The Development of the Rhizosphere-Simulation of Root Exudation at the Example of two Contrasting Rhizodeposits: Citrate and Mucilage Associated with the Growth of Root Architecture

Different types of organic substances released by roots and their effect on soil/rhizosphere properties have received a lot of attention. Their impact on rhizosphere properties and related functional processes depends on the spatial-temporal concentration distribution around roots. Different plant species/genotypes have different root architectures. Root exudates differ in their diffusion coefficients and decomposition rate. Exudation pattern, root growth dynamics and exudate transport in the soil are jointly responsible for exudate distribution in the soil. Hence, a modelling study of root exudation involving four plant species differing in root architecture (Vicia faba, Lupinus albus, Triticum aestivum and Zea mays) and two kinds of rhizodeposits (citrate and mucilage) were conducted. We consider a simplified root architecture where each root is represented by a straight line for each root system. Assuming that root tips move at a constant velocity and that exudation transport is linear, concentration distributions can be obtained from the convolution of the analytical solution of the transport equation for a moving point or line source injection. By coupling the analytical solution with a root growth model that delivers the spatial-temporal pattern of root distribution in 3D space, we simulated exudate concentration distributions for citrate and mucilage with CRootBox. The simulations suggest that rhizosphere development depends in the following way on the root and rhizodeposit properties: the dynamics of the root architecture result in various development patterns of the rhizosphere. Our results improve our understanding of the impact of the spatial and temporal heterogeneity of rhizodeposits input on rhizosphere development for different root system types and substances. In future work, we will use the simulation tool to infer critical parameters that determine the spatial-temporal extent of the rhizosphere from experimental data.