Saturday, February 17, 2007

El Dorado The secret of the soils and the mystery of the carbon sinks

The global transport of carbon (partly in the form of CO2) among the large reservoirs is called the global carbon cycle. Carbon dioxide emitted into the atmosphere together with the uptake by the terrestrial sinks and oceans governs the carbon dioxide content observed by the global sampling networks. Currently 40-60% of the anthropogenically released carbon dioxide remains in the atmosphere. Our current knowledge is ambiguous whether the rest of the CO2 is being detached by oceans or by terrestrial sinks (soil or vegetation) (Baldocchi et al., 1996).Indeed the missing carbon sink around 20% of the gcc is one of the unanswered questions for the IPCC.

The rhectoric of the sustainable carbon neutral society modification experiment is indeed just that. Propaganda from lobbyists and politicians who want us to lock up forests,or reafforestation programmes that which will have adverse daisyworld climatic effects in the future. Indeed increased forestry in non-tropical climates such as NZ have the effect of decreasing the albdeo(reflection of longwave radiation) and INCREASING local temperatures!

In the terrestrial biosphere vegetation accounts for 20% of the carbon sink,the vadose zone the soils and detritus materials 80%.

Here any policies that impact on the biosphere-atmosphere need to account qualitatively for the adverse effects prior to any policy change.ie that will have any equal adverse response.

Here we look at 2 of the mysteries of the vadose zone ,the greatest change mechanism the bacterial transformers 50% of the worlds biomass will be covered in a later post.

It has long been known that soil carbon, aka organic matter, greatly increases soil fertility by making soil nutrients more available to plants. Several processes have been identified related to soil chemistry and texture, the size and shape of soil particles is important too in supporting chemical processes. This is another way that soil carbon is important for fertility since a shortage would reduce the ability of VAM to transport nitrogen.

Vesicular Arbuscular Mycorrhizal fungi (VAM, or just AM) for its role in phosphorus transport as well as sequestration of massive amounts of carbon in the durable form of glomalin which is the threadlike remains of dead VAM lacing undisturbed soil. Phosphorous isn't the only thing VAM transports.

It seems a mighty feat for a microscopic fungus built from threadlike filaments. But collectively, these spindly mushroom relatives help move several billion tons of nutrients out of the soil and into plants each year. . .

"Ignorance (about the movement of nitrogen) limits our understanding ... in what is arguably the world's most important symbiosis," says Yair Shachar-Hill, the lead MSU author on the study. . .

The fungus-plant partnership is one of the planet's oldest and dates back more than 400 million years, when plants began to move out of the oceans and onto land. Plants trade a bit of their sunlight-made sugars for building block nutrients that fungi wring from the soil. Scientists have understood broad outlines of this evolutionary bargain for years, but specific details remained fuzzy, especially those related to nitrogen.

To learn more about nutrient uptake, MSU researchers led by Shachar-Hill, along with collaborators at New Mexico State University and the U.S. Department of Agriculture research center near Philadelphia, tagged nitrogen with easy-to-spot atomic markers and then watched as it traveled from soil to fungus to plant roots.

Many had assumed that the fungus would play a modest role. The team found, however, that the fungus acts more like a four-lane highway than a two-track country road in shuttling the nitrogen into plant roots. More than a third of the total nitrogen taken up by the plants came by way of the fungus,

"The really fascinating part is the mechanism underlying the transfer process," says Maria Harrison, a plant biologist at Cornell University's Boyce Thompson Institute and an expert on fungus-facilitated movement of other soil nutrients into plant roots. "Dr. Shachar-Hill and his colleagues were able to show that the fungus acquires the nitrogen from the soil and then links it to carbon and moves this combination molecule towards the plant. Then just before delivery to the plant cell, it unhitches the carbon and releases only the nitrogen to the plant.

There are many implications. Agronomic practices that impede or destroy VAM hugely impact the functional fertility of soil. If the only nutrients available to plants are those in the immediate vicinity of their roots then they can starve in the midst of plenty. This leads to excessive use of fertilizer which is not only an expense that is increasing it is a pollution hazard since excess nutrients end up in ground and surface water.Around 20% of the dark fertile soils of Amazonia are man made,an area around twice the size of the UK.They date to around 2500 years are a product of char and burn agronomy.

"Terra Preta de Indio" (Amazonian Dark Earths; earlier also called "Terra Preta do Indio" or Indian Black Earth) is the local name for certain dark earths in the Brazilian Amazon region. These dark earths occur, however, in several countries in South America and probably beyond. They were most likely created by pre-Columbian Indians from 500 to 2500 years B.P. and abandoned after the invasion of Europeans (Smith, 1980; Woods et al., 2000). However,many questions are still unanswered with respect to their origin, distribution, and properties.

The global carbon cycle has been brought to wide attention due to its importance for the global climate. The Intergovernmental Panel on Global Change (IPCC, 2001) recently confirmed that the anthropogenic greenhouse effect is a reality, which we have to deal with in the future. The atmospheric CO2 has increased from 280 ppm in 1750 to 367 ppm in 1999 and today's CO2 concentrations have not been exceeded during the past 420,000 years (IPCC, 2001). The release or sequestration of carbon in soils is therefore of prime importance.

Soil organic carbon is an important pool of carbon in the global biogeochemical cycle. The total amount of organic carbon in soils is estimated to be 2011 Gt C, which constitutes about 82% of the global organic carbon in terrestrial ecosystems (Watson et al., 2000).

Amazonian dark earths have high carbon contents of up to 150 g C/kg soil in comparison to the surrounding soils with 20-30 g C/kg soil (Sombroek, 1966; Smith, 1980; Kern and Kämpf, 1989; Sombroek et al., 1993; Woods and McCann, 1999; Glaser et al., 2000). Additionally, the horizons which are enriched in organic matter, are not only 10-20cm deep as in surrounding soils, but may be as deep as 1-2m (average values probably around 40-50cm)! Therefore, the total carbon stored in these soils can be one order of magnitude higher than in adjacent soils.

Furthermore, the organic matter in the dark earths is persistent since we find these elevated carbon contents even hundreds of years after they were abandoned.The reason for the high stability of the soil carbon is currently under discussion. So-called black carbon was identified as a probable reason for the high stability (Glaser et al., 2000). Further research is necessary to quantify the recalcitrance of the soil carbon over long periods of time and determining techniques for creating such soils through application of black carbon (or called "bio-char). The structural similarity to charcoal led the authors to assume that accumulation or purposeful application of organic carbon from incomplete combustion may have been the primary reason for the high carbon contents and fertility of these soils (Glaser et al., 2001), a theory that had been proposed by Smith (1980).

Thus any policy change,or incentive/disincentive mechanism must include the total kinetic geochemical cycle in the carbon neutral algoritmn if not it should be shredded and recycled immediately.This will I predict, see the demise of the "carbon balance" industry and its associated ambulance chasing salesman such as Al Gore and his "vested interests"

0 Comments:

Post a Comment

Links to this post:

Create a Link

<< Home


Web Counters