Stratifed soilless substrates decrease the vertical gravitational water gradient altering Helianthus root morphology

Authors: CRISCIONE, KRISTOPHER - Virginia Tech; Owen Jr, James; FIELDS, JEB - University Of Florida

Submitted to: Plant and Soil
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/12/2025
Publication Date: 4/2/2025
Citation: Criscione, K., Owen Jr, J.S., Fields, J. 2025. Stratifed soilless substrates decrease the vertical gravitational water gradient altering Helianthus root morphology. Plant and Soil. https://doi.org/10.1007/s11104-025-07385-8.
DOI: https://doi.org/10.1007/s11104-025-07385-8

Interpretive Summary: Crop root growth and structure is poorly understood in conventional or emerging growing media used for specialty crop production. Our research explored using a frozen column method to capture snapshots of root growth, root architecture, and the hydrological properties of growing media; allowing us to understand how roots develop over time and space and their impact on growing media water dynamics. The experiment included nursery bark- and greenhouse peat-based growing media. Specifically, sunflower was grown in twelve-inch-tall plastic columns using conventional or stratified (fine bark atop coarse bark; fine peat-lite layered over pine bark) growing media. Conventional growing media is comprised 100% of single growing media whereas stratified is comprised of a fine bark atop coarse bark to promote aeration at the bottom of the pot while not sacrificing moisture at the surface. Individual columns were frozen after 0, 22 or 43 days and then separated into five vertical sections. Root morphological characteristics and media moisture content were measured within each layer when fallow, intermediately rooted, or having a fully developed root system. In our experiment, we showed that container growing media, regardless of the type, have a vertical moisture gradient where it is drier in the top and wetter at the container base. The vertical moisture gradient is reduced from the top-to-bottom in stratified growing media. Additionally, sunflower grown in a stratified growing media had enhanced root development throughout the entire container and especially in the upper layers. This greater root development includes greater overall total root length, more fine root length, and root surface area. We attributed these responses to: (1) roots detect a sharp moisture gradient in in conventional growing media, (2) the large pores in the stratified coarse pine bark growing media contained more air-filled pores, (3) the increased moisture uniformity in stratified growing media facilitated a greater proliferation of roots, and (4) the smaller and increased pore uniformity in the fine bark particles in stratified growing media promoted continuous elongation and lateral root development, resulting in the greater root lengths.

Technical Abstract: Background and aims. Containerized soilless substrates are incredibly porous to allow for optimal water:air storage balance and support root development. Substrate porosity is dynamic, evolving over time as roots invade pores. As a result, the substrate changes its physical structure due to decomposition and in-situ particle movement, ultimately shifting its storage properties and performance. However, research is sparse in understanding how developing roots change their morphology throughout production (temporally) and while growing throughout the 3-dimensional substrate matrix (spatially). Moreover, it would be beneficial to the industry to understand how root development impacts container moisture characteristics. The objective of this study was to quantify root morphological development and water storage (') 4-dimensionally in conventional or engineered substrate systems. Methods. Helianthus annus ‘Rio Carnival’ was grown in 30.5 cm tall PVC columns in a conventional (non-stratified; 100% of the container is filled with a single composite) bark- or peat-based substrates or engineered (stratified; fine bark atop coarse bark; peatlite layered over pine bark) systems. Columns were frozen after roots were partially (22 d) or fully (43 d) grown and were separated in five vertical sections. Root morphological characteristics and ' were measured within each layer. Results. The results herein found that stratified systems overall stored less water, especially in the coarser sub-strata. Partially rooted columns generally stored more water and fully rooted columns drained more. Plus, plants grown in stratified systems had greater fine root development than when grown in non-stratified profiles. Conclusion. Utilizing this method is effective in measuring root development temporally and spatially.