Evidence for Air-Seeding: Watching the Formation of Embolism in Conifer Xylem.

S Mayr, B Kartusch, S Kikuta
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Abstract

Water transport in plants is based on a metastable system as the xylem "works" at negative water potentials (ψ). At critically low ψ, water columns can break and cause embolism. According to the air-seeding hypothesis, this occurs by air entry via the pits. We studied the formation of embolism in dehydrating xylem sections of Juniperus virginiana (Cupressaceae), which were monitored microscopically and via ultrasonic emission analyses. After replacement of water by air in outer tracheid layers, a complex movement of air-water menisci into tracheids was found. With decreasing ψ, pits started to aspirate and the speed of menisci movements increased. In one experiment, an airseeding event could be detected at a pit. The onset of ultrasonic activity was observed when pits started to close, and ultrasonic emission ceased at intense dehydration. Experiments clearly indicated that predictions of the air-seeding hypothesis are correct: At low ψ, pit mechanisms to prevent air entry failed and air spread into tracheids. ψ fluctuations caused complex movements of air-water menisci and pits, and at low ψ, air-seeding caused ultrasonic emissions. Main insights are presented in a video.

空气播种的证据:针叶树木质部栓塞形成的观察。
植物中的水分运输是基于一个亚稳系统,木质部在负水势(ψ)下工作。在极低的ψ值下,水柱会破裂并导致栓塞。根据空气播撒假说,这是由空气通过凹坑进入而发生的。研究了维吉尼亚桧(桧科)木质部脱水后的栓塞形成,并对其进行了显微观察和超声发射分析。外管胞层的水被空气取代后,气-水半月板进入管胞发生复杂的运动。随着ψ值的减小,凹坑开始吸气,半月板运动速度加快。在一个实验中,可以在一个坑中检测到一个空投事件。超声活动的开始是在凹坑开始关闭时观察到的,超声发射在强烈脱水时停止。实验清楚地表明,空气播撒假说的预测是正确的:在低ψ值下,防止空气进入的坑洞机制失效,空气扩散到管状管中。ψ的波动引起气-水半月板和坑的复杂运动,在低ψ时,空气播种引起超声波发射。主要观点在视频中呈现。
本文章由计算机程序翻译,如有差异,请以英文原文为准。
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