The rhizosphere is the small soil volume around the roots. There, complex interactions between plants and organisms that are in close association with the root occur.
In the rhizosphere, roots release compound such as water-soluble exudates and mucilages, insoluble materials and enzymes, and dead root cells. This process, called rhizodeposition, affects the ability of plant roots to extract water and nutrients from the soil.
As with most soil processes, it is difficult to directly measure the spatio-temporal distribution patterns of rhizodeposits around a root system.
Magdalena Landl of Forschungszentrum Jülich is part of a team of researchers who developed a novel model approach to compute the spatiotemporal distribution patterns of rhizodeposits around growing root systems. The authors created a rhizodeposition model and coupled it with the existing 3D root architecture model CPlantBox.
According to the paper recently published by in silico Plants, rhizodeposition model included factors controlling the spread of rhizodeposits in the soil such as rhizodeposit release from the roots, rhizodeposit diffusion into the soil, rhizodeposit sorption to soil particles, and rhizodeposit degradation by microorganisms.
“3D modelling was important to incorporate because we wanted to identify if and where patches of high rhizodeposit concentration arise around a complex 3D root system. These hotspots significantly influence rhizosphere processes,” said Landl.
They then performed simulations for the two rhizodeposits mucilage and citrate for fava bean (Vicia faba) to evaluate the impact of a complex root architecture on the spatio-temporal distribution patterns of the rhizodeposits.
The authors first confirmed that the model was able to accurately determine the distribution and concentrations of citrate and mucilage in the rhizosphere compared to published measured values. The model output allowed them to evaluate the effects of root architecture features such as root growth rate and branching density on rhizodeposits. They then analyzed hotspots.
The analysis showed that branching caused the rhizospheres of individual roots to overlap, resulting in an increase in the volume of rhizodeposit hotspot zones. Hotspot volumes around roots were at a maximum at intermediate root growth rates. Root branching allowed the rhizospheres of individual roots to overlap, resulting in an increase in the volume of rhizodeposit hotspot zones.
Distance maps showed that the volume of soil that was close to a hotspot continued to increase over the simulated 20 day period. Analysis of hotspot duration showed that long-lasting rhizodeposit hotspots occurred primarily in the part of the root system where branching occurs and where overlapping rhizodeposition zones are therefore more frequent.
According to Landl, “this model allowed us to evaluate the effects of root architecture features such as root growth rate and branching density on the development of rhizodeposit hotspot zones. In the future, we plan to integrate our model into a 3D multi-component root and solute transport model to include water and nutrient transport in the soil. These factors strongly affect rhizodeposits.”
Landl, M., Haupenthal, A., Leitner, D., Kroener, E., Vetterlein, D., Bol, R., Vereecken, H., Vanderborght, J., & Schnepf, A. (2021). Simulating rhizodeposition patterns around growing and exuding root systems. In in silico Plants. Oxford University Press (OUP). https://doi.org/10.1093/insilicoplants/diab028
This manuscript is part of in silico Plant’s Functional Structural Plant Model special issue.