Mucilage: a potential root trait facilitating plant access to soil resources under drying condition

• Applicant: Professor Dr. Mohsen Zare
• Subject Area: Soil Sciences ; Biophysics
• Term: since 2021
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 459978475

Motivation: The rhizosphere, as a hotspot of biological activity, is receiving growing attention as it postulated to promote efficient and sustainable use of limited water and nutrient resources. Defined as the region of soil affected by plant root growth and exudation, the physical and hydrological properties of the rhizosphere are majorly affected by the presence of mucilage, a polymeric gel-like substance exuded at the tip of many plant roots. Despite steady interest in the rhizosphere, we just began to explore its biophysical characteristics, particularly the effect of mucilage on transport of water and nutrients.Objective: the aim of this project is to understand how mucilage affects the transport of nutrients in drying soil and to develop 1) a constitutive model of water flow and nutrient transport across soils embedded with mucilage and 2) a physically-based parameterization of mucilage effects on water- and nutrient-related soil properties, including the water retention curve, the unsaturated hydraulic conductivity, diffusion coefficient, and adsorption. Hypothesis: the underlying hypothesis of this project is that mucilage facilitates the transport of nutrients in drying soil by maintaining the connectivity of the liquid phase within pores. This positive effect originates from the intrinsic properties of mucilage (high viscosity, low surface tension, and high water retention), which are shared among all the mucilage secreted by plant roots. These alterations enhance water retention and liquid connectivity of soil during drying, facilitating both i) the flow of water and ii) transport of nutrients across the rhizosphere and therefore favor water and nutrient uptake by plant roots. Regarding nutrient-related properties of soil, mucilage, besides facilitating the transport and availability of nutrients due to its effect on biophysical and hydrological soil properties (water-related properties), it may alter the buffering capacity of the soil and therefore soil nutrient availability. Methodology: in brief, we will first experimentally quantify the effect of plant mucilage on water and nutrient-related properties of soil. To do so, we will extract mucilage from barley and maize plant roots and mix it with soils of varying textures at varying mucilage contents. We will quantify the effect of mucilage on water-related properties such as soil water retention, hydraulic conductivity, and spatial distribution of liquid phase as a function of mucilage content, soil water content, and soil texture. Similarly, we will quantify the mucilage effect on nutrient-related properties such as diffusion, adsorption, mass flow, and transport of nutrients as function of mucilage content, soil water content, and soil texture. Outcome: we will develop a general conceptual model to describe and parameterize the effects of mucilage on water and nutrient transport within the soil and finally predict their uptake by plant roots under drying soil conditions.

• DFG Programme: Research Grants