本论文于2017年12月4日发表于Nature Plants，原文题目如下：

Maintenance of carbohydrate transport in tall trees

长距离运输是树木的一个严峻的挑战，因为随着树木增高和运输途径增加，维管组织的水力阻力应该增加。这导致许多人疑惑，树木是否可以依靠被动运输机制将碳水化合物从叶子移到根部。尽管一些物种（如藤本植物和草本植物）可以主动的将糖类装载入韧皮部以增加运输的伸长动力，但许多树木不可能产生高的膨压，因为它们不使用转运体将糖加载到韧皮部。在这里，我们通过通过分析筛管的解剖结构（包括筛板几何结构），包括使用最近开发的制备和成像技术以及测量原位高大树木的叶子中的膨压，来检查高大树木如何保持高效的碳水化合物运输。在9个落叶树种中，我们发现韧皮部的水力阻力与植物高度成反比，这是因为沿着单个树木长度的筛管元件结构的变化。尽管解剖结构有很大差异，但这种比例关系在多个物种中看起来很稳健。当使用在成熟的红橡树的叶子测量的膨压来模拟韧皮部运输时，这种关系的重要性变得清楚。这些压力足以驱动韧皮部运输，这与韧皮部的结构变化一致，从而减少运输阻力。因此，随着树木大小的增加，树木维持韧皮部运输的长期秘密的关键在于韧皮部的结构及其随着植物高度而改变水力特性的能力。

Trees present a critical challenge to long-distance transport because as a tree grows in height and the transport pathway increases in length, the hydraulic resistance of the vascular tissue should increase. This has led many to question whether trees can rely on a passive transport mechanism to move carbohydrates from their leaves to their roots. Although species that actively load sugars into their phloem, such as vines and herbs, can increase the driving force for transport as they elongate, it is possible that many trees cannot generate high turgor pressures because they do not use transporters to load sugar into the phloem. Here, we examine how trees can maintain efficient carbohydrate transport as they grow taller by analysing sieve tube anatomy, including sieve plate geometry, using recently developed preparation and imaging techniques, and by measuring the turgor pressures in the leaves of a tall tree in situ. Across nine deciduous species, we find that hydraulic resistance in the phloem scales inversely with plant height because of a shift in sieve element structure along the length of individual trees. This scaling relationship seems robust across multiple species despite large differences in plate anatomy. The importance of this scaling becomes clear when phloem transport is modelled using turgor pressures measured in the leaves of a mature red oak tree. These pressures are of sufficient magnitude to drive phloem transport only in concert with structural changes in the phloem that reduce transport resistance. As a result, the key to the long-standing mystery of how trees maintain phloem transport as they increase in size lies in the structure of the phloem and its ability to change hydraulic properties with plant height.

每日一词：

hydraulic

英[haɪˈdrɔ:lɪk]

美[haɪˈdrɔlɪk]

adj. 水力的，水压的; 用水发动的; [建] 水硬的; 水力学的;

[例句]Reliable electronic controling system and hydraulic system.

可靠的电控系统和液压系统。