It's a big deal. I make no claim to the original science, just how it works in conjunction with the passive HydroSock jug, and even the active nutrient film technique / aeroponic hybrid jug setup.
There is little scientific research or information about plant air roots, especially associated with hydroculture. The biological name for air roots is "adventitious roots." You can find lots of scientific data in regard to cellular respiration (in plants, the photosynthesis and sugar conversion cycle known as the Calvin cycle) but not very much about the use of air roots in water culture. I used what little is out there as part of my original HydroSock design. There is, however, some lively discussion among hobbyists and pros on the various growing and gardening forums concerning roots in water and its effect.
Most hydroculture sites speak of air roots in a very general way, mostly along the lines of that they exist, and that many hydroponic plants only grow water roots. Most growers put a strong emphasis on mechanical aeration of the nutrient solution as the primary means of getting oxygen into their plants.
I have, to date, grown at least four varieties of tomato, two varieties of bean, peas, bell peppers, sweet yellow banana peppers, collards, and a watermelon plant with Plain 2 Grow Systems. Every single plant has grown very distinct and usable air roots! And this has happened REGARDLESS of whether the plant was pump-aerated, hand-aerated, or not aerated at all.
The only plants I drowned were a few from my first system when the sock and plant fell into the nutrient solution when the first type of sock retainer (a rubber band) disintegrated and gave way. I purposely sporadically baster-aerated several tomato and pepper plants as an experiment in aeration and air root effect. They did quite well until the extreme summer heat in my greenhouse affected ALL my plants, including the constant pump-aerated plants. The small reservoir in a milk jug becomes a big disadvantage in a hot environment.
I first mentioned air roots in my You Tube video #2 on my 'Plain 2 Grow Jim' channel. I stated in that video how important they were for the plant to get oxygen. I bring up air roots from time-to-time in other videos.
So what are air roots? Why do they grow? How do I get my plants to grow them? Why does it matter whether my plants get oxygen? Jim, I thought plants needed carbon dioxide and gave off oxygen as a respiration product.
Most plants do expire oxygen as a byproduct of the photosynthesis cycle, and most plants do uptake carbon, in the form of organic matter and carbon dioxide, along with water, to create sugars. Almost all plants require about the same ratio of oxygen to other gases as humans and other animals! That's because the plant Calvin cycle shares many similarities and functions with the animal kingdom Krebs cycle.
Here is something to consider: Water can only absorb an average of 6 parts-per-million (ppm) of dissolved oxygen at a temperature that most hydroponic roots could tolerate. The roots exposed to the water will actually take up significantly less than that due to temperature, pressure, and osmosis.
The higher the temperature, the less oxygen is dissolved into the solution. The rate of uptake is affected by dissolved oxygen, minerals, and a pressure gradient, between the roots and the higher plant, in structures known as xylem and phloem. If the cell membrane is having to contend with oxygen and nutrient ions, there will be a reduced uptake compared to roots which deal with significantly less water and nutrient molecules, and more “free oxygen,” or O2. That's where air roots come into play. Air roots absorb free oxygen at a much higher rate than dissolved oxygen.
I believe that my 8 foot tall tomatoes can grow out of a one gallon milk jug -using a half-gallon of nutrient solution- precisely because of this effect. There isn't enough volume in a half-gallon of nutrient solution to contain all the nutrient ions, water molecules, AND dissolved oxygen needed to maintain plants of that size. The majority of the oxygen that the plants are getting comes from free oxygen being absorbed through the exposed upper roots and the leaves.
Like so many other living things, my plants adapt to their environment and needs. I wouldn't be surprised if some nitrogen fixation wasn't also happening in those air roots, but I can't seem to find much information about it. In soil-based plants, the vast majority of nitrogen fixation in roots happens through friendly bacteria collectively called rhizobia. Do rhizobia exist in hydroponic air roots? Or ANY hydroponic roots? I don't know.
In the videos I stated that the first one-third of my roots are called “air roots” and are exposed to the atmosphere. The substrate or aggregate the plants are growing in have lots of air space and don't heavily wick or retain water right at the upper roots. It is the job of the sock, as a large-area wick, to keep the roots supplied with water further down into the reservoir without drowning the plant.
I really don't have the experience with the other hydroponic systems to know how important air roots are to their functionality. Obviously, aeroponic and nutrient film systems rely heavily on moist but air-exposed roots. In both the passive and active versions of the Plain 2 Grow Systems, it is more of an art and using experience to achieve a balance of air and water roots in the jug reservoir than it is of science. I killed a lot of plants before I got it right! It takes some work to keep air roots above water but still moist and the water-tolerant roots constantly hydrated. My videos give a good representation of air root technique.