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

Abstract Background and aims Containerized soilless substrates are highly porous to ensure adequate air storage to overcome the “container” effect- the lower part of the container nears saturation which can decrease root health and growth. Substrate porosity is dynamic, evolving over time. As roots fill pores, substrate decomposition and in-situ particle movement change the physical structure, shifting its storage properties and performance. Research is sparse in understanding how developing roots change their morphology throughout production (temporally) and while growing throughout the three-dimensional substrate matrix (spatially). Thus, it would be beneficial to understand how root development impacts container moisture characteristics. This study aimed to quantify root morphological development and water storage (θ) spatiotemporally in conventional or engineered soilless 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-grown (43 d) and were separated in five vertical sections. Root morphology and θ were measured within each layer. Results The results showed that stratified systems overall stored less water, especially in coarser sub-stratas. Partially rooted columns generally stored more water and fully rooted columns drained more. Plants grown in stratified systems had greater fine root development than when grown conventionally. Conclusion Container-grown roots can be engineered to produce more fibrous root systems by spatially manipulating substrate θ.