Rotting Equations

Over the past decade, in numerous field sites throughout the world, mesh bags of leaf and root litter sat exposed throughout the four seasons, gradually rotting away.

Now, those bags of decomposing organic matter have allowed researchers to produce an elegant set of equations to calculate the nitrogen released into the soil during decomposition, which in turn could significantly improve the accuracy of global climate change models.

According to the study, the dominant drivers of nitrogen release were the initial concentration of nitrogen and the remaining mass of the leaf and root litter.

"In the world of complex biogeochemistry, we've discovered that this fundamental process of nutrient cycling by plants and microbes turns out to be relatively straightforward," said co-lead author of the study Whendee Silver, a researcher at University of California Berkeley. "Whether it's hot or cold, wet or dry, the equations work."

More than three-fourths of the air we breathe contains nitrogen, an essential element found in all amino acids, the building blocks of protein. In the soil, organic forms of nitrogen are converted by bacteria into the inorganic forms of ammonium and nitrate, primary nutrients plants need for growth. Lack of nitrogen limits plant growth in most regions of the world.

The rate of decomposition, not nitrogen release, was affected by the two key variables of temperature and moisture, the researchers found. The slowest rates of decomposition were in cold regions, such as boreal forests and tundra, and the fastest in the warm, moist, tropical forests. The only places where litter decomposed completely were the humid tropical sites where, over the course of five years, only 10 percent of the initial litter material remained.

The study was detailed in the Jan. 19 issue of the journal Science.

---LiveScience Staff

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Credit: William S. Currie