Plant roots generally require some exposure to air. Deep water culture is a form of hydroponics where plants' roots are left to soak in water. To keep the roots from "suffocating", most online sources recommend some kind of aeration mechanism, such as an air stone.
These systems normally wind up filling the water with bubbles, right under the plants. So my question is: are the bubbles responsible for keeping the plants alive, or is the dissolved oxygen keeping the plants alive? So for example, could plants live immediately downstream of a waterfall (a natural aerator), even out of range of its bubbles?