scholarly journals Composition changes of eroded carbon at different spatial scales in a tropical watershed suggest enrichment of degraded material during transport

2014 ◽  
Vol 11 (12) ◽  
pp. 3299-3305 ◽  
Author(s):  
C. Rumpel ◽  
V. Chaplot ◽  
P. Ciais ◽  
A. Chabbi ◽  
B. Bouahom ◽  
...  
Keyword(s):  
Organic Matter ◽  
Chemical Composition ◽  
Soil Organic Matter ◽  
Isotope Composition ◽  
Spatial Scales ◽  
Suspended Sediments ◽  
Resonance Spectroscopy ◽  
Vertical Decomposition ◽  
Degraded Material ◽  
Soil Units

Abstract. In order to assess whether eroded carbon is a net source or sink of atmospheric CO2, characterisation of the chemical composition and residence time of eroded organic matter (EOM) at the landscape level is needed. This information is crucial to evaluate (1) how fast EOM can be decomposed by soil microbes during its lateral transport and (2) its impact at deposition sites. This study considers a continuum of scales to measure the composition of EOM across a steep hillslope landscape of the Mekong basin with intense erosion. We sampled suspended sediments eroded during rainfall events from runoff plots (1 and 2.5 m2) and the outlets of four nested watersheds (0.6 × 104 to 1 × 107 m2). Here we show that changes in the chemical composition of EOM (measured by nuclear magnetic resonance spectroscopy) and in its 13C and 15N isotope composition from plot scale through to landscape scale provide consistent evidence for enrichment of more decomposed EOM across distances of 10 km. Between individual soil units (1 m2) to a small watershed (107 m2), the observed 28% decrease of the C/N ratio, the enrichment of 13C and 15N isotopes as well as O-alkyl C in EOM is of similar magnitude as changes recorded with depth in soil profiles due to soil organic matter "vertical" decomposition. Radiocarbon measurements indicated ageing of EOM from the plot to the watershed scale. Therefore transport of EOM may lead to enrichment of stabilised soil organic matter compounds, eventually being subject to export from the watershed.

scholarly journals Composition of eroded carbon during its journey through a tropical watershed: a clue to the question whether it is source or sink of CO<sub>2</sub>

2013 ◽  
Vol 10 (11) ◽  
pp. 18175-18192
Author(s):  
C. Rumpel ◽  
V. Chaplot ◽  
P. Ciais ◽  
A. Chabbi ◽  
B. Bouahom ◽  
...  
Keyword(s):  
Organic Matter ◽  
Chemical Composition ◽  
Isotope Composition ◽  
Soil Profiles ◽  
Small Watershed ◽  
15N Isotope ◽  
Lateral Transport ◽  
Vertical Decomposition ◽  
Soil Units ◽  
Tropical Watershed

Abstract. In order to assess whether eroded carbon is a net source or sink of atmospheric CO2, characterisation of the chemical composition and residence time of eroded organic matter (EOM) at the landscape level is needed. This information is crucial to evaluate how fast EOM can be decomposed by soil microbes during its lateral transport. This study considers a continuum of scales to measure the fate of EOM during its transport, across a steep hillslope landscape of the Mekong basin, with intense erosion. Here we show that changes in the chemical composition of EOM (measured by NMR spectroscopy) and in its 13C and 15N isotope composition provide consistent evidence for EOM decomposition during the lateral transport of carbon on time scales of less than 50 yr across distances of 10 km. Between individual soil units (1 m2) to a small watershed (107 m2), the observed 28% decrease of the C/N ratio and the enrichment of 13C and 15N isotopes in EOM is of similar magnitude than the enrichment with depth in soil profiles due to soil organic matter "vertical" decomposition. Radiocarbon measurements indicated that these changes are not related to the slow transformation of soil carbon during pedogenesis, but rather to an acceleration of the SOM stabilisation process during its journey through the watershed.

