Purpose

Root growth, respiration, water uptake as well as root exudation induce biogeochemical patterns in the rhizosphere that can change dynamically over time. Our aim is to develop a method that provides complementary information on 3D root system architecture and biogeochemical gradients around the roots needed for the quantitative description of rhizosphere processes.

Methods

We captured for the first time the root system architecture of maize plants grown in rectangular rhizotrons in 3D using neutron computed laminography (NCL). Simultaneously, we measured pH and oxygen concentration using fluorescent optodes and the 2D soil water distribution by means of neutron radiography. We co-registered the 3D laminography data with the 2D oxygen and pH maps to analyze the sensor signal as a function of the distance between the roots and the optode.

Results

The 3D root system architecture was successfully segmented from the laminographic data. We found that exudation of roots in up to 2 mm distance to the pH optode induced patterns of local acidification or alkalization. Over time, oxygen gradients in the rhizosphere emerged for roots up to a distance of 7.5 mm.

Conclusion

Neutron computed laminography allows for a three-dimensional investigation of root systems grown in laterally extended rhizotrons as the ones designed for 2D optode imaging studies. The 3D information on root position within the rhizotrons derived by NCL explained measured 2D oxygen and pH distribution. The presented new combination of 3D and 2D imaging methods facilitates systematical investigations of a wide range of dynamic processes in the rhizosphere.

中文翻译：

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中子计算机层析成像产生 3D 根系结构并补充时空根际模式的研究

目的

根系生长、呼吸、吸水以及根系分泌物会导致根际生物地球化学模式随时间动态变化。我们的目标是开发一种方法，该方法提供有关根际过程定量描述所需的 3D 根系结构和根部周围生物地球化学梯度的补充信息。

方法

我们首次使用中子计算机层析成像 (NCL) 以 3D 方式捕获了生长在矩形根管中的玉米植物的根系结构。同时，我们使用荧光光极测量 pH 值和氧气浓度，并通过中子射线照相术测量 2D 土壤水分分布。我们将 3D 层析成像数据与 2D 氧和 pH 值图共同注册，以分析传感器信号作为根和光极之间距离的函数。

结果

3D 根系统架构成功地从层析数据中分割出来。我们发现根系在距 pH 光极 2 毫米距离内的渗出物会导致局部酸化或碱化模式。随着时间的推移，根际中的氧气梯度出现在距离最远 7.5 毫米的根部。

结论

中子计算机层析成像允许对横向延伸的根管中生长的根系进行三维调查，这些根系是为 2D 光极成像研究设计的。NCL 获得的根管内根位置的 3D 信息解释了测量的 2D 氧和 pH 值分布。所提出的 3D 和 2D 成像方法的新组合促进了对根际各种动态过程的系统研究。