scholarly journals Hydrogen dynamics in soil organic matter as determined by <sup>13</sup>C and <sup>2</sup>H labeling experiments

2016 ◽  
Author(s):  
Alexia Paul ◽  
Christine Hatté ◽  
Lucie Pastor ◽  
Yves Thiry ◽  
Françoise Siclet ◽  
...  
Keyword(s):  
Organic Matter ◽  
Soil Organic Matter ◽  
Isotopic Composition ◽  
Bulk Material ◽  
Isotopic Signature ◽  
Close Link ◽  
Carbon Cycles ◽  
Exchangeable Hydrogen ◽  
Terrestrial Environments ◽  
Water Hydrogen

Abstract. Understanding hydrogen dynamics in soil organic matter is important to predict the fate of 3H in terrestrial environments. One way to resolve hydrogen fate and to point out processes is to examine the isotopic signature of the element in soil. However, non-exchangeable hydrogen isotopic signal in soil is complex and depends on the fate of organic compounds and microbial biosyntheses that incorporate water-derived hydrogen. To decipher this complex system and to understand the close link between hydrogen and carbon cycles, we followed labeled hydrogen and labeled carbon all along natural-like soil incubations. We performed incubation experiments with three labeling conditions: 1- 13C2H double-labeled molecules in the presence of 1H2O, 2- 13C-labeled molecules in the presence of 2H2O, 3- no molecule addition in the presence of 2H2O. The preservation of substrate-derived hydrogen after one year of incubation (ca. 5 % in most cases) was lower than the preservation of substrate-derived carbon (30 % in average). We highlighted that 70 % of the C-H bonds are broken during the degradation of the molecule which permits the exchange with water hydrogen. Added molecules are used more for trophic resources. The isotopic composition of the non-exchangeable hydrogen was mainly driven by the incorporation of water hydrogen during microbial biosynthesis. It is linearly correlated with the amount of carbon that is degraded in the soil. The quantitative incorporation of water hydrogen in bulk material and lipids demonstrates that non-exchangeable hydrogen exists in both organic and mineral-bound forms. The proportion of the latter depends on soil type and minerals. This experiment quantified the processes affecting the isotopic composition of non-exchangeable hydrogen, and the results can be used to predict the fate of tritium in the ecosystem or the water deuterium signature in organic matter.

scholarly journals Hydrogen dynamics in soil organic matter as determined by <sup>13</sup>C and <sup>2</sup>H labeling experiments

2016 ◽  
Vol 13 (24) ◽  
pp. 6587-6598 ◽  
Author(s):  
Alexia Paul ◽  
Christine Hatté ◽  
Lucie Pastor ◽  
Yves Thiry ◽  
Françoise Siclet ◽  
...  
Keyword(s):  
Organic Matter ◽  
Soil Organic Matter ◽  
Isotopic Composition ◽  
Bulk Material ◽  
Isotopic Signature ◽  
Natural Soil ◽  
Close Link ◽  
Exchangeable Hydrogen ◽  
Terrestrial Environments ◽  
Water Hydrogen

Abstract. Understanding hydrogen dynamics in soil organic matter is important to predict the fate of 3H in terrestrial environments. One way to determine hydrogen fate and to point out processes is to examine the isotopic signature of the element in soil. However, the non-exchangeable hydrogen isotopic signal in soil is complex and depends on the fate of organic compounds and microbial biosyntheses that incorporate water-derived hydrogen. To decipher this complex system and to understand the close link between hydrogen and carbon cycles, we followed labeled hydrogen and labeled carbon throughout near-natural soil incubations. We performed incubation experiments with three labeling conditions: 1 – 13C2H double-labeled molecules in the presence of 1H2O; 2 – 13C-labeled molecules in the presence of 2H2O; 3 – no molecule addition in the presence of 2H2O. The preservation of substrate-derived hydrogen after 1 year of incubation (ca. 5 % in most cases) was lower than the preservation of substrate-derived carbon (30 % in average). We highlighted that 70 % of the C–H bonds are broken during the degradation of the molecule, which permits the exchange with water hydrogen. Added molecules are used more for trophic resources. The isotopic composition of the non-exchangeable hydrogen was mainly driven by the incorporation of water hydrogen during microbial biosynthesis. It is linearly correlated with the amount of carbon that is degraded in the soil. The quantitative incorporation of water hydrogen in bulk material and lipids demonstrates that non-exchangeable hydrogen exists in both organic and mineral-bound forms. The proportion of the latter depends on soil type and minerals. This experiment quantified the processes affecting the isotopic composition of non-exchangeable hydrogen, and the results can be used to predict the fate of tritium in the ecosystem or the water deuterium signature in organic matter.

