Nanoporous synthetic roots: Effect of drying paths on Colloidal Silica-Plants Interaction

Presented herein is an experimental work aimed at investigating the effect of drying on colloidal silica-plants interaction. To delay soil desaturation, maintain high hydraulic transmissivity, and extract water for a longer duration, some plant roots are known to secrete a gelatinous substance, mucilage. This naturally engineered “grout” fills the pore spaces, reduces pore diameter and increases the soil air-entry. In this research, Colloidal Silica hydrogel (CS) is used to create a nanoporous network designed to maintain a high degree of saturation when the water tension is high and, hence, to enable significant capillary flow. CS is non-toxic and inert, and is known for its high injectability into the ground. The experimental campaign showed that acidification of CS allowed for reduced salt built-up in the grout and controlled gel time without hindering the growth of Maize and Runner Bean plants. Results showed that plants can grow from the seed stage to the full plant in the CS-grouted soil. At saturation, a CS-grouted soil provides sufficient hydraulic transmissivity so as not to hinder the tested plants’ growth. Plants can withdraw water through CS gel through a capillary network formed through the injection of CS hydrogel into vegetated soil. To investigate the coupling between CS and plant roots upon drying paths, two different experimental procedures were implemented: i) plant watering was stopped for a given period, or ii) constant suction paths were applied via osmotic pressure. Preliminary evidence showed that the detachment occurring at the root-CS interface is the limiting factor for maintaining high water transmissivity and that volume change upon the first main drying should be reduced or prevented.