In-depth understanding of the patterns of root water uptake (RWU) is the key to improving the water-use efficiency of plants. Superabsorbent polymers (SAPs) can repeatedly absorb and then release water to plants when needed, which substantially increases the water-use efficiency of plants in arid and semiarid farming. However, it also creates a challenge in modeling RWU due to unstable soil hydraulic parameters and the unclear response of root growth to SAP application. A controlled soil column experiment was conducted to investigate the response of two important root indexes, that is, root length density (RLD) and root nitrogen mass density (RND), to SAP application, as well as their relationships with RWU. The results showed that the use of the SAP caused a steady increase in RND, and it also substantially increased the RLD in the early stage, but the rate of increase gradually slowed over time. The effect of unstable soil hydraulic parameters on RWU was analyzed in a numerical experiment, which indicated that the time-dependent effect of SAP on soil hydraulic parameters should be considered to avoid errors in calculating RWU. A specific method for calculating the RWU source/sink term in the Richards equation was proposed and ultimately used as the theoretical value of RWU to verify the RWU models based on RLD and RND to ensure the best one was selected. The results showed that RND was better able to be used for development of the RWU model to simulate the patterns of RWU under SAP application.

中文翻译：

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高吸水性聚合物作用下根系吸水模型的建立和验证

深入了解根系吸水模式（RWU）是提高植物水分利用效率的关键。高吸水性聚合物（SAPs）可以在需要时反复吸收水分，然后向植物释放水分，这大大提高了干旱和半干旱农业中植物的水分利用效率。然而，由于土壤水力参数不稳定和根系生长对 SAP 应用的响应不明确，这也给 RWU 建模带来了挑战。通过控制土柱试验，研究了两个重要的根系指标，即根长密度（RLD）和根系氮质量密度（RND）对 SAP 应用的响应，以及它们与 RWU 的关系。结果表明，SAP的使用导致RND的稳定增加，并且在早期也大幅增加了RLD，但随着时间的推移，增长速度逐渐放缓。数值试验分析了不稳定土壤水力参数对RWU的影响，表明应考虑SAP对土壤水力参数的时间依赖性影响，以避免计算RWU时出现误差。提出了一种计算Richards方程中RWU源/汇项的具体方法，并最终作为RWU的理论值来验证基于RLD和RND的RWU模型，以确保选择最佳模型。结果表明，RND 能够更好地用于开发 RWU 模型，以模拟 SAP 应用程序下的 RWU 模式。这表明在计算 RWU 时应考虑 SAP 对土壤水力参数的时间依赖性影响。提出了一种计算Richards方程中RWU源/汇项的具体方法，并最终作为RWU的理论值来验证基于RLD和RND的RWU模型，以确保选择最佳模型。结果表明，RND 能够更好地用于开发 RWU 模型，以模拟 SAP 应用程序下的 RWU 模式。这表明在计算 RWU 时应考虑 SAP 对土壤水力参数的时间依赖性影响。提出了一种计算Richards方程中RWU源/汇项的具体方法，并最终作为RWU的理论值来验证基于RLD和RND的RWU模型，以确保选择最佳模型。结果表明，RND 能够更好地用于开发 RWU 模型，以模拟 SAP 应用程序下的 RWU 模式。