A 37-year experiment at Harvard Forest has shown that rising temperatures can destabilize carbon long thought to be secure in forest soils. The findings indicate that microbes break down these stable stores, releasing additional carbon dioxide into the atmosphere.
Researchers led by Jerry Melillo of the Marine Biological Laboratory maintained soil temperatures 5 degrees Celsius above ambient levels in plots at Harvard Forest in central Massachusetts. The warming level matched upper-range projections available when the study began decades ago.
During the fourth decade of the experiment, stable forms of soil organic matter began to decompose. This process added extra CO2 beyond what earlier models had anticipated from forest soils.
Melillo noted that microbes drive the breakdown of organic matter and recycle nutrients for plants. He said continued emissions reductions could limit further warming and slow the feedback.
The team recommends including the newly observed process in climate models to refine projections of how Earth's carbon cycle responds to higher temperatures. The results appear in the journal Science of the Total Environment.