Research from Cornell University reveals significant changes in soil molecular diversity as microbes decompose plant materials, a finding that could have profound implications for climate change mitigation. The study, published in Nature Communications on December 10, 2023, shows that molecular diversity in soil increases during the initial month of plant decay, before plateauing and subsequently declining.
Understanding how soil microbes recycle organic materials is crucial since soils store approximately three times as much carbon as what exists in the atmosphere and within all plants combined. This research aims to illuminate the processes that determine whether carbon is released back into the atmosphere or mineralized for long-term storage.
Johannes Lehmann, the senior author and Liberty Hyde Bailey Professor of soil and crop sciences, emphasized the importance of this research. “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?” he stated. Even minor changes in soil organic carbon levels can significantly impact atmospheric CO2 concentrations.
The first author, Rachelle Davenport, who recently completed her Ph.D. at Cornell, noted that the study involved collaboration among 11 co-authors from seven institutions across six U.S. states and the Netherlands. Their work was supported by multiple public and private grants, including two from Cornell: a Schmittau-Novak Small Grant and a Graduate Research Grant from the Cornell Atkinson Center for Sustainability.
For decades, scientists believed that soil organic carbon primarily accumulated due to the resilience of certain plant materials. However, a pioneering paper by Lehmann and colleagues in 2011 challenged this notion, asserting that soil organic carbon results from complex interactions among soil microorganisms, molecules, and minerals. They called for new experiments to explore the mechanisms that govern carbon storage and release in soils.
In a subsequent 2020 study, Lehmann proposed that higher molecular diversity in soils might actually limit decomposition and promote carbon retention. The theory suggests that when molecular diversity is lower, microbes can specialize more easily, consume more organic matter, and consequently release more CO2. Conversely, greater diversity may hinder rapid consumption of materials, allowing minerals to capture and store carbon over extended periods.
The current research is the first to empirically demonstrate that plant decomposition temporarily increases soil molecular diversity, peaking at 32 days. “It’s been a long time coming, since 2011, and has required a series of papers and experiments,” Lehmann said. “We now have some empirical evidence that plant decomposition does increase molecular diversity, if only for a short time.”
To quantify molecular diversity, the researchers extracted organic matter using water and identified the compounds present through high-resolution mass spectrometry. Notably, this study is the first to utilize “18O heavy water” to trace changes in soil molecular composition due to microbial activity. Davenport explained that using heavy water, rather than traditional carbon labeling methods, provided a more accurate measurement of microbial activity.
Davenport highlighted the significance of collaborations, particularly with the Environmental Molecular Sciences Laboratory in Richland, Washington, which played a crucial role in developing this new methodology. She received a Graduate Research Grant from Cornell Atkinson in 2022, which allowed her to hire an undergraduate student, Caleb Levitt, who contributed significantly to measuring soil carbon dioxide emissions and monitoring the effects of decomposition.
Future research aims to explore whether increased diversity among soil molecules, microorganisms, and minerals can enhance carbon storage in soils. If so, the next step would involve developing strategies to support this diversity through improved farm and forest management practices, according to Lehmann.
The study not only advances the understanding of soil carbon dynamics but also opens new avenues for climate change mitigation strategies. With funding from the U.S. National Institute for Food and Agriculture and the Pacific Northwest National Laboratory, this research is poised to contribute meaningfully to the discourse on environmental sustainability.
