Plants roots and air (or oxygen)...

[Externet]

It is known plants need their roots to absorb oxygen for proper development. -I think-

Seems to me the amount of oxygen available deep in packed soils should be minimal or near to nothing, but, there is still some availability.

I would like to know if such oxygen is necessary for the root itself or for the general development of the rest of the plant.

 

If the oxygen is to develop roots, something does not click in the evolution, where plants could had developed some above ground tissues for capturing it or exposing some of their roots to air.

If the little oxygen available in the soil is to develop general above-the-soil tissue growth, well, same situation; with so much air exposed surfaces, why evolution did not grab it from the air ?

 

If some roots are exposed on purpose by excavation, or by soil erosion/landslides; would that bring a healthier growth ?

[Endy0816]

not much lower than atmospheric:

 

 

• Nitrogen: Soil Air: 79.2% Atmosphere: 79.0%
• Oxygen: Soil Air: 20.6% Atmosphere: 20.9%
• Carbon Dioxide: Soil Air: 0.25% Atmosphere: 0.04%

 

http://en.wikipedia.org/wiki/Soil_gas

 

Plants utilize oxygen during aerobic respiration. Daytime you have oxygen production as a byproduct of photosynthesis. Nighttime or in root systems though you have to change tactics.

 

They can utilize anaerobic respiration as well, but not as effective.

[chadn737]

Root cells need oxygen, just as any cell does.

 

In evolutionary terms, you need to remember that plants evolved with their habitat. If oxygen is available in sufficient amounts in the soil, which normally it is, then there is no selective pressure for some other means of supplying oxygen.

 

If you look at species that often must survive under low oxygen conditions (most often due to flooding), such as water lilies, there are specialized adaptations to supply oxygen to the roots. One of these adaptations are the development of aerenchyma. Essentially these are parenchymal tissues, the bulk tissue type of the plant, that have more air pockets between cells than normal. This does allow the movement of oxygen from above ground tissue to the roots. In some species, which experience only periodic flooding and low oxygen conditions, the development of aerenchyma can be induced. There are also other more specialized adaptations, as well as biochemical ones.

[John Cuthber]

Root cells need oxygen, just as any cell does.

 

Not all cells need oxygen.

Some find it toxic.

[chadn737]

Not all cells need oxygen.

Some find it toxic.

 

All plant cells do and we are talking about plants.

Edited May 23, 2014 by chadn737

[CharonY]

I think that needs a bit of a qualifier . As a whole plants and animals are generally aerobic, of course, but individual cells do not necessarily full access to oxygen and still survive. For example in many animal bodies there are steep oxygen gradients as not all cells have equal access to blood and quite a bit are functioning at or close to hypoxic levels for quite some time.

 

Somewhat similar effects are also observed in plants e.g. during seed germination or certain very compact tissues. In fact in plants hypoxic (posttranslational) signaling has been relatively recently discovered that regulate anaerobic respiration.

 

This does not invalidate the point that for proper cell proliferation oxygen is required and that at you cannot cultivate cells endlessly under anerobic conditions, but I think one should point out that there quite a few shades of grey to think about (or I am just nit-picking).

[Moontanman]

If you want to see plants that grow with no oxygen around the roots I suggest you visit a swamp, cypress and water tupelo trees to just name two grow in deep mud with so little oxygen they produce hydrogen sulfide, it doesn't keep the trees from growing..

[Externet]

Thanks all.

 

Endy : Your post does not convince nor impress a bit. Those are percentages of air composition. Air content in soil is greatly lower than atmosphere.

 

In one cubic metre of air there is one million cubic centimetres of air. In one cubic metre of soil, being lucky, there will be a few cubic centimetres of air; comparatively nearly nothing. 20.6% of nearly nothing is still nearly nothing for the roots to gather, when above the soil there is plenty.

 

The amount of oxygen a species need may be genetic, some needing less. If it was critical for the roots, evolution should had developed another approach to gather oxygen. That is the origin of my question.

[Moontanman]

Thanks all.

