Analytical pyrolysis as a tool to probe soil organic matter

Soil organic matter (SOM) is composed of multiple components from the living material, such as phenolic compounds, organic acids, lipids, peptides, polyesters, etc. A relevant part of these compounds forms part of supramolecular structures or mineral associations. Non-exchangeable hydrogen in SOM compounds is worth of study as an approach to estimate dynamic processes such as stabilization, mineralization, or biodegradation. The determination of H isotopes in SOMs faces analytical challenges related with e.g., the strength of the H bond, its exchangeability with ambient H from water or the instability of the isotopic analysis [1]. Nonetheless, along with the study of C isotopes, the study of H isotopes may certainly result in a complementary to give some light in this complex system, estimate the fate of organic compounds, and to better understand the link between hydrogen and carbon cycles in SOM [2].In this communication, we describe and validate a methodology based on analytical pyrolysis for the direct measure of compound-specific H isotope composition (&#948;2H) in soil samples. The technique combines Py-GC with a high-temperature conversion reactor and a continuous flow isotope ratio mass spectrometer (IRMS) (Py-GC-HTC-IRMS).Composite dehesa surface (0-10 cm) soil samples (Pozoblanco, C&#243;rdoba, Spain) were taken from four forced climatic treatment plots representing warming (W), drought (D), its combination (W+D), and control (D), installed in two different habitats: under evergreen oak canopy and in the open pasture. The samples were analysed in triplicate by conventional analytical pyrolysis (Py-GC/MS) and in parallel for &#948;2H Py-CSIA using the same chromatographic conditions and separation column type.Up to 32 compounds were identified by Py-GC/MS, which H isotope composition corresponded presumably to non-exchangeable H, and with origin mainly from lignin (G- and S- units) and lipids. The H isotope composition showed an estimated average of -55 &#8240; &#177; 7.09 for G-lignin units, -64 &#8240; &#177; 8.64 S-lignin units and lighter -112 &#8240; &#177; 4.32 for fatty acids (-109 &#8240; &#177; 3.65) and the n-alkane series (C-19 to C-31). Significant differences are reportedly driven by the differences in habitat: more depleted &#948;2H values were found in SOM produced in the open pasture than under the tree canopy. In addition, a &#948;2H enrichment is observed for lignin-derived compounds in SOM under the W+D treatment.The technique used and tested is expected to bring novelty results in relation to the processes affecting the isotopic composition of non-exchangeable hydrogen exerted by climatic treatments on diverse SOM specific compounds. Besides presenting the analytical challenges that are faced, we will discuss the effects of canopy and climatic treatments to tackle potential harsh climatic conditions as predicted, especially in Mediterranean areas.&#160;Acknowledgement: INTERCARBON project (CGL2016-78937-R), DECAFUN (CGL2015-70123-R). MICIU for funding FPI research grants (BES-2017-07968). Mrs Desir&#233; Monis, Mrs Alba M. Carmona & Mr Eduardo Guti&#233;rrez Gonz&#225;lez are acknowledged for technical assistance.[1] Paul, A. et al (2016). Biogeosciences, 13, 6587&#8211;6598.[2] Seki, O. et al (2010). Geochimica et Cosmochimica Acta,&#160;74(2), 599-613.

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Soil organic matter dynamics in Mediterranean A-horizons—The use of analytical pyrolysis to ascertain land-use history

Journal of Analytical and Applied Pyrolysis ◽

10.1016/j.jaap.2013.07.004 ◽

2013 ◽

Vol 104 ◽

pp. 287-298 ◽

Cited By ~ 14

Author(s):

Judith Schellekens ◽

Gonzalo G. Barberá ◽

Peter Buurman ◽

Guillem Pérez-Jordà ◽

Antonio Martínez-Cortizas

Keyword(s):

Land Use ◽

Organic Matter ◽

Soil Organic Matter ◽

Land Use History ◽

Analytical Pyrolysis ◽

Soil Organic Matter Dynamics ◽

Organic Matter Dynamics

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Effect of Ph and vegetation cover in soil organic matter structure at a high-mountain ecosystem (Sierra Nevada National Park, Granada, Spain)

10.5194/egusphere-egu2020-8246 ◽

2020 ◽

Author(s):

José A. González-Pérez ◽

Gael Bárcenas.Moreno ◽

Nicasio T Jiménez-Morillo ◽

María Colchero-Asensio ◽

Layla M. San Emeterio ◽

...

