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Unraveling spatial and temporal dynamics of microbial necromass destabilization

EMSL Project ID


Microbial necromass—or the extracellular and intracellular remains of dead microbes—can make up a significant portion of soil organic carbon and nitrogen. But a large quantity of necromass doesn’t indicate stability. There is evidence that necromass persistence and turnover are decoupled in soils, but our understanding and model representation of these processes is limited by a lack of appropriate and accessible methodologies to answer the fundamental question of what happens to a microbe after it dies. We seek to address the importance of mineral associations and organic chemistry in necromass destabilization, transport, and re-association with minerals. In addition to providing important insights into the poorly understood process of necromass destabilization, direct quantification of these process will allow us to include necromass dynamics in vertically resolved biogeochemical models that explicitly represent organo-mineral dynamics. We propose to quantify the destabilization, transport, and re-mineral association of three types of 13C enriched necromass: necromass that has been adsorbed, taken up into live microorganisms, or decomposed. Sequential extractions indicate these three necromass types may be associated with different mineral and microbial pools. We will determine whether the 13C enriched microbial necromass is preferentially associated with specific mineral phases using time of flight secondary ion mass spectrometry (ToF-SIMS). Necromass will destabilized during incubations in synthetic soil habitats that have discrete pillars of either the necromass soil or kaolinite. We will quantify how much of each necromass type can be destabilized and re-associated with new mineral surfaces using isotope ratio mass spectrometry (IRMS) of the incubation liquid and kaolinite pillars. Ultra-high resolution mass spectrometry (FTICR-MS) of the incubation water and the kaolinite pillars (using matrix-assisted laser desorption/ionization) will capture the full diversity of transportable and mineral re-associated organics. Destabilization and transport dynamics measured from the micromodels, along with previously collected field and laboratory data, will be incorporated into a vertically resolved biogeochemical model parameterized for the coastal grassland ecosystem where the soils were collected. Because the availability of soluble substrates is often the rate-limiting step in decomposition, quantifying the extent to which necromass is (or isn’t) destabilized is an important first-step in understanding how necromass formation can be decoupled from persistence.

Project Details

Project type
Large-Scale EMSL Research
Start Date
End Date


Principal Investigator

Courtney Creamer
U.S. Geological Survey


Jennifer Druhan
University of Illinois at Urbana-Champaign

Corey Lawrence
U.S. Geological Survey

Marjorie Schulz
US Geological Survey, Menlo Park

Kirsten Hofmockel
Pacific Northwest National Laboratory