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Negative Success In Tiny Tree

机译：小树上的负成功

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摘要

When engineers were building beam engines in the early eighteenth century to pump out water-logged mines, they found that they couldn't pull water up more than about 9 metres (the height of water that can be supported by the drop in pressure between the atmosphere and a vacuum). Trees grow many times taller - more than 100 metres in the case of the tallest redwoods. Yet they supply their leaves with a constant flow of water. They achieve this feat by keeping the water high up in their trunks under pressures many atmospheres below that of a vacuum. Elsewhere in this issue, Wheeler and Stroock report a duplication of this trick: they have created a tiny 'synthetic tree' through whose trunk water flows at pressures of around -10 atmospheres (T. D. Wheeler and A. D. Stroock Nature 455,208-212; 2008). In trees, evaporation of water from leaf cells called spongy mesophyll pulls water up through hollow cells in the trunk (spongy mesophyll is the tissue in the lower half of this picture, a cross-section through a leaf). The strong, cohesive properties of water, responsible for its powerful surface tension, allow the water to exist at large negative pressures. But even the smallest bubble would explosively expand into the water, disrupting its flow in a process known as cavitation. The interface between the plant's water system and the air, formed by the spongy mesophyll, must allow water to pass, but not the gas molecules that would cause cavitation.
机译：工程师在18世纪初建造束流发动机以抽出淹水的矿井时，发现它们不能将水拉出超过9米（水的高度可以通过水位之间的压力下降来支持）。大气和真空）。树木长高了许多倍-如果是最高的红木，则超过100米。然而，它们为叶片提供了恒定的水流。他们通过在许多大气压以下低于真空的压力下将树干中的水保持高位来实现这一壮举。在此问题的其他地方，Wheeler和Stroock报告了此技巧的重复：他们创建了一个微小的“合成树”，树干中的树干水以大约-10个大气压的压力流过（T. D. Wheeler和A. D. Stroock Nature 455,208-212； 2008）。在树木中，水分从称为海绵状叶肉的叶细胞中蒸发，从而使水向上穿过树干中的空心细胞（海绵状叶肉是该图片下半部分的组织，是叶的横截面）。水的强粘性特性决定了其强大的表面张力，可让水以较大的负压存在。但是，即使最小的气泡也会爆炸性地扩散到水中，从而在称为空化的过程中破坏其流动。由海绵状叶肉形成的植物的水系统与空气之间的界面必须允许水通过，但不允许引起气蚀的气体分子通过。

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  • 来源
    《Nature》 |2008年第7210期|p.181|共1页
  • 作者

    Christopher Surridge;

  • 作者单位

    Austrian Academy of Sciences, 1090 Vienna,Austria;

  • 收录信息 美国《科学引文索引》(SCI);美国《工程索引》(EI);美国《生物学医学文摘》(MEDLINE);美国《化学文摘》(CA);
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类 自然科学总论;
  • 关键词

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