Imaging of plant roots is severely limited by the opacity of soil media. Hydroponic (or gel) conditions provide transparency but nonphysiological root phenotypes.

Here, we develop a “transparent soil” with high transparency, good mechanical stability, tunable pore sizes, low cost, and easy scalability. This porous media can support root growth in the presence of air, water, and nutrients, and allows for the imaging of unconstrained root systems in vivo by both photography and microscopy. Our study provides evidence that the roots of soybean developed in this medium are significantly more similar to those developed in real soil than those developed in hydroponic conditions and do not show signs of hypoxia.

Abstract

Root phenotypes are increasingly explored as predictors of crop performance but are still challenging to characterize. Media that mimic field conditions (e.g., soil, sand) are opaque to most forms of radiation, while transparent media do not provide field-relevant growing conditions and phenotypes. We describe here a “transparent soil” formed by the spherification of hydrogels of biopolymers. It is specifically designed to support root growth in the presence of air, water, and nutrients, and allows the time-resolved phenotyping of roots in vivo by both photography and microscopy. The roots developed by soybean plants in this medium are significantly more similar to those developed in real soil than those developed in hydroponic conditions and do not show signs of hypoxia. Lastly, we show that the granular nature and tunable properties of these hydrogel beads can be leveraged to investigate the response of roots to gradients in water availability and soil stiffness.

 

See https://www.pnas.org/content/116/22/11063

 

 

Fig.1:

Fabrication and physical properties of hydrogel-based TS. (A) Sketch of the spherification process to make the hydrogel beads. (B) TS before (Left) and after (Right) saturation with nutrient growth media [0.5× Murashige and Skoog medium (Top), lysogeny broth (Middle), and soil extract (Bottom)]. The logo behind the cuvette is not visible before saturation but becomes clearly visible upon saturation of the TS. (C) Transmittance of TS (at 1,080 nm, in 0.5× MS) as a function of the concentration of the polymer and MgCl2 solutions used during spherification. The colormap also shows the length of the optical path that leads to 10% transmittance at 1,080 nm. (D) Collapse stress of TS (filled with 0.5× MS) as a function of the concentration of the polymer and MgCl2 solutions used during spherification. The colormap also shows the thickness of TS that would collapse at its bottom. (E) Bead size as a function of the inner diameter of the nozzle used during spherification. (F) Total and effective porosity of TS as a function of the size of the beads. (G) Shrinkage of the beads as a function of time (with and without plants) and their recovery upon saturation with media on days 7 and 14.