Compound-specific δ2H using analytical pyrolysis (Py-CSIA) for assessing source and processes of soil organic matter driven by climatic changes within a Mediterranean evergreen oak forest (dehesas)

2021 ◽  
Author(s):  
Layla M. San-Emeterio ◽  
Ignacio Pérez-Ramos ◽  
Maria Teresa Domínguez-Núñez ◽  
Francisco Javier González-Vila ◽  
José Antonio González-Pérez
Keyword(s):  
Organic Matter ◽  
Soil Organic Matter ◽  
Technical Assistance ◽  
Isotope Composition ◽  
Climatic Conditions ◽  
Soil Samples ◽  
Tree Canopy ◽  
Analytical Pyrolysis ◽  
Exchangeable Hydrogen ◽  
Evergreen Oak

&lt;p&gt;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].&lt;/p&gt;&lt;p&gt;In this communication, we describe and validate a methodology based on analytical pyrolysis for the direct measure of compound-specific H isotope composition (&amp;#948;&lt;sup&gt;2&lt;/sup&gt;H) 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).&lt;/p&gt;&lt;p&gt;Composite &lt;em&gt;dehesa&lt;/em&gt; surface (0-10 cm) soil samples (Pozoblanco, C&amp;#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 &amp;#948;&lt;sup&gt;2&lt;/sup&gt;H Py-CSIA using the same chromatographic conditions and separation column type.&lt;/p&gt;&lt;p&gt;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 &amp;#8240; &amp;#177; 7.09 for G-lignin units, -64 &amp;#8240; &amp;#177; 8.64 S-lignin units and lighter -112 &amp;#8240; &amp;#177; 4.32 for fatty acids (-109 &amp;#8240; &amp;#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 &amp;#948;&lt;sup&gt;2&lt;/sup&gt;H values were found in SOM produced in the open pasture than under the tree canopy. In addition, a &amp;#948;&lt;sup&gt;2&lt;/sup&gt;H enrichment is observed for lignin-derived compounds in SOM under the W+D treatment.&lt;/p&gt;&lt;p&gt;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.&amp;#160;&lt;/p&gt;&lt;p&gt;&lt;strong&gt;Acknowledgement:&lt;/strong&gt; INTERCARBON project (CGL2016-78937-R), DECAFUN (CGL2015-70123-R). MICIU for funding FPI research grants (BES-2017-07968). Mrs Desir&amp;#233; Monis, Mrs Alba M. Carmona &amp; Mr Eduardo Guti&amp;#233;rrez Gonz&amp;#225;lez are acknowledged for technical assistance.&lt;/p&gt;&lt;p&gt;[1] Paul, A. et al (2016). &lt;em&gt;Biogeosciences, 13&lt;/em&gt;, 6587&amp;#8211;6598.&lt;/p&gt;&lt;p&gt;[2] Seki, O. et al (2010). &lt;em&gt;Geochimica et Cosmochimica Acta,&amp;#160;74&lt;/em&gt;(2), 599-613.&lt;/p&gt;

Contributions of carbonates to soil CO2 emissions

2012 ◽  
Vol 92 (4) ◽  
pp. 599-607 ◽  
Author(s):  
R. Ramnarine ◽  
C. Wagner-Riddle ◽  
K. E. Dunfield ◽  
R. P. Voroney
Keyword(s):  
Organic Matter ◽  
Soil Organic Matter ◽  
Inorganic Carbon ◽  
Calcareous Soils ◽  
Decomposition Analysis ◽  
Isotope Ratio Mass Spectrometry ◽  
Conventional Tillage ◽  
Isotopic Signature ◽  
Soil Samples ◽  
Soil Carbonates

Ramnarine, R., Wagner-Riddle, C., Dunfield, K. E. and Voroney, R. P. 2012. Contributions of carbonates to soil CO 2 emissions. Can. J. Soil Sci. 92: 599–607. Carbon dioxide (CO2) is released in soil as a by-product of microbial and root respiration, but soil carbonates may also be a source of CO2 emissions in calcareous soils. Global estimates of inorganic carbon range from 700 to 900 Pg as carbonates stored in soils, representing a significant potential source of CO2 to the atmosphere. While previous studies have focused on the total CO2 efflux from the soil, our goal was to identify the various sources and their contribution to total CO2 emissions, by measuring the isotopic signature of the CO2 emitted from the soil. Calcareous Luvisolic silt loam soil samples were obtained from conventional tillage (CT) and no-tillage (NT) plots in southern Ontario, Canada. Soil samples (root- and residue-free) were laboratory-incubated for 14 d and the isotopic signature of the CO2 (δ13CCO2) released was analyzed using isotope ratio mass spectrometry. Isotopic measurement was essential in quantifying the abiotic CO2 production from carbonates, due to the unique δ13C signature of carbonates and soil organic matter. A two-end member mixing model was used to estimate the proportion of CO2 evolved from soil carbonates and soil organic matter decomposition. Analysis of emitted CO2 collected after the 14-d incubation indicate that the proportion of CO2 originating from soil inorganic carbon was 62 to 74% for CT soil samples, and 64 to 80% for NT soil samples. Further work is recommended in the quantification of CO2 emissions from calcareous soils, and to determine the transferability of laboratory results to field studies.

