. Quantification of Ψlethal is typically done by monitoring the recovery of potted plants after exposure to different degrees of water stress. This approach may take months to years for the potted experiments (Brodribb & Cochard, 2009; Kursar et al., 2009), and even years to decades for the studies examining natural drought events (Breshears et al., 2009; McDowell et al., 2016). Added to this is the challenge of identifying tree death during water stress as opposed to seasonal or transient drought-induced leaf deciduousness (Wolfe et al., 2016). Therefore, we need to explore a reliable proxy for Ψlethal to understand forest vulnerability to drought.