Insights into Forest Soil Carbon Dynamics from Nuclear Magnetic Resonance Spectroscopy Chris E. Johnson Dept. of Civil & Environmental Engineering Syracuse University

Organic Chemistry Online: people.stfx.ca/tsmithpa orgchem.colorado.edu Nuclear Magnetic Resonance

Image: orgchem.colorado.edu Nuclear Magnetic Resonance

Electron density of a C-H bond. If entity “Z” is electronegative, electron density is shifted towards “Z”. And vice versa. Tad Koch, Chemistry and Biochemistry Department, University of Colorado The bond will absorb energy at the specific magnetic field strength at which it resonates. Nuclear Magnetic Resonance

Image: orgchem.colorado.edu Nuclear Magnetic Resonance

Solid-State 13 C NMR Alkyl-CO-Alkyl-CAryl C COOH/ Amide O Aryl

NMR Applications in Forest Ecosystem Studies 1.Plant tissues: −Wood quality −Response to environmental stress −Litter quality Image:

1.Plant tissues: −Wood quality −Response to environmental stress −Litter quality 2.Soil organic matter: −Decomposition −Accumulation and role as microbial substrate NMR Applications in Forest Ecosystem Studies Image:

1.Plant tissues: −Wood quality −Response to environmental stress −Litter quality 2.Soil organic matter: −Decomposition −Accumulation and role as microbial substrate 3.Aquatic organic matter: −Similarity to soil organic matter −Substrate for aquatic organisms NMR Applications in Forest Ecosystem Studies Image:

Global Change Context Carbon Sequestration –Understanding SOM decomposition –Adsorption/Desorption processes Land-use Impacts on C cycling –Clearcutting effects –“Old fields” → Forest Conversion Acidification and Recovery –pH effect on soil C forms and pools

Northern Hardwood Forest

Plant Tissues – Wood and Bark

In situ Decomposition Experiment

Plant Tissues – Wood Decomposition

White Rot Decomposition

Plant Tissues – Bark Decomposition 78% Mass Loss

Johnson et al. (1991, 1994)

Oa Horizon: 18 mg DOC L -1 Bh Horizon: 11 mg DOC L -1 Bs Horizon: 5 mg DOC L -1 Soil Solution DOC Concentrations (Tension-Free Lysimetry) Stream Water: 2 mg DOC L -1 Johnson et al. (2000)

NMR analysis of soils Dai et al. (2001); Fahey et al. (2005)

Soil vs. Soil Solution SoilsSoil Solutions Dai et al. (2001)

Clear-cutting – W5 at Hubbard Brook Winter/Spring

Whole-tree harvest – boles and crowns

Most of the wood was chipped

Watershed 5 – Summer 1984

Soil Solution DOC Dai et al. (2001)

Streamwater DOC – Spring Snowmelt Dai et al. (2001)

Contrasting Soil and Solution Composition: % Aromatic C

Why Isn’t Stream DOC like Soil Solution DOC? Selective immobilization in deep mineral soil (below Bs lysimeters). Importance of riparian-zone soils. In-stream consumption of DOC.

Soils – Humification of Organic Matter Balaria and Johnson (2009)

Soils – Humification of Organic Matter Balaria and Johnson (2009)

Hot-Water Extractable Organic Matter Balaria (2011) (Dissertation)

Hot-Water Extractable Organic Matter HorizonSoil CHWEOC† Freeze-dry recovery‡ g C kg -1 soil % of soil C %---- Oi503 ± ± Oe494 ± ± Oa (0-1 cm)475 ± ± Oa (1-2 cm)438 ± ± Oa (2-3 cm)402 ± ± Oa (3-4 cm)387 ± ± Oa (4-5 cm)329 ± ± † HWEOC, Hot-water extractable organic carbon ‡ Recovery is the percentage of HWEOC isolated in the freeze-drying process Balaria and Johnson (2009)

Hot-Water Extractable Organic Matter Balaria and Johnson (2009)

Conclusions 1.NMR spectroscopy can yield insight into process-level questions related to organic matter: Land-use effects. Decomposition chemistry. DOC mobilization/immobilization. Humification and soil development. 2.Organic matter in soils and soil solutions is depleted in O-alkyl- C and enriched in alkyl-C downward in the soil profile. 3.Stream DOC differs significantly from soil solutions, suggesting the importance of deep-soil and/or riparian processes. 4.Fifteen years after clear-cutting, soil solutions were more aromatic than in a nearby control watershed. 5.NMR is particularly useful in studying more dynamic OM such as DOM, water-soluble OM, and fractionated SOM.