Chemical composition of cover crops and soil organic matter pools in no‐tillage systems in the Cerrado

2021 ◽  
Author(s):  
Arminda Moreira de Carvalho ◽  
Luana Ramos Passos Ribeiro ◽  
Robélio Leandro Marchão ◽  
Alexsandra Duarte de Oliveira ◽  
Karina Pulrolnik ◽  
...  
Keyword(s):  
Organic Matter ◽  
Chemical Composition ◽  
Soil Organic Matter ◽  
Cover Crops ◽  
No Tillage ◽  
Tillage Systems

Effects of climate change on soil organic matter chemical composition and carbon content in different physical fractions

2021 ◽  
Author(s):  
Moritz Mohrlok ◽  
Victoria Martin ◽  
Alberto Canarini ◽  
Wolfgang Wanek ◽  
Michael Bahn ◽  
...  
Keyword(s):  
Climate Change ◽  
Organic Matter ◽  
Chemical Composition ◽  
Soil Organic Matter ◽  
Soil C ◽  
Size Classes ◽  
Soil Fractions ◽  
Total Soil ◽  
C And N ◽  
Amp Clay

&lt;p&gt;Soil organic matter (SOM) is composed of many pools with different properties (e.g. turnover times) which are generally used in biogeochemical models to predict carbon (C) dynamics. Physical fractionation methods are applied to isolate soil fractions that correspond to these pools. This allows the characterisation of chemical composition and C content of these fractions. There is still a lack of knowledge on how these individual fractions are affected by different climate change drivers, and therefore the fate of SOM remains elusive. We sampled soils from a multifactorial climate change experiment in a managed grassland in Austria four years after starting the experiment to investigate the response of SOM in physical soil fractions to temperature (eT: ambient and elevated by +3&amp;#176;C), atmospheric CO&lt;sub&gt;2&lt;/sub&gt;-concentration (eCO&lt;sub&gt;2&lt;/sub&gt;: ambient and elevated by +300 ppm) and to a future climate treatment (eT x eCO&lt;sub&gt;2&lt;/sub&gt;: +3&amp;#176;C and + 300 ppm). A combination of slaking and wet sieving was used to obtain three size classes: macro-aggregates (maA, &gt; 250 &amp;#181;m), micro-aggregates (miA, 63 &amp;#181;m &amp;#8211; 250 &amp;#181;m) and free silt &amp; clay (sc, &lt; 63 &amp;#181;m). In both maA and miA, four different physical OM fractions were then isolated by density fractionation (using sodium polytungstate of &amp;#961; = 1.6 g*cm&lt;sup&gt;-3&lt;/sup&gt;, ultrasonication and sieving): Free POM (fPOM), intra-aggregate POM (iPOM), silt &amp; clay associated OM (SCaOM) and sand-associated OM (SaOM). We measured C and N contents and isotopic composition by EA-IRMS in all fractions and size classes and used a Pyrolysis-GC/MS approach to assess their chemical composition. For eCO&lt;sub&gt;2&lt;/sub&gt; and eT x eCO&lt;sub&gt;2 &lt;/sub&gt;plots, an isotope mixing-model was used to calculate the proportion of recent C derived from the elevated CO&lt;sub&gt;2 &lt;/sub&gt;treatment. Total soil C and N did not significantly change with treatments.&amp;#160; eCO&lt;sub&gt;2&lt;/sub&gt; decreased the relative proportion of maA-mineral-associated C and increased C in fPOM and iPOM. About 20% of bulk soil C was represented by the recent C derived from the CO&lt;sub&gt;2&lt;/sub&gt; fumigation treatment. This significantly differed between size classes and density fractions (p &lt; 0.001), which indicates inherent differences in OM age and turnover. Warming reduced the amount of new C incorporated into size classes. We found that each size class and fraction possessed a unique chemical fingerprint, but this was not significantly changed by the treatments. Overall, our results show that while climate change effects on total soil C were not significant after 4 years, soil fractions showed specific effects. Chemical composition differed significantly between size classes and fractions but was unaffected by simulated climate change. This highlights the importance to separate SOM into differing pools, while including changes to the molecular composition might not be necessary for improving model predictions.&amp;#160;&amp;#160;&amp;#160;&amp;#160;&lt;/p&gt;

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;

Chemical composition of soil organic matter and potential enzyme activity in the topsoil along a moisture gradient in the High Arctic (Svalbard)

Geoderma ◽  
2020 ◽  
Vol 368 ◽  
pp. 114304 ◽  
Author(s):  
Ekaterina Pushkareva ◽  
Kai-Uwe Eckhardt ◽  
Vivien Hotter ◽  
Aline Frossard ◽  
Peter Leinweber ◽  
...  
Keyword(s):  
Organic Matter ◽  
Enzyme Activity ◽  
Chemical Composition ◽  
Soil Organic Matter ◽  
High Arctic ◽  
Moisture Gradient ◽  
Potential Enzyme Activity

scholarly journals Spatial patterns in soil organic matter dynamics are shaped by mycorrhizosphere interactions in a treeline forest

