Interactive effects of mucilage and drying and wetting cycles on rhizosheath development

Abstract

Abstract Aims: Mucilage is vital for rhizosheath formation, the soil adhering to plant roots after gentle shaking. We hypothesized that alternating drying-wetting cycles affect mucilage's role in rhizosheath development and soil aggregation within the rhizosphere. To explore this, we employed flax cord as an artificial root model, subjecting it to soils with varying clay contents (22% and 32%), both sterilized and unsterilized. Methods: We moistened the model roots with 0.12 g of dry chia seed mucilage per g of water and incubated them under controlled conditions. Soil moisture levels were maintained at 75% of water holding capacity (reference) & subjected to five dry-wet (DW) cycles, mimicking wet-dry fluctuations. Control experiments omitted mucilage addition. Subsequently, we isolated the rhizosheath through gentle shaking and analyzed surrounding soil particle-size distribution and aggregate properties using laser diffraction and scanning electron microscopy (SEM). Results: Mucilage presence doubled the rhizosheath quantity compared to mucilage-free soil. Remarkably, constant wet conditions had an even more pronounced impact, significantly enhancing rhizosheath development, particularly in unsterilized soil with 22% clay. Conversely, DW cycles led to a notable reduction in rhizosheath compared to the wet treatment, likely due to physical interactions affecting rhizosheath formation. Notably, there were minimal treatment effects on particle aggregation outside the rhizosheath, with an average diameter of < 10 µm and limited influence from the water regime. Conclusions: We conclude that water regime emerged as the key factor influencing mucilage's contribution to rhizosheath formation, while clay content and microbial activity played minor roles in this laboratory-based experiment.