Drought impacts on tree phloem: from cell-level responses to ecological significance
Drought impacts on tree phloem: from cell-level responses to ecological significance
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DOI：
10.1093/treephys/tpy153
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发表时间：
2019-02
期刊：
影响因子：
4
通讯作者：
Yann Salmon;L. Dietrich;S. Sevanto;T. Hölttä;M. Dannoura;D. Epron
中科院分区：
文献类型：
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作者：
Yann Salmon;L. Dietrich;S. Sevanto;T. Hölttä;M. Dannoura;D. Epron
持续不断的气候变化正在增加全球大片地区干旱压力的风险。这类干旱事件降低了生态系统的生产力，并日益与树木死亡联系在一起。了解树木对缺水的反应是预测生态系统功能未来的关键。韧皮部是树木功能的核心，在整个植物中运输非结构性碳水化合物、营养物质以及防御和信息分子等资源。韧皮部的功能和运输资源的能力受到树内碳和水通量平衡的严格控制。因此，干旱预计会通过减少可用水和新的光合作用物质来影响韧皮部的功能。然而，在过去的几十年里，干旱对韧皮部的影响出人意料地没有受到关注。在这里，我们回顾了关于干旱对韧皮部运输的影响的现有知识，从细胞水平的装卸过程到可能对长途运输的影响，以及通过生态生理反馈对生态系统的影响。我们还指出了需要探索的新的研究前沿，以提高我们对干旱条件下韧皮部功能的理解。特别是，我们展示了增加干旱强度如何不同地影响韧皮部运输，而不是对放缓的反应，并探索严重干旱如何实际上扰乱韧皮部运输，足以威胁树木的生存。由于资源的运输影响到与树木相互作用的其他生物，我们还回顾了韧皮部对干旱的反应的生态后果，特别是捕食、互惠和竞争关系。最后，由于韧皮部是碳从源头吸收的主要途径，我们展示了干旱如何通过改变韧皮部运输来影响生物地球化学循环。总体而言，现有的知识与韧皮部对干旱的反应对于理解树木和生态系统功能的假设是一致的。然而，未来迫切需要对大范围的物种和生态系统进行研究，以全面了解这一问题。
On-going climate change is increasing the risk of drought stress across large areas worldwide. Such drought events decrease ecosystem productivity and have been increasingly linked to tree mortality. Understanding how trees respond to water shortage is key to predicting the future of ecosystem functions. Phloem is at the core of the tree functions, moving resources such as non-structural carbohydrates, nutrients, and defence and information molecules across the whole plant. Phloem function and ability to transport resources is tightly controlled by the balance of carbon and water fluxes within the tree. As such, drought is expected to impact phloem function by decreasing the amount of available water and new photoassimilates. Yet, the effect of drought on the phloem has received surprisingly little attention in the last decades. Here we review existing knowledge on drought impacts on phloem transport from loading and unloading processes at cellular level to possible effects on long-distance transport and consequences to ecosystems via ecophysiological feedbacks. We also point to new research frontiers that need to be explored to improve our understanding of phloem function under drought. In particular, we show how phloem transport is affected differently by increasing drought intensity, from no response to a slowdown, and explore how severe drought might actually disrupt the phloem transport enough to threaten tree survival. Because transport of resources affects other organisms interacting with the tree, we also review the ecological consequences of phloem response to drought and especially predatory, mutualistic and competitive relations. Finally, as phloem is the main path for carbon from sources to sink, we show how drought can affect biogeochemical cycles through changes in phloem transport. Overall, existing knowledge is consistent with the hypotheses that phloem response to drought matters for understanding tree and ecosystem function. However, future research on a large range of species and ecosystems is urgently needed to gain a comprehensive understanding of the question.