Plant mucilage effects on rhizosheath formation

Abstract

The formation of rhizosheaths, protective layers encasing plant roots, involves various factors, including mucilage presence. Yet, the specific impact of mucilage concentration on rhizosheath growth remains unexplored. <br /> Hence, I conducted comprehensive experiments to assess rhizosheath formation across varied mucilage concentrations, soil moisture levels, and alternating dry-wet cycles. Using an artificial root system, I investigated (i) the influence of chia seed mucilage concentration on rhizosheath formation in different soils, <br /> (ii) a comparison between chia and flax seed mucilage regarding rhizosheath formation, (iii) the impact of diverse chia seed mucilage concentrations on rhizosheath development under different water contents, (iv) the effect of drying and wetting cycles on rhizosheath formation, <br /> (v) and evaluated the particle size distribution and stability of rhizosphere soil under dry and wet conditions in the presence of mucilage. Additionally, a novel model was proposed to describe the pore distribution of dry mucilage. <br /> The experiments involved jute cord models as roots placed in sandy loam and quartz sand with varying chia seed mucilage concentrations. Soil was filled into PVC cylinders, artificial roots inserted, and wet mucilage solutions prepared at five concentrations were uniformly applied to simulate mucilage exudation. Soil samples were kept for 48 hours at room temperature, after which rhizosheath development was weighed. <br /> Similarly, I explored rhizosheath development under flax seed mucilage concentrations in quartz sandy soil, and, using the same method, studied the effect of chia seed mucilage under different volumetric water contents. <br /> Further experiments examined rhizosheath formation with 0.12 g dry mucilage g^-1 water in sterilized and unsterilized soils with varying clay contents under dry-wet cycles to 75% of the water holding capacity. I also analysed particle size distribution and stability of rhizosphere soil using laser diffraction and SEM imaging. <br /> Notably, the findings revealed that in dry soil, rhizosheath formation peaked at an intermediate mucilage concentration. This observation aligned with our model, suggesting that extremely low mucilage concentrations lack the molecules required for soil particle adhesion, while highly concentrated gels limit diffusion. <br /> Flax seed mucilage showed no significant impact on rhizosheath formation, whereas increasing soil moisture levels up to a certain point enhanced rhizosheath development, doubling with mucilage presence. <br /> Additionally, constant wet conditions significantly augmented rhizosheath development, particularly in soils with 22% clay, while drying-wetting cycles reduced rhizosheath formation. Outside the rhizosheath, interactions with particle aggregation exhibited an average size diameter of < 10 µm, minimally affected by water regimes. <br /> Overall, both water and mucilage concentrations drive rhizosheath formation, synergizing within an optimal range observed at 0.12 g mucilage g^-1 rhizosphere water. The water regime significantly controls mucilage contribution to rhizosheath formation, while factors like clay content or microbial activity showed minor influences within controlled laboratory conditions.