The energetic and chemical signatures

of persistent soil organic matter

Pierre Barré1,*, Alain F Plante2, Lauric Cécillon3, Suzanne Lutfalla1,4, François Baudin5, Sylvain Bernard6, Bent T Christensen7, Thomas Eglin8, Jose M Fernandez2, Sabine Houot4, Thomas Kätterer9, Corentin Le Guillou10, Andy Macdonald11, Folkert van Oort4 & Claire Chenu4

1Laboratoire de Géologie de l'ENS - PSL Research University – CNRS UMR8538, 75005 Paris, France.

2Earth and Environmental Science, University of Pennsylvania, Philadelphia, USA

3Université Grenoble Alpes, Irstea, UR EMGR, 2 rue de la Papeterie-BP 76, F-38402 St-Martin-d'Hères, France.

4AgroParisTech - INRA, UMR 1402 ECOSYS, 78850 Thiverval Grignon, France

5Sorbonne Université-UPMC-Univ Paris 06, Institut des Sciences de la Terre de Paris, 75005 Paris, France.

6IMPMC, UMR7590, CNRS, MNHN, 61 rue Buffon, 75005 Paris, France

7Department of Agroecology, Aarhus University, AU-Foulum, DK-8830 Tjele, Denmark

8Direction Productions et Energies Durables – Service Agriculture et Forêt, ADEME, Angers 49000, France

9Department of Ecology, Swedish University of Agricultural Sciences, Sweden

10Unité matériaux et transformation (UMET), Université Lille1, CNRS - UMR8207, 59 Villeneuve d’Ascq, France

11Department of Sustainable Soils and Grassland Systems, Rothamsted Research, Harpenden, Hertfordshire, UK

*Corresponding author:

Supplementary Figures

Supplementary Figure 1: Soil organic content evolution as a function of long-term bare fallow duration.


Supplementary Figure 2: (a) NEXAFS spectra at the C K-edge. To avoid overlap, spectra were sorted from largest to smallest peaks and scaled by factor addition. At each site, darker lines represent samples from the initiation of the bare fallow experiments and the lighter lines represent samples from the most recent last sampling date (i.e., longest bare fallow duration). (b) Principal Components Analysis (PCA) scores for the first two components of heights of deconvoluted Gaussian curves derived from C K-edge NEXAFS data in the range of 283-291.5 eV.

Supplementary Figure 3: (a) Loadings of principal component 1 of the Principal Component Analysis (PCA) on DRIFT spectra in the mineral free CH3/CH2 stretching absorption bands region (2800-3000 cm-1). (b) Loadings of the principal component 2. The first two axes of the PCA of DRIFT spectra in the alkyl-C region accounted for 91% of total variance. High PC1 scores are characterized by an increase in CH2 relative to CH3. High PC2 scores are characterized by an increase in CH3 relative to CH2.

Supplementary Figure 4: Rock-Eval HI index plotted against NEXAFS aliphatic peak height.

Supplementary Table

Variable / Site / Slope / Intercept / R2 / p-value
T50-CO2-Ox / Versailles / 0.576 ± 0.033 / 416 ± 1.49 / 0.946 / < 0.01
Rothamsted / 0.307 ± 0.026 / 406 ± 0.76 / 0.931 / 0.01
Ultuna / 0.070 ± 0.035 / 410 ± 1.11 / 0.340 / 0.07
Grignon / 0.220 ± 0.020 / 436 ± 0.47 / 0.940 / 0.01
Askov / 0.221 ± 0.044 / 401 ± 0.73 / 0.676 / < 0.01
DSC ρE / Versailles / -147 ± 28.8 / 21495 ± 1322 / 0.591 / < 0.01
Rothamsted / -95.2 ± 21.8 / 25500 ± 575 / 0.680 / < 0.01
Ultuna / -83.7 ± 29.6 / 26928 ± 954 / 0.500 / 0.02
Grignon / -137 ± 14.8 / 26576 ± 356 / 0.916 / < 0.01
Askov / -195 ± 49.3 / 26703 ± 797 / 0.547 / < 0.01
HI / Versailles / -0.723 ± 0.143 / 154 ± 6.57 / 0.587 / < 0.01
Rothamsted / -0.693 ± 0.303 / 197 ± 8.78 / 0.343 / 0.04
Ultuna / -0.825 ± 0.269 / 150 ± 8.68 / 0.540 / 0.02
Grignon / -0.466 ± 0.176 / 133 ± 4.24 / 0.466 / 0.03
Askov / -0.807 ± 0.516 / 243 ± 8.34 / 0.158 / 0.14
OI / Versailles / -0.617 ± 0.148 / 217 ± 6.81 / 0.490 / < 0.01
Rothamsted / 0.763 ± 0.196 / 215 ± 5.67 / 0.603 / < 0.01
Ultuna / 0.059 ± 0.276 / 205 ± 8.91 / 0.006 / 0.84
Grignon / -0.152 ± 0.172 / 214 ± 4.14 / 0.089 / 0.40
Askov / -0.403 ± 0.415 / 201 ± 6.71 / 0.068 / 0.35

Supplementary Table 1: Summary of the linear regression analyses of the evolution of soil organic matter thermal stability (T50-CO2-Ox, temperature at which 50% of the total CO2 is evolved during the oxidation step in RockEval analysis; °C), energy density (DSC ρE, integral of the exothermic region of the differential scanning calorimetry thermogram normalized to sample C concentration; J g-1 C), hydrogen index (HI) and oxygen index (OI), with bare fallow duration.

Variable / Site / Slope (× 104) / Intercept / R2 / p-value
Aromatic / Versailles / 2.18 ± 0.86 / 0.045 ± 0.004 / 0.262 / 0.02
Rothamsted / -2.56 ± 1.00 / 0.054 ± 0.003 / 0.450 / 0.03
Ultuna / -3.03 ± 0.84 / 0.062 ± 0.003 / 0.649 / < 0.01
Askov / -4.84 ± 2.00 / 0.073 ± 0.004 / 0.494 / 0.05
Carboxyl / Versailles / -0.45 ± 0.94 / 0.180 ± 0.004 / 0.012 / 0.64
Rothamsted / 3.40 ± 0.82 / 0.175 ± 0.002 / 0.684 / < 0.01
Ultuna / 1.76 ± 2.06 / 0.189 ± 0.007 / 0.094 / 0.42
Askov / 5.25 ± 2.47 / 0.159 ± 0.004 / 0.430 / 0.08
Aliphatic / Versailles / 1.56 ± 0.78 / 0.079 ± 0.004 / 0.179 / 0.06
Rothamsted / 0.50 ± 1.18 / 0.080 ± 0.003 / 0.022 / 0.68
Ultuna / -4.12 ± 0.91 / 0.087 ± 0.003 / 0.744 / < 0.01
Askov / -5.36 ± 2.38 / 0.090 ± 0.004 / 0.458 / 0.06
Carbonyl / Versailles / 1.37 ± 1.26 / 0.102 ± 0.006 / 0.061 / 0.29
Rothamsted / -2.35 ± 1.33 / 0.104 ± 0.003 / 0.282 / 0.11
Ultuna / -5.55 ± 1.32 / 0.113 ± 0.004 / 0.715 / < 0.01
Askov / -7.03 ± 2.14 / 0.125 ± 0.004 / 0.644 / 0.02

Supplementary Table 2: Summary of linear regression analyses of the evolution of soil organic matter composition with bare fallow duration, as measured by atomic environment of carbon observed using NEXAFS spectroscopy of the non-carbonate soils (i.e., excluding Grignon).

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