The role of lipids and polysaccharides in model root mucilage with implications for the surface activity of the rhizosphere

The main goal of this study was to evaluate the role of polysaccharide and phospholipids on the surface activity of model root mucilage in its liquid and solid phases. Polygalacturonic acid (PGA) and Phosphatidylcholine (PC) were used as representative polysaccharide and phospholipid, respectively. The surfactant performance of the PC found to be superior relative to the PGA–reducing the surface tension (ST) down to 32.9 mN m −1 at 0.04 mg mL −1 while the PGA reduced the ST to 47.7 mN m −1 at 15.9 mg mL −1 . The minimum ST of the PC/PGA mixture was similar to the pure PC for total concentration of 2 and 10 mg mL −1 at PC mass-fraction of 0.01 and 0.1, respectively. The PC, PGA and the PC/PGA mixtures induced subcritical soil water repellency to sand particles. The maximum contact angle (CA) obtained for the PC and PGA were 85° (at 0.7 mg g −1 ) and 75° (4.5 mg g −1 ), respectively. The maximum CA obtained for the PC/PGA mixture was 85°, depending on the total concentration and the PC mass-fraction. It is suggested that during the rehydration of sand coated with air-dried mucilage, water flow at the rhizosphere may initially affected by the induced water repellency. However, with elapsed time, dissolution or detachment of surface-active constituents of the mucilage from the sand surface into the soil solution may reduce the ST of the soil solution at the liquid-air interface and consequently the CA at the wetting front.