%0 Journal Article
%9 ACL : Articles dans des revues avec comité de lecture répertoriées par l'AERES
%A Verchot, L. V.
%A Dutaur, L.
%A Shepherd, K. D.
%A Albrecht, Alain
%T Organic matter stabilization in soil aggregates : understanding the biogeochemical mechanisms that determine the fate of carbon inputs in soils
%D 2011
%L fdi:010053417
%G ENG
%J Geoderma
%@ 0016-7061
%K Carbon sequestration ; Carbohydrates ; C-13 ; FTIR ; Aggregates ; Improved ; fallow
%M ISI:000288474300009
%N 3-4
%P 182-193
%R 10.1016/j.geoderma.2010.12.017
%U https://www.documentation.ird.fr/hor/fdi:010053417
%> https://www.documentation.ird.fr/intranet/publi/2011/04/010053417.pdf
%V 161
%W Horizon (IRD)
%X We studied the biochemical and biophysical processes of carbon sequestration in an intensive agroforestry system on two soils (Feralsol - Luero; Arenosol - Teso) in W. Kenya to elucidate the mechanisms associated with long-term carbon storage. Specifically, we looked at a top-down model (macro-aggregates form around organic matter particles and micro-aggregates form within the macro-aggregates) and a bottom-up model (micro-aggregates form independently and are incorporated into macro-aggregates) of soil aggregate formation. Soil samples were collected from experiments on improved tree fallows using different species and two tillage treatments; water-stable aggregates were extracted and sorted into three size classes: macro-aggregates (>212 mu m), meso-aggregates (53-212 mu m) and micro-aggregates (20-53 mu m). Organic matter characterization of each fraction was based on C-13 isotope abundance, Fourier transform infrared (FTIR) spectroscopy and the abundance of polysaccharides. Improved fallows increased soil C by 0.28 and 0.26 kg m(-2) in the top 20 cm of the soil profile in Luero and Teso, respectively. Tillage altered the distribution of aggregates among size classes. Changes in the delta C-13 signature in each fraction indicated that more of the new carbon was found in the macro-aggregates (35-70%) and mesa-aggregates (18-49%) in Luero and less (9-17%) was found in the micro-aggregates. In Teso, about 40-80% of the new aggregate C was found in the mesa-aggregates. 14-45% was found in the micro-aggregates and only 4-26% was found in the macro-aggregates. The mesoaggregates and macro-aggregates to a lesser extent, in both sites, were enriched in carboxylic-C and aromatic-C, indicating the importance of OM decomposition and plant-derived C in the stabilization of larger aggregates, supporting the top-down model of aggregate formation. Microbially derived polysaccharides play a leading role in the formation of stable micro-aggregates and carboxylic-C promotes stabilization through surface occlusion. This bottom-up process is essential to promote long-term carbon sequestration in soils. Additionally, the micro-aggregates at both sites were enriched in polysaccharides and had elevated ratios of galactose + mannose:arabinose + xylose than the other aggregate fractions, indicating the importance of microbial processes in the formation of stable micro-aggregates and supporting the bottom-up model.
%$ 068