Structural and dynamic properties of soil organic-matter as reflected by 13C natural-abundance, pyrolysis mass-spectrometry and solid-state 13C NMR-spectroscopy in density fractions of an oxisol under forest and pasture

Soil Research ◽  
1995 ◽  
Vol 33 (1) ◽  
pp. 59 ◽  
Author(s):  
A Golchin ◽  
JM Oades ◽  
JO Skjemstad ◽  
P Clarke
Keyword(s):  
Organic Matter ◽  
Soil Organic Matter ◽  
Isotopic Composition ◽  
Particulate Organic Matter ◽  
Organic Materials ◽  
Natural Abundance ◽  
13C Natural Abundance ◽  
Clay Particles ◽  
Density Fractions ◽  
Soil Organic Matter Turnover

Changes in the content and isotopic composition of organic carbon as a consequence of deforestation and pasture establishment were studied in three neighbouring areas on an Oxisol from Australia and used to measure the turnover of forest-derived carbon (C3) under pasture (C4) over 35 and 83 year time scales. The results indicated that the quantity of forest-derived carbon declined rapidly during the first 35 years under pasture but the content remained nearly stable thereafter, suggesting the presence of two pools of carbon with different turnover times. The calculated values for turnover time of labile and resistant fractions of forest-derived carbon were 35 and 144 years respectively. The soil samples were separated into five fractions with densities <1.6 (free and occluded), 1.6-1.8, 1.8-2.0 and >2.0 Mg m-3. Based on the spatial distribution of organic materials within the mineral matrix of soil, the soil organic matter contained in different density fractions was classified as free particulate organic matter (1.6 free), occluded particulate organic matter (<1.6 occluded, 1.6-1.8 and 1.8-2.0) and clay associated organic matter (>2.0 Mg m-3). The 13C natural abundance showed that the free particulate organic matter formed a significant pool for soil organic matter turnover when the forest was replaced by pasture. Compared with free particulate organic matter, the organic materials occluded within aggregates had slower turnover times. The occluded organic materials were in different stages of decomposition and had different chemical stabilities. Comparison of the chemistry and isotopic composition of occluded organic materials indicated that the O-alkyl C content of the occluded organic materials was inversely related to their stabilities whereas their aromatic C content was directly related to their stabilities. In soils under pasture, a considerable amount of forest-derived carbon was associated with clay particles in the fractions .2.0 Mg m-3. The rate of accumulation of pasture-derived carbon was also rapid in this fraction, indicating the presence of two different pools of carbon (C3 and C4) associated with clay particles. The forest-derived carbon had the highest stability in the fractions >2.0 Mg m-3, probably due to strong interaction with active aluminium or iron and aluminium oxides associated with clay surfaces.

Bioavailability and isotopic composition of CO2 released from incubated soil organic matter fractions

2014 ◽  
Vol 69 ◽  
pp. 168-178 ◽  
Author(s):  
Carsten W. Mueller ◽  
Martin Gutsch ◽  
Katja Kothieringer ◽  
Jens Leifeld ◽  
Janet Rethemeyer ◽  
...  
Keyword(s):  
Organic Matter ◽  
Soil Organic Matter ◽  
Isotopic Composition ◽  
Soil Organic Matter Fractions ◽  
Organic Matter Fractions

Dynamics of soil organic matter in a cultivated chronosequence in the Cerrado (Minas Gerais, Brazil)

Soil Research ◽  
2017 ◽  
Vol 55 (8) ◽  
pp. 750
Author(s):  
Thalita M. Resende ◽  
Vania Rosolen ◽  
Martial Bernoux ◽  
Marcelo Z. Moreira ◽  
Fabiano T. d. Conceição ◽  
...  
Keyword(s):  
Organic Matter ◽  
Soil Organic Matter ◽  
Isotopic Signature ◽  
C4 Plants ◽  
Mixed System ◽  
Native Vegetation ◽  
Pasture Management ◽  
Cultivation Time ◽  
C Stock ◽  
Depth Reduction

The vegetation of the Cerrado has been replaced by pastures and agriculture, affecting the stock and dynamic of soil organic matter (SOM). The present study was conducted in a cultivated chronosequence with a mixed system (agriculture+pasture for 15 years; Agric+P15) and cultivated pasture (30 years; P30), taking the native Cerrado as a reference to assess changes in the stock of SOM, the dynamics (δ13C) and the carbon replacement derived from the C3 in native vegetation to C4 in cultivated vegetation. Compared to Cerrado, there was a reduction in C stock in cultivated soils at 0–15-cm depth (reduction of 26.5% in Agri+P15 and 6% in P30). The close similarity between Cerrado and P30 indicates that the pasture management enhanced the stock relative to Agri+P15, but was not effective in sequestering C. Only in the 0–15cm depth was there a marked replacement of C derived from the C3 of Cerrado plants associated with cultivation time. In the chronosequence, the isotopic signature of C4 plants dominated in the soil below 30cm depth, suggesting a paleoclimatic effect on SOM.

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