Does phloem osmolality affect diurnal diameter changes of twigs but not of stems in Scots pine?
Does phloem osmolality affect diurnal diameter changes of twigs but not of stems in Scots pine?
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DOI：
10.1093/treephys/tpy121
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发表时间：
2019-02-01
期刊：
影响因子：
4
通讯作者：
Sterck, Frank J.
中科院分区：
文献类型：
--
作者：
Lazzarin, Martina;Zweifel, Roman;Sterck, Frank J.
在温带树种的树干底部测得的树干直径变化主要可以用蒸腾作用被动驱动的流动和储藏隔室的液压系统来解释。活跃的渗透过程被认为只起着次要的作用。在这里，我们探索这种渗透过程是否对枝条直径的变化比茎直径的变化有更大的影响，因为枝条更靠近叶片，叶是新获得碳的主要来源。我们研究了松树木材和树皮的树干和树枝直径的变化，与针叶和树皮的渗透压的波动是平行的。我们发现，在白天，树枝树皮大小的增加与树枝木材的大小同步减少，而针叶渗透压即使在晴朗的日子也不会持续增加。从下午晚些时候到第二天早上，树皮和木材的大小变化要么颠倒，要么平行。在茎底部没有可测量到的这种模式。树干木材大小变化不大，树干树皮呈白天减少、夜间增加的规律。茎基部的渗透压在24小时内没有表现出特定的变化过程。我们认为，从针叶中的同化物被迅速运输到树枝，在那里糖负荷增加了树皮组织的渗透压，解释了树皮大小的增加(过度)补偿了木质部大小的减少。茎基座在很大程度上遵循了被动式液压系统的预期，没有可测量的渗透调节作用。因此，在枝条和茎基处直径的变化遵循不同的日动态。
Diel stem diameter changes measured at the stem base of temperate tree species can be mostly explained by a hydraulic system of flow and storage compartments passively driven by transpiration. Active, osmotic processes are considered to play a minor role only. Here we explore whether such osmotic processes have a stronger impact on diel changes in twig diameter than in stem diameter because twigs are closer to the leaves, the main source of newly acquired carbon. We investigated stem and twig diameter changes of wood and bark of pine trees in parallel to fluctuations of the osmolality in needles and in the bark at the stem base. We found consistent twig bark size increments concurrent with twig wood size decreases during daylight hours whereas needle osmolality was not consistently increasing even on sunny days. The size changes of bark and wood either reversed or ran in parallel from late afternoon onwards until the next morning. No such patterns were measurable at the stem base. Stem wood was hardly changing in size, whereas stem bark followed the regular pattern of a decrease during the daylight hours and an increase during the night. Osmolality at the stem base showed no particular course over 24 h. We conclude that assimilates from the needles were rapidly transported to the twigs where they increased the osmolality of the bark tissue by sugar loading, explaining the bark size increase (over-) compensating the xylem size decrease. The stem base largely followed the expectation of a passive, hydraulic system without a measurable role of osmoregulation. Diameter changes thus follow different diurnal dynamics in twigs and at the stem base.