Plant mucilage increases pull-out resistance of root analogues from soil

Abstract The interface between plants' roots and soil is strongly affected by rhizodeposits, especially mucilage, that change mechanical and hydrological behaviour. In addition to impacts to aggregation, water capture and root penetration, rhizodeposits may also affect the pull-out resistance of plant roots. Due to the complex architecture of plant roots and an inability to restrict rhizodeposit production, this study used a simplified system of wooden skewers to simulate roots and chia seed mucilage as a model to simulate rhizodeposit compounds. Pull-out tests were then carried out to measure the impacts of mucilage, and one (WD1) or two (WD2) cycles of wetting and drying of soils. Using a mechanical test frame, the maximum pull-out resistance (Fmax) and pull-out displacement (dL) were recorded, allowing for pull-out energy (E), average pull-out force (F?$$ \overline{F} $$) and bond strength (τmax) to be calculated. The results showed that all pull-out parameters of the samples with added rhizodeposit compounds tended to decrease between WD1 and WD2, but they were still significantly greater than without the added mucilage. The model rhizodeposit increased all pull-out parameters by a minimum of 30%. With an additional wet?dry cycle, the mucilage tended to cause a decline in pull-out parameters relative to a single wet-dry cycle. This suggests mucilages could enhance the mechanical resistance of roots to pull-out, but resistance decreases over time with cycles of wetting and drying. To conclude, an important role of mucilage is pull-out resistance, which has relevance to plant anchorage and root reinforcement of soils.