by Maria Conthe
Soil dwelling microbes need copper to stop the release of nitrous oxide, a greenhouse gas, from fields into the atmosphere. (Photo: Stock)
There is more than meets the eye among the fields of barley. Underneath the rows of neatly planted grass, sown and fertilized each year, lies a rich microscopic world, teeming with life. Microorganisms living in the soil are key players in nature’s cycling of nutrients as they grow, metabolize and respire. As such, they have a direct effect on the environment and even the climate.
Enter N2O, short for nitrous oxide, a gas produced and consumed by these microbes in the soil. A part of Earth’s nitrogen cycle, N2O gas is naturally present in very small quantities (in parts per million!) in the environment.
However, like CO2, N2O levels in the atmosphere have increased significantly during the past century. If the main reason for the increase of CO2 is the use of fossil fuels as an energy source, the main reason for the increase of N2O is the use of synthetic fertilizers to grow crops. The extra input of nitrogen from man-made fertilizers, since they were first developed at the beginning of the 20th century, is altering Earth’s nitrogen cycle. Microbial processes in the soil are affected, and with increasing agriculture to feed the world’s increasing population, N2O levels are rising.
Despite its more common name “laughing gas” (in reference to the euphoric state it induces in users who inhale it as a party drug) nitrous oxide increase in the atmosphere is actually no laughing matter. N2O is a very strong greenhouse gas, with a global warming potential over 300 times greater than CO2. It is also considered the major ozone-depleting substance of the 21st century.
But why exactly does the increased nitrogen turnover in the environment caused by excessive fertilizer use lead to more emissions of nitrous oxide? “In a system as complex as soil, the answer is surely not a simple one” warns Manuel Soriano Laguna, a young researcher at the University of East Anglia (UEA) funded by the European initiative NORA (Nitrous Oxide Research Alliance). However Manuel’s team may have part of the answer, and it involves copper.
In soils and other ecosystems, N2O production is kept in check by N2O consumption. “Some microbes produce N2O as a product of their metabolism, but many can also consume N2O for respiration, much like we respire oxygen,” explains Manuel. “Copper is an essential ingredient of the cell machinery needed for respiration of nitrous oxide. Our research in the lab clearly shows that N2O respiration stops when microorganisms don’t have access to enough copper”.
A simple solution?
Extrapolated to the environment these results suggest that in soils lacking copper, microbes will not be able to consume N2O, leading to its accumulation and emission into the atmosphere. A very serious concern considering that up to 40% of agricultural soils worldwide may be currently copper deficient.
The bright side is that the remedy may be straightforward: “judicious use of copper in fertilizer regimes” says David Richardson, the head researcher at the UEA group. Just a pinch of copper may keep our fields of barley, romantic- and greenhouse gas free- fields of gold.