Study of the composition of the macromolecular refractory fraction from an acidic sandy forest soil (Landes de Gascogne, France) using chemical degradation and electron microscopy

The composition of the insoluble, non-hydrolysable, macromolecular fraction from an acidic sandy forest soil (Cestas, Landes de Gascogne, S.W. France) was examined via chemical degradation and high resolution transmission electron microscopy (HRTEM). Chemical degradation was performed using four reagents (sodium persulfate followed by potassium permanganate, sodium perborate and ruthenium tetroxide). Large differences in the level of degradation of this refractory organic material (ROM) and in the nature and relative abundance of the GC-amenable reaction products were observed between these reagents. Chemical degradation supported the presence of condensed tannins in the ROM, previously suggested from NMR data, and showed the contribution of lipid-derived moieties condensed to the macromolecular refractory material. The contribution of black carbon was revealed with ruthenium tetroxide oxidation and by HRTEM observations that showed the presence of charcoal particles probably related to fire events. All the oxidation treatments point to the lack of a significant contribution of bacteria-derived moieties to the Cestas ROM. The different oxidants revealed different components of the ROM. Thus, the occurrence of suberin was better indicated by the perborate treatment, the contribution of moieties originating from the oxidative cross-linking of unsaturated acids by alkaline permanganate and RuO4, and the presence of condensed tannins and black carbon was only revealed by the RuO4 treatment.Financial support to this work was provided by Picasso program.Peer Reviewe

The development of soil organic matter in restored biodiverse Jarrah forests of South-Western Australia as determined by ASE and GCMS

Background, aim and scope Soil organic matter (SOM) is known to increase with time as landscapes recover after a major disturbance; however, little is known about the evolution of the chemistry of SOM in reconstructed ecosystems. In this study, we assessed the development of SOM chemistry in a chronosequence (space for time substitution) of restored Jarrah forest sites in Western Australia. Materials and methods Replicated samples were taken at the surface of the mineral soil as well as deeper in the profile at sites of 1, 3, 6, 9, 12, and 17 years of age. A molecular approach was developed to distinguish and quantify numerous individual compounds in SOM. This used accelerated solvent extraction in conjunction with gas chromatography mass spectrometry. A novel multivariate statistical approach was used to assess changes in accelerated solvent extraction (ASE)-gas chromatography-mass spectrometry (GCMS) spectra. This enabled us to track SOM developmental trajectories with restoration time. Results Results showed total carbon concentrations approached that of native forests soils by 17 years of restoration. Using the relate protocol in PRIMER, we demonstrated an overall linear relationship with site age at both depths, indicating that changes in SOM chemistry were occurring. Conclusions The surface soils were seen to approach native molecular compositions while the deeper soil retained a more stable chemical signature, suggesting litter from the developing diverse plant community has altered SOM near the surface. Our new approach for assessing SOM development, combining ASE-GCMS with illuminating multivariate statistical analysis, holds great promise to more fully develop ASE for the characterisation of SOM