"Soil organic matter : dynamics and function" team

Team leader : Claire Chenu

Scientific themes

Soil organic matter (SOM) has major functions in soils and terrestrial ecosystems. Being a source of mineral nutrients it contributes to soil chemical fertility and it acts on soil physical fertility through its role on soil structure. Soil organic matter is a key component of soil quality. Furthermore, SOM influences the dynamics of pollutants in terrestrial ecosystems by influencing the transport of pesticides and other organic pollutants through its chemical reactivity and it is a source of pollution for waters (e.g. nitrates) and of greenhouse gases. SOM is a natural resource that must be taken into account and managed for a sustainable agriculture.


The objectives of the team are to:

-          quantify turnover rates of SOM
For this we use stable isotope tracing (¹³C, ¹⁵N). We have expertise in natural abundance of ¹³C to measure in situ turnover rates of C in C3 /C4 plants successions. For these studies we maintain specific long term field studies (see..). ¹³C natural abundance is applied to total soil carbon as well as to SOM physical fraction and to molecular fractions. The combination of gas chromatography with isotope ratio mass spectrometry via a combustion interface (GC-c-IRMS) now enables us to measure the isotopic signature of specific compounds.

We also use ¹⁴C dating in order to have access to very long turnover rates.

Scientists: C.  Chenu, MF. Dignac, S. Huon, D. Rasse, C. Rumpel
Post docs and graduate students: M. Alexis, H. Bahri, M. Mendez, C. Moni, I. Virto

Dignac, M.F., Bahri, H., Rumpel, C., Rasse, D.P., Bardoux, G., Balesdent, J., Girardin, C., Chenu, C., Mariotti, A., 2005. Carbon-13 natural abundance as a tool to study the dynamics of lignin monomers in soil: an appraisal at the Closeaux experimental field (France). Geoderma 128.

-           analyze the processes leading to the stabilisation of OM in soils (recalcitrance, physical and physico-chemical protection, microbial controls)
We aim to identify, quantify and hierarchize the processes responsible for the stabilization of organic matter in soils for decades to centuries.

Recalcitrance: We are investigating the dynamics of molecular entities assumed to be recalcitrant such as lignins, cutins and suberins, which are plant polymers, as well as charcoal and black carbon.

Physical and physicochemical protection: Our work is focused on SOM protected by inclusion in microaggregates (separated by size and density fractionation or by adsorption to clay minerals or iron oxides.

Microbial controls on decomposition: We are studying the effects of climatic change (T°, soil water content) on the biodegradation and stabilization of organic compounds via the impacts these have on soil microbial community structure. Profiling tec hniques (Phospholipid fatty acid and enzyme activity) are used to characterise microbial community structure and catabolic potential.  We are also investigating the spatial distribution of microorganisms in soil structure in order to understand the consequences of microbial – soil structure interactions for SOM decomposition.

These studies make use of soils from various sites and long term experiments (Les Closeaux trial, ORE PCBB) or of microscosm experiments involving ¹³C labelled compounds.

Scientists: C.  Chenu, MF. Dignac, N. Nunan, D. Rasse, C. Rumpel
Post docs and graduate students : M. Alexis, H. Bahri, E. Coucheney, M. Mendez, C. Moni, I. Virto

Bahri, H., Dignac, M.-F., Rumpel, C., Rasse, D.P., Chenu, C., Mariotti, A., Lignin turnover kinetics in an agricultural soil is monomer specific. Soil Biology and Biochemistry on line.

Eusterhues, K., Rumpel, C., Kogel-Knabner, I., 2005. Stabilization of soil organic matter isolated via oxidative degradation. Organic Geochemistry 36, 1567.

Poirier, N., Derenne, S., Balesdent, J., Chenu, C., Bardoux, G., Mariotti, A., Largeau, C., Dynamics and origin of the non-hydrolysable organic fraction in a forest and a $ cultivated temperate soil, as determined by isotopic and microscopic studies. European Journal of Soil Science, on line

Rasse, D.P., Rumpel, C., Dignac, M.F., 2005. Is soil carbon mostly root carbon? Mechanisms for a specific stabilisation. Plant and Soil 269.

Vieublé Gonod, L., Chadoeuf, J., Chenu, C., 2006. Spatial distribution of a microbial function (2,4-D mineralisation) from parcel to microhabitat. Soil Science Society of America Journal 70, 64-71.