 

Endy : Your post does not convince nor impress a bit. Those are percentages of air composition. Air content in soil is greatly lower than atmosphere.

 

In one cubic metre of air there is one million cubic centimetres of air. In one cubic metre of soil, being lucky, there will be a few cubic centimetres of air; comparatively nearly nothing. 20.6% of nearly nothing is still nearly nothing for the roots to gather, when above the soil there is plenty.

 

The amount of oxygen a species need may be genetic, some needing less. If it was critical for the roots, evolution should had developed another approach to gather oxygen. That is the origin of my question.

 

 

The amount of air or oxygen in soils is hugely variable, in swamps it's practically zero, in dry deserts soils are quite porous, being somewhat of an amateur horticulturalist I am intimately acquainted with many different plants from underwater plants to cacti to trees and plants that grow completely with out soil.

 

I can say with some experience that water plants that are provided with oxygenated roots will grow root systems far bigger than their anoxic controls. This is true even with trees...

[StringJunky]

In one cubic metre of air there is one million cubic centimetres of air. In one cubic metre of soil, being lucky, there will be a few cubic centimetres of air; comparatively nearly nothing. 20.6% of nearly nothing is still nearly nothing for the roots to gather, when above the soil there is plenty.

You not are taking into account air spaces created by movement of subterranean organisms eg worms and size variation in adjacent substrate particles. The denser the substrate and more anoxic it is plants adapted to that environment will have their roots, or at least a proportion of them, nearer the surface.

[Endy0816]

^The above posts explain it much better than I could.

 

Transport costs and oxygen reactivity are what makes the most sense as to the reasoning. Don't want to be shuttling more of the nasty stuff around than you have to.

 

Some plants can actually support photosynthesis underground. A lot of interesting adaptations out there. Kind of curious if we could set up an artificial environment to allow a 'normal' plant to manage it. Be interesting, maybe useful even.

[Acme]

It is known plants need their roots to absorb oxygen for proper development. -I think-

Seems to me the amount of oxygen available deep in packed soils should be minimal or near to nothing, but, there is still some availability.

...

If some roots are exposed on purpose by excavation, or by soil erosion/landslides; would that bring a healthier growth ?

Yes, exposing roots to air, and per se oxygen, can bring a healthier growth. While the specifics are conditional as others have pointed out, lawns are frequently aerated using mechanical means that remove cylindrical plugs of soil or make wedge-shaped indentations.

Lawn aerators @ Wiki

[chadn737]

I think that needs a bit of a qualifier . As a whole plants and animals are generally aerobic, of course, but individual cells do not necessarily full access to oxygen and still survive. For example in many animal bodies there are steep oxygen gradients as not all cells have equal access to blood and quite a bit are functioning at or close to hypoxic levels for quite some time.

 

Somewhat similar effects are also observed in plants e.g. during seed germination or certain very compact tissues. In fact in plants hypoxic (posttranslational) signaling has been relatively recently discovered that regulate anaerobic respiration.

 

This does not invalidate the point that for proper cell proliferation oxygen is required and that at you cannot cultivate cells endlessly under anerobic conditions, but I think one should point out that there quite a few shades of grey to think about (or I am just nit-picking).

 

While true, plant cells will only survive for so long under anaerobic conditions. During flooding, roots will respond through anaerobic metabolism for some time, but unless longer term solutions are induced, such as the development of aerenchyma, they will die. Even species that are capable of limited induction of aerenchyma, like maize, will die under prolonged flooding stress due to hypoxia.

 

And of course, the soil is rarely hypoxic for long unless under prolonged flooding, which means that in most environments, the roots have access to oxygen.

If you want to see plants that grow with no oxygen around the roots I suggest you visit a swamp, cypress and water tupelo trees to just name two grow in deep mud with so little oxygen they produce hydrogen sulfide, it doesn't keep the trees from growing..

