Desert sands are an important storehouse of CO2

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Washington, April 2 : Scientists have determined that the sands of the desert are an important and forgotten storehouse of carbon dioxide taken from the world's atmosphere, taking the case of the Kalahari Desert in particular.

This statement was given by scientists at the Society for General Microbiology's 162nd meeting being held this week at the Edinburgh International Conference Centre.

"Desert soils are unusual because the sand grains at the surface are bound together into a crust by bacteria, reducing wind erosion and adding nutrients to the soil," said Dr Andrew Thomas of Manchester Metropolitan University.

Deserts cover over one third of the world's land surface and yet our understanding of their contribution to the atmospheric carbon dioxide balance is poor, according to Dr Thomas.

Sands like those in the Kalahari Desert of Botswana are full of cyanobacteria. These drought resistant bacteria can fix atmospheric carbon dioxide, and together they add significant quantities of organic matter to the nutrient deficient sands.

According to Dr Thomas, in deserts, the bacteria have to be able to cope with long periods without rain and extreme temperatures, so they lie dormant in the desert soil only springing to life when there is enough moisture.

The exchange or flux of carbon between the soils and the atmosphere is much smaller over deserts than for areas with more organically rich soils, but the sheer size of deserts makes it globally significant.

Even small changes in the carbon balance of desert soils will also be important locally, where soil organic matter underpins fragile ecosystems currently supporting millions of poor pastoral farmers.

"We discovered that even after light rainfall, the gains and losses of carbon dioxide through the sands of the Kalahari Desert were similar in size to those reported for more organic rich grassland soils," said Dr Thomas.

"Despite being short lived, these raised pulses of activity are a significant and previously unreported contributor to atmospheric carbon dioxide," he added.

Dr Thomas with his colleagues, Dr Stephen Hoon and Dr Patricia Linton, found that in some conditions, the cyanobacteria in the surface crust were taking net amounts of carbon dioxide out of the atmosphere as they photosynthesised.

But after heavy rainfall, other types of bacteria deeper in the subsoil became active and their activity masked the uptake of carbon by the surface cyanobacteria by consuming the organic matter in the soil, releasing large quantities of carbon dioxide.

"These desert soils are contributing significantly to the global carbon dioxide budget. Until recently, they have been ignored," said Dr Thomas.

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