Ultrasounds for Biological Applications and Materials Science

Ultrasonic assessment of plant tissues water potential

The main characteristics of the ultrasonic method to determine plants water status (water content or water potential) are:

  • Measurements are performed in the leaves
  • Air-coupled ultrasound is used; through transmission configuration
  • Thickness resonant modes in the leaves are excited and sensed
  • Magnitude and phase spectra of the thickness resonant modes are analysed
  • Leaf properties: thickness, density, elastic modulus, elastic damping are extracted form these spectra
  • Water conent and turgor pressure are inferred from these properties

The technique is based in three main pilars:

  • The availability of efficient air-coupled ultrasonic transducers. Capable of:.
    • Sensitive enough to transmit ultrasonic pulses through plant leaves
    • Bandwidth wide enough so that it is possible to measure the full spectrum of, at least, the first thickness resonance.
    • So far, the CSIC air-coupled transducers technology have bee used for this purposes as they present the best available sensitivity and widest bandwidth within the frequecy range of interest for this pplication: 0.1-2.0 MHz. LINK 
  • Techniques to solve the inverse problem, of plate thickness resonances, so that it is possible to extract the leaf parameters from the measure spectra
  • Knowledge of the relationship between ultrasonic properties and plant physiology to extract water content and turgor pressure from the leaf ultrasonic properties. LINK

The main advantages of this technology are:

  • It is completely non-invasive and non destructive. Unlike most of the other technologies aimed to determine plant water status, that require to cut leaves or other parts of the plant to process the samples.
  • Equipment is fully portable. Compared with the Scholander pressure chamber, which is the golden standard which is bulky and heavy.
  • the time to take and process a measurement is very reduced (few seconds), once again compared with other technologies (Pressure chamber) that are quite time consuming

The first demonstration that it is possible to measure thickness resonances in plant leaves using air-coupled ultrasound and to extract leaf prperties from these measurements was published in 2009:

Shortly after that, it was possible to establish a procedure to extract water potential form the ultrasonic measurements

And to correlate changes in the celular structure of the tissues due to the loss of water with the ultrasonic measurements

and hence, to analyse the relationship between ultrasonic leaf properties, leaf elasticity and leaf water content and turgor pressure

and compare this technique with other technologies:

Then, the applicability of this technology to a broader number of species was studied:

and to monitor in vivo plant water status changes under different stimulii

More recently we have introduced Machine Learning procedures to process the leaf ultrasonic information and to correlate it with plant water status and water potential

Plant_water_Prototype

Prototype developed in 2015 for vine leaves

Vine_leaf

Taking a measurement in a vine leaf.

 

Projects:

SOST-WINE

0034 915618806-058
t.gomez@csic.es
Skype: usbiomat_csic
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