What happens if you overwater a plant?

This question is from Mel, for plant scientist Nadia Radzman...

Nadia - If you overwater a plant, what happens is that you would have this stagnant water around the soil, right? So this would create a waterlogging effect. In all plant tissues, you need to have access to oxygen. So if you have a waterlogged plant, meaning that it couldn't access the oxygen anymore, this would create a low oxygen environment.

Chris S - Well how does hydroponics work then? Because you dangle the roots in water all the time, don't you?

Nadia - Yeah, so there are two types of hydroponics. So in large scale hydroponics, what you have is the water is aerated so you wouldn't have these low oxygen effects. And another one is a passive method where just a bit of the root actually touches the water so the plant is still happy.

Phil - But otherwise it seems like it's actually drowning, because it's not go enough oxygen.

Nadia - It is drowning. So what happens is if it's low oxygen, you cannot take up water inside the plant.

Chris S - Well I was going to say, what about plants that live in water?

Nadia - So they have special modifications in their roots. The tissues are called aerenchyma and they actually store, well, air! To actually provide the oxygen to the plant.

Chris S - Do they pump it there then? How does the air get into those bodies then?

Nadia - I'm actually not sure about that.

Chris S - I know that if you cut a water lily across, the stems have got a lot of hollow voids, in the stems.

Nadia - Yes. That is to actually provide the oxygen to the whole of the plant.