The sands of the Kalahari desert, a large and forgotten storehouse of carbon dioxide – sciencedaily
Desert sands are a large and forgotten storehouse of carbon dioxide from the global atmosphere, scientists heard on April 2, 2008 at the 162nd meeting of the Society for General Microbiology.
âDesert soils are unusual because the sand grains on the surface are crusted together by bacteria, reducing wind erosion and adding nutrients to the soil. Deserts cover over a third of the world’s land surface and yet our understanding of their contribution to the atmospheric carbon dioxide balance is poor, âsays Dr Andrew Thomas of Manchester Metropolitan University.
Sands like those of the Kalahari Desert in Botswana are teeming with cyanobacteria. These drought tolerant bacteria can fix atmospheric carbon dioxide and together add significant amounts of organic matter to nutrient poor sands.
âWe know that on a global scale there is a huge exchange of carbon between the atmosphere and the soil. As global average temperatures rise, scientists fear that bacteria are breaking down organic matter in soils faster, releasing more carbon dioxide into the atmosphere, âsays Dr Thomas. âHowever, there have been very few actual field studies of this carbon exchange across the world’s soils and little information on how they respond to changes in temperature and humidity. true for deserts. Here bacteria have to be able to cope with long periods without rain and extremes of temperature, so they sleep in the desert floor and only come to life when there is sufficient humidity. “
The exchange or flux of carbon between soils and the atmosphere is much lower over deserts than in areas with soils richer in organic matter, but the size of deserts makes it significant overall. Even small changes in the carbon balance of desert soils will also be important at the local level, where soil organic matter underpins fragile ecosystems that currently support millions of poor pastoral farmers.
âWe found that even after low rainfall, the gains and losses of carbon dioxide through the sands of the Kalahari Desert were similar in size to those reported for grassland soils richer in organic matter. Despite their short duration, these high activity pulses are a significant and previously unreported contributor to atmospheric carbon dioxide, âsays Dr Thomas. “Global models of climate change have forgotten them.”
Dr Thomas and colleagues Dr Stephen Hoon and Dr Patricia Linton, also from Manchester Metropolitan University, found that under certain conditions, cyanobacteria in the surface crust took up net amounts of carbon dioxide from the atmosphere during photosynthesis. But after heavy rains, other types of bacteria deeper in the subsoil became active, and their activity masked carbon uptake by surface cyanobacteria by consuming organic matter in the soil, releasing large amounts of carbon. carbon dioxide.
“We also found that carbon dioxide fluxes from the soil were very temperature sensitive. Warmer air but similar soil moisture levels caused greater losses of carbon from desert soils to the atmosphere.” says Dr. Thomas. “These desert soils contribute significantly to the global carbon dioxide balance. Until recently, they were overlooked.”
âWe need to know exactly what’s going on, because a better understanding of the factors controlling the activity of cyanobacteria in surface-living soil could help inform grazing policy. Millions of poor semi-subsistence pastoralists depend on the soils of the Kalahari to provide nutrients for grazing. The carbon produced by cyanobacteria is a major contributor to soil fertility and it is essential to understand how their metabolism is affected by environmental conditions, âexplains Dr Thomas.
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