Effects of Root Exudates on Nutrient Transport in the Rhizosphere

Root exudates are organic compounds secreted by the plant root. They have been found to shape the properties of the rhizosphere (the soil in close vicinity to the root) and play an important role in protecting the plant against pathogens, drying, changing chemical composition and more. Recently, it has been found that root exudates impact the hydraulic properties of the rhizosphere. Due to the relation between flow and transport properties, we suggest that root exudates will also affect nutrient transport properties and uptake.

Our goal is to quantify the impacts of root exudates on nutrient transport in the rhizosphere and on uptake by the plant.

Using scanning electron microscope (SEM) equipped with energy-dispersive X-ray spectroscopy detector (EDS), we obtained elements concentration profiles in the rhizosphere, showing high concertation of carbon near the root, possibly related to the presence of exudates. In addition, a potassium gradient toward the root, with the lowest concentration at the root-soil interface was also observed.

Soil batch experiment with synthetic root exudates showed that in sandy soil, multiple elements were released into the fluid phase, while in the clayey soil, calcium and phosphorous were the two primary elements released. We suggest that those elements were released due to several chemical mechanisms affected by pH change, increase organic content and cation exchange. Preliminary results obtained by solute breakthrough curve experiment shows higher dispersivity in the rhizosphere, compared to the bulk soil.

These findings suggest that root exudates have an impact on the nutrient transport properties and affect nutrient availability to the plant. Future research will assist in improving the ability of rhizosphere nutrient-uptake models to simulate nutrient dynamics and plant nutrient uptake.