Container Gardening: Container Soils - Water Movement and Re

[KAMasud]

Plants don't actually drink water. They absorb it molecule by molecule from colloidal surfaces and from vapor in macropores. Plants use CO2 for photosnythesis, and O2 is a byproduct of their metabolism, but they need O2 in the root zone for normal root function and metabolism. If soils are soggy, they CAN adapt to some degree, but they don't handle the back & forth transition from saturated to well-aerated without rebelling.

The roots produced under hypoxic (soggy soil) conditions or under water are quite different from those produced in a quality container soil or other well-aerated medium (perlite - screened Turface - calcined DE - seed starting mix, e.g.). These 'water roots' are much more brittle than their counterparts growing in soil; this, due to a much higher percentage of aerenchyma (a tissue with a greater percentage of intercellular air spaces than normal parenchyma), and their construction is different as well.

Aerenchyma tissue is filled with airy compartments. It usually forms in already rooted plants as a result of highly selective cell death and dissolution in the root cortex in response to hypoxic conditions in the rhizosphere (root zone). There are 2 types of aerenchymous tissue. One type is formed by cell differentiation and subsequent collapse, and the other type is formed by cell separation without collapse ( as in water-rooted plants). In both cases, the long continuous air spaces allow diffusion of oxygen (and probably ethylene) from shoots to roots that would normally be unavailable to plants with roots growing in hypoxic media. In fresh cuttings placed in water, aerenchymous tissue forms due to the same hypoxic conditions w/o cell death & dissolution.

Note too, that under hypoxic (airless - low O2 levels) conditions, ethylene is necessary for aerenchyma to form. This parallels the fact that low oxygen concentrations, as found in water rooting, generally stimulate plants to produce ethylene. For a long while it was believed that high levels of ethylene stimulate adventitious root formation, but lots of recent research proves the reverse to be true. Under hypoxic conditions, like submergence in water, ethylene actually slows down adventitious root formation and elongation.

In essence, the structural variation of roots that forms in aqua culture allows the roots of the plant to get oxygen needed for root metabolism from plant parts above the ground instead of from the soil, as they normally would. The reason saturated soils in conventional container culture are so limiting is because roots cannot make the transition from a media that is hypoxic part of the time and well-aerated the rest of the time. The roots, when deprived of oxygen, simply die or are significantly impaired in function until aeration returns to the soil, a condition that is often seriously limiting and can even kill the plant outright.

Al

[M Farooq]

It would be better to share the original link rather, if we wish to share someone else's piece of writing. Anyway, the discussion raises a question in my mind: How does water reach the top of very tall trees? Has this issue been sorted out clearly?

There is an interesting connection of hypoxia (lack of oxygen) with humans illnesses when the author says that "the roots produced under hypoxic (soggy soil) conditions or under water are quite different from those produced in a quality container soil." Same is true for human cancers. It is now known that tumours are short of oxygen and the cells learn to survive in low oxygen- and they are different, just like those plant roots! What a similarity. And because of low oxygen content in the tumours, radiotherapy is not very effective.

Regards,

Farooq

[Muhammad Arif Khan]

It would be better to share the original link rather, if we wish to share someone else's piece of writing. Anyway, the discussion raises a question in my mind: How does water reach the top of very tall trees? Has this issue been sorted out clearly?

There is an interesting connection of hypoxia (lack of oxygen) with humans illnesses when the author says that "the roots produced under hypoxic (soggy soil) conditions or under water are quite different from those produced in a quality container soil." Same is true for human cancers. It is now known that tumours are short of oxygen and the cells learn to survive in low oxygen- and they are different, just like those plant roots! What a similarity. And because of low oxygen content in the tumours, radiotherapy is not very effective.

Regards,

Farooq

Here is the link

http://forums2.gardenweb.com/forums/contain/

Search for Container soil, container fertilizers,water movement and other related posts.

[Muhammad Arif Khan]

Farooq, How does a giraffe maintain blood pressure of his brain while drinking water and feeding on high branches? Nature has its ways.
You want the answer or to search for the answer?

[M Farooq]

Farooq, How does a giraffe maintain blood pressure of his brain while drinking water and feeding on high branches? Nature has its ways. You want the answer or to search for the answer?

Nature has its ways but as Allah says "Then will you not give thought?". We had a in-house plant horticulturist, who after joining never posted again!