Plants redistribute water from wet to dry soil layers through their roots, in the process called hydraulic redistribution. Although the relevance and occurrence of this process are well accepted, resolving the spatial distribution of hydraulic redistribution remains challenging. Here, we show how to use neutron radiography to quantify the rate of water efflux from the roots to the soil. Maize (Zea mays L.) plants were grown in a sandy substrate 40 cm deep. Deuterated water (D₂O) was injected in the bottom wet compartment, and its transport through the roots to the top dry soil was imaged using neutron radiography. A diffusion–convection model was used to simulate the transport of D₂O in soil and root and inversely estimate the convective fluxes. Overnight, D₂O appeared in nodal and lateral roots in the top compartment. By inverse modeling, we estimated an efflux from lateral roots into the dry soil equal to j_r = 2.35 × 10⁻⁷ cm⁻¹. A significant fraction of the redistributed water flew toward the tips of nodal roots (3.85 × 10⁻⁸ cm³ s⁻¹ per root) to sustain their growth. The efflux from nodal roots depended on the roots’ length and growth rate. In summary, neutron imaging was successfully used to quantify hydraulic redistribution. A numerical model was needed to differentiate the effects of diffusion and convection. The highly resolved images showed the spatial heterogeneity of hydraulic redistribution.

中文翻译：

---

利用中子射线照相技术定量分析玉米根系中水力的重新分布

植物通过根部将水从湿的土壤层重新分配到干燥的土壤层，这一过程称为水力重新分配。尽管已经很好地接受了这一过程的相关性和发生性，但是解决水力再分配的空间分布仍然具有挑战性。在这里，我们展示了如何使用中子射线照相术来量化从根部到土壤的水外排率。玉米（Zea mays L.）植物生长在40 cm深的沙质基质上。将氘化水（D ₂ O）注入底部潮湿隔室中，并使用中子射线照相术成像其通过根向顶部干燥土壤的迁移。扩散-对流模型用于模拟D ₂ O在土壤和根系中的迁移，并反演对流通量。一夜之间，D₂ Ó出现在节点和侧根在顶室中。通过逆模型，我们估计从侧根到干燥土壤的外排量等于j _r = 2.35×10 ^-7 cm ^-1。重新分配的水的很大一部分飞向了节根的尖端（每个根为3.85×10 ^-8 cm ³ s ^-1）以维持其生长。结根的流出取决于根的长度和生长速率。总而言之，中子成像已成功用于量化水力重新分配。需要一个数值模型来区分扩散和对流的影响。高度分辨的图像显示了水力重新分配的空间异质性。