 

Those roots still require oxygen. Cypress trees, for example, have extensive aerenchyma tissue. They also develop specialized root structures called pneumatophores (the knees that stick above the water) that further enable gas exchange. They have especially shallow roots which are closer to the surface to further enable more efficient gas exchange.

Edited May 25, 2014 by chadn737

[Moontanman]

 

While true, plant cells will only survive for so long under anaerobic conditions. During flooding, roots will respond through anaerobic metabolism for some time, but unless longer term solutions are induced, such as the development of aerenchyma, they will die. Even species that are capable of limited induction of aerenchyma, like maize, will die under prolonged flooding stress due to hypoxia.

 

And of course, the soil is rarely hypoxic for long unless under prolonged flooding, which means that in most environments, the roots have access to oxygen.

 

Those roots still require oxygen. Cypress trees, for example, have extensive aerenchyma tissue. They also develop specialized root structures called pneumatophores (the knees that stick above the water) that further enable gas exchange. They have especially shallow roots which are closer to the surface to further enable more efficient gas exchange.

 

 

While cypress trees do indeed produce "knees? Water tupelo do not and both are quite good at with standing hurricane force winds, I've seen cypress trees dug out of the mud growing in the middle of pods, very deep root systems no knees...

 

In "captivity" cypress will do their best to establish a deep tap root, not allowing them to stunts their growth significantly..

[chadn737]

Thanks all.

 

Endy : Your post does not convince nor impress a bit. Those are percentages of air composition. Air content in soil is greatly lower than atmosphere.

 

In one cubic metre of air there is one million cubic centimetres of air. In one cubic metre of soil, being lucky, there will be a few cubic centimetres of air; comparatively nearly nothing. 20.6% of nearly nothing is still nearly nothing for the roots to gather, when above the soil there is plenty.

 

The amount of oxygen a species need may be genetic, some needing less. If it was critical for the roots, evolution should had developed another approach to gather oxygen. That is the origin of my question.

 

Oxygen is critical for roots and plants have evolved specialized mechanisms to cope with this. See my continued mention of aerenchyma. As for there being "nearly nothing" that is false. While certainly lower than the atmosphere, its more than adequate under normal conditions in most environments. For one, depending on soil type, there is actually a lot of pores through the soil that are not visible to the eye and there is a constant diffusion of gasses between the soil and the atmosphere.

[Moontanman]

 

Oxygen is critical for roots and plants have evolved specialized mechanisms to cope with this. See my continued mention of aerenchyma. As for there being "nearly nothing" that is false. While certainly lower than the atmosphere, its more than adequate under normal conditions in most environments. For one, depending on soil type, there is actually a lot of pores through the soil that are not visible to the eye and there is a constant diffusion of gasses between the soil and the atmosphere.

 

 

In porous soil rain water takes oxygen down with it when i rains as well..

[chadn737]

 

 

While cypress trees do indeed produce "knees? Water tupelo do not and both are quite good at with standing hurricane force winds, I've seen cypress trees dug out of the mud growing in the middle of pods, very deep root systems no knees...

 

In "captivity" cypress will do their best to establish a deep tap root, not allowing them to stunts their growth significantly..

 

Water tupelo does produce pneumatophores, they are just less prominent and typically only under chronic flooding. Furthermore, water tupelo also produces extensive aerenchyma tissue.

 

Many of these adaptations are induced.

[Moontanman]

 

Water tupelo does produce pneumatophores, they are just less prominent and typically only under chronic flooding. Furthermore, water tupelo also produces extensive aerenchyma tissue.

 

Many of these adaptations are induced.

 

 

From what I have observed cypress only produce knees when they are in shallow water or very muddy soil, they do grow very deep tap roots, in fact the tap root will actually bore through quite thick plastic in garden ponds. I have no doubt that swamp plants produce pneumatphores but they are stunted, at least cypress, when they grow in substrates that prevent tap roots. This is generally seen when cypress grow on mud that has solid rock under them on in captivity where I need to stop the tap root tendencies... Even under good conditions cutting the tap root and planting the tree stunts the grown considerably resulting in a short stubby tree...