Plants absorbing carbon dioxide

 

Plants absorb 30 times all man made emission.  This is a huge absorption of carbon dioxide. At first sight this would indicate that carbon levels should be dropping – yet they are rapidly rising – so what has gone wrong?

Unfortunately most of the carbon absorbed by plants goes straight back into the atmosphere.

 Plant materials are complex organic molecules which are readily degraded to simpler molecules, such as carbon dioxide.  This happens from a number of mechanisms.  The combination of UV light and oxygen in the atmosphere is highly destructive to these complex organic molecules.

Agricultural and forestry waste left on the surface and exposed to sunlight quickly breaks down to return carbon dioxide to the atmosphere.

 If they are not broken down by UV light there are likely to be decomposed by bacteria working in aerobic conditions.  These aerobic bacteria will release large amount of carbon dioxide back into the atmosphere.

In other words plants absorb large amounts of carbon but most is returned to the atmosphere.  It is often said that the largest emitter of carbon is coal fired electricity generation followed by close seconds such as farming and transport.

This is not true, the largest source of carbon entering the atmosphere, by far is the break down of plant material. Some 97% of the carbon entering the atmosphere is from degrading plant material.  The level of carbon in the atmosphere is a dynamic situation with carbon continuously entering and leaving the atmosphere. 

People often make the mistake of thinking of carbon as a static problem e.g. we should strive to take carbon out of the atmosphere and permanently store it. This has led to the mistaken view that forestry is storing carbon in the soil - mistaken, because the carbon is not permanently stored.

We should think of the atmosphere as a giant lake with carbon, like water, pouring in and out.  If there is more carbon pouring in the level will rise and if there is more carbon pouring out the level will drop.

Man made emission are a relatively small part of this carbon flow which is dominated by the natural extraction and return of carbon from the plants.  Man has upset the balance by increasing carbon emission and reducing the ability of plants to remove carbon.

 The critical issue is the rate at which carbon is being extracted versus the rate at which it is returned. 

A tropical rain forest rapidly absorbs carbon from the atmosphere, but carbon is equally rapidly returned.  Any carbon that may be captured in the soil is quickly washed away by the heavy tropical rain, so the system is close to being in balance with only a small reduction in atmospheric carbon.

A temperate forest, with a lower and more seasonal rainfall, on the other hand has a much slower rate of decomposition so there is time for the micro organisms to capture carbon into the soil, so there will be a reduction of carbon in the atmosphere. 

Every molecule will eventually return to the atmosphere but the rate of return will be  less than the rate of capture so the system is not in equilibrium and the balance of the carbon ends up captured in the soil.  Individual molecules will be entering and leaving the soil, may be at a fairly rapid rate, but there will still be a net increase in the total carbon in the soil. They are different molecules but still the net volume will be increasing.

Modern agriculture has of course changed the carbon balance and land that was once forest that has been converted to agriculture increasing the rate at which carbon is returned to the atmosphere so the net volume of carbon in the soil will be reduce over time.  Modern agriculture is a major net emitter of carbon. This is bad for the climate and bad for food production.

The technology of reducing the rate at which the plant based carbon returns to the atmosphere must be one of the most important technologies for safeguarding our future, yet it remains in a scientific backwater.

Bacteria and fungi both degrade dead organic material, but in very different ways. 

Bacteria are very effective at degrading soft organic material but have difficulty in digesting the hard material particularly the lignin in wood.

They can generate ionic bonds (Van de Waal forces) between the organic material and the soil particles which assist in retaining the carbon in the soil.

Anaerobic bacteria can release significant amounts of carbon dioxide and methane back into the atmosphere.  Anaerobic bacteria lead to lower green house emissions.

Bacteria are microscopic with no cohesion between individual bacteria. 

Fungi are very different. They send out hyphae to form a complex network of mycelium which can be huge.  In fact the largest living creature on the earth is a fungus.  This network reinforces the soil giving it mechanical strength which helps the soil resist wind and water erosion.  It also increases the pore size so the soil can hold more water.

The hyphae inject powerful enzymes into the organic material which can decompose even the hardest of woods.  They can also dissolve soil particles, even rocks, to release minerals for plant use.

Certain fungi form beneficial or symbiotic relationships with plants (mycorrhizal fungi).  The area or spread of the fungi is far greater than the roots of the plants increasing the nutrient supply to the plant.  Some fungi actually enter the root system and in return for minerals receive sugars from the plant.

 Fungi also stabilize the carbon in the soil, even their body mass, which is largely carbon, is significant and fungi can live for hundreds of years.

Whether the problem is looked on as a way of increasing food production or of absorbing carbon into the soil for long periods of time fungi play a crucial role.

Wicking beds can be used to capture the carbon captured by plants and retain in the soil.  Fungi are the most effective method of converting plant material into carbon in the soil. This retained carbon improves the soil, increasing the water holding capacity and making nutrients more available to the plant.

Fungi are particularly sensitive to water content,

Wicking beds provide this high humidity environment in which fungi flourish and can be part of that critical chain of converting carbon into soil. Special versions of the wicking bed have been developed to capture carbon within an agricultural system.

We have the technology now. Of course it can still be refined, as any technology can, but we have simple methods that work well right now.  Technology is not a problem.

The immediate problem is that the actions of individual farmers are determined (in the main) by short term economic considerations.  There needs to be a fundamental shift in the attitude of society and Governments away from seeing food production as just another economic commodity to be traded around the world and to regard the farm as a community asset to provide us with food security in the long term and to manage the climate.  This has to be given real meaning by Government action.

The immediate problem is there is no structure - legislative or preferably financial incentives - to make this happen.

Governments and the International community need to set up a system of financial incentives whatever the method, trading schemes, tax incentives, subsidies or whatever scheme is preferred. Farmers cannot be expected to make the changes so they can absorb carbon without some reward for their efforts and expenditure..

 

The costs would be well below other schemes such as carbon sequestration at the power stations.  In any case sequestration only reduces the rate at which carbon is emitted and does nothing to remove carbon from the atmosphere.

The wicking bed is a new generation of agricultural system which is more productive, improves water use and can capture carbon from the atmosphere to stabilize climate change and to improve soil quality.

 

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