Research Group for Environmental Science, Nuclear Science and Engineering Directorate, Japan Atomic Energy Agency, 2-4 Shirakata-Shirane, Tokai-mura, Naka-gun, Ibaraki 319-1195, Japan.
J Environ Radioact. 2012 Jul;109:94-102. doi: 10.1016/j.jenvrad.2012.02.004. Epub 2012 Mar 3.
To investigate the role of belowground root uptake of tritiated water (HTO) in controlling land-surface tritium (T) dynamics, a sophisticated numerical model predicting tritium behavior in an atmosphere-vegetation-soil system was developed, and numerical experiments were conducted using the model. The developed model covered physical tritiated hydrogen (HT) transport in a multilayered atmosphere and soil, as well as microbial oxidation of HT to HTO in the soil, and it was incorporated into a well-established HTO-transfer organically bound tritium (OBT)-formation model. The model performance was tested through the simulation of an existing HT-release experiment. Numerical experiments involving a hypothetical acute HT exposure to a grassland field with a range of rooting depths showed that the HTO release from the leaves to the atmosphere, driven by the root uptake of the deposited HTO, can exceed the HTO evaporation from the ground surface to the atmosphere when root water absorption preferentially occurs beneath the ground surface. Such enhanced soil-leaf-atmosphere HTO transport, caused by the enhanced root HTO uptake, increased HTO concentrations in both the surface atmosphere and in the cellular water of the leaf. Consequently, leaf OBT assimilation calculated for shallow rooting depths increased by nearly an order of magnitude compared to that for large rooting depths.
为了探究地下根系吸收氚水（HTO）在控制陆地表面氚（T）动态中的作用，开发了一个复杂的数值模型，用于预测大气-植被-土壤系统中的氚行为，并使用该模型进行了数值实验。所开发的模型涵盖了多层大气和土壤中物理氚化氢（HT）的传输，以及土壤中 HT 向 HTO 的微生物氧化，它被纳入了一个成熟的 HTO 转移有机结合氚（OBT）形成模型中。通过模拟现有的 HT 释放实验来测试模型性能。涉及一系列根系深度的假设性急性 HT 暴露于草原的数值实验表明，当根系优先吸收地下 HTO 时，由叶片向大气中沉积的 HTO 吸收驱动的 HTO 释放可以超过地面向大气中 HTO 的蒸发。这种由增强的根系 HTO 吸收引起的增强的土壤-叶片-大气 HTO 传输增加了地表大气和叶片细胞水中的 HTO 浓度。因此，与根系较深相比，浅层根系的叶片 OBT 同化计算增加了近一个数量级。
