Simovic Milos, Michaletz Sean T
Department of Botany, The University of British Columbia, Vancouver, British Columbia, Canada.
Biodiversity Research Centre, The University of British Columbia, Vancouver, British Columbia, Canada.
Plant Cell Environ. 2025 Sep;48(9):6912-6923. doi: 10.1111/pce.15660. Epub 2025 Jun 5.
Xylem conduit morphology is shaped by the challenges of minimizing hydraulic resistance and preventing conduit wall collapse during vertical sap transport. While hydraulic theories predict that conduits widen from tip to base to minimize resistance, theory has not addressed how collapse prevention influences vertical variation in conduit morphology. Additionally, scaling relationships in roots remain largely unexplored. Here, we evaluate existing theories for conduit diameter scaling and synthesize new theory for vertical variation in thickness-to-span ratios. We test these theories using a novel bootstrapping approach to minimize sampling biases and analyze a data set of nearly 600 000 xylem conduits spanning above- and belowground organs from five conifer species. As predicted, conduits widened with distance from the leaf tip, with scaling exponents closely aligning with theoretical predictions. Conduits also widened from fine roots to coarse roots, mirroring aboveground patterns. Thickness-to-span ratios increased from base to tip and consistently exceeded the predicted critical collapse limit. These findings reveal how the physics of sap transport shape xylem morphology to balance hydraulic efficiency and structural stability. By combining novel theory, robust statistical methods, and comprehensive data, this study refines scaling predictions and advances understanding of mechanisms shaping xylem anatomy across plant organs.
木质部导管形态受到在垂直液流运输过程中最小化水力阻力和防止导管壁塌陷挑战的影响。虽然水力理论预测导管从顶端到基部会变宽以最小化阻力，但该理论尚未探讨防止塌陷如何影响导管形态的垂直变化。此外，根系中的比例关系在很大程度上仍未得到探索。在这里，我们评估了现有的导管直径比例理论，并综合了关于厚度与跨度比垂直变化的新理论。我们使用一种新颖的自举方法来测试这些理论，以最小化采样偏差，并分析了一个包含近60万个木质部导管的数据集，这些导管来自五种针叶树的地上和地下器官。正如预测的那样，导管随着离叶尖距离的增加而变宽，比例指数与理论预测密切吻合。导管也从细根到粗根变宽，与地上模式相似。厚度与跨度比从基部到顶端增加，并始终超过预测的临界塌陷极限。这些发现揭示了液流运输的物理学如何塑造木质部形态，以平衡水力效率和结构稳定性。通过结合新理论、强大的统计方法和全面的数据，本研究完善了比例预测，并推进了对塑造植物器官木质部解剖结构机制的理解。
