Coutand Catherine, Dupraz Christian, Jaouen Gaëlle, Ploquin Stéphane, Adam Boris
INRA, UMR PIAF- Université Blaise Pascal, 234 avenue du Brézet, 63100 Clermont-Ferrand, France.
Ann Bot. 2008 Jun;101(9):1421-32. doi: 10.1093/aob/mcn054. Epub 2008 Apr 29.
Plastic tree-shelters are increasingly used to protect tree seedlings against browsing animals and herbicide drifts. The biomass allocation in young seedlings of deciduous trees is highly disturbed by common plastic tree-shelters, resulting in poor root systems and reduced diameter growth of the trunk. The shelters have been improved by creating chimney-effect ventilation with holes drilled at the bottom, resulting in stimulated trunk diameter growth, but the root deficit has remained unchanged. An experiment was set up to elucidate the mechanisms behind the poor root growth of sheltered Prunus avium trees.
Tree seedlings were grown either in natural windy conditions or in tree-shelters. Mechanical wind stimuli were suppressed in ten unsheltered trees by staking. Mechanical stimuli (bending) of the stem were applied in ten sheltered trees using an original mechanical device.
Sheltered trees suffered from poor root growth, but sheltered bent trees largely recovered, showing that mechano-sensing is an important mechanism governing C allocation and the shoot-root balance. The use of a few artificial mechanical stimuli increased the biomass allocation towards the roots, as did natural wind sway. It was demonstrated that there was an acclimation of plants to the imposed strain.
This study suggests that if mechanical stimuli are used to control plant growth, they should be applied at low frequency in order to be most effective. The impact on the functional equilibrium hypothesis that is used in many tree growth models is discussed. The consequence of the lack of mechanical stimuli should be incorporated in tree growth models when applied to environments protected from the wind (e.g. greenhouses, dense forests).
塑料树木防护套越来越多地用于保护树苗免受食草动物啃食和除草剂漂移的影响。常见的塑料树木防护套会严重干扰落叶树幼苗的生物量分配，导致根系发育不良，树干直径生长减缓。通过在底部打孔形成烟囱效应通风对防护套进行了改进，从而促进了树干直径的生长，但根系不足的问题依然存在。为此开展了一项实验，以阐明受防护的甜樱桃树根系生长不良背后的机制。
将树苗种植在自然有风的环境中或树木防护套内。通过打桩抑制了10棵未加防护树木的机械风刺激。使用一种原始的机械设备对10棵有防护套的树木施加茎干的机械刺激（弯曲）。
有防护套的树木根系生长不良，但有防护套且经过弯曲处理的树木基本恢复，这表明机械感应是控制碳分配和地上部与根系平衡的重要机制。施加少量人工机械刺激会增加根系的生物量分配，自然风摇曳也有同样效果。结果表明植物对施加的应变存在适应性。
本研究表明，如果使用机械刺激来控制植物生长，为达到最佳效果应低频施加。讨论了对许多树木生长模型中使用的功能平衡假说的影响。在应用于防风环境（如温室、茂密森林）的树木生长模型中，应纳入缺乏机械刺激的影响。
