Mini-Horhizotron: An Apparatus for Observing and Measuring Root Growth of Container-grown Plant Material In Situ

Abstract

<jats:p>An apparatus was developed that allows for a range of non-destructive measurements on root growth in containers (pot culture). The mini-Horhizotron was designed to measure root growth of small plant material such as seedlings, herbaceous plugs, or woody plant liners normally grown in containers less than 3.8 L. The mini-Horhizotron design has three chambers extending away from the center that could be filled with the same substrate or filled separately with different substrates/treatments to observe root growth response from a single plant. The objectives were: 1) to test the suitability of the mini-Horhizotron’s design and its effects on plant growth with several different species; 2) to test two different experimental designs on the mini-Horhizotrons for research purposes; and 3) to test the effect of wood-amended substrates on root length of a single species. Measurement included quantification of the longest roots growing away from the center (where the plug was transplanted). Herbaceous and woody plants grown in the mini-Horhizotrons included: <jats:italic>Echinacea purpurea</jats:italic> (L.) Moench ‘Prairie Splendor’, <jats:italic>Chrysanthemum</jats:italic> L. ‘Garden Alcala Red’, <jats:italic>Rudbeckia hirta</jats:italic> L. ‘Becky Yellow’, and <jats:italic>Ilex crenata</jats:italic> Thunb. ‘Steeds’. These plants produced root and shoot growth similar to plants grown in traditional greenhouse containers with approximately equal heights and volumes, allowing for root observations in the mini-Horhizotrons to be considered simulations of traditional container-grown crop production. Results from the initial root growth measurements provide evidence that the mini-Horhizotron may be used with a different substrate in each chamber, effectively altering a portion of the rhizosphere of one plant and reducing the number of mini-Horhizotrons needed for replications during scientific studies. Root growth was measured in three substrates containing by volume 70:30 peat:perlite (control), peat:pine-wood chips, or peat:shredded pine wood. For the species grown in pine-wood chips or shredded pine wood-amended substrates, root growth equaled or exceeded that observed in the control substrate at all time periods. The mini-Horhizotron was used to non-destructively measure treatment/substrate effects on root growth while providing full visual access to the root zone and developing root system.</jats:p>

Advancements in Root Growth Measurement Technologies and Observation Capabilities for Container-Grown Plants

“…The design of the mini-Horhizotron is comprised of a three-chamber configuration suitable for observing and measuring root growth by utilizing the clear walls as demonstrated in Figure 2 . The mini-Horhizotrons have a substrate volume similar to a standard greenhouse container, and the height of the mini-Horhizotron (10.2 cm) is also similar to a 16.5 cm diameter container (11.8 cm), providing similar air and water profiles comparatively [ 66 ]. However, the surface area of the mini-Horhizotron is almost three times larger than a container, allowing for an increase in potential viewing of roots as they explored the substrate [ 66 ].…”

“…The mini-Horhizotrons have a substrate volume similar to a standard greenhouse container, and the height of the mini-Horhizotron (10.2 cm) is also similar to a 16.5 cm diameter container (11.8 cm), providing similar air and water profiles comparatively [ 66 ]. However, the surface area of the mini-Horhizotron is almost three times larger than a container, allowing for an increase in potential viewing of roots as they explored the substrate [ 66 ]. Previous work has shown that plants grown in the mini-Horhizotron had similar dry root masses when compared to plants grown in a greenhouse container, supporting using the mini-Horhizotron to observe and measure effects during production conditions [ 66 ].…”

“…However, the surface area of the mini-Horhizotron is almost three times larger than a container, allowing for an increase in potential viewing of roots as they explored the substrate [ 66 ]. Previous work has shown that plants grown in the mini-Horhizotron had similar dry root masses when compared to plants grown in a greenhouse container, supporting using the mini-Horhizotron to observe and measure effects during production conditions [ 66 ]. In order to block sunlight from the rhizosphere, shade panels slide directly against the clear walls ( Figure 2 B).…”

An overview of new and revised methodologies and technologies in substrate analysis and characterization

“…It includes shade panels to allow root development in the dark but can easily be removed to allow measurements. Comparisons with equivalent round containers showed no significant difference in root mass over a three to six week period (Judd et al, 2014b. In previous studies the MHT has been used to measure root length and root segments (Judd et al, 2015b).…”

“…Clockwise from top left: water penetration, root exploration and branching, disease effects of healthy (circles) and damaged (arrow) roots, disease spread (inoculated from left side of image). (Image originally published inJudd et al, 2014b).…”