Tree responses to drought.
Tree responses to drought.
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DOI：
10.1093/treephys/tpr022
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发表时间：
2011-03
期刊：
影响因子：
4
通讯作者：
M. G. Ryan
中科院分区：
文献类型：
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作者：
M. G. Ryan
随着全球气候变化，干旱可能会在未来变得更加普遍（IPCC 2007）。有几个因素将促使干旱更加频繁：融雪更早、气温更高和降水变化更大。对于水循环以融雪为主的生态系统，气温升高会导致融雪提前（Stewart et al. 2005）和无雪期延长、干燥（Westerling et al. 2006）。如果蒸散量不增加，温度升高也会增加水汽压差。降水量的较大变化对植物水分平衡有两个影响：更长时间没有水，在更强烈的风暴中土壤中捕获的更少。最近许多树木死亡事件与干旱有关（艾伦等人，2010），但我们对树木的干旱反应了解多少？树木对低土壤水势的生理反应各不相同，但已得到相当好的表征（McDowell等人，2008年）-它们从伴随较低的叶水势（非等水反应）到保持叶水势高于阈值（等水反应），其间有各种策略。许多树种在严重干旱期间落叶，减少蒸腾作用和光合作用，并调整分配到根部和储存（McDowell等人，2008年）。干旱也会“削弱”树木，使其更容易受到昆虫和病原体的攻击（McDowell等人，2008年）。生长可通过细胞分裂和细胞扩增受损而降低（Hsiao 197 3），这发生在比光合抑制更低的水分胁迫阈值下（Hsiao et al. 1976）。事实上，多种生理过程响应于不同的植物水势（Hsiao 1973，Ditmarova et al. 2010），因此干旱的严重程度将影响生理响应。干旱也是相对的，适应低降水气候的物种可以在低土壤水势下生存，而低土壤水势会杀死或严重伤害更多中温带气候的树木，而中温带气候的树木可能会遭受干旱，这对干旱气候的树木来说是正常的。最后，我们知道有许多耐旱机制，其中许多涉及整个树木的协调。本期的两篇论文试图解开树木对干旱的一些复杂而多变的反应。Larcheveque等人（2011年）将两种不同的杂交白杨树苗（每棵都有
With global climate change, drought may become more com-mon in the future (IPCC 2007). Several factors will promote more frequent droughts: earlier snowmelt, higher temperatures and higher variability in precipitation. For ecosystems where the water cycle is dominated by snowmelt, warmer tempera-tures bring earlier melt (Stewart et al. 2005) and longer, drier snow-free periods (Westerling et al. 2006). Higher tempera-tures will also increase vapor pressure deficit if evapotranspira-tion does not also increase. Greater variability in precipitation has two implications for plant water balance: longer periods without water, and less captured in the soil in the more intense storms.Many recent tree mortality events have been linked to drought (Allen et al. 2010), but how much do we really know about the drought responses of trees? Physiological responses of trees to low soil water potential vary, but have been fairly well characterized (McDowell et al. 2008)—they vary from concomitantly lower leaf water potential (anisohydric response) to maintenance of leaf water potential above a threshold (isohydric response) with various strategies in between. Many tree species shed leaves during a strong drought, reducing transpiration and photosynthesis, and adjust partitioning to roots and storage (McDowell et al. 2008). Drought also ‘weakens’ trees and makes them more susceptible to insect attacks and pathogens (McDowell et al. 2008). Growth can be reduced through impairment of cell division and cell expansion (Hsiao 197 3), which occurs at a lower water stress threshold than does photosynthetic inhibi-tion (Hsiao et al. 1976). In fact, a variety of physiological processes respond at different plant water potentials (Hsiao 1973, Ditmarova et al. 2010), so that the severity of the drought will influence the physiological response. Drought is also relative—species adapted to low precipitation climates can survive low soil water potentials that would kill or seriously wound trees in more mesic climates and trees in mesic cli-mates might suffer from ‘drought’ that would be normal to trees in xeric climates. Finally, we know that there are many mechanisms of drought tolerance, and that many of these involve coordination within the whole tree.Two papers in this issue try to untangle some of the complex and variable responses of trees to drought. Larcheveque et al. (2011 ) droughted two different hybrid poplar saplings (each with