Effect of changing chemical environment on physical properties of maize root mucilage

Abstract

Aims High viscosity, low surface tension and hydrophobicity are specific properties of maize root mucilage which contribute to modulate the spatial configuration of the liquid phase in soil pores. Several processes in the rhizosphere, in particularly nutrient absorption, root exudation and microbial activity, may cause strong temporal variations in the chemistry of the soil solution of the rhizosphere. Although the physical properties of maize root mucilage have been repeatedly measured in the last years, their variation upon a changing chemical environment and understanding of the chemical mechanisms governing these properties remain unexplored. Methods We investigated how flow and surface properties of maize root mucilage varied by changes in pH, calcium chloride (CaCl2) and lecithin concentrations. Results The physical properties of mucilage can strongly vary depending on the environmental conditions. Low surface tension of maize root mucilage at pH7 was increased by addition of calcium. Upon pH change and lecithin addition, hydrophobic mucilage turned hydrophilic. High Ca concentration above 0.83 mmol Ca (g dry mucilage)−1, the addition of 167 μg lecithin (g dry mucilage)−1 and a pH rise to 9 decreased the viscosity of mucilage. Conclusion Such variations strongly suggest that the role of mucilage in hydraulic processes in the rhizosphere depends on changes of solutes concentration and composition, which themselves vary according to plant growth and soil water content. It seems that mucilage can best serve as a hydraulic bridge only under certain chemical environments, whose spatio-temporal occurrence in the changing rhizosphere remains to be defined.

Differences in mucilage properties and stomatal sensitivity of locally adapted Zea mays in relation with precipitation seasonality and vapour pressure deficit regime of their native environment

“…Similarly, the adaptation to atmospheric drought-stomatal sensitivity-is a fast, reversible process; on the other hand, mucilage properties are properties expressed over an individual's entire life stage as its function is manifold, for example, for belowground biotic and abiotic interactions (el Zahar Haichar et al, 2014). Although mucilage properties and stomatal sensitivity represent adaptations to two different environmental phenomena, we found a relationship between contact angle, viscosityboth of them important properties for mucilage's behavior during drying and rewetting cycles (Ahmed et al, 2016;Kaltenbach et al, 2018;Knott et al, 2022)-and stomatal sensitivity to increased VPD. As stomatal regulation controls the current transpirational water loss, the plant indirectly affects the speed of soil drying and ultimately delays the drying out of mucilage.…”

“…These high contact angles, causing a hydrophobic surface of mucilage, can be caused by differences in mucilage chemical composition, the amphiphilic nature of mucilage composing polymers and the amount of cations (Knott et al, 2022). Mucilage with high contact angles often contains more phospholipids than those with a lower contact angle.…”

Purification effects show seed and root mucilage's ability to respond to changing rhizosphere conditions

“…[ 36 ] Also, wettability of dried mucilage generally increased with increasing viscosity, with highest significance for Dia samples (Figure 4c, d, Figure S4e) suggesting that the reduced mobility of surface‐active substances mitigated a surface hydrophobization during drying. [ 37 ]…”

“…[36] Also, wettability of dried mucilage generally increased with increasing viscosity, with highest significance for Dia samples (Figure 4c, d, Figure S4e) suggesting that the reduced mobility of surface-active substances mitigated a surface hydrophobization during drying. [37] 4. stable network. This dense network results in higher viscosity, leading to reduced mobility of surface-active substances and ions, which contributes to higher surface tension and lower EC compared to root mucilage.…”

Special issue: Rhizosphere spatiotemporal organisation: an integrated approach linking above and belowground

“…The potential role of mucilage for water uptake at the pore scale is addressed in case study four by Schnepf et al (2022), demonstrating that the interaction between mucilage, water and soil particles increases the connectivity of the liquid phase across the rhizosphere. Knott et al (2022) add to this topic, establishing how physical properties of mucilages change with pH and the presence of divalent cations. Furthermore, Werner et al (2022) have shown that not only the chemical environment changes the mucilage properties, but that mucilage composition strongly depends on the growth conditions, the collection system and the age of the plant.…”