Issues and Limitations  Solid-state 13 C-NMR is time consuming (>24-hr for some samples).  Paramagnetic interferences (Fe – in Spodosols).  CP/MAS 13 C-NMR is semi-quantitative: Generally suitable for comparisons. Other NMR approaches exist (with their own limitations).  Low DOC concentrations: we used ~150 L of water to isolate stream DOC.  Difficult to collect high-volume soil solutions.

Research Impacts  Post-Doctoral Supervision: 1 (K.H. Dai)  Doctoral Supervision: 2 David Ussiri (U. Illinois/Illinois State Geological Survey) Ankit Balaria (Arcadis)  Master’s and Undergraduate Students

Research Impacts Collaborations:  Griffith University (Brisbane, Australia) Zhihong Xu, Environmental Futures Centre Two funded projects – Australian Research Council Adjunct Professor: 2005-present Student exchange: 2004, 2007  University of Adelaide, CSIRO (Adelaide, Australia) Ron Smernik, Waite Ag. Institute (U. Adelaide) Jeff Baldock, CSIRO  Forestry Tasmania, (Hobart, Australia) Simon Grove, Sandra Roberts Warra LTER site, long-term eucalyptus decomposition experiment

Research Impacts Adoptions:  Textbook Essington, M.E. Soil and Water Chemistry: An Integrative Approach.  HF Pre-treatment method (Dai and Johnson, 1999) Commonly used for removal of Fe and other paramagnetics 49 citations  Hot-water extractable organic matter (Balaria and Johnson, 2009) Growing use in ecological studies 9 citations

Research Impacts Publications, Citations and Synergies:  NMR-related publications, peer-reviewed, 1 book chapter 219 citations (Web of Science)  Invited talks to chemists: Eastern Analytical Symposium Northeastern ACS Meeting  Hubbard Brook carbon monograph Fahey et al. Biogeochemistry (2005) 75:

Johnson et al. 1994

Clearcutting Effects – Whole-soil 13 C CPMAS NMR Uncut Clearcut Oa Bh Bs

Clearcutting Effects – Whole-Soil 13 C NMR

Deconvolution of NMR Spectra Keeler et al. (2003) Analytical Chemistry

Molecular Mixing Model Chemical ShiftFunctional GroupCarbohydrateProteinLigninLipidCarbonylChar ppm %%% Alkyl C N-Alkyl/ Methoxyl C O-Alkyl Di-O-Alkyl Aromatic Phenolic Amide/Carboxyl NMR Results for a sample. Solve for best- fitting set of f- values.

Molecular Mixing Model – Results Balaria and Johnson (In Review)

Molecular Mixing Model - Results Balaria and Johnson (In Review)

Molecular Mixing Model - Results Balaria and Johnson (In Review)

Adsorption of OM by mineral soils “Initial Mass Isotherm” Approach (Nodvin et al. 1986): R = Net DOC sorbed (+) or released (-) per mass of soil C i = Initial concentration of DOC in solution per mass of soil m = Regression slope ≈ partition coefficient (m ≤ 1) b = Regression intercept ≈ desorption parameter (b ≥ 0)

Adsorption isotherms for hydrophilic and hydrophobic OM fractions extracted from Bh horizon soils (Similar results for OM extracted from O horizons) (R 2 = )

Isotherm Parameters HydrophobicHydrophilic HorizonpHmbmb Bh Bs Bs C

13 C CPMAS NMR Spectra of OM Used in Adsorption Experiments f COOH = f COOH = f COOH = f COOH = 0.107

The C p :Fe d ratio may be a good indicator of sorption potential

Adsorption “envelopes”

Calcium Effects on Microbial Processes Expected: Less acidic conditions  Increased microbial biomass  Increased nitrification  Increased respiration  Reduced soil C in forest floor

Calcium Effects on Microbial Processes Expected: Less acidic conditions  Increased microbial biomass  Increased nitrification  Increased respiration  Reduced soil C in forest floor Observed: Less acidic conditions  No effect on microbial biomass  No effect on nitrification  No effect on respiration  No effect soil C in forest floor

Calcium Effects on Microbial Processes Hypotheses: Microbial community is adapted to low-pH environment (Groffman). Possible P limitation on microbial activity (Fisk) Calcium “protects” labile Ca from microbial attack (Johnson)

SoilHWEOM Control High Ca Low Ca Ca + P P only

Ankit Balaria (2011) Dissertation Calcium Effects on Microbial Processes