Swiss Federal Research Institute WSL, Zurcherstrasse 111, 8903 Birmensdorf, Switzerland.
J Exp Bot. 2011 May;62(8):2763-71. doi: 10.1093/jxb/erq443. Epub 2011 Jan 27.
Drought has been frequently discussed as a trigger for forest decline. Today, large-scale Scots pine decline is observed in many dry inner-Alpine valleys, with drought discussed as the main causative factor. This study aimed to analyse the impact of drought on wood formation and wood structure. To study tree growth under contrasting water supply, an irrigation experiment was installed in a mature Scots pine (Pinus sylvestris L.) forest at a xeric site in a dry inner-Alpine valley. Inter- and intra-annual radial increments as well as intra-annual variations in wood structure of pine trees were studied. It was found that non-irrigated trees had a noticeably shorter period of wood formation and showed a significantly lower increment. The water conduction cells were significantly enlarged and had significantly thinner cell walls compared with irrigated trees. It is concluded that pine trees under drought stress build a more effective water-conducting system (larger tracheids) at the cost of a probably higher vulnerability to cavitation (larger tracheids with thinner cell walls) but without losing their capability to recover. The significant shortening of the growth period in control trees indicated that the period where wood formation actually takes place can be much shorter under drought than the 'potential' period, meaning the phenological growth period.
干旱常被认为是森林衰退的触发因素。如今，许多干燥的阿尔卑斯山内部山谷都观察到了大规模的苏格兰松树衰退，干旱被认为是主要的致病因素。本研究旨在分析干旱对木材形成和木材结构的影响。为了研究不同供水条件下的树木生长情况，在一个干燥的阿尔卑斯山内部山谷的干旱地点，在成熟的苏格兰松树（Pinus sylvestris L.）森林中安装了灌溉实验。研究了松树的年际和年内径向增量以及年内木材结构的变化。结果发现，未灌溉的树木的木材形成期明显缩短，增量明显较低。与灌溉树木相比，输水细胞明显增大，细胞壁明显变薄。研究结论表明，在干旱胁迫下，松树会构建一个更有效的输水系统（较大的导管），但代价是可能更容易发生空化（较大的导管和较薄的细胞壁），但不会丧失其恢复能力。对照树木生长周期的显著缩短表明，在干旱条件下，木材形成的实际时间可能比“潜在”时间（即物候生长时间）短得多。