Keyword(s):

Climate Change ◽

Organic Matter ◽

Soil Organic Matter ◽

Organic Carbon ◽

Sierra Nevada ◽

Soil Ph ◽

National Park ◽

High Mountain ◽

Analytical Pyrolysis ◽

Organic Matter Dynamics

Keywords: Soil reaction, analytical pyrolysis, soil respiration, carbon stabilizationDuring the last decade, soil organic matter dynamics and its determining factors have received increased attention, mainly due to the evident implication of these parameters in climate change understanding, predictions and possible management. High-mountain soil could be considered as hotspot of climate change dynamic since its high carbon accumulation and low organic matter degradation rates could be seriously altered by slight changes in temperature and rainfall regimes associated to climate change effects. In the particular case of Sierra Nevada National Park, this threat could be even stronger due to its Southern character, although its elevated biodiversity could shed some light on how could we predict and manage climate change in the future.In this study, a quantitative and qualitative organic matter characterization was performed and soil microbial activity measured to evaluate the implication of pH and vegetation in soil organic matter dynamics.The sampling areas were selected according to vegetation and soil pH; with distinct soil pH (area A with pH<7 and area B with pH>7) and vegetation (high-mountain shrubs and pine reforested area). Soil samples were collected under the influence of several plant species representatives of each vegetation series. Six samples were finally obtained (five replicates each); three were collected in area A under Juniperus communis ssp. Nana (ENE), Genista versicolor (PIO) and Pinus sylvestris (PSI) and other three were collected in area B under Juniperus Sabina (SAB), Astragalus nevadensis (AST) and Pinus sylvestris (PCA).Qualitative and quantitative analyses of soil organic matter were made to establish a possible relationship with microbial activity estimated by respiration rate (alkali trap) and fungi-to-bacteria ratio using a plate count method. Soil easily oxidizable organic carbon content was determined by the Walkley-Black method (SOC %) and organic matter amount was estimated by weight loss on ignition (LOI %). Analytical pyrolysis (Py-GC/MS) was used to analyse in detail the soil organic carbon composition.Our results showed that the microbial and therefore the dynamics of organic matter is influenced by both, soil pH and soil of organic matter. So that the pH in acidic media prevail as a determining factor of microbial growth over soil organic matter composition conditioned by vegetation.Acknowledgement: Ministerio de Ciencia Innovaci&#243;n y Universidades (MICIU) for INTERCARBON project (CGL2016-78937-R). N.T. Jim&#233;nez-Morillo and L. San Emeterio also thanks MICIU for funding FPI research grants (BES-2013-062573 and Ref. BES-2017-07968). Mrs Desir&#233; Monis is acknowledged for technical assistance.&#160;

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Characterization of wildfire effects on soil organic matter using analytical pyrolysis

Geoderma ◽

10.1016/j.geoderma.2012.01.032 ◽

2012 ◽

Vol 191 ◽

pp. 24-30 ◽

Cited By ~ 42

Author(s):

José María De la Rosa ◽

Silvia Regina Faria ◽

María Eufemia Varela ◽

Heike Knicker ◽

Francisco Javier González-Vila ◽

...