2019 ◽  
Vol 447 (1-2) ◽  
pp. 521-535
Author(s):  
Nina L. Friggens ◽  
Thomas J. Aspray ◽  
Thomas C. Parker ◽  
Jens-Arne Subke ◽  
Philip A. Wookey
Keyword(s):  
Organic Matter ◽  
Soil Organic Matter ◽  
Spatial Scales ◽  
Mountain Birch ◽  
Organic C ◽  
Soil C ◽  
Soil Organic Matter Dynamics ◽  
C Stocks ◽  
Organic Matter Dynamics ◽  
Individual Trees

Abstract Aims In the Swedish sub-Arctic, mountain birch (Betula pubescens ssp. czerepanovii) forests mediate rapid soil C cycling relative to adjacent tundra heaths, but little is known about the role of individual trees within forests. Here we investigate the spatial extent over which trees influence soil processes. Methods We measured respiration, soil C stocks, root and mycorrhizal productivity and fungi:bacteria ratios at fine spatial scales along 3 m transects extending radially from mountain birch trees in a sub-Arctic ecotone forest. Root and mycorrhizal productivity was quantified using in-growth techniques and fungi:bacteria ratios were determined by qPCR. Results Neither respiration, nor root and mycorrhizal production, varied along transects. Fungi:bacteria ratios, soil organic C stocks and standing litter declined with increasing distance from trees. Conclusions As 3 m is half the average size of forest gaps, these findings suggest that forest soil environments are efficiently explored by roots and associated mycorrhizal networks of B. pubescens. Individual trees exert influence substantially away from their base, creating more uniform distributions of root, mycorrhizal and bacterial activity than expected. However, overall rates of soil C accumulation do vary with distance from trees, with potential implications for spatio-temporal soil organic matter dynamics and net ecosystem C sequestration.

scholarly journals The influence of C<sub>3</sub> and C<sub>4</sub> vegetation on soil organic matter dynamics in contrasting semi-natural tropical ecosystems

2015 ◽  
Vol 12 (10) ◽  
pp. 8085-8130 ◽  
Author(s):  
G. Saiz ◽  
M. Bird ◽  
C. Wurster ◽  
C. A. Quesada ◽  
P. Ascough ◽  
...  
Keyword(s):  
Organic Matter ◽  
Soil Organic Matter ◽  
Soil Depth ◽  
Spatial Scales ◽  
Abiotic Factors ◽  
Carbon Isotopic Composition ◽  
Precipitation Gradient ◽  
Tropical Ecosystems ◽  
Carbon Isotopic ◽  
Closed Canopy

Abstract. Variations in the carbon isotopic composition of soil organic matter (SOM) in bulk and fractionated samples were used to assess the influence of C3 and C4 vegetation on SOM dynamics in semi-natural tropical ecosystems sampled along a precipitation gradient in West Africa. Differential patterns in SOM dynamics in C3/C4 mixed ecosystems occurred at various spatial scales. Relative changes in C / N ratios between two contrasting SOM fractions were used to evaluate potential site-scale differences in SOM dynamics between C3- and C4-dominated locations. These differences were strongly controlled by soil texture across the precipitation gradient, with a function driven by bulk δ13C and sand content explaining 0.63 of the observed variability. The variation of δ13C with soil depth indicated a greater accumulation of C3-derived carbon with increasing precipitation, with this trend being also strongly dependant on soil characteristics. The influence of vegetation thickening on SOM dynamics was also assessed in two adjacent, but structurally contrasting, transitional ecosystems occurring on comparable soils to minimise confounding effects posed by climatic and edaphic factors. Radiocarbon analyses of sand-size aggregates yielded relatively short mean residence times (τ) even deep in the soil, while the most stable SOM fraction associated to silt and clay exhibited shorter τ in the savanna woodland than in the neighbouring forest stand. These results together with the vertical variation observed in δ13C values, strongly suggest that both ecosystems are undergoing a rapid transition towards denser closed canopy formations. However, vegetation thickening varied in intensity at each site and exerted contrasting effects on SOM dynamics. This study shows that the interdependence between biotic and abiotic factors ultimately determine whether SOM dynamics of C3- and C4-derived vegetation are at variance in ecosystems where both vegetation types coexist. The results highlight the far-reaching implications that vegetation thickening may have for the stability of deep SOM.

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