Soil Microbes Key to Long-Term Carbon Storage

By Blake Jackson

Soils worldwide store roughly three times more carbon than the atmosphere and all plant life combined, making them a critical factor in regulating climate change. Understanding how soil microbes break down dead plant material sometimes releasing carbon dioxide and sometimes storing carbon long term is key to determining whether soils can help slow rising atmospheric CO₂ levels.

New research from Cornell University sheds light on this process, revealing that soil molecular diversity increases during early plant decomposition, peaks after about one month, and then declines.

“This is a hugely important question: can we lose less carbon from soil, or can we even increase our soil carbon stocks, which will help regulate CO2 in the atmosphere?” said Johannes Lehmann, senior author on the paper and Liberty Hyde Bailey Professor of soil and crop sciences in the College of Agriculture and Life Sciences.

“Because soils contain so much organic carbon, even small, incremental changes can make a big, big difference in the atmosphere and therefore for climate change.”

The study was led by Rachelle Davenport, Ph.D. ’24, formerly a graduate researcher in Lehmann’s lab and now an independent consultant. The research team included 11 co-authors from seven institutions across the U.S. and the Netherlands and was supported by several grants, including two from Cornell.

For many years, scientists believed soil carbon accumulated mainly from hard-to-decompose plant material. However, a landmark 2011 Nature paper co-authored by Lehmann showed that soil carbon instead forms through complex interactions among microbes, molecules, and minerals.

Building on that work, Lehmann and colleagues proposed in 2020 that higher molecular diversity in soils could slow decomposition and increase carbon retention.

The new study provides the first direct evidence supporting that idea, showing molecular diversity rises during early decomposition but peaks at 32 days before declining.

“It’s been a long time coming, since 2011, and has required a series of papers and experiments, but we now have some empirical evidence that plant decomposition does increase molecular diversity, if only for a short time,” Lehmann said. “We still have much to learn, but this is one important piece of the bigger puzzle.”

The research also pioneered the use of oxygen-18 labeled “heavy water” to trace microbial activity without altering natural soil processes. Davenport noted, “I think that method was a major success.”

Future research will explore whether increasing soil diversity through farm and forest management can lead to greater long-term carbon storage.

Photo Credit: gettyimages-zoran-zeremski