Split-flow NFT for Marchantia

Experiments with different propagation techniques for Marchantia polymorpha strongly indicated that nutrient film technique (NFT) hydroponics could produce rapidly growing plants, and avoid some of the difficulties associated with solid media. However, most hydroponic culture systems rely on different ways of providing nutrient directly to the plant root system. Plants are generally supported by some sort of collar, and the nutrient and roots are shielded from light to avoid algal overgrowth. Marchantia, like other bryophytes, does not have a root system, instead it produces single-cell rhizoids from the lower surface of its flat thallus, and grows outwards, not upwards. Marchantia tissues can be cast over the surface of a medium, will germinate/regenerate with very high efficiency, and are capable of high rates of growth. Unfortunately, cultures grown in the open will be rapidly colonised by algae and other microbes.

The development of efficient hydroponic systems for Marchantia has required tackling two main challenges: (i) how to to produce a growing surface that will provide water and nutrient to gemmae or thalli that have been transferred to the surface, while avoiding access of algae to the same exposed nutrient, and (ii) how to provide a sub-compartment that allows growth and feeding of rhizoids, but suppresses algae by excluding light. This is analogous to the covered tubes or trays that contain root systems in conventional NFT approaches.

My current approach is to print custom trays for nutrient film technique (NFT) hydroponics where the flow of recycled nutrient is split into two separate flows. Nutrient is pumped into a small reservoir of nutrient at the top of an NFT tray - formed behind a dam wall printed on the tray. First: this reservoir feeds a capillary mat draws and siphons nutrient down through the top growing surface of the tray, eventually dripping into the outlet ports. Second, the dam is set with spillways that allow media to flow onto the the lower surface of the tray and to flow as a film between the support pegs, down to the outlet ports. These lower compartments promote prolific growth of rhizoids as they emerge from the upper growing surface.

In the 'Technique' section of this website, I describe some of the observations that informed the current design: the testing different membrane surfaces and use of support pegs to create a subsurface chamber for rhizoid growth and feeding. I'll use "Split-flow NFT" as shorthand term to distinguish this approach from standard NFT.

First, I tested the delivery of nutrient solution to trays that had a dam around the inlet port(s), and looked for even delivery of liquid across the tray. Videos of a suitable tray are shown below - showing flow from the inlet dam onto the tray, and exit as the nutrient solution flows to the outlet ports. The tray was printed with a 4% downwards slope. I normally use generic Black PLA filaments for the tray prints. Some filaments produce a surface that is initially hydrophobic and flows across the surface that can bead, and not spread evenly over the surface. Curious, I tried spraying the trays with commercial Anti-fog products (Motoverde Fog-Away and Rain-X Anti-Fog - used to reduce condensation on car windows). These were both effective at reducing beading on the tray surface. However, running the trays for a day or two without other treatment also produced even-flowing films - either by washing the surface and/or forming some surface layer. Either way, this doesn't seem to eb a problem with PLA printed trays, and also easy to check.