The researchers discovered that changes in the levels of airborne aerosols resulted in changes to the terrestrial carbon cycle, or the cycle in which CO2 is absorbed by plant photosynthesis and then emitted by the soil.

Besides documenting the effects of aerosols on the carbon cycle, the research also showed that the type of landscape also influenced whether a surface area served as a carbon sink, an area that absorbs more CO2 than it emits, or as a carbon source, an area that emits more CO2 than it absorbs. In the research project, six locations across the United States encompassing forests, croplands and grasslands were studied. Increased amounts of aerosols over forests and croplands resulted in surface areas below becoming carbon sinks, but increased amounts of aerosols over grasslands resulted in surface areas becoming carbon sources.

Dr. Dev Niyogi, research assistant professor of marine, earth and atmospheric sciences at NC State and lead author of the study, hypothesizes that the differences among landscapes can be attributed to the amount of shade provided by tree and plant leaves in forests and croplands. The lack of shading in grasslands changes the ground surface temperature, which alters the rate of photosynthesis in plants and the CO2 emissions by soil. Since plants want to take in CO2 but also preserve water at the same time, Niyogi believes the lack of shade and increased temperatures may cause plants to slow the rate of photosynthesis, causing less CO2 to be absorbed and thus more CO2 to be effectively emitted. That would make the surface area a carbon source.

The research was published in Geophysical Research Let
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8-Dec-2004