Molecular Diversity of Dissolved Organic Matter Shown to Drive Variable Microbial Respiration Responses
Findings reveal that soil respiration dynamics cannot be explained by organic matter chemistry alone, emphasizing the need to link molecular diversity with microbial metabolism to guide future soil respiration models.
A team of researchers from the Environmental Molecular Sciences Laboratory analyzed data using the Molecular Observation Network database to assess whether incorporating chemodiversity of organic matter improves predictions of soil respiration. (Photo by Andrea Starr, Pacific Northwest National Laboratory)
The Science
Soils store vast amounts of organic matter (OM), which microbes consume and release as carbon dioxide through respiration. Scientists have proposed that the chemical diversity of this OM—the variety of carbon-based molecules it contains—regulates this process. Using data from soil samples collected across the United States as part of the Molecular Observation Network (MONet), a team of researchers from the Environmental Molecular Sciences Laboratory (EMSL) found that this relationship is more complex than expected, underscoring the need to improve how soil respiration kinetic models are parameterized. In soils rich in OM, higher OM diversity correlated with lower respiration, while in soils poor in OM, the opposite was true. These contrasting patterns suggest that current soil respiration models oversimplify how microbial metabolism responds to molecular diversity. Capturing these nonlinear effects will be essential for predicting how soil OM responds to environmental disturbances such as fire or drought.
The Impact
Soils are living systems that control how OM is transformed and stored, shaping the foundation of the Earth's biological and energy cycles. Understanding these transformations is essential for predicting how soil OM supports sustainable food, energy, and bio-based systems that fuel life and the bioeconomy. Using advanced chemical analyses of soil samples from MONet, this study showed that the molecular diversity of dissolved OM influences microbial respiration in different ways, depending on soil conditions. These findings reveal that soil respiration dynamics cannot be explained by OM chemistry alone, emphasizing the need to link molecular diversity with microbial metabolism to guide future models of soil function and resource use in bioenergy and biomanufacturing systems.
Summary
To investigate the link between the chemical diversity of water-extractable OM and microbial respiration, a team of researchers from EMSL analyzed standardized data from topsoil (0–10 cm) using 63 cores obtained from across the continental United States. The soil was collected through the 1,000 Soils Pilot program of MONet and data included soil respiration rates, water-extractable OM concentration and chemistry, and more than 20 other biogeochemical parameters. Using regression analysis and kinetic models, OM chemical diversity was quantified as the number of organic compounds detected via Fourier transform ion cyclotron resonance (FTICR) mass spectrometry, and respiration was measured using a CO2 burst method. The team also applied advanced bioenergetic theory to derive microbial traits from the FTICR data to inform kinetic models. The results revealed that OM molecular diversity exerts context-dependent control on microbial respiration—enhancing it in low-OM soils while suppressing it in high-OM soils. However, current soil respiration kinetic models could not fully capture these nonlinear relationships, suggesting that improved mechanistic representations of microbial responses to molecular diversity are needed. This research demonstrates how MONet's standardized, continental-scale datasets can be used to reveal fundamental controls on soil OM transformations that underpin sustainable bioenergy, and soil management strategies.
Contact
Arjun Chakrawal
EMSL
arjun.chakrawal@pnnl.gov
Funding
Soil data were provided by the Molecular Observation Network at the Environmental Molecular Sciences Laboratory, a Department of Energy Office of Science user facility sponsored by the Biological and Environmental Research program. Work was also conducted using capabilities provided by the Joint Genome Institute, another Department of Energy Office of Science user facility located at Lawrence Berkeley National Laboratory. Soil samples collected for the project were obtained through the National Ecological Observatory Network, a program sponsored by the National Science Foundation and operated under a cooperative agreement by Battelle.
Publication
C. Arjun, et al. "Challenges in integrating dissolved organic matter chemodiversity into kinetic models of soil respiration." Soil Biology and Biochemistry, 211,109954 (2025). [DOI: 10.1016/j.soilbio.2025.109954]