Mathematical Modelling of the Root-Mycorrhiza-Soil System System

Arbuscular mycorrhizal fungi (AMF) are widespread symbiotic partners of most terrestrial plants and form close associations with their roots. While their role in enhancing nutrient uptake, particularly phosphorus, has been well studied, their effects on and of soil structure, and plant water uptake have not been investigated as broadly.

The complexity of interactions between plants, fungi, and soil under varying environmental conditions is difficult to disentangle experimentally. In-silico investigations offer an alternative means to explore these effects. We developed a 3D-model describing AMF colonization of a growing root structure and the growth of extraradical mycelium. We used the model to simulate how extraradical hyphae extend from colonized roots into the soil volume. The model is being implemented as an extension of CPlantBox, a functional-structural model for water and carbon processes at the whole-plant level.

Model parameterization is based on experimental and additional literature data. This includes information on root architecture, AMF colonization rates and locations, and nutrient transport and water flow in tomato plants and their associated hyphal networks. The plants were grown in sandy and loamy soils under both drought and well-watered conditions.

The 3D AMF colonization model explicitly represents hyphal extension rates, branching angles, and the spatial propagation of the extraradical mycelium from infection points along the root system. Key components of the model are the representation of the dynamics of root growth, growth of the intraradical and extraradical mycelium, anastomosis, and the ability of AMF hyphae to fuse and form complex networks.

The model is used to assess, visualize, and quantify how AMF networks develop, branch, and interconnect, providing mechanistic insight into their contribution to plant nutrition and drought tolerance.