Table 2.

Advantages and inconveniences of methods, alternative to portable MRI, used to measure water content, plant structure, xylem and phloem fluxes, and cavitation

Parameter measured	Method	Advantages	Disadvantages
Anatomy	Microscopy	Affordable; easy to perform; high spatial resolution (from a few hundredths of a nanometer for electronic to a couple of tenths of a micrometer for optic)	Destructive; Limited to laboratory; only a small portion of sample can be observed at once
	X-ray (µ)radiography	High spatial (~ 50–100 μm) and temporal (~ tens of seconds per scan) resolution; non-invasive	Limited to laboratory; possible impact of ionizing radiation; expensive; not easily accessible
	Neutron radiography	High spatial (~ 100 μm) and temporal (~ tens of seconds per scan) resolution; non-invasive; adapted to dense materials	Limited to laboratory; expensive; not easily accessible; possible impact of neutron radiation on plant tissue; limited to plants that fit in a thin container
	Dye tracing	Affordable; easy to perform; portable	Destructive
	Air-coupled ultrasound	Non-invasive; high temporal resolution (a few seconds per scan); easy to perform; affordable; portable	Indirect; large variation in results
	Laser-based guided waves	High temporal resolution (~ a few seconds per scan); easy to perform; portable	Indirect; large variation in results; laser beam can cause tissue damage
	High-field MRI	Non-invasive; high spatial (~ 100 μm) and temporal (from a few minutes to a few hours depending upon the experiment) resolution	Limited to laboratory; expensive equipment and maintenance; not easily accessible; mainly horizontal orientation; limited plant size and shape
Water content	Fresh weight/Dry weight	Affordable; Easy to perform	Limited to laboratory; Destructive; time consuming (overnight drying required)
	NIRS	Non-invasive; portable; affordable; easy to perform	Indirect, results must be interpreted through models (problem of genericity); calibration particularities for a given species and/or context; limited to outermost layers of sample
	THz spectroscopy	Non-invasive; easy to perform; affordable; portable	Indirect; results must be interpreted through models; limited to outermost layers of sample
	High-field MRI	Non-invasive; high spatial (~ 100 μm) and temporal (from a few minutes to a few hours depending upon the experiment) resolution	Limited to laboratory; expensive equipment and maintenance; not easily accessible; mainly horizontal orientation; limited plant size and shape
Xylem flux	Sap flow meters	Portable; affordable; easy to perform	Invasive; limited to organs with sufficient diameter
	Porometers	Portable; affordable; easy to perform	Indirect, large margin of error in estimating sap flow due to variation between leaves
	2D light transmission	Non-invasive; affordable; spatial resolution (~ 200–500 μm), offers real-time data on water uptake by roots	Indirect, limited to laboratory; limited to certain plants that fit in a thin container and sandy soil; no other light sources than the instrument during measurement
	Gravimetric	Affordable; portable; easy to perform; non-invasive	Indirect
	Isotopic tracing	Portable	Destructive; results must be interpreted through models; can be expensive (cost of radiotracers and mass spectroscopy analyses)
	Dye tracing	Affordable; easy to perform; portable	Destructive
	High-field MRI	Non-invasive; high spatial (~ 100 μm) and temporal (from a few minutes to a few hours depending upon the experiment) resolution	Limited to laboratory; expensive equipment and maintenance; not easily accessible; mainly horizontal orientation; limited plant size and shape
Phloem flux	Aphids	Affordable	Limited to laboratory; Indirect, limited to certain plant species; approximative with large margin of error; can be complicated to execute
	11C PET imaging	Non-invasive; sufficient spatial resolution to capture water dynamics (a couple of millimeters) and high temporal (a few minutes) resolution	Limited to laboratory; expensive and cumbersome equipment; possible impact of ionizing radiation
	High-field MRI	Non-invasive, high spatial (~ 100 μm) and temporal (from a few minutes to a few hours depending upon the experiment) resolution	Limited to laboratory; expensive equipment and maintenance; not easily accessible; mainly horizontal orientation; limited plant size and shape
Cavitation	Acoustic emissions	Portable; easy to perform; affordable	Indirect, more qualitative than quantitative, can be destructive
	Dye tracing	Affordable; easy to perform; portable	Destructive
	Xylem Embolism Meter	Affordable; easy to perform	Indirect, Destructive; limited to laboratory; not suitable for very small (fine roots) or large samples (> 10 cm diameter)
	Microscopy	Affordable; easy to perform; high spatial resolution (from a few hundredths of a nanometer for electronic to a couple of tenths of a micrometer for optic)	Destructive; Limited to laboratory; only a small portion of sample can be observed at once
	X-ray (µ)radiography	High spatial (~ 50–100 μm) and temporal (~ tens of seconds per scan) resolution; non-invasive	Limited to laboratory; possible impact of ionizing radiation; expensive; not easily accessible
	Neutron radiography	High spatial (~ 100 μm) and temporal (~ tens of seconds per scan) resolution; non-invasive; adapted to dense materials	Limited to laboratory; expensive; not easily accessible; possible impact of neutron radiation on plant tissue; limited to plants that fit in a thin container
	High-field MRI	Non-invasive; high spatial (~ 100 μm) and temporal (from a few minutes to a few hours depending upon the experiment) resolution	Limited to laboratory; expensive equipment and maintenance; not easily accessible; mainly horizontal orientation; limited plant size and shape