Sometimes I don't get roots.

[phillicondor]

Just a quick question about how soil oxygen works. I know that roots need oxygen to survive. I've just had a look at some hard wood cuttings I took early this year that I've had in a Styrofoam box completely sealed with cling wrap. The one I checked had some pretty healthy roots. I probably only opened the box three times in a few months to water it a bit and I sealed it pretty air tight and had no drainage holes. It made me think about how the roots got any oxygen. I thought the oxygen would be all used up. So I guess my question is How much oxygen do roots need? And Is it oxygen or just empty space that the roots need?
Cheers in advance phillo

[evan]

To begin with, the reason plants require oxygen is to synthesis the necessary proteins, sugars and other components such as cells required for growth. The leaves are where most of the production of these components occurs, with the energy produced being stored in the "trunk" as sugars. So when cuttings are taken they don't require as much oxygen as mature plants because usually the leaves are also removed to reduce evaporative loss. This means that the cuttings can't produce any of these components and relies on the stored energy to produce roots and leaves. So the reason the roots were able to grow in such a lower oxygen environment is because they don't really have use for it until they have leaves to create more cells and stuff. Also the Styrofoam is able to allow enough oxygen in because it is quite porous and not completely air tight.

Now to the roots.
Oxygen for plants is very dependent on the soil it grows in, as the pore space size of soil dictates how much oxygen the roots can obtain. Pore space is determined by the particle size of the soil, so larger particles such as gravel allows more oxygen than heavy clay would. These spaces are filled with oxygen, so essentially it is this tiny "empty space" that is required.

Roots require oxygen because they can't readily access the oxygen taken in as CO2 by the leaves. And the amount of oxygen is extremely complicated to calculate as there are many factors to determine this.

[phillicondor]

Cheers Evan. I need to study up on my science I think. I remember some of this stuff from biology and agriculture at high school but my only real gardening experience is from the last year or so keeping a few bonsai. I've just started reading bonsai by Deborah koreshoff and she has a big chapter on soil.