October 12, 2022
Research Highlight

Microbial Decomposition Shapes Organic Matter Composition in Grassland Soils

Biochemical preservation and mineral association retain carbon in grassland soils, resulting in consistent molecular composition across ecosystems

Grassland site

A grassland field test site in Sevilleta, NM.

(Image courtesy of Qian Zhao | Pacific Northwest National Laboratory)

The Science                                 

Increased human activity, such as environmental pollution, has a critical impact on ecosystem structure and function at the global scale, including on soil carbon (C) cycling in grasslands. Grassland soils store a substantial proportion of the global soil C stock. The chemical composition and persistence of C in grasslands strongly regulate global carbon cycling. There’s controversy, however, surrounding the importance of mineralogical versus biochemical preservation of soil C. This study provides original evidence that it takes contributions of both physicochemical and biochemical preservation in order to have persistent C across grassland soils.

The Impact

This study provides empirical evidence behind the fundamental science of soil C. The results allow researchers to apply similar methods to other ecosystems to determine the importance of mineralogical and biochemical preservation and how human activity contributes to the changing environment.


Grassland ecosystems are one of the largest terrestrial C reservoirs, covering approximately one-third of the global terrestrial surface and storing ~20% of the global soil C stock. Increased atmospheric nitrogen (N) deposition caused by human activities (i.e., environmental pollution) has a critical impact on ecosystem structure and function at the global scale, including on soil C cycling in grasslands. In this study, researchers evaluated grassland soils from diverse locations in an 8-month aerobic incubation experiment. They posited—and proved—that C decomposition in grassland soil is constrained by both biochemicals and minerals, even with N deposition from human activities. This work unveiled that N addition to grassland soils dampened C respiration and diminished the convergence of C chemistry across diverse grassland ecosystems.


This work was funded by a National Science Foundation (NSF) award to K. S. Hofmockel and the FY16 Laboratory Directed Research and Development program at Pacific Northwest National Laboratory. The research was performed at the Environmental Molecular Sciences Laboratory (EMSL), a DOE Office of Science User Facility sponsored by the Biological and Environmental Research program.