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How do temperature and soil organic matter inputs mediate the organic molecular composition of soils?


EMSL Project ID
48033

Abstract

The potential release of stored soil carbon under a warming climate will be at least partially dependent on the temperature response of soil organic matter (SOM) mineralization. However, it has become apparent in recent years that the heterogeneous nature of SOM and organic-microbial-mineral interactions may mediate the relationship between temperature and SOM decomposition in unexpected ways. Additionally, the historical dependence on operationally defined proximate SOM fractions may have led to erroneous assumptions about mechanisms of SOM protection in soils. We propose to use laser-ablation aerosol mass spectrometry (LA-AMS) and nanospray desorption electrospray ionization (nanoDESI) coupled with high-resolution mass spectrometry to provide high-resolution molecular characterization of SOM in soils exposed to litter-input exclusion or addition for 20 years, and subsequently incubated at 25 C and 35 C for more than a year. These treatments have measurably different total carbon content and carbon and nitrogen mineralization rates. Thus, these samples provide a unique opportunity to examine questions of chemical SOM recalcitrance and thermal stability. The proposed experiment would utilize soils from the Detritus and Input Removal Treatment (DIRT) experiment located in a deciduous hardwood forest in Meadville, PA. These soils were subjected to either litter and root exclusion, root exclusion, litter exclusion, double litter, or ambient inputs for 20 years. We have subsequently incubated these soils at 25 C and 35 C for more than a year. For this pilot study, we propose to use LA-AMS and nanoDESI at EMSL to examine SOM chemistry in samples from the no-litter inputs and double-litter inputs before and after laboratory incubation at the two temperatures. Additionally, we propose to examine a number of operationally defined SOM fraction for each of these treatments: bulk soil, microaggregates, silt and clay fractions, light, intra-aggregate light, and heavy fractions (via sodium polytungstate density fractionation), and a “humic” fraction.

Project Details

Project type
Exploratory Research
Start Date
2014-04-01
End Date
2014-09-30
Status
Closed

Team

Principal Investigator

Scott Bridgham
Institution
University of Oregon

Team Members

Kristyn Roscioli
Institution
Pacific Northwest National Laboratory

Related Publications

Reynolds L.L., K. Lajtha, R.D. Bowden, M.M. Tfaily, B.R. Johnson, and S.D. Bridgham. 2018. "The path from litter to soil: Insights into soil C cycling from long-term input-manipulation and high-resolution mass spectrometry." Journal of Geophysical Research. Biogeosciences 123, no. 5:1486-1497. PNNL-SA-121067. doi:10.1002/2017JG004076