Biffdoggie that would sound like a logical explanation, however, what I meant was that 90% of the root area that is available to absorb oxygen is supplied with oxygen when the water drops completely from an ebb and flow system.
This means that near perfect nutrients surround this available root area during it's flood cycle, providing almost perfect plant feeding, and this is followed by an equally perfect oxygen supply during the "dry" cycle.
An ample amount of nutrient filled water is retained, (as Biffdoggie said), by the media that should be as porous as possible for this purpose, during the "dry" cycle. That's also what I meant by "available root area". A lot of the root area is covered because of it's use by the plant to "hold" itself to the media. About 10 percent of the total root mass is unavailable to absorb anything. It's used by the plant as structural support.
The other 90% has near-perfect cycling of nutrients and oxygen.
This rate is improved upon by aeroponics, but that type of system has mechanical problems that surpass that of ebb and flow.
DWC, (Deep Water Culture), is good at the nutrient side of the equation, but not as proficient at the oxygen side.
The necessary combination of nutrients, water and oxygen is the reason watering in soil properly is also so important.
If the soil is too wet, no oxygen.
If the soil is too dry, no water.
Too wet or dry and the plant can't properly absorb nutrients.
I hope this clears some of the mystery behind MJ's root functions.
Root functions.....hahahahaha, sounds like a math problem.