Water and phosphorus uptake by upland rice root systems unraveled under multiple scenarios: linking a 3D soil-root model and data

Abstract

2Background and aims 3 Upland rice is often grown where water and phosphorus (P) are limited and these two factors 4 interact on P bioavailability. To better understand this interaction, mechanistic models 5 representing small-scale nutrient gradients and water dynamics in the rhizosphere of full-grown 6 root systems are needed. 7 Methods 8Rice was grown in large columns using a P-deficient soil at three different P supplies in the 9 topsoil (deficient, suboptimal, non-limiting) in combination with two water regimes (field 10 capacity versus drying periods). Root architectural parameters and P uptake were determined. 11Using a multiscale model of water and nutrient uptake, in-silico experiments were conducted by 12 mimicking similar P and water treatments. First, 3D root systems were reconstructed by 13 calibrating an architecure model with observed phenological root data, such as nodal root 14 number, lateral types, interbranch distance, root diameters, and root biomass allocation along 15 depth. Secondly, the multiscale model was informed with these 3D root architectures and the 16 actual transpiration rates. Finally, water and P uptake were simulated. 17 Key results 18The plant P uptake increased over threefold by increasing P and water supply, and drying periods 19 reduced P uptake at high but not at low P supply. Root architecture was significantly affected by 20 the treatments. Without calibration, simulation results adequately predicted P uptake, including 21 the different effects of drying periods on P uptake at different P levels. However, P uptake was 22 underestimated under P deficiency, a process likely related to an underestimated affinity of P 23 uptake transporters in the roots. Both types of laterals (i.e. S-and L-type) are shown to be highly 24 important for both water and P uptake, and the relative contribution of each type depend on both 25 soil P availability and water dynamics. Key drivers in P uptake are growing root tips and the 26 distribution of laterals. 27 Conclusions 28 This model-data integration demonstrates how multiple co-occurring single root phene responses 29 to environmental stressors contribute to the development of a more efficient root system. Further 30 model improvements such as the use of Michaelis constants from buffered systems and the 31 inclusion of mycorrhizal infections and exudates are proposed. 32 33 34