BACKGROUND AND AIMS Upland rice is often grown where water and phosphorus (P) are limited. To better understand the interaction between water and P availability, functional-structural models that mechanistically represent small-scale nutrient gradients and water dynamics in the rhizosphere are needed. METHODS Rice was grown in large columns using a P-deficient soil at three P supplies in the topsoil (deficient, suboptimal, non-limiting) in combination with two water regimes (field capacity versus drying periods). Root system characteristics, such as nodal root number, lateral types, interbranch distance, root diameters, and the distribution of biomass with depth, as well as water and P uptake were measured. Based on the observed root data 3D root systems were reconstructed by calibrating the structural architecure model CRootBox for each scenario. Water flow and P transport in the soil to each of the individual root segments of the generated 3D root architectures were simulated using a multiscale flow an transport model. Total water and P uptake were then computed by adding up the uptake by all the root segments. KEY RESULTS Measurements showed that root architecture was significantly affected by the treatments. The moist, high P scenario had 2.8 times the root mass, double the numer of nodal roots, and more S-type laterals than the dry, low P scenario. Likewise, measured plant P uptake increased over threefold by increasing P and water supply. However, drying periods reduced P uptake at high but not at low P supply. Simulation results adequately predicted P uptake in all scenarios when the Michaelis Menten constant (Km) was corrected for diffusion limitation. They showed that the key drivers for P uptake are the different types of laterals (i.e. S- and L-type) and growing root tips . The L-type laterals become more important for overall water and P uptake than the S-type laterals in the dry scenarios. This is true across all the P treatments, but the effect is more pronounced as the P availability decreases. CONCLUSIONS This functional-structural model can predict the function of specific rice roots in terms of P and water uptake under different P and water supplies, when the structure of the root system is known. A future challenge is to predict how root systems' structure responds to nutrient and water availability.

中文翻译：

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旱稻根系的功能结构模型揭示了侧枝和生长的根尖对于从潮湿和干燥土壤中吸收磷酸盐的重要性


背景和目的 旱稻通常在水和磷 (P) 有限的情况下种植。为了更好地理解水和磷有效性之间的相互作用，需要能够机械地代表根际小规模养分梯度和水动态的功能结构模型。方法 使用缺磷土壤在表层土壤中提供三种磷（缺乏、次优、非限制）并结合两种水分状况（田间持水量与干旱期），在大柱中种植水稻。测量根系特征，如节根数量、侧根类型、分枝间距离、根直径、生物量随深度的分布，以及水和磷的吸收。基于观察到的根数据，通过校准每个场景的结构架构模型 CRootBox 来重建 3D 根系统。使用多尺度流传输模型模拟土壤中的水流和磷传输到生成的 3D 根结构的每个单独根段。然后通过将所有根段的吸收量相加来计算总水和磷吸收量。主要结果 测量表明根结构受到处理的显着影响。与干燥、低磷情景相比，潮湿、高磷情景的根质量是其 2.8 倍，节根数量是其两倍，并且 S 型侧根较多。同样，通过增加磷和水供应，测量到的植物磷吸收量增加了三倍以上。然而，干燥期减少了高磷供应时的磷吸收，但不减少低磷供应时的磷吸收。当米氏常数 (Km) 针对扩散限制进行校正时，模拟结果充分预测了所有情况下的 P 吸收。他们表明，磷吸收的关键驱动因素是不同类型的侧向（即 S型和L型）和生长的根尖。在干旱情况下，L 型侧管对于整体水和磷吸收比 S 型侧管更重要。所有磷处理都是如此，但随着磷利用率的降低，效果更加明显。结论 当根系结构已知时，该功能结构模型可以预测不同磷和水供应下特定水稻根系在磷和吸水方面的功能。未来的挑战是预测根系结构如何响应养分和水的可用性。