Miguel Rosales may help you, for sure.

He worked with this technique in those papers:Article Abscisic Acid Coordinates Dose-Dependent Developmental and H...

and

Philippe Nacry, Miguel Angel Rosales Villegas, Christophe Maurel. Abscisic acid mediates and coordinates the developmental and hydraulic responses of plant roots to water deficit. 10th Symposium of the International Society of Root Research, Jul 2018, Jérusalem, Israel. ⟨hal-02954526⟩

Article Abscisic Acid Coordinates Dose-Dependent Developmental and H...

https://www.sciencedirect.com/topics/agricultural-and-biological-sciences/root-hydraulic-conductivity

“Do you need to put the root in water”

-Yes

"What is the order of pressures you apply?"

-0, 0.2, 0.4, 0.6, 0.8 according to your plant.Pressure-velocity curve. The slope of the curve is Lpr.

Mª Angeles Zorrilla Lopez-Perea

Q1. I need a gel like substance, like agar? I grow the plant hydroponically, so I plan to just put the root in the nutrient solution.

Q2. Yes, the question is more about technique. Measuring root volume is much easier and more accurate than measuring root surface area, so I don't know if I can substitute the surface area with volume in the equation, or convert between them somehow.

Q3. I mean that in one reference the authors applied pressure 0.3 MPa, then 0.4 MPa, then 0.2MPa. They didn't apply in an increasing or decreasing order. I want to know if there is a reason for that, or a specific order to apply pressure which we need to follow.

Yushi Liu Thank you very much.

Is an increasing order of pressure sufficient? I saw in some reference the authors didn't use an increasing order. I am not sure if there is a technical reason for that.

J.D. Franco-Navarro Thank you. I'll check out the reference.

I think these papers could help you;

They're available on the ResearchGate Server for download.

Duy Minh Pham according to your plants. The increasing ording of pressure is depends on your sample. Some plants need large pressure ruler, while others need small pressure ruler