Embolism spreading in angiosperm xylem occurs via mesoporous pit membranes between vessels. Here, we investigate how the size of pore constrictions in pit membranes is related to pit membrane thickness and embolism resistance. In three models, pit membranes are modelled as multiple layers to investigate how pit membrane thickness and the number of intervessel pits per vessel determine pore constriction sizes, the probability of encountering large pores, and air-seeding. These estimations were complemented by measurements of pit membrane thickness, embolism resistance, and number of intervessel pits per vessel (n = 31, 31, and 20 species, respectively). Constriction sizes in pores decreased with increasing pit membrane thickness, which agreed with the measured relationship between pit membrane thickness and embolism resistance. The number of pits per vessel affected constriction size and embolism resistance much less than pit membrane thickness. A strong relationship between estimated air-seeding pressures and measured embolism resistance was observed. Pore constrictions provide a mechanistic explanation why pit membrane thickness determines embolism resistance, and suggest that hydraulic safety can be uncoupled from hydraulic efficiency. Although embolism spreading remains puzzling and encompasses more than pore constriction sizes, angiosperms are unlikely to have leaky pit membranes, which enables tensile transport of water.

中文翻译：

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血管间窝膜的缩孔减少了被子植物木质部中栓塞扩散的风险

栓塞在被子植物木质部中扩散是通过血管之间的中孔凹坑膜发生的。在这里，我们调查了坑膜中的孔收缩的大小与坑膜的厚度和抗栓塞性之间的关系。在三个模型中，将凹坑膜建模为多层，以研究凹坑膜的厚度和每个容器的脉管间凹坑的数量如何确定孔道收缩的大小，遇到大孔的可能性和播种。这些估计值是通过测量坑膜厚度，抗栓塞性和每个容器的小窝间坑数（分别为n = 31、31和20种）来补充的。孔的收缩尺寸随凹坑膜厚度的增加而减小，这与测得的凹坑膜厚度和抗栓塞性之间的关系一致。每个容器的凹坑数影响收缩尺寸和抗栓塞性，其远小于凹坑膜厚度。观察到了估计的播种压力与测得的抗栓塞性之间的密切关系。孔收缩提供了机械解释，解释了为什么坑膜厚度决定了抗栓性，并建议水力安全性与水力效率脱钩。尽管栓塞的扩散仍然令人困惑，并且所涵盖的范围不仅仅包括收缩孔的大小，但被子植物不大可能具有渗漏的坑膜，从而可以进行水的拉伸输送。孔收缩提供了机械解释，解释了为什么坑膜厚度决定了抗栓性，并建议水力安全性与水力效率脱钩。尽管栓塞的扩散仍然令人困惑，并且所涵盖的范围不仅仅包括收缩孔的大小，但被子植物不大可能具有渗漏的坑膜，从而可以进行水的拉伸输送。孔收缩提供了机械解释，解释了为什么坑膜厚度决定了抗栓性，并建议水力安全性与水力效率脱钩。尽管栓塞的扩散仍然令人困惑，并且所涵盖的范围不仅仅包括收缩孔的大小，但被子植物不大可能具有渗漏的坑膜，从而可以进行水的拉伸输送。