Keyword(s):

Organic Matter ◽

Soil Organic Matter ◽

Analytical Pyrolysis ◽

Wildfire Effects

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Direct soil organic matter compound specific δ13C analysis using pyrolysis (Py-CSIA): identification of biomarkers in a dehesa from Southern Spain

10.5194/egusphere-egu2020-19596 ◽

2020 ◽

Author(s):

José A. González-Pérez ◽

Lyla M. San Emeterio ◽

Francisco J. González-Vila ◽

María T. Domínguez-Núñez ◽

José M. de la Rosa

Keyword(s):

Organic Matter ◽

Soil Organic Matter ◽

Mediterranean Climate ◽

Technical Assistance ◽

Plant Biomass ◽

Isotope Composition ◽

Soil Samples ◽

C3 Plants ◽

Analytical Pyrolysis ◽

Isotopic Characterization

Dehesa are woodlands typical of southern Mediterranean climate species modified by human to seasonal wood-pastures adapted to the unpredictability of the Mediterranean climate. Changes in climatic and environmental conditions can affect both, plant biomass chemical and isotope composition that will eventually be reflected in soil organic matter (SOM). Nowadays, many ecological studies use bulk isotope values, which represent a weighted mean average of the different necromass compounds. An isotopic characterization of individual compounds is desirable to differentiate the isotopic composition of the main plant components. Soil organic matter is composed mainly of high MW biopolymers i.e. polysaccharides, polypeptides, polypeptides, polyesters, etc. not amenable to most chromatographic techniques without the use of intense extraction and sample preparation steps.Here, an analytical pyrolysis technique combining Py-GC with a continuous flow isotope ratio mass spectrometer (IRMS) (Py-CSIA) is described and validated for the direct study of compound specific isotope composition in soil samples.The consistency of the Py-CSIA was tested using a standard n-alkanes mixture (dissolved C16 to C30 series with increasing concentrations along three pentads, Indiana Univ. SIL mix. Type B). The values obtained fitted to a straight line (R2 > 0.999). No induced thermal cracking nor deviations from the acclaimed isotope composition (fractionation) was observed up to high pyrolysis temperature (< 500 &#176;C).Composite dehesa (Pozoblanco , C&#243;rdoba, Spain) surface soil samples were taken under evergreen oak canopy . A detailed SOM study was performed using conventional analytical pyrolysis (Py-GC/MS) and &#948;13C for specific compounds released after pyrolysis was done using Py-CSIA.Well-resolved chromatograms were obtained by Py-GC/MS and a total of 40 pyrolysis compounds were detected that represented the chemical variability of soil organic matter and consisted mainly of polysaccharide, lignin-derived compounds (G- and S- units), fatty acids and n-alkanes. When coupling Py with GC-C-IRMS, many c peaks were well resolved and with a sufficient chromatographic separation to give accurate &#948;13C readings. Nonetheless, there were compounds with high &#948;13C standard deviations considered not sufficiently resolved for a reliable estimation of their isotope composition due to coelution and were discarded.The &#948;13C for specific biomass compounds released by pyrolysis of soil was in line with the expected values for C3 plants i.e. Quercus spp. Polysaccharide derived products (furans, cyclopentanones), showed slightly enriched &#948;13C values (-26.0 &#177; 0.47 &#8240;) in accordance with their naturally 13C enriched composition. Although no statistical differences were found, lignin-derived units showed slightly depleted &#948;13C ( -27.4 &#177; 0.78 &#8240;). Accordingly, depleted &#948;13C values for lipids (-35.1 &#177; 2.41 &#8240;) and alkanes (-35.5 &#177; 2.20 &#8240;) were found, the latter with lighter isotope composition with increasing the hydrocarbon length.Here we show the possibility of using this particular analytical pyrolysis technique (Py-CSIA) for the direct measurement of &#948;13C in relevant specific soil organic matter components including those from polysaccharides (cellulose/hemicellulose), lignin, lipid/waxes and also peptide/protein-derived compounds.Acknowledgement: Ministerio de Ciencia Innovaci&#243;n y Universidades (MICIU) for INTERCARBON project (CGL2016-78937-R) DECAFUN (CGL2015-70123-R). L. San Emeterio also thanks MICIU for funding FPI research grants (BES-2017-07968). Mrs Desir&#233; Monis & Mr Eduardo Guti&#233;rrez Gonz&#225;lez are acknowledged for technical assistance.

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