Vieublé Gonod, L., Jones, D.L., Chenu, C., 2006 Sorption differentially regulates the fate of the amino-acids lysine and leucine in soil aggregates. European Journal of Soil Scienceon line

-           Improve modelling of soil organic matter dynamics by improving the description of stabilization processes
Programs are focused on modelling the fate of molecular entities (e.g. lignins) and the distribution of microbial communities in heterogeneous, structured space.

Scientists:  D. Rasse

Rasse, D.P., Dignac, M.F., Bahri, H., Rumpel, C.Mariotti, A., Chenu, C., Assessing lignin turnover in an agricultural field: from plant residues to soil-protected fractions. European Journal of Soil Science, accepted.

-           analyse the relationships between the nature, location, dynamics of SOM and their functions (C sequestration, pesticides retention, soil aggregation, erosion)
Contribution and behavior of black carbon in soil: We analyse qualitatively and quantitatively the contribution of black carbon to C sequestration and to SOM nature. We invesitigate their fate in soils in the long term (mineralization, transport and erosion).

Scientists: C. Rumpel
Post docs et doctorants : M. Alexis

Rumpel, C., Alexis, M., Chabbi, A., Chaplot, V., Rasse, D.P., Valentin, C., Mariotti, A., 2006: Black carbon contribution to soil organic matter composition in tropical sloping land under slash and burn agriculture. Geoderma, 130, 35-46.

Pesticide retention: We are investigating the formation of bound residues of pesticides by incorporation into microbial metabolites. We focus on microbial lipids which also are biomarkers for microorganisms.

Scientist: MF. Dignac
Graduate student: T. Lerch


Chemical nature of composts: We aim to identify chemical indicators of compost maturity and biodegradability. We analyse the chemical nature of composts with pyrolysis and 13CNMR.

Scientist: MF. Dignac

Dignac, M.F., Houot, S., Francou, C., Derenne, S., 2005. Pyrolytic study of compost and waste organic matter. Organic Geochemistry 36.

Soil aggregation: Ourexperiments are designed to establish quantitative relationships between the amount and quality of soil organic matter or of OM added to soil and aggregate stability improvements via microbial decomposers.

Scientists: C.Chenu
Graduate students: D. Cosentino

Cosentino, D., Chenu, C., Le Bissonnais, Y. 2006 Aggregate stability and microbial community dynamics under drying-wetting cycles in a silt loam soil. Soil Biology and Biochemistry On  line.

Erosion and its “off site effects”: We are involved in the characterization, monitoring and quantification of soil erosion (SOM, charcoal, soluble OM) in tropical agroecosystems as a function of land use change and climate variability. We investigate the off site fate of eroded organic matter and its impacts on hydrosystems.

Scientists: S. Huon, C. Rumpel

Huon S., Valentin C., Bonté P. & Mariotti A. (2005) - Suivi de l'érosion du carbone organique des sols à l'aide de traceurs isotopiques : deux études de cas pour des bassins versants cultivés sur fortes pentes (Laos, Venezuela). Bulletin du Réseau Erosion 22 : 309-322.

Huon S., Bellanger B., Bonté P. Sogon S., Podwojewski P., Girardin C., Valentin C., de Rouw A., Velasquez F., Bricquet J.-P. & Mariotti A. (2006). Monitoring soil organic carbon erosion with isotopic tracers : two case studies on cultivated tropical catchments with steep slopes (Laos, Venezuela). In : Soil erosion and Carbon Dynamics, Roose E., Lal R., Barthès B., Feller C. & Stewart B.A. eds. pp. 301-328, N° Spécial Advances in Soil Science. CRC Press, Boca Raton. Florida (USA).

Collaboration

Sites and long term experiments

“Les Closeaux” site

The site is a unique C3/C4 continuous chronosequence in which ¹³C natural labelling of SOM enables the measurement of C dynamics. The wheat-maize succession experiment was initiated in 1992 at the “Les Closeaux” INRA field experiment in the park of Versailles’ palace by J. Balesdent.

Thirty-two research plots of 15´6.4-m each were installed on a wheat field that had been cultivated for at least 50 years and had never received any C4 plant material. Each growing season from 1993 to 2001, three randomly-selected plots were sown to maize, the other ones being cropped with winter wheat. Four control plots remained under wheat. The site now contains a random distribution of plots that have been cropped to maize for either 0 or from 4 to 12 years. Plots are managed according to standard agricultural practices in the Paris basin. The soil is a eutric cambisol.

Contact: C. Chenu

Long term experiment of Les Closeaux. © J.P. Pétraud

ORE PCBB
>> http://www.ore.fr/rubrique.php3?id_rubrique=18


Publications

For paper older than 2005 please refer to individual web pages.


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