New Research Shows How Soil Microbes Shape Carbon Storage
Soil ecosystems are among the planet’s most important carbon reservoirs, storing roughly three times more carbon than the atmosphere and all living plants combined. This immense capacity makes soils a key player in climate change mitigation. Whether soils release carbon dioxide or lock carbon away long term depends on how microbes break down dead plant matter.
A new Cornell University study helps clarify this complex process. Researchers found that soil molecular diversity increases during the early stages of decomposition, peaks after roughly one month, and then begins to decline. These changes appear to influence how much carbon remains stored in soil.
“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?” asked Johannes Lehmann, senior author of the study and Liberty Hyde Bailey Professor of soil and crop sciences at Cornell’s 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 laboratory and now an independent consultant. The international research team included 11 co-authors from seven institutions across the United States and the Netherlands, supported by several funding sources, including two Cornell grants.
Earlier scientific thinking assumed soil carbon accumulated mainly from plant compounds that were difficult to decompose. That view shifted after a landmark 2011 Nature paper co-authored by Lehmann demonstrated that soil carbon forms through interactions among microbes, organic molecules, and minerals. In 2020, Lehmann and colleagues proposed that greater molecular diversity could slow decomposition and enhance carbon storage.
The new study delivers the first direct evidence backing that idea, showing diversity peaks around day 32 of decomposition. “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.”
Researchers also successfully used oxygen-18 labeled “heavy water” to trace microbial activity without disturbing natural soil conditions. “I think that method was a major success,” Davenport said. Future studies will investigate whether farming and forest management practices can boost soil diversity and increase long-term carbon storage.
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