Global Warming, Stanford researchers: "Farming is likely to impact greenhouse gas emissions"

Stanford researchers have found that global warming and certain land use practices such as farming may increase greenhouse gas emissions released into atmosphere, according to journal Nature Communications on Friday. 

A new study led by Scott Fendorf, a professor of Stanford's School of Earth, Energy and Environmental Sciences, showed that tiny, scattered populations of bacteria living in soil, which are oxygen-starved, have an unaccounted effect on the amount of greenhouse gas released into the air. It is generally known that about a third of the carbon dioxide released into atmosphere annually is attributed to bacteria living in the soil, where they break down plants and animal matter for energy, according to the new study published in the journal. 

Fendorf's study discovered that in small pockets of soil that lack oxygen, bacteria, called anaerobic microsites, have evolved to extract energy from organic matter without oxygen. These oxygen-starved microbes produce significantly less carbon dioxide, because they are unable to break down certain carbon-rich biomolecules such as waxes and lipids, said the study. Normally, soil contains carbon that is trapped underground through chemical reactions with minerals. But it can also be created after plants and animal matter are decomposed and broken down by microorganisms, thus producing energy for them and carbon dioxide. 

In a lab experiment, Fendorf's team created an environment in which they controlled the flow of oxygen to soil samples and measured the output of carbon dioxide. They observed that when oxygen became scarce, the soil microbes shifted from aerobic to increasingly less efficient anaerobic respiration. As a result, fewer carbon-rich lipid and wax molecules were decomposed and the production of carbon dioxide fell by 90 percent. Their lab results matched their findings the researchers obtained from their field study in agricultural field sites in Oregon on the U.S. west coast. They reached a scientific conclusion that unlike conventional belief, upland soils actually contain high volumes of anaerobic microsites that protect specific types of carbon molecules. Both natural factors and human activities, such as a warmer climate and human farming practices, could disturb these microsites and change the amount of carbon dioxide discharged from the soil into atmosphere, the study showed. 

The warmer the soil becomes, the more metabolic activities microbes will produce when they become warmer as well. As a result, they consumed more oxygen and created more carbon dioxide. Changes in soil moisture arising from irrigation or climatic patterns will alter the distribution of microbial metabolisms and the rate of carbon dioxide, according to Fendorf's observation. Their findings highlight a benefit of low tilling practices and other land use behaviors that impact the pattern of greenhouse gas emissions. This will help model future carbon emissions by better predicting how much carbon dioxide might be released from the soil.