Biomolecular linkages between detrital inputs and soil organic matter decomposition across temperate forest regions
EMSL Project ID
51052
Abstract
Limited knowledge of the molecular mechanisms behind soil organic matter (SOM) stabilization and destabilization processes impedes improving models of earth systems and global carbon dynamics, as well as our ability to understand important linkages among global climate change drivers and responders. To investigate SOM dynamics across disparate forest systems, the Detrital Input and Removal Treatment (DIRT) project was established in 1990 and comprises a network of multi-decadal detrital manipulation experiments at sites spread across three continents. Detrital manipulations performed at these sites include additions of needle litter or woody debris inputs, elimination of aboveground or belowground inputs, as well as the elimination of both above- and belowground inputs. By studying the time course of changes in soil organic matter resulting from these manipulations, this network of study sites is ideally suited to address such questions as: what controls the long-term storage of carbon (C) in SOM? Does the chemical quality of detrital inputs affect SOM stability? What is the relative role of aboveground vs. belowground inputs for SOM stabilization? What chemical and physical fractions of SOM are the most stable C pools? What generalizable and key differences exists between SOM processing and stabilization in disparate forest systems?
Initial FTICR-MS results from our EMSL RAPID proposal have provided an exciting insight into the molecular processing of SOM across the DIRT manipulations, showing distinct differences in the molecular character of SOM in bulk soils with altered detrital inputs. However, this previous study provides information pertaining to only one specific ecosystem in a uniquely wet and C rich temperate forest. For this Exploratory proposal opportunity, we propose to probe the molecular chemistry of organic matter in bulk as well as in the mineral-associated, stable fraction of soil from 3 of the DIRT sites, along with the dissolved organic carbon in site-specific litter leachates. A comparative analysis of the molecular signatures in these SOM pools will allow us to track the molecular processing of detrital inputs from surface litter through the soil profile. Such an analysis of SOM across the unique forests and soils represented in the DIRT network would vastly broaden the scope and application of our findings, providing a requisite and robust test of competing hypotheses regarding the connections between detrital input sources, microbial processing, soil mineralogy, and underlying controls over soil C turnover.
For this proposal, we hypothesize that:
(1) Addition of low quality litters (e.g. woody debris) will alter the chemistry of light fraction, plant-derived soil but not alter the chemistry of the mineral-associated, stable heavy fraction of soil due to extensive microbial processing of these materials, and (1b) this microbial homogenization of litter inputs will also be observed in soil DOC that serves as a conduit between litter inputs and the mineral soil;
(2) Addition of high quality litter will result in efficient stabilization of microbial by-products due to high microbial CUE, although these results could be tempered by microbial mining and priming, both of which are known to increase with high quality litter inputs;
(3) The effects of litter additions will be seen more clearly in highly reactive soils in our network (i.e. Andisols) and less in very unreactive soils (i.e. sandy Alfisols), and thus we expect increased plant-based signatures in our reactive soils due to direct stabilization of soluble products of litter leaching;
(4) Similarly, we expect microbial mining and priming to be less evident in N-rich soils that have experienced significant N deposition, and thus will show fewer molecular-level differences in soil characteristics between control and litter amended treatments.
We will use EMSL's 12T FTICR-MS and the soil extraction protocol developed by Tfaily et al. (2017). At EMSL, two solvents (water, and chloroform) with different polarities will be used to sequentially extract a representative fraction of organic matter from soils according to protocol 1 in Tfaily et al. (2017). A 12 Tesla Bruker SolariX FTICR spectrometer will be used to collect high resolution mass spectra and identify chemical formulas of individual SOM compounds in the extracts. A standard Bruker ESI source will be used to generate negatively charged molecular ions. Unique biochemical compounds and abundances will be determined from the resulting data using established compound identification algorithms (Formularity software (Tolic et al., 2017)). Additionally, to determine linkages in SOM processing pathways, we will use mass-mass differences between mass spectral peaks to identify parallel metabolic reactions under the assumption that certain mass differences corresponding to specific chemical changes are related by the equivalent metabolic transformation. We will complement our FTICR-MS analyses with liquid-state nuclear magnetic resonance (NMR) spectroscopy measurements to enhance our ability to characterize changes in small primary core metabolites.
Project Details
Project type
Exploratory Research
Start Date
2019-11-26
End Date
2021-03-31
Status
Closed
Released Data Link
Team
Principal Investigator
Co-Investigator(s)
Team Members