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Poster De Conférence Année : 2013

Are chemical oxidation methods relevant to isolate a stable pool of centenial carbon ? Using soils from a long term bare fallow to answer this question

Résumé

Several mechanisms are developed to explain carbon stabilization in soils: (i) physical protection, (ii) protection through interaction with the soil matrix and (iii) chemical recalcitrance. To date there is still no successful experimental way to isolate the stable pool of soil organic matter (SOM), i.e., the SOM that has a residence time of centuries to millennia. Moreover, the relevance of the latter mechanism is currently being discussed at this time scale (Schmidt et al., 2011). A recent study showed that long term bare fallows (LTBF) offer a unique opportunity to study the stable compartment of SOM (Barré et al., 2011), as without carbon inputs and with continuing biodegradation and mineralization, SOM becomes progressively enriched in its most stable components. At the INRA 42-plot experiment, initiated in 1928 in Versailles, over 80% of total SOM is stable. Here, we take advantage of the 42-plot LTBF to test the relevance of chemical oxidation methods to isolate a stable pool of carbon (Mikkuta et al., 2005). We selected two reagents -hydrogen peroxide, H2O2, and sodium hypochlorite, NaOCl- and studied their effect on soil carbon content and SOM chemical nature after 0 and 80 years of LTBF. If these methods can isolate the stable C, then chemical oxidation resistant-C from 0 and 80 years of bare fallow should equate, both in amount and chemical nature, TOC after 80 years of bare fallow. Materials and methods. We used 0-20 cm depth soil samples from the 42 plots archive collection. In order to prevent the influence of decomposing plant debris, we fractionated the soil samples, and separated the fraction of particles <50μm (i.e. silt+clay). These were subjected to H2O2, and NaOCl oxidation according to (Jagadamma et al., 2010; Bruun et al., 2008). We used Curie point pyrolysis coupled with gas chromatography and mass spectroscopy (Py-GC-MS) to analyse SOM chemical nature. Results showed that, after chemical oxidation, both soils contained approximately the same amount of chemical oxidation resistant OC (≈ 1 mgC g-1 soil), with slightly more for 1929 soils than for 2008 soils. This amount was five times smaller than TOC in the untreated 2008 soils, after 80 years of biological oxidation. Moreover the chemical signatures of the soils, as seen with Py-GC-MS, showed that, after chemical oxidation, very few identifiable pyrolysis products remained. The characteristic alkanes and alkenes peaks of 1929 samples and the alkylbenzenes of 2008 samples had disappeared. In conclusion, the two reagents isolated a subset of total soil organic carbon, but removed too much SOM. The resistant C fraction was smaller than century stable C in this soil and its chemical nature was different. We conclude that chemical oxidation methods cannot efficiently isolate a stable pool of carbon. Références bibliographiques : Barré et al., 2010, Biogeosciences, Vol 7: 3839-3850, Quantifying and isolating stable soil organic carbon using long-term bare fallow experiments Bruun et al., 2008, European Journal of Soil Science, Vol 59, Issue 2: 247–256, In search of stable soil organic carbon fractions: a comparison of methods applied to soils labelled with 14C for 40 days or 40 years Jagadamma et al., 2010, Biogeochemistry, Vol 98: 29–44, Evaluation of structural chemistry and isotopic signatures of refractory soil organic carbon fraction isolated by wet oxidation methods 22 Mikutta et al., 2005, Soil Science Society of America Journal, Vol 69: 120-135, Organic matter removal from soil using hydrogen peroxide, sodium hypochlorite, and disodium peroxodisulfate Schmidt et al., 2011, Nature, Vol 478: 49-56, Persistence of soil organic matter as an ecosystem property
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Dates et versions

hal-01629016 , version 1 (05-11-2017)

Identifiants

  • HAL Id : hal-01629016 , version 1
  • PRODINRA : 411202

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Suzanne Lutfalla, Katell Quenea, Folkert van Oort, Daniel Billiou, Claire Chenu. Are chemical oxidation methods relevant to isolate a stable pool of centenial carbon ? Using soils from a long term bare fallow to answer this question. Colloque RESMO (Réseau Matières organiques), Jan 2013, Biarritz, France. 2013. ⟨hal-01629016⟩
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