Drought induced tree mortality - a tree-ring isotope based conceptual model to assess mechanisms and predispositions
Drought induced tree mortality - a tree-ring isotope based conceptual model to assess mechanisms and predispositions
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DOI：
10.1111/nph.15154
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发表时间：
2018-07-01
期刊：
影响因子：
9.4
通讯作者：
Saurer, Matthias
中科院分区：
文献类型：
--
作者：
Gessler, Arthur;Cailleret, Maxime;Saurer, Matthias
由于气候模型预测干旱事件的频率增加以及气温升高，干旱导致的树木死亡率可能会在未来增加（Dai，2013年;艾伦等人，2015）。除了存在刺激（例如热和干旱事件）和贡献（例如机会主义生物因子，如树皮甲虫）因素之外，特定物种或给定物种的个体的易感性被认为是理解为什么一些树木存活而另一些树木屈服于干旱的核心（Manion，1981; McDowell等人，2008; Voltas等人，2013; Gessler等人，2016; Martin-StPaul等人，2017年）。这对于在动态植被模型中模拟树木死亡率也是至关重要的（Meiret等人，2015）。诱发因素被认为与长期的气候压力有关（Voltas等人，2013），普遍的长期营养供应（Gessler等人，2016），水资源利用战略（Hentschel等人，2014）、树高以及种间和种内竞争（Grote等人，2016）和害虫、病原体或空气污染（艾伦等人，2010年）。即使在干燥环境中生长的植物可能具有最宽的水力安全裕度（Choat等人，2012; Martin-StPaul等人，2017年），干旱事件迫使这些和碳安全边际的点，树木可能处于生理失败或未能抵御生物攻击的风险（麦克道尔，2011年）。水力和共质体衰竭以及碳库的强烈减少（也称为“碳饥饿”）被假定为导致树木死亡的两种主要的非排他性生理机制（亚当斯等人，2017），与生物制剂强烈相互作用（Anderegg et al.，2015）。水力破坏概括了细胞干燥的所有方面，导致共质体生化功能的停止，以及通过木质部栓塞的水运输的破坏（McDowell等人，2011年）。碳饥饿描述了由于来自光合作用和储存的低碳水化合物供应而不能充分满足维持细胞和防御代谢的碳需求的情况（McDowell等人，2008年）。最近，亚当斯等人。（2017）表明，木质部水力衰竭在整个分类群中普遍存在，而碳饥饿并不普遍，但对裸子植物来说仍然很常见（另见Martınez-Vilaltaet al.，2016）可能是在长期中度干旱胁迫后（McDowell等人，2008年）。此外，水力功能和碳水化合物代谢密切相关，因此水力衰竭和碳饥饿之间可能存在相互依赖性（McDowell，2011; Sevanto等人，2014年）。尽管水力失效可能独立于碳饥饿而发生，但已经观察到许多情况，其中碳平衡和水力学都受损（亚当斯等人，2017年）。这里应用的碳饥饿-水力破坏概念是一个连续体，其中一个过程对死亡率的影响相对较强。一棵树的碳饥饿或液压故障（图1a）的倾向可能是由特定的性状综合征（Anderegget等人，2016）反映了面对干旱的不同策略（Eschervaroff等人，2016年），根据当地资源可用性的差异进行了修改。我们已经选择了我们的概念模型的主要方法是一个同种同步比较的增长和树木年轮同位素信号之间的后期死亡和存活的树木在较长的时间内从同一立场，旨在了解死亡机制和各自的易感性在给定的环境背景下。我们并不声称我们的结果是可推广的一个给定的物种，因为它们不仅会受到物种的具体特征，但也树的个人…
Drought-induced tree mortality is likely to increase in future as climate models forecast increased frequency of drought events together with higher air temperatures (Dai, 2013; Allen et al., 2015). Besides the presence of inciting (eg heat and drought events) and contributing (eg opportunistic biotic agents such as bark beetles) factors, predisposition of particular species or individuals of a given species is considered as central for understanding why some trees survive while others succumb to drought (Manion, 1981; McDowell et al., 2008; Voltas et al., 2013; Gessler et al., 2016; Martin-StPaul et al., 2017). This is also crucial for simulating tree mortality in dynamic vegetation models (Meiret al., 2015). Predisposing factors are assumed to be related to long-term climatic stressors (Voltas et al., 2013), prevailing longterm nutrient supply (Gessler et al., 2016), water-use strategies (Hentschel et al., 2014), tree height and interspecific and intraspecific competition (Grote et al., 2016) and pests, pathogens or air pollution (Allen et al., 2010). Even though plants growing in dry environments may have the broadest hydraulic safety margins (Choat et al., 2012; Martin-StPaul et al., 2017), drought events force these and also the carbon safety margins to points where trees may be at risk of physiological failure or failure to defend against biotic attacks (McDowell, 2011). Hydraulic and symplastic failure, and strong reduction in carbon pools (also called ‘carbon starvation’) have been postulated as the two main, nonexclusive physiological mechanisms leading to tree mortality (Adams et al., 2017), in strong interaction with biotic agents (Anderegg et al., 2015). Hydraulic failure summarizes all aspects of cellular desiccation causing cessation of symplastic biochemical functioning, and disruption of water transport through xylem embolism (McDowell et al., 2011). Carbon starvation describes the situation when the carbon demand for maintenance of cellular and defensive metabolism is not sufficiently met owing to low carbohydrate supply from photosynthesis and storage (McDowell et al., 2008). Recently, Adams et al.(2017) showed that xylem hydraulic failure was ubiquitous across taxa, while carbon starvation was not universal but still common for gymnosperms (see also Martınez-Vilaltaet al., 2016) probably after long-term moderate drought stress (McDowell et al., 2008). Moreover, hydraulic function and carbohydrate metabolism are strongly linked and thus there might be interdependencies between hydraulic failure and carbon starvation (McDowell, 2011; Sevanto et al., 2014). Even though hydraulic failure might occur independently of carbon starvation, many cases have been observed where carbon balance and hydraulics were both impaired (Adams et al., 2017). The carbon starvation–hydraulic failure concept as applied here is rather a continuum with relatively stronger influence of the one or the other process on mortality. A tree’s predisposition to carbon starvation or to hydraulic failure (Fig. 1a) may be indicated by specific syndromes of traits (Anderegget al., 2016) reflecting different strategies to face drought (Pivovaroff et al., 2016), modified by differences in local resource availability. The main approach we have chosen for our conceptual model is a conspecific synchronic comparison of growth and tree ring isotopic signals between later dying and surviving trees over longer time periods from the same stand aiming to understand mortality mechanisms and the respective predisposition in a given environmental context. We do not claim our results to be generalizable for a given species as they will not only be affected by species specific traits but also by tree individual …